The Arsenic Eaters of Styria

Interestingly, arsenic has long been suspected of being an essential nutrient in mammalian biology. There are wasting diseases that are nominally caused by extreme arsenic deficiency and adding arsenic to animal feed in certain regions of the world (presumably with extremely low environmental arsenic levels) has been practiced because it increases animal weight and fertility. And fact is, in some parts of the world (including some regions of the US), extremely high natural arsenic levels in the water and environment exist at several times the EPA maximum designated levels with no obvious adverse consequences. I do not think there is any rigorous scientific evidence for acquired tolerance but it is a possibility; at a minimum, populations living in naturally very high arsenic environments don't seem to accumulate notable pathologies as a result.

The old saying that "the dose makes the poison" probably applies here, and bioavailability of the arsenic forms probably plays a role. However, the line from poison to harmless is rarely straight and in many cases is bimodal i.e. too little is as bad as too much. Many common vitamins have a similar toxicity curve. Even alcohol consumption has a bimodal distribution in terms of its effects on mortality. Arsenic having a bimodal toxicity would not be surprising, even though it is presumed to be linear by the EPA. It would be somewhat surprising to learn that a high degree of tolerance can be developed but not unprecedented.

An alternative hypothesis is that arsenic bioavailability varies considerably. What may be interpreted as tolerance is actually a circumstantial lack of bioavailability. There is scientific evidence lending credence to the idea of incredibly low bioavailability of dietary arsenic in some cases such that it might be possible to consume large quantities without actually absorbing it. Some plants are known to be aggressive concentrators of environmental arsenic without being particularly toxic to critters that eat them. In some contexts most of the arsenic may go in one end and out the other.

Arsenic is quite interesting from a biochemistry perspective. It can be extremely toxic, which is well understood, but the variability and the effects in lower doses is not. Plenty of interesting research still to be done.

I was born in Cilli, now named Celje, part of Slovenia, but have never heard of this.

Google gave me http://www.ncbi.nlm.nih.gov/pubmed/23070617?dopt=AbstractPlu...: "Possible positive selection for an arsenic-protective haplotype in humans"

PDF at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3553437/pdf/ehp....