How dangerous are low (not moderate or high) doses of lead for childrenʹs intellectual development?

This paper addresses the points raised by five groups of scientists who were invited to respond to my article on the relationship of low blood lead to IQ loss. I dealt with these comments as a scientist who believes that the case is not closed on this topic, as some respondents believe, but that debate is healthy and can move the field to the next level. The criticisms about the measurement of parentsʹ IQ, multiple comparisons, the linearity of the lead–IQ relationship, and the societal consequences of a few points of IQ loss appear weak in the face of an array of evidence that bears on these topics. However, criticisms about my emphasis on the need to control for a wide variety of potential confounders has validity. Ultimately, however, the case for the relationship of low blood lead to IQ loss seems to rest tenuously on data obtained from samples that included numerous subjects with moderate to severe levels of blood lead.