Stool as a novel biomarker for arsenic exposure through diet: a case-control study in a West Bengal population

Abstract

Geogenic groundwater arsenic (As) contamination is a persistent health threat in the district of Nadia, West Bengal India. Despite provision of safe piped water, local populations in these areas are still exposed to As through diet as the cultivation is majorly dependent on As contaminated shallow groundwater causing significant As accumulation in agricultural foodstuffs. Although urine is an established biomarker for As exposure through drinking water yet, it does not reflect the actual exposure through diet. Hence, stool-As concentration of exposed population should be evaluated to assess the true exposure through diet. The present case-control study evaluates As concentration in stool samples of exposed (n = 24) and unexposed (n = 36) populations. Average stool-As concentration found was 234 ± 207 µg/kg in exposed population while only 66 ± 22 µg/kg in control samples; comparable to those of urine samples of case and control; respectively. Positive Pearson correlation and a significant difference of variance through ANOVA (p = 0.01; Fcrit= 1.65) among stool-As, urine-As, groundwater-As, age and BMI found for case samples indicate that stool also presents comparable and measurable As concentrations upon exposure. Mann-Whitney U test confirms that random values of stool-As in case samples varied significantly (p < 0.001) than those of control samples. Besides, multi-metal analysis of stool digest indicated that stool-As correlated negatively with most of the metals in case and positively with control samples. These observations along with ease of collection and detection due to higher concentration in the matrix, suggest that stool may act as a decisive biomarker of As exposure through diet. To the best of our knowledge, this is a pioneering study to establish stool as a reliable and significant biomarker for assessing As exposure as limited investigations exist focused on human faecal samples on long term naturally exposed adult human population.