Risks to Children from Exposure to Lead in Air During Remedial Or Removal Activities at Superfund Sites: a Case Study of the RSR Lead Smelter Superfund Sitey

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Risks to children from exposure to lead in air during remedial or removal activities at Superfund sites: A case study of the RSR lead smelter Superfund sitey

GHASSAN A. KHOURYa AND GARY L. DIAMONDb aU.S. EPA, Region 6 Superfund Branch, Mail Code (6SF-LT), 1445 Ross Avenue, Dallas, Texas 75202, USA bSyracuse Research Corporation, Syracuse, New York 13212, USA

Superfund sites that are contaminated with lead and undergoing remedial action generate lead-enriched dust that can be released into the air. Activities that can emit lead-enriched dust include demolition of lead smelter buildings, stacks, and baghouses; on-site traffic of heavy construction vehicles; and excavation of soil. Typically, air monitoring stations are placed around the perimeter of a site of an ongoing remediation to monitor air lead concentrations that might result from site emissions. The National Ambient Air Quality (NAAQ) standard, established in 1978 to be a quarterly average of 1.5 g/m3, is often used as a trigger level for corrective action to reduce emissions. This study explored modeling approaches for assessing potential risks to children from air lead emissions from the RSR Superfund site in West Dallas, TX, during demolition and removal of a smelter facility. The EPA Integrated Exposure Uptake Biokinetic (IEUBK) model and the International Commission of Radiologic Protection (ICRP) lead model were used to simulate blood lead concentrations in children, basedon monitored air lead concentrations. Although air lead concentrations at monitoring stations located in the downwind community intermittently exceeded the NAAQ standard, both models indicated that exposures to children in the community areas did not pose a significant long-term or acute risk. Long-term risk was defined as greater than 5% probability of a child having a long-term blood lead concentration that exceeded 10 g/dl, which is the CDC and the EPA blood lead concern level. Short-term or acute risk was defined as greater than 5% probability of a child having a blood lead concentration on any given day that exceeded 20 g/dl, which is the CDC trigger level for medical evaluation (this is not intended to imply that 20 g/dl is a threshold for health effects in children exposed acutely to airborne lead). The estimated potential long-term and short-term exposures at the downwind West Dallas community did not result in more than 5% of children exceeding the target blood lead levels. The models were also used to estimate air lead levels for short-term and long-term exposures that would not exceed specified levels of risk (risk-based concentrations, RBCs). RBCs were derived for various daily exposure durations (3 or 8 h/day) and frequencies (1–7 days/week). RBCs based on the ICRP model ranged from 0.3 (7 days/week, 8 h/day) to 4.4 g/m3 (1 day/week, 3 h/day) for long-term exposures and were lower than those based on the IEUBK model. For short-term exposures, the RBCs ranged from 3.5 to 29.0 g/m3. Recontamination of remediated residential yards from deposition of air lead emitted during remedial activities at the RSR Superfund site was also examined. The predicted increase in soil concentration due to lead deposition at the monitoring station, which represented the community at large, was 3.0 mg/kg. This potential increase in soil lead concentration was insignificant, less than 1% increase, when compared to the clean-up level of 500 mg/kg developed for residential yards at the site. Journal of Exposure Analysis and Environmental Epidemiology (2003) 13, 51–65 doi:10.1038/sj.jea.7500254

Keywords: children, inhalation, lead, risk, smelter, Superfund.

1. Abbreviations: ATSDR, Agency for Toxic Substances and Disease Introduction Registry; CDC, Centers for Disease Control; DOE, Department of Energy; EPA, Environmental Protection Agency; GM, geometric mean; GSD, Superfund sites that are contaminated with lead and un- geometric standard deviation; ICRP, International Commission on Radiologic Protection; IEUBK, Integrated Exposure Uptake Biokinetic; dergoing remedial action generate lead-enriched dust that

NAAQ, National Ambient Air Quality; NPL, National Priority List; P10, can be released into the air. Activities that can emit lead- probability of a child having a blood lead concentration of 10 g/dl; P20, enriched dust include demolition of lead smelter buildings, probability of a child having a blood lead concentration of 20 g/dl; stacks, and baghouses; on-site traffic of heavy construc- PM10, particulate matter having an aerodynamic diameter less than or tion vehicles; and excavation of soil. Typically, air moni- equal to 10 m; RI/FS, Remedial Investigation/Feasibility Study; RBC, Risk-Based Concentration; TSP, Total Suspended Particulate toring stations are placed around the perimeter of a site 2. Address all correspondence to: Dr. Ghassan A. Khoury, U.S. Envi- of an ongoing remediation to monitor air lead concentra- ronmental Protection Agency, Region 6 Superfund Branch, Mail Code tions that might result from site emissions. The National 6SF-LT, 1445 Ross Avenue, Dallas, TX 75202, USA. Tel.: +1-214-665- Ambient Air Quality (NAAQ) standard is often used as 8515. Fax: +1-214-665-6660. a trigger level for corrective action to reduce emissions. E-mail: [email protected] The U.S. Environmental Protection Agency (EPA) estab- Received 19 August 2002. 3 yViews expressed in this report are those of the authors and do not lished an NAAQ standard for lead at 1.5 gPb/m air, represent the views of any federal agency or department. averaged over a calendar quarter (U.S. EPA, 1978). In Khoury and Diamond Lead risks to children from Superfund remedial activities establishing the standard, the EPA determined that young secondary lead smelting facility that occupied approxi- children (ages 1–5 years) should be regarded as a group mately 6.5 acres in a heavily populated, mixed residential within the general population that is particularly sensitive and industrial area of Dallas. From 1991 to 1995, various to lead exposure. The EPA considered 15 g Pb/dl blood inspections, investigations, and removal actions were as the maximum safe blood lead level (geometric mean, performed by the EPA. On September 29, 1995, the site GM) for a population of young children and, of this was finalized on the National Priorities List (NPL). The amount, 12 g/dl should be attributed to exposure sources EPA then conducted a Remedial Investigation/Feasibility other than air. The difference between these values, 3.0 g Study (RI/FS) and, in February 1996, signed a Record of Pb/dl, was estimated to be the allowable safe contribution Decision. The remedial action at the smelting facility of air lead exposure to the population GM. Based on consisted of: (1) demolition of site buildings and off-site epidemiological evidence, which indicated that the ratio of disposal; (2) demolition of the smelter stack and off-site air lead (gPb/m3) to blood lead (g Pb/dl) was 1:2, the disposal; (3) excavation of concrete foundations, pavement, EPA determined that the level for the proposed standard contaminated soil, and off-site disposal; and (4) backfilling should be 1.5 gPb/m3. the site with a soil cover. Subsequent to establishing the NAAQ standard, the EPA Potential impacts of air lead exposures at the RSR site on developed a modeling approach for estimating the effec- blood lead concentrations in young children were assessed tiveness of alternative NAAQ standards for lead, particu- using the EPA IEUBK model (v.99d) and the International larly for regulating point sources of air lead emissions such Commission of Radiologic Protection (ICRP) lead model as smelters (U.S. EPA, 1989a). An expanded version of the (Leggett, 1993; Pounds and Leggett, 1998). Although there model (0.99d) was released in 1994 as the Integrated are many differences between the two models, one Exposure Uptake Biokinetic (IEUBK) Model for Lead in difference particularly relevant to this analysis is the Children; a Windows version (IEUBKwin) was released in exposure time step (the shortest time interval over which 2001. The IEUBK model converts estimates of childhood the exposure can be varied in a simulation). The IEUBK exposures to lead in air, soil and dust, drinking water, and model allows lead intake to vary over intervals (steps) of food into predictions of blood lead concentrations, and risks 12 months or longer, whereas the ICRP model simulates of exceeding blood lead concentrations of concern (U.S. lead intakes that can vary in intensity over time spans as EPA, 1994b,c). The EPA currently recognizes blood lead small as 1 day. The 1-day time step was useful in this concentrations greater than 10 g/dl as levels of concern analysis for evaluating impacts of rapidly changing air lead (U.S. EPA, 1994a) and, in regulatory actions, the EPA seeks concentrations. The potential for recontamination of to limit exposures sufficiently to ensure that a typical child remediated residential yards from deposition of air lead or group of similarly exposed children would have an emitted during remedial actions at the site was also estimated probability of no more than 5% of exceeding a examined. blood lead concentration of 10 g/dl (P 10 =5%; U.S. EPA, 1994a, 2001a). The 10 g/dl concern threshold is based on analyses conducted by the Centers for Disease Control Methods (CDC, 1991; ATSDR, 1999) and the EPA (Smith et al., 1989; U.S. EPA, 1989b) that have associated blood lead Air Monitoring concentrations of 10 g/dl and higher with health effects in Air sampling was conducted before and during the remedial children. The CDC has also recommended that a blood lead activities to monitor particulate and lead concentrations at concentration of 20 g/dl, or higher, in a child should the site perimeter and at off-site community areas, such trigger a medical evaluation of the child to determine the as schools and other designated off-site locations. Air need for immediate intervention (CDC, 1991). monitoring included time-integrated air sampling using In this study, modeling approaches were explored in an high-volume PM10 samplers (particulate matter with assessment of the potential impacts of air lead emissions on an aerodynamic diameter less than or equal to a nominal risks to children living near the RSR Superfund site in West 10 m) and total suspended particulate (TSP) samplers for Dallas, TX (Figure 1). In particular, the applicability of the metal constituent analysis, including lead. The trigger levels NAAQ standard was assessed as a trigger for corrective for corrective actions were as follows (ENTACT, 2000): actions during remedial actions at the site, which had the potential to produce short-term emissions of airborne lead that would exceed the standard. Modeling approaches to Monitoring Regulatory Regulatory Site daily deriving risk-based concentrations (RBCs) for air lead limit (g/m3) time interval action level 3 emissions that could provide a more site-specific alternative (g/m ) to the NAAQ standard for establishing corrective action PM10 150 24-h average 100 trigger levels were also explored. The RSR site was a Lead 1.5 quarterly average 1.5

