OVERVIEW OF THE ENVIRONMENTAL IMPACT OF FLUORIDATION

C.E. Herold1 and M. van Veelen2

1Umfula Wempilo Consulting, PO Box 98578, Sloane Park, 2152. Tel:+27(0)11 463-5203. Fax +27(0)11 706-8524. E-mail: [email protected] 2BKS (Pty) Ltd.

ABSTRACT

The environmental impact of fluoridation on representative downstream water bodies is presented. An assessment system was developed to derive preliminary management objectives against which to compare receiving water fluoride concentrations. A simple methodology was developed to estimate the change in downstream median and peak fluoride concentrations. More detailed assessments carried out by Rand Water were used for the Vaal River system and a portion of the upper Crocodile River system.

Fluoridation to 0.7 mg/l could lead to substantial problems in the strategic Vaal Barrage and downstream Vaal River, Crocodile River, Waterval River and Sand River systems. Problems can be anticipated in the Modder River upstream and downstream of Krugersdrift Dam. Insignificant impacts were indicated in the Msunduzi River, Berg River and Buffalo River systems.

The limitations of the methodology and key knowledge gaps are highlighted. More detailed evaluations taking account of monthly hydrological fluctuations, dam storage and system operating rules need to be carried out to optimise the fluoridation targets in the identified key problem areas. The coarse overview should be extended to embrace other potential problem areas. The long-term effect on irrigated lands, groundwater and irrigation return flow quality warrants attention.

INTRODUCTION

The Department of National Health legislated regulations requiring water service providers to fluoridate the water supplied to up to 0.7 mg F/l. The Water Research Commission (WRC) has conducted an overview of the feasibility of using water as a vehicle for the distribution of fluoride to the South African population. Specialist teams were assembled to deal with the health, environmental, social and legal, technical and economic aspects. This paper focuses on the environmental impact on downstream water bodies after fluoridation of water supplies (1).

Return flows are the main driving force controlling the environmental impact of fluoridation. The most significant impact arises in areas where effluent discharge makes a major contribution to river flow and present fluoride concentrations in the effluent are low. This is exacerbated by relatively high diffuse input from industrial or natural sources, evaporative concentration in arid and semiarid regions and cascading water use down the river system. Inland areas with substantial downstream water use are of greater concern than systems where the effluent is discharged to marine outfalls.

The resources of the overview did not permit investigation of every locality. Instead effort was concentrated on a few carefully selected priority systems where significant impacts are likely to arise. These included the Vaal Barrage - Middle Vaal River, upper Crocodile River, Msunduzi River, Sand River, Modder River, Berg River, Buffalo River and Waterval River systems.

Figure 1 shows the areas covered in the assessment and some additional areas that may warrant further attention.

Proceedings of the 2004 Water Institute of Southern Africa (WISA) Biennial Conference 2 –6 May 2004 ISBN: 1-920-01728-3 Cape Town, South Africa Produced by: Document Transformation Technologies Organised by Event Dynamics

Figure 1. Identified potential problem areas.

ASSESSMENT SYSTEM

A generic assessment system was developed, taking account of the requirements for domestic and agricultural use and the aquatic ecosystems. The change in concentration that may arise from fluoridation of drinking water is not expected to manifest in acute effects, but rather as chronic effects manifesting themselves after a long period of exposure. In this range the central tendency is more important than the instantaneous concentration. Hence the statistical distribution of the individual measurements over time should be used to determine the fitness for use.

As water quality is not statistically normally distributed (a concentration can not be negative), non-parametric statistics are used to describe the statistical distribution of fluoride concentrations. The following parameters were used:

50th percentile: An indication of average conditions. 75th percentile: The upper limit of the inter-quartile range, which indicates the upper limit of what a user will be exposed to on average. 95th percentile: Indicative of extreme conditions of short duration. This should still fall below acute effect levels.

Water quality can also not be described simply as “good” or “bad”, but as a gradual change from one to the other.

