Summary of current understanding of the role of metals in CKDu epidemic

Kathy James, Colorado School of Public Health, University of Colorado, Denver, USA

Which metals that have been explored?

Total (very few studies have speciated arsenic in urine) • In one study in Nicaragua investigated total arsenic in urine (total arsenic), and found no change in lead levels before and after the work shift (zafra). Sample size was small 100 workers 20 each from 5 different job titles including miners. Measurement was collected 1 day (2 samples) and no differences across job titles. Arsenic levels were not associated with concurrently collected markers of kidney disease (NGAL, NAG, ACR, eGFR). • Arsenic pollution is a global problem with areas such as Bangladesh, Taiwan, and Western US having high levels >100µg/L in drinking water. Arsenic is also present in regions of Central America with MeN and , with variable levels that ranging from < 10µg/L to ~ 50µg/L in drinking water. • One study investigated arsenic levels in both urine and water in Sri Lanka and both were not found to be elevated [2]. • Two studies investigated drinking water levels of inorganic arsenic and found levels to be below the USEPA MCL (10 µg/L) [5, 6] and one study did not find a difference between water sources in a case control study [11]. • In Sri Lanka, a study examining urinary arsenic found no difference in urinary arsenic levels (CKDu: 45.447 μg/g creatinine, noncases in endemic areas: 92.443; non-cases from nonendemic areas: mean 56.572) [13] • In Sri Lanka another study did not find differences in urinary arsenic levels by case status [9]. • Arsenic levels in hair were significantly higher in CKDu cases (n = 80; mean = 0.144 μg/g) compared to controls (n = 48; mean = 0.125 μg/g) (P < 0.05).[5] Cadmium • In one study in Nicaragua investigated in urine, and found no change in urine levels before and after the work shift (zafra). Sample size was small 100 workers 20 each from 5 different job titles including miners. Measurement was collected 1 day (2 samples) [3] • Cadmium has been detected in water in areas of El Salvador (3.0µg/L) [17,23] however not wide spread in other areas of MeN [18] • Higher levels were found in 5 reservoirs in Sri Lanka in CKDu endemic areas (0.03– 0.06 mg/L) compared to the MCL of 0.005 mg/L [4] however, in subsequent studies in Sri Lanka, cadmium in drinking water consumed by individuals with CKDu was not elevated above MCL [5, 6] and one study did not find a difference between water sources in a case control study [11]. • In Sri Lanka three studies have investigated cadmium levels in rice and tobacco and where one study found higher levels in endemic areas compared to non-endemic areas [7], however follow-up studies were not able to replicate findings [5,8]. • In Sri Lanka a study examining urinary Cd levels found higher levels in CKDu cases (mean: 1.039 μg/g creatinine) compared with non-cases (0.646 μg/g creatinine) and non-cases from nonendemic areas (0.345 μg/g creatinine) [5]. Study was cross-sectional in nature and therefore subject to reverse causation. • Other studies in Sri Lanka did not find differences in urinary cadmium levels by case status [6,9]. • One study found higher than expected levels of cadmium and lead in blood samples [19] • A dose-response effect was seen for cadmium and CKDu (12, 13). • Higher cadmium concentration was seen in the nails of CKDu cases (n = 80, mean = 0.017 μg/g) compared to controls (n = 48; mean = 0.009 μg/g) (P < 0.05). [5]

Iron • In one study levels of iron were found to be higher in with higher CKDu prevalence than wells with low prevalence of CKDu [11] Mercury • In thesis work completed in El Salvador water samples ranged from 0.0003 to 0.0065 mg/L (0.3-6.5µg/L) [23] Lead • Higher levels were found in 5 reservoirs in Sri Lanka in CKDu endemic areas [4] and one study did not find a difference between water sources in a case control study [11]. • No dose-response effect was seen in Sri Lanka study [12, 13]. • Lead has been variably detected in El Salvador (12.8-21.1µg/L) [23] but not in other areas of MeN [18] • In one study in Nicaragua investigated lead in blood, and found no change in lead levels before and after the work shift (zafra). Sample size was small 100 workers 20 each from 5 different job titles including miners. Measurement was collected 1 day (2 samples) [3]

Uranium • Two studies investigated drinking water levels of uranium and found levels to be below the USEPA MCL [5, 6] and one study did not find a difference between water sources in a case control study [11]. • In one study in Nicaragua investigated uranium in urine, and found no change in levels before and after the work shift (zafra). Sample size was small 100 workers 20 each from 5 different job titles including miners. Measurement was collected 1 day (2 samples) • Uranium has not been detected in areas of MeN [18]

Other metals (Manganese, tungsten, antimony, platinum, beryllium, and thallium) • A study in Sri Lanka examined sodium, potassium, calcium, magnesium, copper, zinc and titanium in urine and selenium, aluminum, strontium and chromium in hair and nails.

Exposure assessments used in past studies Biological A. Urine a. Limitation is the potential issue of reverse causality where impaired kidney function can alter release of metals from kidney through urine b. Arsenic requires speciation to determine exposure to inorganic arsenic c. Lead is not stable in urine and whole blood is the better matrix d. Mercury requires a preservative e. Most common method: 500 µL aliquot (spot urine sample) is collected aliquoted into 5 ml analysis tubes for analysis. Samples are frozen for shipment and remain frozen until analyzed. Samples are diluted in dilute nitric acid and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Typical standards and QA/QC (blanks and spikes) are used for precision testing. Detection limits range between 0.1-0.09 µg/L for cadmium, ~ 0.01 µg/L for uranium, and 0.2-0.22 µg/L for arsenic. B. Hair and Nails a. One study tested hair and nail samples in a small subset (n=80) however laboratory and collection methods were not discussed. C. Serum/Whole Blood a. Lead is the main metal analyzed in whole blood. Collection methods can range from a finger stick to a 500 µL venous draw. The samples are then diluted with ammonium hydroxide / Triton-X solution and analyzed by ICP-MS. The detection limit can range from 0.2- 0.22 µg/L.