52 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond

Figure 1. Dallas residential area impacted by the smelter demolition activities at the RSR facility Superfund site.

Meteorological parameters were monitored at an on-site high-volume samplers and nine PM10 samplers were used, weather station. The predominant wind direction at the site including one duplicate set which served quality assurance (21%) was from the south. Secondary wind directions and control purposes. On-site locations included a high- included south–southwest, south–southeast, southeast, and volume TSP sampler for metals and a PM10 sampler located north. Samplers were positioned to monitor air quality from at the south and east boundaries of the remediation the primary and secondary wind directions. A total of nine activities, which monitored potential dispersion of emis-

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 53 Khoury and Diamond Lead risks to children from Superfund remedial activities sions from the north and west, respectively. Off-site In order to simulate intermittent exposures (e.g., 5 days/ community locations included four high-volume TSP week), air lead concentrations were time-averaged as samplers for metals and four PM10 samplers located at each follows: of three separate locations north and northwest of the remediation site, with one set of high-volume samplers PbAÂEF þ PbAbaseðATÀEFÞ serving quality and assurance control purposes. Three high- PbATWA ¼ ð1Þ AT volume TSP samplers for metals and three PM10 samplers were located at schools northeast of the site. Twenty-four- 3 hour samples were collected daily, except when no on-site where PbATWA (g/m ) is the time-averaged exposure work activity occurred and on days in which there was no concentration, PbA is the observed or expected air lead 3 potential for dust generation because of precipitation. Air concentration (g/m ), PbAbase is the baseline air lead monitoring began prior to initiation of remediation activities exposure concentration that would be expected to occur in and concluded after the activities were completed, for a total the absence of site exposure (0.1 g/m3, the IEUBK model monitoring period of 232 days (October 2000–May 2001). default value), EF is the exposure frequency (day/week), During this period, approximately 150 samples were col- and AT is the averaging time (7 days/week). lected from each site. Data capture was greater than 90%. Simulation of exposures to air lead concentrations Lead was sampled using a high-volume sampler with a measured at monitoring locations was achieved by assum- glass fiber filter and a sampling rate of 1100–1700 l/min for ing exposure to the arithmetic mean concentration measured a 24-h period (U.S. EPA, 2001b). PM10 was sampled using at each station. Use of the arithmetic mean, as opposed to a high-volume sampler consisting of a size-selective inlet other central tendency estimates such as the GM, is con- head with a glass fiber filter and a sampling rate of 1100– sistent with recommended guidance for use of the model 1700 l/min for a 24-h period (U.S. EPA, 2001c). Lead was (U.S. EPA, 1994b). The mean exposure concentration was measured according to EPA method SW-846, Method calculated by assigning values to each of the 232 con- 6010B, Inductively Coupled Plasma (ICP) Atomic Emis- secutive monitoring days as follows: (1) the monitored sion Spectroscopy. Sample turnaround time was arranged so outdoor air lead concentration was used if a concentration that results of air sample analysis were available within was reported; (2) if the concentration was reported as