The categories and descriptors that have been generally accepted are: Ideal water quality: where there is no effect even after continual prolonged use. Acceptable water quality: where only in rare instances some sensitive users may be affected after a long period of use. Tolerable water quality: where sensitive users may be affected after prolonged use. Unacceptable water quality: where there is a risk that chronic effects may occur. The SA Water Quality Guidelines (2) showed that domestic use is the most sensitive user across all categories. This finding was unaffected after consideration of the proposed ecological classes for fluoride. Table 1 shows the resulting assessment system.

Table 1. Assessment system for fluoride (mg/l).

Class Percentile upper limit 50% 75% 95% Ideal 0.7 0.7 0.7 Acceptable 0.7 1.0 1.0 Tolerable 1.5 1.5 1.5 Unacceptable Any other combination

Even the tolerable category will have a significant risk of undesirable effects, either on humans or the aquatic ecosystem, and is therefore cause for concern. Moreover, Table 1 should be viewed as a means of categorising a water body, rather than as defining a management objective.

Management Objective It would be an exercise in brinkmanship to load the system with a pollutant to raise its concentration to the very limits of the acceptable range. Responsible management requires the setting of management objectives somewhat below the limits of acceptability. This is necessary to allow for future growth, unforeseen circumstances and the coarse nature of the current evaluation.

The purpose of this investigation is not to set such management objectives. However, a tripwire is required to determine if more detailed investigation is required.

A 30% buffer was used for this purpose. The preliminary management targets are given in Table 2.

Table 2. Preliminary management targets for fluoride (mg/l).

Class Percentile upper limit 50% 75% 95% Ideal 0.5 0.5 0.5 Acceptable 0.5 0.7 0.7 Tolerable 1.05 1.05 1.05 Unacceptable Any other combination

The upper limit of the acceptable level (i.e. a median of 0.5 mg/l, and a 95-percentile value of 0.7 mg/l) represent the tripwire level above which more detailed investigation is indicated.

ESTIMATION OF CHANGE IN QUALITY AFTER FLUORIDATION

The results of a preliminary impact assessment of fluoridation of the Rand Water supply (Herold, 2002) were used for the Vaal Barrage-Middle Vaal River and parts of the Crocodile River systems. This analysis was based on an 11-year time series of monthly effluent and river flow data ending December 2001, the current change in fluoride concentration from the raw water to effluent discharge and estimation of river losses between sampling points. While this preliminary methodology does not handle storage changes in major reservoirs well, it is considered to give an adequate initial estimate of the likely impact of fluoridation.

For other areas a much cruder assessment was based on the average effluent discharge, the median river flow and 5-years of fluoride data at key points in each river system. The method is discussed below. Estimation of Median Concentration For pre-fluoridation conditions the mean and 95 percentile concentrations were obtained from the last 5-years record.

Assuming no change in the fluoride load added by users, the load added to the effluent by fluoridation was estimated as the difference between the post- and pre-fluoridation average concentration multiplied by the average effluent discharge. This was then added to any increase in load calculated for upstream stations (after allowing for abstractions) and divided by the observed median flow at the downstream river station to arrive at the median increase in fluoride concentration at this point. This was then added to the observed median concentration to yield the estimated post-fluoridation concentration at the downstream river station.

This methodology is intended to provide a rapid coarse evaluation of the fluoride concentration likely to arise in river reaches below effluent discharge points. Time and budgetary constraints did not permit application of the mass balance to a long time series reflecting fluctuations in runoff rate and catchment fluoride export concentration. Median conditions were chosen, since the main concern is with chronic conditions, which are governed by long-term exposure.

Knowledge of the present or future effluent fluoride concentrations or of the change in fluoride concentration through use is not needed. All that is required is the increase in load brought about by fluoridation.

For river stations the median flow was used since this more closely represents the typical day by day exposure (the average is too strongly influenced by short duration flood discharges). For dam stations the average is a better approximation of exposure because dams trap much of the floodwater, which continues to dilute the base flow entering the dam for long periods. This remains an approximation since part of the flood water spills from the dam and is not available to dilute subsequent base flow runoff and evaporative concentration.

