Generally we assume that pollution is harmful to human health, and that the level of harm increases linearly with the level of pollution. Indeed, that is the assumption that many regulatory agencies adopt when setting pollution standards. For example, most air quality indices assume increasing harm as air quality deteriorates. But humans – indeed life on Earth more generally – have evolved under at times harsh conditions, while some stresses on our bodies (e.g. frequent and regular exercise) are commonly thought to be a good thing. Furthermore, we are sometimes told that drinking alcohol – a toxin – in moderation can have life-enhancing benefits. These apparent inconsistencies in the assumed relationship between (pollutant) dose – (human health) response are encapsulated in the phenomenon known as Hormesis, or the process in which low levels of toxins appear to have beneficial biological effects.
The attached study by Heinz et al. (2010), published in the journal Environmental Science and Technology, is said to provide evidence of hormesis ~ in the form of enhanced fecundity among breeding pairs of mallard ducks (Anas platyrhynchos) linked to very low concentrations of methylmercury in their diet. At higher concentrations methylmercury is extremely harmful, but at low concentrations in this example appeared to have increased birth and survival rates of ducklings.
Hormesis is controversial, and no doubt more work needs to be done on the topic, but some have suggested that its widespread adoption might allow a weakening of pollution regulations (which might then make pollution regulations cheaper and easier to implement).
Of course, we’d be better off not polluting at all, even it pollution was not harmful ….
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