54 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond each simulation; this modification allowed discrete simu- using the IEUBK model, a baseline simulation that lation of the daily monitoring data. An integration time replicated as closely as possible the age-year average blood step of 0.1 day and a communication interval of 1 day lead concentrations predicted by the IEUBK model with all were used in all ICRP model runs. The shortest com- values set to their default values (see Figure 3) was partment half-time in the ICRP model is 0.5 min; thus, developed. This same baseline was used in all ICRP model some integration error in calculating rapidly changing runs. The probabilities of exceeding a given blood lead blood lead concentrations may occur if integration time concentration of 10 g/dl (P10 )or20g/dl (P20 ) were steps larger than 0.0001 days are used (Leggett et al., calculated assuming that the output of the model represented 1993). However, in typical simulations used in this a GM of a lognormal distribution of blood lead concentra- analysis, predicted blood lead concentrations varied by tions having a GSD of 1.6, the IEUBK model default value. less than 2% when the integration time step was varied over a range of 0.1–0.0001 days; thus, an integration step Deposition and Accumulation of Lead in Soil of 0.1 day achieved acceptable stability of the blood lead The deposition rate for a specific particle size can be output at reasonable run times of less than 1 min. represented as follows: The ICRP model uses lead intakes to the respiratory tract X (or gastrointestinal tract) as input, rather than air lead D ¼ viCi ð3Þ concentrations; therefore, air lead concentrations were i converted to air lead intakes (g/day) as follows: 2 where D is the particle deposition rate (g/s m ), v i is the INair ¼ V½ðPbAoutÂOUTSIDEÞþðPbAinÂINSIDEÞ ð2Þ deposition velocity (m/s) of particles of size i, and C i is the airborne particulate concentration (g/m3) of particles of size i. where, INair is the amount of lead deposited in the res- Air sampling was conducted only during days on which piratory tract (g/day); PbAout is the outdoor air lead 3 it did not rain; thus, the average values for the 232-day concentration (g/m ); PbAin is the indoor air lead con- 3 sampling period may tend to overestimate actual annual centration (PbAoutÂ0.3 g/m ); V is the ventilation rate 3 averages because they do not take into consideration the (5 m /day, IEUBK model default for the age range 24– effect of precipitation, which removes particulate matter 36 months); OUTSIDE is the fraction of hours spent from the air column and suppresses the emission of fugitive outside each day (the IEUBK model default value for the dust from the site. Wet deposition was not considered age range 24–36 months is 3 h/day); and INSIDE is the further in this analysis. Although mechanisms of dry fraction of hours spent indoors each day (1ÀOUTSIDE). deposition include gravitational settling and impaction, for Eq. (2) is identical to the intake calculation used in the the estimation purposes, it was assumed that all dry de- IEUBK model (U.S. EPA, 1994c). All inhaled lead was position occurred by gravitational settling. Gravitational assumed to be deposited in the respiratory tract. All ex- settling velocities vary with particle size. The only data on posures were assumed to begin on age-day 730. particle size available for the site were the PM10 values The ICRP model simulates lead intakes that can vary in recorded at the monitoring stations. We assumed, for mod- intensity over time spans as small as 1 day; this obviated the eling purposes, that all particles in the PM10 fraction had need to average the air exposure concentrations over an actual diameter of 10 m. The gravitational settling intervals longer than 1 day — the actual air monitoring velocities for spheres 10 m in diameter were assumed to be unit interval. Exposures of frequencies less than 7 days/ 0.6 cm/s (Lapple, 1961). The retention of atmospheric lead week were simulated as such; e.g., a 5-day/week exposure 3 in surface soil is dependent upon the organic matter content to 1.5 g/m was simulated as a repeated series of five and pH of the soil. When atmospheric lead is deposited on consecutive days of exposure to 1.5 g/m3 followed by 3 undisturbed soil, it is retained in the upper 1–5 cm of the 2 days to the baseline exposure concentration (0.1 g/m ). soil column (U.S. EPA, 1986). The cumulative concentra- Similarly, daily monitoring data were simulated discretely tion of lead in uncontaminated soil due to atmospheric without averaging over longer time intervals. Values for air deposition was calculated as follows (U.S. EPA, 1998): lead concentrations were assigned to each of the 232 air monitoring days using the same procedure described above ÀkstD for the IEUBK model simulations. 100ÂðDyd þ DywÞð1Àe Þ Cs ¼ ð4Þ Potential exposures to air emissions from the site were ZsÂBDÂk s assumed to occur above a baseline exposure from other environmental media (e.g., soil and dust, drinking water, and where C s is the average soil concentration over the duration diet). Although there are many possible ways to represent of the remedial actions (mg/kg); D yd is the yearly dry 2 the baseline exposure, to be consistent with simulations run deposition from particle phase (g Pb/m year); D yw is the

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 55 Khoury and Diamond Lead risks to children from Superfund remedial activities

2 yearly wet deposition rate (g Pb/m year); k s is the loss analysis to represent the West Dallas community. Station À 1 constant for lead in soil (year ); t D is the time period over ET6 was located at a nearby elementary school northwest of which deposition occurs (year); 100 is a unit conversion the site perimeter. Station BGCT3 was located at the north 2 2 factor (mg m /kg cm ); Z s is the soil mixing zone depth perimeter of the site. Station BGCT4 was co-located with (cm); and BD is the soil bulk density (g soil/cm3 soil). BCGT3 and served quality assurance and control data Since only dry deposition by gravitational settling was needs. Although the maxima at the two co-located 3 considered in this analysis, the values for D yd were perimeter stations were different (24.8 vs. 10.8 g/m ), in estimated based on Eq. (3) (D) and D yw was assigned a general, similar values were obtained at the two stations; value of zero. Losses of lead deposited to the surface soil 50% of the measurements differed by less than 10 and 75% from leaching, degradation, or volatilization were assumed of the samples differed by less than 20%. Similarly, high to be negligible — a conservative assumption. A value of values at BGCT3 were associated with high values at 1 year was assigned to the deposition period (t D ). The BGCT4 (correlation coefficient=0.9). value used for soil mixing zone depth (Z s ) was 1 cm. A The highest average and maximum air lead concen- site-specific value for the soil bulk density (BD) was not trations were recorded at the two stations located closest available; thus, the default value of 1.5 g/cm3 was used to the site (e.g., BGCT3: mean 0.95 g/m3, maximum 24.8 (U.S. EPA, 1998). With the above assumptions, Eq. (4) g/m3 ). Air lead concentrations were considerably lower simplifies to Eq. (5): in the two community locations, CST5 (mean 0.3 g/m3) and ET6 (mean 0.06 g/m3 ). By comparison, atmospheric 100ÂðD þ D Þt lead concentrations in the US have ranged from 0.0046 yd yw D 3 3 Cs ¼ : ð5Þ g/m in remote areas to 1.1 g/m in urban areas (U.S. Z ÂBD s EPA, 1986). In 1988, the average lead concentration for 139 urban air monitoring sites around the US was 0.085 g/m3 and remained relatively unchanged, at 0.04 g/m3, when Results estimated between 1994 and 1995 (ATSDR, 1999). Corrective actions that included modification of opera- Air Lead Concentrations at the Site and Adjacent tions to reduce fugitive dust levels were implemented when Community Areas air monitoring trigger levels were exceeded; for lead, the A summary of the air lead monitoring data collected at four trigger level was the NAAQ standard of 1.5 g/m3. Over sampling stations considered to be representative of all the 232-day monitoring period, the 1.5-g/m3 action level monitored locations is presented in Table 1. Station CST5 was exceeded at 21 days at the BCGT3 station, at 20 days at was located in the community northwest of the site the BCGT4 station, at 8 days at the CST5 station, and was (Figure 1). Data collected at this site were used in this never exceeded at the ET6 station. Corrective actions Table 1. Summary of air monitoring results (October 2000–May included wetting the area of concern, application of a dust 2001). suppressant, and filtering or otherwise controlling dust at the emission source. Measures taken to prevent dust Statistic Monitoring station air lead concentration (g/m3 ) emissions at all times included draping plastic tarps over BGCT3 BGCT4 CST5 ET6 openings in the smelter building to prevent dust from (perimeter) (perimeter) (residential) (school) escaping the building during activities inside, covering debris stored outside with plastic tarps, and increasing the Location north north northwest northwest Distance (m)a 30 30 300 850 wetting down of outside concrete surfaces. Dust-generating Height (m) 5 5 5 7 activities were ceased whenever wind gusts exceeded Days sampled 158 158 159 158 20 miles/h at the on-site weather station. The monitoring Meanb 0.95 0.88 0.30 0.06 data reflect the impacts of the above preventative measures b SD 2.65 1.96 0.78 0.13 and corrective actions, and may not represent air lead Minimum 0.007 0.007 0.001 0.002 5th Percentile 0.012 0.010 0.007 0.006 concentrations that might have occurred had these proce- 50th Percentile 0.21 0.18 0.063 0.025 dures not been applied at the site. 95th Percentile 3.81 4.76 1.59 0.21 Maximum 24.8 10.8 6.73 1.18 c Predicted Blood Lead Impacts from Outdoor Air Lead Mean (232) 0.68 0.63 0.24 0.07 Monitoring at the Site aDistance from site perimeter. Figure 2 shows the results of ICRP and IEUBK model b Arithmetic mean, standard deviation, and percentiles of measured simulations of air lead exposures at each of the four concentrations. cArithmetic mean including default concentrations for days on which data locations in Table 1. The increase in blood lead concentra- were not available (used in IEUBK model simulations; see Methods tion above the baseline represents the predicted incremental section). increase that corresponds to the air lead exposures measured

