Thank you for sharing your epiphany on the impact of low levels of lead on children’s intellectual abilities and the contribution of lead from water, as well as your question about seasonal variation in blood lead concentrations. It is difficult to appreciate how exceedingly small amounts of lead can impact brain function, especially for pediatricians who can recall when blood lead concentrations <30 μg/dL (<300 ppb) were considered “acceptable.” The Canfield et al study, along with dozens of other studies from around the world,2,3  have confirmed that blood lead concentrations <5 μg/dL (<50 ppb) can adversely impact brain development. This shouldn’t be surprising; the concentrations of toxic chemicals in children’s blood that are harmful, like lead, polybrominated diphenyl ethers, and polychlorinated biphenyls, are comparable to the therapeutic range of chemicals administered as drugs to alter behaviors, like methylphenidate. Moreover, on an evolutionary scale, the levels...

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