Main contaminants included mercury and lead.
Put this headline together with the recent article on environmental causes of autism:
Landrigan, Philip J. What causes autism? Exploring the environmental contribution. Current Opinion in Pediatrics: 16 January 2010.
A review of the Landrigan's essay is available here by Steven Higgs:
I believe we are poisoning ourselves by allowing the world's fresh water to be polluted by heavy metals...