Estimation of 75 and 95 Percentile Values An approximation was used to estimate the likely range of fluoride concentrations arising from flow variation. The observed river fluoride record for the last 5-years was ranked to produce percentile values, including the record median. The simplifying assumption was made that the calculated increase in the median concentration can be added to all the observed present day percentile values.

POTENTIAL PROBLEM AREAS

Relevant data at key sampling points was collected and the methodology used to estimate the change likely to ensue from fluoridation.

Vaal Barrage - Vaal River System Table 3 shows that the median (50%) fluoride management target was historically exceeded in the Riet River (C2H005) and in the Vaal River at the Sedibeng Water intakes (C2H061). The 95-percentile management target was also exceeded in the Rietspruit. After fluoridation to 0.7 mg/l the median target would be exceeded at all of the key points. This indicates a possible danger of chronic effects occurring in this region. Fluoridation would also present a danger of moving the Blesbokspruit (B10) and the Suikerbosrand (C2H004) into the "Unacceptable" range (i.e. 95-percentile concentrations above 1.05 mg/l).

The impact on the Middle Vaal River (C2H007 and C2H061) is of particular concern for Midvaal Water and Sedibeng Water users. These include large numbers of underground mine workers, who work in high humidity hot environments that force abnormally high water consumption (about three times the per capita consumption of other inhabitants). Such workers will be placed at high risk since they will be exposed to three times the amount of fluoride through consumption of water. ERWAT East 49 Rand WWTWs

Johannesburg Vlakplaats Southern WWTWs Dekema Key: Rondebult WWTWs River 165 Vaal 47 Blesbokspruit Effluent input (106m3 p.a.) 49 Klip River

K21 Flow and quality monitoring gauge Rietspruit B10 Dam K21 R6

Waterval Heidelberg Sebokeng Meyerton Ratanda WWTWs Orkney Midvaal Ennerdale WWTWs 4 Klerksdorp Water 50 34 6 3 Kroonstad 65x10 m River Riet Klip RiverKlip Suikerbosrand River Bothaville Vereeniging Vanderbijlpark 10 10 Parys C2H005 C2H071 C2H004 Potchefstroom C2H061 Vaal Vaal River Dam C2H007 Vaal Barrage

Sedibeng Water 73x106m3

Figure 2. Vaal Barrage – Vaal River system.

Table 3. Fluoride concentrations in Vaal Barrage – Middle Vaal catchment (mg/l).

Station Before fluoridation After fluoridation to 0.7 mg/l 50% 95% 50% 95% B10 – Blesbokspruit 0.31 0.42 0.60 1.12 C2H004 - Suikerbosrand 0.28 0.39 0.53 1.09 K21 - Upper Klip River 0.33 0.43 0.68 0.80 R6 – Rietspruit 0.33 0.43 0.51 0.60 C2H071 - Klip River 0.38 0.39 0.54 0.72 C2H005 - Groot Riet River 0.63 0.84 0.73 0.99 C2H007 - Vaal at Midvaal 0.33 0.46 0.50 0.79 C2H061 – Vaal at Sedibeng 0.54 0.64 0.73 0.84 NOTE: Values that exceed the management objective for fluoride are shown in bold.

The short period covered in the analysis for the Middle Vaal River was abnormally wet. The resulting surplus system yield permitted continual operation of the Vaal Barrage salinity dilution option with consequent elevated base flows in the Middle Vaal River. Unacceptable fluoride levels arose even with these exceptional dilution factors (with the minimum monthly base flow at least twice as high as required to meet downstream requirements). Significantly worse fluoride concentrations can therefore be expected during more restrained (even normal) conditions, especially in future years when water requirements grow to more nearly match system yield.

The elevated fluoride levels primarily threaten domestic use (with some 138x106m3 of potable water supplied to the strategic North-West province and Freestate Goldfields) and the natural environment.