56 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond

8.0 40 8.0 40 BGCT3 BGCT4

dL) 7.0 35 7.0 35 Air Concentration Lead ( g/

µ ICRP Model 6.0 30 6.0 30 IEUBK Model 5.0 25 5.0 25

4.0 20 4.0 20

3.0 15 3.0 15 Baseline

2.0 10 µ 2.0 10 g/m Air Lead 3 Blood Lead Concentration ( Concentration Lead Blood 1.0 5 ) 1.0 5

0.0 0 0.0 0 0 365 730 1095 1460 1825 2190 2555 0 365 730 1095 1460 1825 2190 2555

8.0 40 8.0 40 CST5 ET6 7.0 35 7.0 35 Air Concentration Lead ( g/dL)

µ 6.0 30 6.0 30

5.0 25 5.0 25

4.0 20 4.0 20

3.0 15 3.0 15 µ

2.0 10 2.0 10 g/m 3 ) Blood Lead Concentration ( Concentration Lead Blood 1.0 5 1.0 5

0.0 0 0.0 0 0 365 730 1095 1460 1825 2190 2555 0 365 730 1095 1460 1825 2190 2555 Age (days) Age (days)

Figure 2. Simulations of a 232-day exposures at four monitoring locations (BGCT3, BGCT4, CST5, ET6). The line labeled ICRP model shows the daily blood lead concentrations predicted by the ICRP model. The dotted line labeled IEUBK model shows the age-month values from the IEUBK model. Exposures were assumed to begin at age 730 days (ICRP model)or 24 months (IEUBK model).Time spent outdoors was assumed to be 3 h/day. The exposure concentrations used in the IEUBK simulation were the arithmetic means at each location for the 232-day monitoring period (see Table 1). at that given location, keeping all other exposure variables concentration was 5.7 g/dl compared to the highest in the simulation at baseline values. Daily values for blood single-day value of 6.7 g/dl. lead concentrations predicted from ICRP model simulations Table 2 summarizes the results of the ICRP model follow the general pattern of air exposure levels, with the simulations of exposures at the four locations. Simulations highest values occurring at the perimeter locations, BGCT3 of exposures at BGCT3 and BGCT4, representing the and BGCT4, and lowest at the school, ET6 — the sampling downwind site perimeter, indicated that if a population of station located furthest from the site. The results shown for children of ages 24–36 months were to be exposed to the IEUBK model simulations are predicted monthly blood air lead levels measured at this monitoring station, the lead averages, the shortest blood lead averaging time that GM blood lead concentration in this population would be can be accessed from IEUBK v99d. Daily upward 4.6 g/dl and the probability of exceeding a blood lead excursions of predicted blood lead concentrations above concentration of 10 g/dl would be 4.8%. The model the baseline profile that are evident in the ICRP model predicted that the highest single-day blood lead concentra- simulations are not represented in the IEUBK model runs, tion in the population would be 6.8 g/dl, which corres- principally because of time averaging of the daily exposure ponds to probabilities of 20.5% of exceeding 10 g/dl and concentrations. A small dampening effect also results from 1.1% of exceeding 20 g/dl (BGCT4). The predicted monthly averaging of blood lead concentrations in the highest single-day blood lead value is an acute event asso- IEUBK model. For example, in the ICRP simulation of ciated with the highest air lead concentration at the location location BGCT3, the highest monthly average blood lead (Figure 2). Therefore, it is highly unlikely that the maxi-

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 57 Khoury and Diamond Lead risks to children from Superfund remedial activities

6.0 recorded by the monitoring station, would have a predicted ICRP Model GM blood lead concentration of 4.5 g/dl with a pro- 5.0 g/dL)

µ IEUBK Model bability of 4.4% of exceeding a blood lead concentration of 10 g/dl (Table 2). The highest single-day GM blood 4.0 lead concentration in the population was predicted to be 5.2 g/dl, which corresponds to probabilities of 8.0% of 3.0 exceeding 10 g/dl and 0.2% of exceeding 20 g/dl. Baseline Predicted daily blood lead concentrations were above the 2.0 baseline for 103 days; however, during this period, neither

1.0 the P10 nor the P20 exceeded 5%. In order to account for the Blood Lead Concentration ( Lead Concentration Blood Air Exposure Period possibility that some residents might keep their windows 0.0 open for ventilation during the entire 8-h work day, the 0 365 730 1095 1460 1825 2190 2555 outdoor air exposure time assumed in the simulation was Age (days) increased from 3 to 8 h/day. With the longer daily exposure duration, the predicted GM blood lead concentration was Figure 3. Simulations of 3-month exposure at the NAAQ standard 4.6 g/dl with a probability of 4.8% of exceeding 10 g/dl. of 1.5 g/m3. Exposures were assumed to begin at age 730 days (ICRP model)or 24 months (IEUBK model).Time spent outdoors The highest single-day GM blood lead concentration was was assumed to be 3 h/day. The exposure frequency was 5 days/ predicted to be 5.6 g/dl with a probability of 0.3% of week. The solid line labeled ICRP model shows the daily blood lead exceeding a blood lead concentration of 20 g/dl. These concentrations predicted by the ICRP model. The dotted line labeled IEUBK model shows the age-month values from the IEUBK model results suggest that at no time during the remedial activities for an air lead exposure of 1.5 g/m3, time-averaged for an exposure was the RSR community exposed to air lead levels that frequency of 5 days/week to a value of 1.10 g/m3 (Eq. (1), Methods could pose a significant human health concern. section). The baseline simulation is also shown. The filled squares indicate the age-year average values predicted from IEUBK model Data from the air monitoring station at the ET6 station with all inputs set to default values. were selected to represent schools downwind from the site. ICRP model simulations of the air lead concentrations at mum air lead levels recorded at the site would have resulted this site predicted a blood lead concentration similar to the in an acute blood lead concentration exceeding the CDC baseline blood lead concentration with no days above the (1991) trigger level of 20 g/dl for medical evaluation. baseline level (Table 2). The highest single-day GM blood ICRP model simulations of location CST5, representing lead concentration was predicted to be 4.5 g/dl with a the downwind community, showed that a population of probability of 0.1% of exceeding 20 g/dl. When a longer similarly exposed children living at or near the CST5 loca- daily exposure time of 8 h was considered, the GM blood tion, and who were exposed to the air lead concentrations lead concentration predicted by the model was 4.4 g/dl

Table 2. ICRP model predictions of blood lead concentrations associated with exposures to outdoor air lead levels monitored at locations near the RSR site.

Monitoring location Highest single daya Above-baseline meanb Days above c d baseline g/dl P10 (%) P20 (%) g/dl P10 (%) P20 (%) Assuming 3 h/day spent outdoors BGCT3 6.7 19.9 1.0 4.6 4.8 0.1 389 BGCT4 6.8 20.5 1.1 4.6 4.8 0.1 356 CST5 5.2 8.0 0.2 4.5 4.4 0.1 103 ET6 4.5 4.3 0.1 – e – e – e 0

Assuming 8 h/day spent outdoors BGCT3 7.7 29.3 2.2 4.7 5.3 0.1 483 BGCT4 7.8 30.1 2.3 4.7 5.3 0.1 449 CST5 5.6 10.8 0.3 4.6 4.8 0.1 141 ET6 4.5 4.3 0.1 4.4 3.9 0.1 1 Monitoring was conducted for a 232-day period, October 12, 2000–May 31, 2001. A 232-day exposure was assumed to occur over the age range 730– 962 days. aHighest single-day blood lead concentration for the simulation. bArithmetic mean blood lead concentration for days above baseline. cProbability (%) of exceeding a blood lead concentration of 10 g/dl, assuming a GSD of 1.6. dProbability (%) of exceeding a blood lead concentration of 20 g/dl, assuming a GSD of 1.6. eNo days above baseline.

