The participant’s physical and demographic characteristics are presented in . The median drinking water concentration for the 47 tube wells sampled was 1.6 μg/L (range, < 1–450 μg/L). Overall, 60% were below the WHO’s 10-μg/L drinking water standard (WHO 1985
), and 70% were below the Bangladesh drinking water standard of 50 μg/L (BGS and DPHE 2001
). On average, participants consumed 1,636 g food (wet weight) and 2,676 mL water per day. Participants consumed significantly more food in winter (1,700 ± 338 g wet weight) than in summer (1,571 ± 324 g wet weight), but no seasonal difference was detected in the concentration of As in the composite food samples. The number of servings collected did not vary significantly over the course of the study. Also, we did not find a significant difference in the amount of food collected within each season. No seasonal or daily difference was observed in the drinking water intake rate.
Physical and demographic characteristics of the 47 female participants.
The frequency of each food type collected in the duplicate diet study is shown in . Vegetables and rice were the most commonly consumed food items. Rice, the dietary staple, was present in 91% of all collected meals, with 405 g (wet weight) consumed in an average serving. Vegetables were present in 94% of all meals collected, with an average serving size of 72 g wet weight. Freshwater fish was the most commonly consumed protein. Pabna is far enough inland that seafood is not readily available in the local markets, and no participants reported eating either seafood or shrimp during this study period. Furthermore, all participants reported purchasing their food at local markets. These items would most likely be produced domestically, if not locally. However, this data was not collected.
Frequency of food types collected in the duplicate diet study.
The distribution of total dietary As intake and dose were heavily skewed, driven by the overwhelming contribution from contaminated drinking water for the upper 25th percentile of the population (). When drinking water As concentrations decreased, the relative contribution of As from dietary sources increased. Background dietary total As intake for the population, calculated using the dietary exposures for the participants with no detectable As in their drinking water, was 46 μg/day or 0.91 μg/kg-day. For all participants, the combined median daily total As intake from both food and drinking water was 68 μg/day (IQR, 191 μg/day). The median daily total As intake from food only was 48 μg/day (IQR, 34 μg/day) and drinking water only was 4 μg/day (IQR, 150 μg/day).
Distribution of average daily As intake (μg/day) from both drinking water and dietary sources for all 47 participants sorted by tube well As concentration.
A subset of 35 samples (12% of the total sample collected) analyzed for both total As and iAs were used to estimate the iAs fraction in the 24-hr dietary composite samples. The average inorganic fraction (± SD) in dietary samples was 82.1 ± 13.9%. Linear regression showed that iAs explained 90% of the variability in total As measurements. To estimate the daily iAs dose, all dietary doses were adjusted by the inorganic fraction before being added to the drinking water doses because it is assumed that all As present in drinking water is in the inorganic form. These values were compared to the WHO’s iAs PTDI of 2.1 μg/kg-day (WHO 1985
). Overall, 34% (95% CI, 21–49%) of all participants had an average daily dose that exceeded this recommended limit. Of the four women who used tube wells containing 10–50 μg As/L, two exceeded the PTDI. For women who used a tube well containing < 10 μg As/L, diet was the only substantial source of ingested As.
Using both GEE and median regression models, we found a significant association between the concentration of As in a given household’s drinking water and the total As concentration measured in their food (). This likely reflects the effect of cooking and preparing food with As-contaminated water. The median regression model provided the best fit to the average dietary total As intake, as indicated by the smaller SE. This model estimated that dietary total As exposure increased by 0.5 μg/day (95% CI, 0.2–0.7 μg/day) for every 10% increase in drinking water As concentration.
Figure 2 Average dietary As intake (μg/day) plotted against the logarithm of drinking water As (μg/L). The mean and median regressions were obtained from the model Y = (α + β) × (log10 X + ), where either the mean (more ...)
It is interesting to note that only one participant was diagnosed with As-induced skin lesions (melanosis, leukomelanosis, and hyperkeratosis of the palms and soles). This 38-year-old woman reported using the same tube well—one with an average As concentration of 360 μg/L—for the past 12 years. She had the highest observed average daily total As intake (1231.3 μg/day) and subsequent average daily total As dose (25.7 μg/kg-day). However, another participant with no visible As-induced skin lesions had a higher well concentration. This reinforced the notion that interindividual differences in ingestion rates and duration of exposure are an important contributing factor in exposure assessments.