Thursday, January 14, 2010

Arsenic, Geology and Public Health

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I am by no means an Environmental Geologist nor am I particularly active on the side of Medical or Forensic Geology. Nevertheless I discovered much to my pleasure the fascinating thematical width of geology. Specialising myself in Economic Geology and Carbonate Sedimentology has lead me to consider human health effects of natural rock, soil and water contaminants. In my case arsenic.

Arsenic is a common constituent of metallic ores and used in a variety of applications. However, even in areas that are not mineralised in terms of ores high arsenic values can be encountered. Arsenic poisoning can be acute or chronic. In the geological context acute arsenic poisoning is rather rare and the actual risk lies within chronic arsenic poisoning or arsenocosis. Arsenocosis leads to skin problems, skin cancer, cancer of internal organs, diseases of blood vessels, legs and feet (Black Foot Disease). The most common source of arsenic poisoning is low-level arsenic intake from contaminated drinking water. One of the most severe cases of wide-spread arsenocosis can be found in Eastern India and Bangladesh where groundwater has replaced surface water as the main source of drinking water. Elevated As content now affects millions of people. Even As levels as low as 0,005 - 0,01 mg/l have been found to have negative effects on human health.

Mesozoic limestones in Alsace contain elevated As levels between 20 and 77 ppm. Mineralised faults reach As level as high as 2738 ppm. The global average for limestones is around 2 to 3 ppm. Limestones in southern Alsace function as karst aquifers and are important sources of potable water extracted locally at various springs both natural and artifical. Several studies of the French Bureau de Recherche Géologique et Minière (BRGM) have investigated the As contamination in my thesis area. Groundwater from both natural and artificial springs can contain as much as 5960 µm/l of As. Average values are significantly lower though they still exceed values considered harmless. Studies showed the strong connection to faults and deep, chlorine enriched waters making their way to the surface along them.

The recommendations of the BRGM have, to my knowledge, largely been implemented. Highly contaminated springs have been closed and replaced with springs containing only small amounts of arsenic. The irregular and sometimes unpredictable nature of the karst aquifers causes some springs to be exceptionally contaminated - in connection with local faults. Medium contaminated springs have been recommended to receive water treatment by coagulation to remove As with FeCl3.

In the end these aspects also influence my work. Limestones with elevated As are unsuitable for usage in foodstuffs and animal feeds. However, and I will try to elaborate on this aspect a little in my thesis, with the proven connection to deep seated faults and the studies of the BRGM, it may be possible to delineate areas of limestone with only low As content, which seems to be decreasing rapidly away from major faults and also with decreasing amounts of insoluble residue (Fe- and clay minerals).

Finally, the influence of natural contaminants on human health can be found where one might not expect. Even in projects unrelated to mineralised areas. It has to be considered especially where it seems unlikely to occur - when the groundwater pumps where installed in India and Bangladesh no one considered Arsenic.

References:

Takahiko Yoshida, Hiroshi Yamauchi, Gui Fan Sun, 2004. Chronic health effects in people exposed to arsenic via the drinking water: dose–response relationships in review. Toxicology and Applied Pharmacology. 198 (2004) 243– 252

SANJUAN B., DAESSLE M. (1997) Caractérisation des aquifères contaminés par de l'arsenic dans le Haut-Rhin. Rapport final . Rapport BRGM R39799. Download here.

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