Arsenic in Urine and Drinking Water.

We found the article by Calderon et al., "Excretion of Arsenic in Urine as a Function of Exposure to Arsenic in Drinking Water" (1), to be interesting and informative. The study they reported provides some useful new information concerning the stability of urinary arsenic measurements over time. We were surprised, however, that the authors failed to cite the extensive amount of related work that has been conducted by the Arsenic Health Effects Research Program at the University of California, Berkeley. This includes a study published in 1994 concerning 36 adults in Nevada; the study used a variety of arsenic exposure measures based on both water and urinary arsenic concentrations (2). We have also completed extensive studies in Chile involving approximately 200 study subjects in which we examined the relationship of both water and urine arsenic measurements to arsenic methylation patterns (3) and bladder cell micronuclei prevalence (4). The relationship of water arsenic intake measures with urinary arsenic concentrations (both with and without adjustment for creatinine) was also assessed in this population, and correlation coefficients between the different methods of arsenic exposure assessment have been reported (5). In addition, we conducted an intervention study involving 73 individuals who were given low arsenic water; we assessed urinary arsenic methylation patterns (6) and bladder cell micronuclei (7) in these individuals. Although Calderon et al. (1) provide some valuable additional knowledge to this field, we feel that readers would benefit by being made aware of these studies that were not cited in their paper.

Calderon et al. (1) state that "Previous studies have been inconsistent in methodologies used for the collection of urine samples." In our own studies, we have adhered to a consistent approach, the basis of which is to ensure that urine samples are collected in an identical manner from the groups being compared. In the studies mentioned above (2-7), we used first-of-the-morning samples to measure urinary arsenic, while in our current studies in India we use spot samples taken during field trips to villages during the day. In all of these studies, sample collection is the same for those groups being compared; thus bias is not introduced into comparisons. Regarding precision, it is important to note that groups are being compared in epidemiologic investigations. Single spot urine samples give lower precision than 24-hr urine samples in assessing individuals, but a group average of many individual spot urine samples may give excellent precision. In any case, 24-hr samples are more expensive and difficult to collect, and they put a tremendous burden on study subjects. The difficulties associated with saving 24-hr urine samples likely leads to problems in compliance and thus errors in exposure assessment. In contrast, spot urine samples require little effort by the subject, and if collected properly, they will serve as a valid measure of group exposure. The key to this validity is to use the same procedures to collect samples from all subjects within the study.

REFERENCES AND NOTES

(1.) Calderon RL, Hudgens E, Le XC, Schreinemachers D, Thomas DJ. Excretion of arsenic in urine as a function of exposure to arsenic in drinking water. Environ Health Perspect 107:663-667 (1999).

(2.) Warner ML, Moore LE, Smith MT, Kalman DA, Fanning E, Smith AH. Increased micronuclei in exfoliated bladder cells of individuals who chronically ingest arsenic-contaminated water in Nevada. Cancer Epidemiol Biomark Prev 3:583-590 (1994).

(3.) Hopenhayn-Rich C, Biggs ML, Smith AH, Kalman DA, Moore LE. Methylation study of a population environmentally exposed to arsenic in drinking water. Environ Health Perspect 104:620-628 (1996).

(4.) Moore LE, Smith AH, Hopenhayn-Rich C, Biggs ML, Kalman D, Smith MT. Micronuclei in exfoliated bladder cells among individuals chronically exposed to arsenic in drinking water. Cancer Epidemiol Biomark Prev 6:31-36 (1997).

(5.) Biggs ML, Kalman DA, Moore LE, Hopenhayn-Rich C, Smith MT, Smith AH. Relationship of urinary arsenic to intake estimates and a biomarker of effect, bladder cell micronuclei. Mutat Res 386:185-195 (1997).

(6.) Hopenhayn-Rich C, Biggs ML, Kalman DA, Moore LE, Smith AH. Arsenic methylation patterns before and after changing from high to lower concentrations of arsenic in drinking water. Environ Health Perspect 104:1200-1207 (1996).

(7.) Moore LE, Smith AH, Hopenhayn-Rich C, Biggs ML, Kalman DA, Smith MT. Decrease in bladder cell micronucleus prevalence after intervention to lower the concentration of arsenic in drinking water. Cancer Epidemiol Biomark Prev 6:1051-1058 (1997).