58 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond

Table 3. IEUBK model predictions of blood lead concentrations (such as wetting down areas being remediated and limiting associated with exposures to outdoor air lead levels monitored at dust-generating activities during high gust windy days). locations near the RSR site. Monitoring data were used to estimate lead deposition rates at the four locations summarized in Table 1. Based on the Monitoring location Outdoor air 12-Month 12-Month c average air lead concentration at station CST5 of 0.24 g/ lead mean mean P10 3 concentrationa blood leadb (%) m , which represented the West Dallas community at large, 2 (g/m3 ) (g/dl) an average yearly deposition rate of 0.045 g/m year was calculated from Eq. (3). Eq. (5) (Methods section) yields a Assuming 3 h/day spent outdoors BGCT3 0.68 4.4 3.7 soil concentration (C s ) of 3.0 mg/kg, with the assumptions BGCT4 0.63 4.3 3.4 noted in the Methods section that included: (1) only dry CST5 0.24 4.3 3.2 deposition; (2) negligible loss of lead deposited to the ET6 0.074 4.2 3.2 surface soil from leaching; (3) a 1-year deposition period (t D ); (4) a mixing zone depth of 1 cm; and (5) a value of Assuming 8 h/day spent outdoors 3 BGCT3 0.68 4.4 3.7 1.5 g/cm for soil bulk density (BD; U.S. EPA, 1998). BGCT4 0.63 4.4 3.7 Therefore, the air lead concentrations resulting from CST5 0.24 4.3 3.2 remedial activities at the site are predicted to have ET6 0.074 4.2 3.2 potentially contributed to a 3.0-mg/kg increase in soil lead Monitoring was conducted for a 232-day period, October 12, 2000–May concentration at the monitoring location that represented the 31, 2001. A 12-month exposure was assumed to occur over the age range community at large. This predicted increase in soil lead 24–36 months. concentration would not have had a significant impact on aArithmetic mean for the 232-day monitoring period with 0.1 g/m3 assumed for days not monitored (see Table 1 and Eq. (1); Methods the remediated residential yards of the West Dallas section). community located next to the RSR Superfund site, since bArithmetic mean blood lead concentration for age range 24–36 months. cProbability (%) of exceeding a blood lead concentration of 10 g/dl, assuming a GSD of 1.6. Table 4. Quarterly RBCs predicted by the ICRP model resulting in an above-baseline average blood lead concentration corresponding to a

P10 of 5%. with a probability of 3.9% of exceeding 10 g/dl and the highest single-day GM blood lead concentration was Exposure frequencya Outdoor airb Air lead intakec Days above predicted to be 4.5 g/dl with a probability of 0.1% of (day/week) concentration (g/day) baseline 3 exceeding a blood lead concentration of 20 g/dl. Thus, (g/m ) the ET6 location did not appear to be impacted by air lead Assuming 3 h/day spent outdoors levels resulting from the remedial activities that took place 1 4.4 (18) 8.5 194 on RSR site. 2 2.3 (9.2) 4.4 196 The results of corresponding IEUBK model simulations 3 1.5 (6.2) 3.0 198 4 1.2 (4.6) 2.3 198 are shown in Table 3. Exposure for the entire age year, 24– 5 1.0 (3.7) 1.9 197 36 months, was simulated using the arithmetic mean 6 0.8 (3.1) 1.6 191 outdoor air lead concentration for the 232-day monitoring 7 0.7 (2.7) 1.4 189 period. IEUBK model predictions of the average blood lead Assuming 8 h/day spent outdoors concentration for the above-baseline period (Table 2) were 1 1.6 (13) 4.3 113 lower than the ICRP model predictions for the 12-month 2 0.9 (6.4) 2.3 115 average (ages 24–36 months) (Table 3). The correspond- 3 0.6 (4.3) 1.6 113 ing P 10 values predicted by the IEUBK model were also 4 0.5 (3.2) 1.3 114 lower, and were less than 5% at all locations. This difference 5 0.4 (2.6) 1.1 113 6 0.4 (2.2) 0.9 112 may reflect, in part, the effect of averaging the exposure 7 0.3 (1.9) 0.8 109 concentrations for use in the IEUBK model (i.e., to arrive at a 1-year average exposure concentration), which would In ICRP model simulations, a quarterly (90-day) exposure was assumed to occur over the age range 730–820 days at the indicated frequencies tend to dampen the effects of exposure spikes, which (days/week). In IEUBK model simulations, a 12-month exposure was occurred during the monitoring period. assumed to occur over the age range 24–36 months. aExposure to 0.1 g/m3 was assumed on days when there was no site Potential for Recontamination of Remediated Areas by exposure. b Ongoing Deposition of Airborne Lead Numbers in parentheses are corresponding RBC values estimated with the IEUBK model. Airborne lead generated with dust emissions due to on-site cInputs to the ICRP model (inhalation intake, g/day on days of remedial activities could not be avoided in spite of dust exposure) that correspond to the outdoor air lead concentrations (see Eq. generation control measures taken during remedial activities (2), Methods section).

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 59 Khoury and Diamond Lead risks to children from Superfund remedial activities it would represent less than a 1% potential increase in soil blood lead predicted by the ICRP model is less evident in lead concentration, when compared to the site-specific soil the IEUBK model simulation. clean-up level of 500 mg/kg. Estimation of Risk-Based Outdoor Air Lead Simulation of Blood Lead Impacts for Exposure to the Concentrations Based on Potential Blood Lead Impacts NAAQ Lead Standard The term RBC is used in this report to refer to an outdoor air Figure 3 shows the results of ICRP and IEUBK model lead concentration that satisfies two criteria: (1) exposure to simulations of a 3-month exposure to 1.5 g/m3, 5 days/ the RBC results in an above-baseline average blood lead week, beginning at age 24 months (or 730 days). The ICRP concentration no greater than that corresponding to a P10 of model predicts a gradual build-up of blood lead from the 5%; and (2) a blood lead concentration on any single day no baseline of 4.4 g/dl to a maximum of approximately greater than that corresponding to a P20 of 5%. 5.4 g/dl at the end of the exposure period. This is followed ICRP model simulations were run (i.e., 3-month by a similarly paced decline to the preexposure blood exposures, days 730–810) to various outdoor air lead concentration in approximately 100 days, followed by a concentrations and at various exposure frequencies. For more gradual return to the baseline blood lead profile. Blood each exposure concentration and frequency, three measures lead concentrations were above the baseline values (by of blood lead impacts were determined: the number of more the 0.1 g/dl) for a total of 281 days. The figure also days in which the blood lead concentration exceeded that shows the agreement between the baseline ICRP model of the baseline profile by at least 0.1 g/dl (days above simulation and the blood lead profile for the IEUBK model baseline), the arithmetic mean of blood lead concentrations default input settings. This same baseline was used in for the days above baseline (above-baseline average), and all ICRP model runs. In the IEUBK model simulation, the highest single-day blood lead concentration (highest). the outdoor air lead concentration for the age range 24–36 The outdoor air lead concentration that yielded a P 10 of 5% months (the minimum 12-month exposure time step) was was then determined based on the predicted above-baseline adjusted from the default value of 0.1–1.1 g/m3, the time- average blood lead concentration. RBCs based on the averaged exposure concentration equivalent to 1.5 g/m3 above-baseline average blood lead concentration ranged for 5 days/week (Eq. (1), Methods section). The IEUBK from 0.7 to 4.4 g/m3, if children were assumed to spend model predicted monthly blood lead averages that increased 3 h/day outdoors, and from 0.3 to 1.6 g/m3, if children from 4.4 g/dl at month 24, to 4.5 g/dl during months 26 were assumed to spend 8 h/day outdoors (Table 4). Table 4 through 30, and then returned to preexposure levels over a shows that the RBC drops below 1.5 g/m3, the corrective subsequent 3-month period. The much higher build-up of action level adopted for the site, if the exposure frequency

Table 5. ICRP model predictions of air lead concentrations resulting in the highest single-day blood lead concentration corresponding to a P10 or P20 of 5%.