The Rand Water analysis did not extend beyond Sedibeng Water. However, the data for the last five years ending September 2002 shows historical median fluoride concentrations in Bloemhof Dam and other points in the Vaal River down to Douglas Weir that are close to those at the Sedibeng Water intakes. This implies that storage attenuation in Bloemhof Dam and dilution by the small incremental catchment runoff is outweighed by evaporative concentration in the arid Lower Vaal River. It is therefore reasonable to expect that fluoridation by Rand Water would lead to similar deterioration in fluoride concentrations further down the Vaal River. This would adversely affect the domestic water supply to Kimberley, Vaal-Gamagara, Douglas and other smaller communities (30x106m3), the biggest irrigation scheme in South Africa at Vaalharts (some 36 000 ha), riparian irrigation along the Vaal and Harts Rivers (19 400 ha) and the natural environment.

Upper Crocodile River The annual municipal effluent discharge to the upper Crocodile River system is 281x106m3 (see Figure 3). This more than doubles the natural mean annual runoff (MAR) of the 3958 km2 Hartbeespoort Dam catchment. Industries, such as the Modderfontein chemical complex and Kelvin and Rooiwal power stations add to this discharge. Elevated fluoride concentrations already occur at several points in the river system. This is attributable to local pollution sources, exacerbated by natural sources, cascading water use and increasing aridity in a downstream direction.

Figure 3. Upper Crocodile River system.

The results of the Rand Water assessment for Rietvlei Dam (A2H090) and Hartbeespoort Dam (A2R001) are shown in Table 4.

Fluoridation would result in violation of the management objective at Rietvlei Dam, with unacceptable peak concentrations arising in Hartbeespoort Dam. The elevated historical peak concentrations in Hartbeespoort Dam are attributable to pollution sources in the upper Jukskei River. The impact of fluoridation has probably been understated due to abnormally wet conditions during the observation period. Urban consumers in Pretoria, Brits and Cosmos and citrus farming below Hartbeespoort Dam would be affected.

Table 4. Fluoride concentrations upper Rietvlei and Hartbeespoort Dams (mg/l).

Station Before fluoridation After fluoridation to 0.7 mg/l 50% 95% 50% 95% A2H090 – Rietvlei Dam 0.32 0.53 0.61 0.89 A2R001 – Hartbeespoort Dam 0.46 0.81 0.80 1.09 The study did not include analyses of the effect of fluoridation at other monitoring stations of the upper Crocodile River system. Instead inferences were drawn from the historical fluoride concentrations shown in Table 5.

Table 5. Observed fluoride concentrations in upper Crocodile catchment (mg/l).

Station Before fluoridation Code Description 50% 95% A2H040 Upper Jukskei River 2.34 4.40 A2H042 Jukskei River 1.67 3.04 A2H044 Jukskei below Johannesburg Northern Works 0.82 1.56 A2H012 Crocodile River above Hartbeespoort Dam 0.54 1.04 A2R015 Crocodile River at Roodekopjies Dam 0.71 0.94 A2R009 Pienaars River at Roodeplaat Dam 0.33 0.47 A2R002 Apies River at Bon Accord Dam 0.36 0.57 A2H061 Apies River 0.40 0.56 A2R012 Pienaars River at Klipvoor Dam 0.48 0.62 A2H021 Lower Pienaars River 0.58 0.76

The fluoride management target is already exceeded at 60% of the stations. The upper Jukskei River is seriously polluted, with all three stations in the "Unacceptable" range. Even the dilution afforded by the large Johannesburg Northern Works fails to reduce fluoride concentrations to acceptable conditions in the Crocodile River at A2H012. The median fluoride concentration in Roodekopjes Dam is substantially (33%) higher than that in Hartbeespoort Dam. This shows that evaporative concentration outweighs dilution by the incremental catchment runoff. This could indicate continuing impact far down the Crododile River, where users are highly dependent on this water source.

