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Much has been written recently about the acid rain and mercury precipitation and its effects upon fish stocks. Although data and advice remains contradictory, a number of studies highlight the potential health impacts of consuming fish that may be contaminated by via these chemicals. As with any health scare, however, it is important to view sensational press reports from an informed position and this article sets out to present the facts as they are currently understood and to dispel some of the hype that has surrounded the stories.

It is largely undisputed that the emissions from coal fed power stations leads to the development of sulfates in the atmosphere, resulting in so-called "acid" rain. This can affect the soil it falls upon, slow the growth of forests and affect streams and lakes. This latter effect can damage fish stocks, as many species will be unable to reproduce effectively in acidic conditions. There have been several global attempts to reduce the occurrence of acid rain, including the Convention on Long-Range Transboundary Air Pollution, and these treaties appear to be having a positive effect.

The solution is not yet total, however, and concerns remain in certain parts of the US, particularly in Minnesota, where lakes contain sulfate-reducing bacteria (SRBs). These clever little creatures are adept at minimizing the effects of acid rain - but at a price. The presence of mercury in the atmosphere, again largely from power stations, causes these SRBs to produce methylmercury, which tends to acculate in fish stocks and is unhealthy for humans.

Mercury in fish is of particular concern to the young and pregnant mothers. The UK Food Standard Agency, in consultation with the independent Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment advises pregnant women and children under 16 against long-living fish which can absorb large quantities of mercury, such as marlin, shark and swordfish. They also advise caution with tuna.

Presumably the same advise would apply to fish caught within Minnesota and regions with similar ecological conditions. It should be stressed, however, that the regular comsumption of fish, particular oily fish with a high Omega 3 content are believed to be beneficial to health, and as with most nutritional advice the old maxim of a "little of what you fancy does you good" still applies.

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