The following article, published yesterday in Chemical & Engineering News, explains recent discoveries made regarding acid rain, and it's relation to mercury levels in fish. Released from a study conducted in Norway, the reduction of acid rain is contributing to the rise of pH levels in lakes, which has been linked to increased mercury levels in fish living in those lakes. As pH becomes less acidic (due to the decrease in acid rain), organic material from soil surrounding the lakes becomes more soluble (read more about this here), including dissolved organic carbon. Further studies have shown that dissolved organic carbon can react with relatively inert forms of mercury, to produce methylmercury. Fish in aforementioned lakes are then consuming this metal, and subsequently through the process of bioaccumulation, methylmercury is ingested by humans. While acid rain presents many harmful implications on both the environment and humans alike, this study shows that acid rain may in fact be a good thing in terms of helping to keep the pH of lakes at a higher acidity, and thus prevent the production and ingestion of methylmercury, the most toxic form of mercury. I think this presents a conundrum of sorts, however I still do believe that the implications acid rain poses to us, outweigh the 'benefits,' if you can call them that.
Wow! This is a new side to the story that you don't usually hear about. I'd also like to hear more about the longer list of other possible causes aside from the acid rain that Mark Marvin-DiPasquale mentions.
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