The median fluoride concentrations at all of the stations are well above that of the sewage effluent. (Rand Water supplies water at 0.18 to 0.2 mg/l, with very little increase expected for this predominantly domestic effluent.) This implies that the sewage effluent is currently a very substantial diluter of fluoride in this catchment. This will cease after fluoridation, resulting in a substantial increase in fluoride concentrations.

Although the historical fluoride concentrations at four of the points in the Pienaars River catchment do not yet violate the management target, sewage effluent comprises a large proportion of the MAR at these points (35% to 75% of the MAR). It follows that reversal of the dilution after fluoridation of the Rand Water supply will substantially increase the fluoride concentrations. Moreover, exeedance of the management target at the lowest point (A2H021) indicates that the available assimilative capacity is already exhausted.

Sand River Fluoridation is expected to push fluoride concentrations in the Sand River below Welkom above the management target.

Modder River The median fluoride concentration in the Modder River at Krugersdrift Dam was calculated to reach 0.47 mg/l after fluoridation. While this is just below the management target, problems are expected in the long reach of the Modder River and the Bloemspruit between the Dam and Bloemfontein, especially during the prevalent low flow conditions. This is because the river will derive only temporary relief from passing floods, while the Dam benefits from more prolonged dilution by trapped floodwater.

Higher fluoride concentrations are also expected in the Modder River downstream of Krugersdrif Dam. Considerable concentration of salts occurs in this arid river reach due to cascading irrigation use and evaporative concentration.

Msunduzi, Berg and Buffalo Rivers The Msunduzi River, which receives effluent from Pietermaritzburg, appears to be the river most likely to be affected by fluoridation in the Mgeni River catchment. The Berg River could be affected by effluent discharged by Paarl and Wellington. Effluent from King Williams Town and Zwelitsha enters the Buffalo River, with a feedback loop through Laing Dam. The initial analyses indicate little cause for concern in any of these systems.

Waterval River The study resources did not permit estimation of the post-fluoridation situation in the Waterval River. However, readily available information from an earlier DWAF water quality situation analysis (Stewart Scott, 1992) included assessment of fluoride concentrations at the key points shown in Figure 4.

3 Evander

Secunda Sasol 2/3 Key: eMbalenhle Grootspruit 5 2 River 26 23

49 Effluent input (106m3 p.a.) Trichardspruit K21 Flow and quality 3 monitoring gauge Leeupan 2 Dam C1H004 Waterval River

C1H008

Figure 4. Waterval River catchment.

The observations for the two-year period ending September 1989 are summarised in Table 6.

Table 6. Observed fluoride concentrations in Waterval River catchment (mg/l).

Station Before fluoridation Code Description 50% 95% 3 Trichardtspruit above eMbalenhle 1.0 2.4 23 Grootspruit below three gold mines 0.6 5.8 2 Tributary of Waterval River below Leeupan 0.5 5.7 26 Waterval River at Lesie Gold Mine 0.5 5.7 C1H004 Upper Waterval River at Roodewal weir 1.1 1.8 C1H008 Lower Waterval River above confluence with Vaal 0.7 1.4

For median conditions the fluoride management target was equalled or exceeded at all points, with very high peak concentrations causing unacceptable conditions throughout the system. Fluoridation of the water supply would increase fluoride loads in the effluent from Sasol/Secunda, eMbalenhle and Evander, thereby reducing the assimilative capacity and producing even higher fluoride concentrations.

The small tributary entering Leeupan (point 2) would be unaffected by fluoridation as there is no significant upstream municipal effluent source. More recent flow and water quality data has not been assessed, therefore any significant changes in water quality will not be reflected. Significant increases in effluent discharge have occurred over the last decade.

Other Potential Problem Areas The constraints of the overview did not permit evaluation of other areas. The following two areas (see Figure 1) were identified from the experience of the authors.

The Molopo River, with a partial feedback loop via Modimola Dam, may deserve attention. Severe aridity and poor dam basin shape result in significant evaporative concentration, especially during dry sequences. Since Modimola Dam cuts off most of the runoff to the downstream Disaneng Dam, further severe evaporative concentration can be anticipated.

