In a recent cross-sectional investigation, we reported the intellectual function of adolescents (aged 14 and 15 years) in Bangladesh who had been exposed to arsenic (As). Here, we report a consecutive investigation on the intelligence quotient (IQ) of 408 children who are living in the Sonargoan Thana of Bangladesh (two age groups: 9 and 10 years; 4 and 5 years) were exposed to high levels of As in the groundwater.

Urine and water samples were collected to assess As exposure. The IQ of the children was estimated using the Raven’s Standard Progressive Matrices and the Kaufman Brief Intelligence Test. Information on parents’ socioeconomic status (SES) was collected as confounding factors.

The results indicate that As exposure was responsible for a lower IQ. The concentration of urinary As ([As]_u) was associated with reduced intellectual function in a dose–response manner. A stronger association was found between reduced intellectual function (IQ) and [As]_u than the level of As in the drinking water [As]_w. There was no association between verbal IQ scores and [As]_u of children in early childhood (aged 4 and 5 years).

Based on these results, we conclude that current levels of As in the urine ([As]_u), which we considered to reflect recent exposure to As from all possible sources, including groundwater, food, among others, were negatively associated to the IQ of the children tested, and that this adverse effect of As may also gradually accumulate over time among the poor.