Resolving scientific controversy over smelter risks and neurodegenerative effects of metals

Although it is well known that metals pollution can cause neurotoxic effects, scientists are currently divided about the neurodegeneration hypothesis. That is, some scientists accept, while others fail to accept, the hypothesis that metals/metalloids, at exposure levels below those capable of causing neurotoxicity, can cause neurodegeneration—progressive or worsening neurological disease. Partly because of controversy over the neurodegeneration hypothesis, the US and other governments do not require cleanup of smelter-site metals, to the level (that many scientists say is) necessary to prevent site-caused neurodegenerative disease. The purpose of this review article is to help clarify and resolve conflict over the neurodegeneration hypothesis. This analysis (1) surveys the global problem of smelter-related metals pollution; (2) quickly gives an overview of metals pollution at one of the worst US Superfund or hazardous-waste sites, a former smelter in DePue, Illinois; (3) outlines the debate over the neurodegeneration hypothesis; and (4) assesses the current science on both sides of the neurodegeneration hypothesis by means of three classic methods of causal assessment: the mechanism, unification-coherence, and experimental-counterfactual methods. Using these classic methods, the authors (5) show that available scientific evidence argues for accepting the neurodegeneration hypothesis. This finding is significant because it suggests that much current science about smelters and metals’ risks may be incomplete or flawed. It also shows that, as a result, there may be sound scientific reasons for strengthening environmental-metals standards.