Fluoridation of Grahamstown’s water supply may lead to elevated fluoride concentrations in the Cowie River, thereby affecting the water supply to Port Alfred.

MANAGING FLUORIDE IN THE ENVIRONMENT

The responses available for dealing with elevated fluoride concentrations fall into the following broad categories:

Do Nothing This option most often arises by default when insidious long-term effects are not immediately apparent. Economic constraints can also come into play, whereby the exploitation of sub-optimal local resources takes precedence over costly alternative supplies or treatment.

Dilution A favourable system layout might permit in-stream dilution by catchment runoff or release from other sources.

Avoidance This involves partial or complete switching to an alternative water source. Blending is an example of the former. In blending only the water actually supplied to consumers is mixed with another source to eliminate peak concentrations, rather than dilution of the entire river flow. This option is dependent on a favourable system layout and the availability of an alternative water source.

Resource Treatment This is generally the most expensive and usually the least practical option. This would involve defluoridation of the entire river.

Supply Treatment This calls for treatment (in this case defluoridation) of the water supplied to users.

Source Control Source control is generally much cheaper than resource treatment because the volume of water to be defluoridated is much smaller. Source control can be achieved by defluoridation, alternative use, reduction of intake, containment or simply cessation of the polluting activity.

The preliminary results show that new problem areas can emerge after implementing fluoridation. This creates a dilemma. When fluoridation causes erstwhile acceptable conditions to become unacceptable, who will be responsible for defluoridation? (Existing dischargers, those carrying out the fluoridation or both?) Source control is directed at reducing man-made pollution inputs at source. Logically the largest and most accessible pollution sources would be prioritised for removal. In this context fluoridation would constitute the largest single source of fluoride input to Vaal Barrage and its tributaries. It would also be the easiest to remove. DISCUSSION AND CONCLUSIONS

The results show that fluoridation to 0.7 mg/l would lead to substantial problems in the strategic Vaal Barrage and downstream Vaal River, Crocodile River, Waterval River and Sand River systems. Problems can be anticipated in the Modder River upstream and downstream of Krugersdrift Dam. Insignificant impacts were indicated in the Msunduzi River, Berg River and Buffalo River systems.

Four out of the five problem areas highlighted above would result from fluoridation of the Rand Water supply. Hence this is the most critical area for further investigation.

The overview necessitated the use of a number of simplifying assumptions.

The overview results show the need to optimise the fluoridation targets in the identified key problem areas. More comprehensive investigations are required in these areas, circumventing the limitations imposed by the simplifying assumptions of the overview.

RECOMMENDATIONS

More detailed evaluations are needed taking better account of monthly hydrological fluctuations, dam storage, river losses and system operating rules. Future time horizons should be assessed to take account of growth in effluent discharge. The water resource implications of constraints imposed on system operation (such as minimum releases from Vaal Dam) also need to be investigated. This can best be achieved by means of hydro-salinity modelling.

There is a dearth of effluent fluoride data. This needs to be collected to investigate the possible concentration of fluoride through water use in municipal and industrial demand centres.

The coarse overview should be extended to embrace other potential problem areas.

Investigation of the long-term effect on irrigated lands, groundwater and irrigation return flow quality also warrants attention.

Responsible management of the most strategically important river systems in South Africa requires proper evaluation of fluoridation impacts and careful selection of fluoridation targets. The time frame set for implementation of fluoridation is too short to carry out these essential investigations.

REFERENCES

1. C.E. Herold and M. van Veelen, "Feasibility of using water as the vehicle for the distribution of fluoride to the South African population: Environmental Assessment", Umfula Wempilo Consulting report to Water Research Commission, Pretoria (2003). 2. Department of Water Affairs and Forestry, "The South African Water Quality Guidelines", Pretoria (1996). 3. C.E. Herold, "Evaluation of the impact of fluoridation of the Rand Water supply", Stewart Scott Water Quality report to Water Treatment Technology Division, Rand Water, (2002).