Exposure frequency Outdoor air concentration (g/m3) Air lead intake (g/day) Days above baseline (day/week) P10 P20 P10 P20 P10 P20 Assuming 3 h/day spent outdoors 1 1.9 29.0 3.7 56.2 106 720 2 1.0 14.8 1.9 28.7 105 729 3 0.7 10.2 1.4 19.7 109 740 4 0.6 7.8 1.1 15.1 110 750 5 0.5 6.4 0.9 12.4 110 760 6 0.4 5.5 0.8 10.6 112 772 7 0.4 4.8 0.8 9.4 113 781

Assuming 8 h/day spent outdoors 1 1.1 20.8 2.9 55.5 92 713 2 0.6 10.6 1.7 28.3 94 721 3 0.5 7.3 1.2 19.5 94 734 4 0.4 5.6 1.0 14.9 96 742 5 0.3 4.6 0.9 12.3 96 754 6 0.3 3.9 0.8 10.5 98 766 7 0.3 3.5 0.7 9.3 99 776

A 90-day exposure was assumed to occur over the age range 730–820 days at the indicated frequencies (days/week). P10 and P20 are the probability of exceeding a blood lead concentration of 10 or 20 g/dl, respectively, assuming a GSD of 1.6. The highest single-day blood lead concentration was 4.6 g/dl for all P10 simulations and 9.2 for all P20 simulations, respectively.

60 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond is greater than 3 days/week for 3 h/day, or greater than carrying out remedial or removal activities without 1 day/week for 8 h/day. contributing significant risk to nearby communities. To Corresponding RBCs estimated from the IEUBK model ensure that no or minimal contaminants leave the site are also shown in Table 4. Simulations were run of 12- through the air pathway, project managers employ air month exposures (ages 24–36 months), 1–7 days/week, to monitoring programs and strategies to control contaminants various outdoor air lead concentrations (default values were from leaving the site. The RSR Superfund site was a used for other ages), representing time-weighted average secondary lead smelting facility. The Record of Decision for air lead concentrations (PbATWA, Eq. (1)), and the TWA air the RSR site called for the demolition of the smelter stack lead concentrations that resulted in a P 10 of 5% were and the buildings associated with the lead smelting determined. These values were 2.7 and 1.9 g/m3 if activities. These remedial activities raised several concerns: children were assumed to spend 3 or 8 h/day outside, (1) risks from episodic exposures to high lead levels in air respectively. The corresponding air lead concentrations for for a short periods of time (e.g., days); (2) long-term various exposure frequencies calculated from Eq. (1) (PbA; impacts from exposure to lead released from the reme- see Methods section) are shown in Table 4 (numbers in diation activities; and (3) possible recontamination of parentheses). The RBCs ranges were 2.7–18 or 1.9–13 g/ remediated residential yards in the nearby community. In m3 for 3 or 8 h/day outside, respectively. These values are response to these concerns, continuous air particulate higher than those predicted from the ICRP model (Table 4), (PM10 ) and lead monitoring was conducted at strategic even for exposure frequencies of 7 days/week, for which locations downwind from the site, before and during the the exposure concentration was not time-averaged in the entire remedial project. This risk analysis has utilized the air IEUBK model runs. The effect of time averaging on the monitoring data and models of lead biokinetics to evaluate, predicted RBC appears to be pronounced at low exposure retrospectively, whether or not emissions control strategies frequencies. For example, the RBCs for an exposure employed at the site successfully mitigated potential risks to frequency of 1 day/week, assuming 3 h/day spent outside, the adjacent community. were 18 g/m3 from the IEUBK, model and 4.4 g/m3 An acceptable air lead level that is frequently used to from the ICRP model. The RBC predicted by the ICRP monitor air emissions from Superfund sites is the quarterly model was 8.5 g/m3 for the same scenario when it was average NAAQ standard of 1.5 g/m3. Monitoring data at based on the 12-month average blood lead concentration the site indicated that 24-h air lead concentrations exceeded (more analogous to the 1-year averaging time used in the this level periodically. In order to assess the potential IEUBK model). impacts of these exceedences, air lead exposures estimated ICRP model simulations were also run to predict the air from air monitoring were converted into predicted blood lead concentrations that would yield a P 10 or P 20 of 5% for lead concentrations using the EPA IEUBK model (U.S. the highest single-day blood lead concentration (Table 5). EPA, 1994b) and the ICRP lead biokinetic model (Leggett, 3 RBCs based on a P 10 of 5% ranged from 0.4 to 1.9 g/m , 1993). The IEUBK model has been used extensively in if children were assumed to spend 3 h/day outdoors, and assessing lead risks to children at Superfund sites where from 0.3 to 1.1 g/m3, if children were assumed to spend 8 lead contamination of residential soils is a concern (U.S. h/day outdoors. If based on a P 20 of 5%, the RBCs ranges EPA, 1994a; White et al., 1998). The ICRP model has been were 4.8–29 or 3.5–21 g/m3, for the 3 or 8 h/day used by the ICRP, Department of Energy (DOE), and EPA scenarios, respectively. The time required to obtain to develop cancer risk coefficients for internal radiation laboratory results from monitoring at the RSR site was exposures to lead and other alkaline earth elements that have approximately 3 days. Thus, exposure to any given air lead biokinetics similar to those of calcium (ICRP, 1993; U.S. concentration might have gone undetected for that length of EPA, 1997). Both models simulate age-dependent kinetics time before actions could be taken, if needed. In order to of uptake of lead from the gastrointestinal and respiratory estimate a maximum air lead concentration that might pose tracts; distribution of absorbed lead to blood, bone, liver, an acceptable level of risk for a 3-day period, an exposure kidney, and other soft tissues; and excretion of lead. The of 3 days/week was simulated with the ICRP model. The air IEUBK model simulates lead biokinetics in children up to lead concentrations that corresponded to a P 20 of 5% were age 84 months and includes a multipathway age-dependent 10.2 g/m3, for exposures of 3 days/week, 3 h/day, and exposure model and a blood lead variability model. The 7.3 g/m3 for exposures of 3 days/week, 8 h/day. ICRP model simulates lead biokinetics from birth through adulthood. The EPA IEUBK model is the only risk model that has Discussion been validated for use in the Superfund program for assessing lead risks to children where residential exposures Remedial project managers responsible for cleaning up to lead in soil and dust are known to be the major Superfund sites are usually faced with the problem of contributors to exposure (U.S. EPA, 1994b; Hogan et al.,

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 61 Khoury and Diamond Lead risks to children from Superfund remedial activities