Environmental A. Water a. 200 mL polyethylene bottles were acid washed with nitric acid and the samples were capped and refrigerated. Following the collection of samples, bottle were bagged and then stored in a cooler box. All bottles were refrigerated (under 4°C) and subsequently transported in a cooler b. Laboratory analysis Major and trace elements were measured using an Inductively Coupled Plasma Mass Spectrometer B. Air a. Metals in air have not been analyzed in studies investigating CKDu. b. Assessment would include use of personal monitors for dust and particulate matter. Chemical composition of dust/PM matter can identify metal components. C. Soil a. Soil concentrations of metals (arsenic, cadmium, lead) have been reported in regions with CKDu. D. Food a. Rice, tobacco, lotus root, fish in Sri Lanka have been investigated—levels in vegetables, fish, and tobacco were higher in the endemic areas [12,13], however not rice. Overall the contribution of cadmium from diet in Sri Lanka was higher than the allowable limit [12, 13]. This is most likely due to the higher levels of cadmium found in the corresponding soil samples.

Setting for hypothesized exposure (occupational, community) (drinking water, diet, smoking, inhalation)

Occupational/Community/Residential/Individual Behaviors A. Ingestion a. Drinking Water b. Diet B. Inhalation a. Air pollution is novel and beginning to be considered due to the process of burning sugar cane prior to harvesting. b. Dust and particulate matter with metal adsorbed to particles c. Smoking C. Dermal a. Important source of exposure given that many in endemic areas do not wear personal protective equipment and dermal absorption in pesticide sprayers is high given that glyphosate easily dissolves in sweat. b. Systemic dermal absorption of metals is considered low relative to ingestion and inhalation (for example: dermal arsenic absorption ~1.0-6.4%; dermal cadmium absorption ~8.8-12.7%) [20,21,22]

Factors to consider with research • Studies should consider the role of smoking on metal exposure especially cadmium. • Need to consider pesticide contamination, one study found significant contamination of rock phosphate with cadmium and lead [12,13] and arsenic in other pesticides • Metal exposure in diet also needs to be considered (cadmium was a major source in Sri Lanka study). • Glyphosate is a chelating agent and can leach metals from containers and infrastructure and soils o Question: Does glyphosate leach metals in vivo (from bones) • Studies must include inferential statistical tools in order to improve external validity and generalizability. • Temporality is a major factor with exposure assessment. Most studies have assessed exposure either concurrently or after diagnosis. • Reverse causation is another major factor to consider. Most metals are assessed through urinary biomarkers and there may be evidence of elevated metals in cases of CKD due to declined kidney function and altered excretion of metals and other toxicants. • Most studies have only looked at total arsenic in urine samples versus speciated arsenic to parse out inorganic arsenic. • Clinically MeN presents with lower eGFR without proteinuria

Recommended exposure assessment methods for metals across research projects to be able to share information

Biological A. Urine a. Limitation is the potential issue of reverse causality where impaired kidney function can alter release of metals from kidney through urine. b. 24-hour urine samples are the best method, however not feasible with majority of studies so spot urine samples are mostly collected c. ICPMS is the preferred laboratory method

B. Hair/Nail a. Use of nail or hair as a secondary matrix with urine in CKD patients where altered excretion of metals may occur and lead to accumulation of As and Cd in the body. C. Serum a. Serum is the preferred matrix for lead and selenium b. Lead can be analyzed with the finger stick, however most use venous draw

Environmental A. Water a. Grab samples are commonly used for analysis b. Most metals are temporally stable in groundwater sources that draw from deep wells unless there is a major rain or drought event. Shallow wells can have less stability with soil disruption, agrochemical application, and chemistry changes. Surface water is not temporally stable for grab sample however, passive sampling devices (e.g. Chemcatcher/diffusive gradient in thin film device sampler) provide time- weighted average concentrations of metals. c. Ideal exposure assessment for metals involves both spatial and temporal variability assessment. B. Air a. Personal monitors are considered the best. The issue is cost and feasibility for use in research studies. b. Stationary monitors in the field are feasible and can collect dust and particulate matter for metal composition analysis. C. Soil a. Metals in soil can be influenced by physical disturbance and chemical changes due to irrigation, rain, agrochemical application, temperature. b. Spatial variability based on soil type is the important consideration. c. Soil metal concentration needs to be considered in 3 dimensions spatially so soil type and chemistry related to depth is important because wells draw in at the screening depth which may be different soil type and chemistry than surface soil.

Methods for assessing interaction and rationale for interactions (heat stress, dehydration, pesticides)

Metal Mixtures • Most CKDu endemic areas have hard or very (high Ca and Mg) which can impact toxicity of other such as arsenic. Must take into account water hardness. Additionally, glyphosate has a much longer half-life in hard water.

Metal and Pesticide Mixtures • Consideration of the GMC complex as a potential source of exposure. [14, 10]. Methods are complex and may be difficult to implement in occupational setting.

Metal and Heat Stress Interaction • Simultaneously assess metal exposure through spot urine sample or serum sample (whichever matrix is most appropriate) while collecting heat stress indicators such as core body temperature.

References

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