nce of
2. Assist epidemiologists interested in
evaluating the intake of arsenic from drinking
3. Provide a basis for evaluating the costs
of adopting a particular value for a drinking-
water standard or Maximum Contaminant Level
To that end, Welch, et al (1999) undertook an extensive review of existing literature and scientific studies of the contamination of groundwater to determine which regions of the country are most likely to be affected by this problem and to identify the common causes of groundwater contamination by arsenic. They found that widespread high arsenic concentrations in groundwater are most commonly the result of:
1. The upflow of geothermal water.
2. Dissolution of or desorption from, iron-
3. Dissolution of sulfide minerals.
Concentrations of naturally occurring arsenic in groundwater vary on a regional basis as a consequence of climate and geology, but at a broad regional scale, arsenic concentrations exceeding 10mg/L are more frequently observed in the Western U.S. than in the East though investigations of groundwater in Maine, Michigan, Minnesota, South Dakota, and Wisconsin in the 1990s indicated that arsenic concentrations exceeding 10mg/L are both more widespread and common than previously recognized.
Paoloni, Fiorentino, Sequeira, and Echeverria (2000) point out that while arsenic is widely found in the natural environment, mainly as an outcome of processes related to vulcanicity, and as a consequence of anthropogenic use of inorganic forms such as arsenate and arsenite. Material of volcanic origin is transported in suspension in the atmosphere and then deposited as lenticular layers in the sediment on plains. These layers undergo a constant washing process. The resulting fragments are mobilized by means of various infiltration and straining mechanisms. They end up in both surface and groundwater, from which human beings are placed at risk for arsenic poiso...