1998; Zaragoza and Hogan, 1998); however, the model has Of particular interest to this analysis is the reliability of several limitations for the application intended at the RSR the model for predicting the biokinetics of inhaled lead in site. Although the model has been evaluated for predicting children. Since lead absorbed into the systemic circulation quasi-steady state blood lead concentrations associated would be expected to have similar biokinetics, regardless of with exposures of several months or years in duration, it has the route of absorption, the concern resides in how well the not been evaluated for predicting blood lead concentrations model simulates deposition and absorption of lead in the that might occur with rapidly varying exposures, such as respiratory tract. The respiratory tract portion of the ICRP those encountered during remedial activities at the RSR site. model is empirically based on experimental observations The IEUBK model simulates exposures as averages over from inhalation studies conducted in adults, which revealed 12 months or longer intervals and outputs blood lead multicompartmental absorption kinetics for deposited lead concentrations as monthly or longer interval averages. Time (Hursh and Mercer, 1970; Hursh et al., 1969; Wells et al., averaging of exposures and blood lead concentrations will 1975; Chamberlain et al., 1978; Morrow et al., 1980). In attenuate spikes in blood lead concentration that would be these studies, exposures were to particles having mass expected to occur with short-term elevations in air lead median aerodynamic diameters below 1 m and, therefore, levels, such as those that were observed at the RSR site, deposition of the inhaled lead particles can be assumed to where single-day air lead levels ranged from 0.007 to have been primarily in the bronchiolar and alveolar regions 25 g/m3 (Table 1). Although several other research mod- of the respiratory tract (James et al., 1994) where transport els that are structured to provide a more dynamic simulation of deposited lead to the gastrointestinal tract is likely to have of short-term exposures (Bert et al., 1989; O’Flaherty, been only a minor component of particle clearance (Hursh 1991, 1993, 1995) are available, these have not been vali- et al., 1969). The ICRP lead model includes four deposition dated for such uses in a regulatory context (LaKind, 1998). compartments from which a total of 95% of deposited lead The ICRP model provided a useful alternative to the is absorbed with half-times ranging from 1 h to 2 days, and IEUBK model for this application because it accepts daily 5% is transferred to the stomach (Chamberlain et al., 1978). intakes through the inhalation (and ingestion) route and The slowest respiratory tract compartment would be simulates daily changes in blood lead concentrations. expected to have the largest impact on blood lead Although both the IEUBK and ICRP models yielded concentrations resulting from acute inhalation exposures. similar predictions of long-term (e.g., 12-month) average However, since the slow compartment in the ICRP model blood lead concentrations (e.g., Tables 2 and 3), short-term receives only 10% of the deposited dose, it is not likely to (daily or monthly) variations in blood lead concentrations greatly influence prediction of peak blood lead concentra- evident in the ICRP model simulations were not present in tions following acute exposures. Absorption from the faster the IEUBK model simulations (Figure 2). Thus, if potential compartments (half-times of 1, 3, and 9 h) would be nearly short-term elevations of blood lead resulting from highly complete within a 1- to 2-day period; thus, if the half-times variable air lead levels are a concern, as was the case in this were underestimated in the model, predicted acute blood analysis, the ICRP model provides a useful approach to lead concentrations would not be substantially affected. We supplementing information gained from IEUBK model verified this by adjusting the half-times of all four simulations. Similar conclusions have been offered by EPA respiratory tract compartments to 1 h. The highest blood (U.S. EPA, 2001d). lead concentration predicted at the CST5 site was 5.18 g/ The ICRP model has not been validated as a regulatory dl when a half-time of 1 h was assigned to all four model for assessing lead risks in children. However, compartments compared to 5.16 g/dl when the default comparisons made between the ICRP and IEUBK models values were used — a difference of less than 0.5%. Thus, an have shown that the ICRP model tends to predict higher underestimation of the rate or extent of the absorption of quasi-steady state blood lead concentrations than the inhaled lead is not likely to have been a significant IEUBK model for the same rates of lead absorption uncertainty in this analysis. (Pounds and Leggett, 1998). Thus, predicted blood lead We assumed for this analysis that 100% of inhaled lead concentrations and corresponding risk estimates (e.g., P10 ) would be deposited in the respiratory tract of children. This for long-term exposures that are based on the ICRP model is most likely a conservative assumption, since deposition can be expected to be higher than those based on the IEUBK fractions, in general, are less than 100% for particle sizes model. In general, this was the case in the present analysis of ranging from 0.005 to 10 m, respectively; below 0.005 the RSR site where the exposure duration considered was m, deposition increases to 100% (James et al., 1994). The the 232-day monitoring period (Tables 2 and 3). Thus, we actual particle size distribution of the PM10 fraction can be reasonably certain that the ICRP model did not collected at the RSR site is not known. If the distribution underestimate risk associated with the long-term average was dominated by particles larger than 0.005 m, the model exposures resulting from site remediation activities, relative is likely to have overestimated deposition and peak blood to the IEUBK model risk estimates. lead concentrations following acute changes in exposure

62 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond

(James et al., 1994). If the particle size distribution was blood lead concentrations compared to those predicted by dominated by particles larger than 1 m, the model is also the IEUBK model. likely to have overestimated lead absorption of deposited Given the above uncertainties, we can, nevertheless, lead because a substantial fraction of the inhaled particles draw certain conclusions about risks to children presented larger than 1 m would have been deposited in the upper by air lead exposures at the RSR site during the remediation respiratory tract and subsequently transferred by mucocili- activities. The IEUBK model predicted that, if children were ary transport to the gastrointestinal tract where absorption exposed to the long-term average air lead concentration at would be less than 100%. The sensitivity of model any of the monitored locations, including the downwind predictions to assumptions about the deposition pattern perimeter location (BGCT3, BGCT4) and at a location was evaluated in simulations in which alternative assump- representing the West Dallas community at large (CST5), tions were made regarding transfer of deposited lead to the the probability of their blood lead concentrations exceeding gastrointestinal tract. For particle sizes in the range 1– 10 g/dl would be less than 5% (Table 3). A nearly 10 m, approximately 45–75% of the inhaled dose would identical conclusion is supported by ICRP model predic- be expected to be deposited in the nasopharyngeal or tions of long-term blood lead impacts (Table 2). We can tracheobronchial regions where mucociliary transport conclude from these results that air lead concentrations mechanisms occur (James et al., 1994). If 80%, rather than resulting from remediation activities at the site did not result 5%, of the lead that was deposited in the respiratory tract in significant risk to children living near the site. was assumed to have been transferred to the gastrointestinal This analysis also demonstrates how a modeling tract, then the highest single-day blood lead concentration approach can be used to develop RBCs for air lead predicted for the CST5 monitoring location was 4.5 g/dl, emissions based on predicted probabilities of occurrence compared to 5.2 g/dl — a difference of approximately of a specific blood lead concentration. We opted to base the 12%. Similarly, the above-baseline average blood lead RBCs on a 5% probability of the long-term (i.e., 3 months concentration for the CST5 location was 4.3 g/dl when or longer) average blood lead concentration exceeding transfer to the gastrointestinal tract was assumed to be 80%, 10 g/dl or of a single-day blood lead concentration compared to 4.5 g/dl when a value of 5% was assumed. exceeding 20 g/dl. Use of the 10 g/dl as a level of The relatively small effect of the gastrointestinal tract concern for long-term, quasi-steady state exposures is transfer parameter on the predicted blood lead concentration consistent with EPA guidance for lead risk assessments reflects the relatively small contribution of inhaled lead to (U.S. EPA, 1994a, 2001a). Selection of a concern level for total lead intake (on average, 1% of total) at the CST5 acute elevations in blood lead concentrations is more location. Even during periods of exposure to the highest air problematic since there is no real consensus about health lead levels at the CST5 location, intake from inhalation was risks that might be associated with acute elevations in blood less than half of total intake. The above considerations lead concentrations below 20 g/dl that persist for only few suggest that the ICRP model, as configured for this analysis, days. The use of 20 g/dl in this analysis reflects the CDC’s is unlikely to have underpredicted peak blood lead recommendation that 20 g/dl should be a trigger level for concentrations associated with the short-term fluctuations medical evaluation (CDC, 1991) and is not intended to in air lead concentrations that were observed at the site. imply that 20 g/dl is a threshold for health effects in The default assumption in the IEUBK model is that 32% children exposed acutely to airborne lead. Use of 20 g/dl of inhaled lead is absorbed (U.S. EPA, 1994c). The IEUBK or any other blood lead concentration as an acute concern default value was based on an assumed particle size level is controversial because there is no real consensus distribution in the vicinity of an active lead smelter (less about health risks that might be associated with acute than 1 m, 12.5%; 1–2.5 m, 12.5%; 2–15 m, 20%; 15– elevations in blood lead concentrations below 20 g/dl that 30 m, 40%; greater than 30 m, 15%); size-specific persist for only few days. Little information is available on deposition fractions for the nasopharyngeal, tracheobron- effects of acute lead exposures in humans. This may be a chial, and alveolar regions of the respiratory tract; and function of the time required for the expression of effects region-specific absorption fractions. Lead deposited in the and the usual modes of exposure in humans, which are alveolar region is assumed to be completely absorbed from repeated or continuous exposure to high lead levels in dirt, the respiratory tract, whereas lead deposited in the paint, or in air. Nevertheless, there is general agreement that nasopharyngeal and tracheobronchial regions (30–80% of elevations in blood lead concentration above 20 g/dl, the lead particles in the size range 1–15 m) is assumed to acute or otherwise, should be avoided and, within the range be transported to the gastrointestinal tract where 30% would 30–40 g/dl, aggressive medical intervention should be be absorbed at low total intakes to the gastrointestinal tract. considered (CDC, 1991). Health effects such as decreased The assumptions made in the ICRP model simulations of heme synthesis, neurobehavioral changes, increased blood 100% deposition and 95% absorption of deposited lead pressure, interference with vitamin D metabolism, and would contribute to predictions of higher long-term average severe poisoning, with tragic central nervous system

Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) 63 Khoury and Diamond Lead risks to children from Superfund remedial activities involvement, are expressed at blood lead concentrations of tions. The average value of the air lead concentrations 30 g/dl and higher (CDC, 1991). Acute effects on the recorded at the CST5 air monitoring station (0.24 g/m3), central and peripheral nervous system in children have been which represented the West Dallas community, was reported to occur in association with blood lead concentra- considered as a conservative estimate of the yearly average. tions above 60 g/dl (ATSDR, 1999). By utilizing a The potential increase of soil lead concentration from a predicted 1-day blood lead concentration that corresponds yearly dry deposition of a yearly average lead concentration 3 to a P 20 of 5%, the remedial project manager for the site of 0.24 g/m was calculated to be 3.0 mg/kg. Thus, would have a safe margin and ample time to control surface soil lead concentration at the CST5 location, at the remedial activities on-site without jeopardizing the health downwind residential yards, would be expected potentially of the nearby residential community. to increase by 3.0 mg/kg lead concentration for the duration Tables of RBCs, such as Tables 4 and 5, can be useful of the demolition project. This increment is relatively tools for evaluating the risk potential of air lead concentra- insignificant, less than a 1% increase, compared to the site tions emanating from remediation activities at a site. In this specific clean-up goal of 500 mg/kg. This does not exclude case, the tables relate to a potential 3-month exposure the possibility that lead-laden dusts emanating from the site duration in children who might spend 3 or 8 h/day outside, could land on interior or exterior surfaces that children may where there is a source of airborne lead, such as the RSR contact. Although the potential contribution of this pathway site. However, RBCs for other exposure scenarios could be was not explored explicitly in this analysis, the outdoor constructed using a similar general approach. If the above- contribution of lead to the indoor environment was included baseline average blood lead concentration is the basis for the in simulations as a 0.3:1 ratio of indoor-to-outdoor air RBC, then RBCs for a 3-month exposure ranged from 0.7 lead concentration and an indoor dust lead concentration of to 4.4 g/m3 (1–7 days/week, 3 h/day), or from 0.3 to 200 g/g (IEUBK model default values) was also included. 1.6 g/m3 (1–7 days/week, 8 h/day) (Table 4). RBCs In summary, intensive control measures that took place estimated with the IEUBK model, based on 12-month on-site to suppress dust emissions and release of lead into average blood lead concentrations, were higher (Table 4). air appear, based on risk modeling, to have resulted in The ICRP model predicted that the above RBCs for long- insignificant increments in health risks to children from lead term exposures would also pose minimal risk of acutely emissions. elevated blood lead concentrations since the RBCs based on the highest single-day blood lead concentration (Table 5) are above the RBCs for long-term exposure predicted by Acknowledgments either the ICRP or IEUBK models. A similar approach can be used to evaluate the potential The authors gratefully acknowledge Dr. Joel Pounds risks associated with exposures to the NAAQ standard of (Pacific Northwest Laboratory) for providing us with the 1.5 g/m3, a commonly used trigger for corrective action Fortran code for the ICRP model and EPA Region 6 internal during site remedial activities. Table 4 indicates that, if review workgroup and the U.S. EPA Technical Review based on the ICRP model, the predicted risk associated with Workgroup for Lead for their helpful comments on the exposure to 1.5 g/m3 would be within an acceptable range analysis described in this report. The authors also acknowl- (no more than a 5% probability of exceeding 10 g/dl), if edge the efforts of Mr. Carlos Sanchez, the Remedial Project the exposure frequency was no more than 3 days/week and Manger for RSR Superfund site, in providing the data and the time spent outdoors was no more than 3 h/day. How- other site-specific information. This work was supported, in ever, if children spend 8 h/day outside, then a 3-month part, by GSA contract no. GS-10F-0137K. exposure to 1.5 g/m3 at an exposure frequency greater than 1 day/week may not be acceptable. The IEUBK model References predicted that exposure to 1.5 g/m3 would not pose an unacceptable level of risk at any exposure frequency. Based ATSDR. Toxicological Profile for Lead (Update). U.S. Department of on ICRP model predictions, acute risk of exposure to 1.5 Health and Human Services, Public Health Service, Agency for Toxic g/m3 is negligible for all exposure frequencies, if the risk Substances and Disease Registry, Atlanta, GA, 1999. estimate is based on a concern level of 20 g/dl (Table 5). Bert J.L., Van Dusen L.J., and Grace J.R. A generalized model for the prediction of lead body burdens. Environ Res 1989: 48: 117–127. Possible recontamination of remediated residential yards CDC. Preventing Lead Poisoning in Young Children. Centers for Disease of the surrounding community from on-site demolition Control and Prevention, Atlanta, GA, October 1991. activities was also assessed in this analysis by applying the Chamberlain A.C., Heard M.J., Little P., Newton D., Wells A.C., and lead monitoring data and the EPA Combustion guidance Wiffen R.D. Investigations into Lead from Motor Vehicles. United (U.S. EPA, 1998). Modeling of air emissions was not Kingdom Atomic Energy Authority, Harwell, Oxfordshire, 1978; AERE-R 9198. needed since 232 days of monitoring data were available ENTACT. Remedial Action Workplan for RSR Corporation Superfund with which to estimate annual average air lead concentra- Site. Operable Unit No. 4, Irving, TX, 2000.

64 Journal of Exposure Analysis and Environmental Epidemiology (2003) 13(1) Lead risks to children from Superfund remedial activities Khoury and Diamond

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