The contamination of groundwater by arsenic in Bangladesh is the largest poisoning of a population in
history. In this paper we provide new estimates of: 1) the effects of the consumption of foods grown and cooked in arsenic-contaminated water on individual arsenic concentrations and of; and 2) the effects of the ingestion and retention of inorganic arsenic on direct measures of cognitive and physical capabilities as well as on the schooling attainment, occupational structure, entrepreneurship and incomes of the rural Bangladesh population. We use data from a panel survey of rural Bangladesh households with information on individual’s retained arsenic based on toenail clippings that we collected from over 7,000 respondents. We employ an estimation strategy for identifying the causal effects of retained arsenic that exploits the known genetic linkages in abilities to methylate arsenic among family members who reside in different villages net of the effects of diet and the water quality in their villages. We also use genomic data to verify alternative explanations for our results.