WHO asserts that a water level of 0.01 mg/L (10 ppb) poses a risk of 6 in 10,000 chance of lifetime skin cancer risk and contends that this level of risk is acceptable.One of the worst incidents of arsenic poisoning via well water occurred in Bangladesh, which the World Health Organization called the "largest mass poisoning of a population in history" recognized as a major public health concern. The contamination in the Ganga-Brahmaputra fluvial plains in India and Padma-Meghna fluvial plains in Bangladesh demonstrated adverse impacts on human health.Mining techniques such as hydraulic fracturing may mobilize arsenic in groundwater and aquifers due to enhanced methane transport and resulting changes in redox conditions, and inject fluid containing additional arsenic. Groundwater
In the US, the U.S. Geological Survey estimates that the median groundwater concentration is 1 μg/L or less, although some groundwater aquifers, particularly in the western United States, can contain much higher levels. For example, median levels in Nevada were about 8 μg/L but levels of naturally occurring arsenic as high as 1000 μg/L have been measured in the United States in drinking water.Geothermally active zones occur at hotspots where mantle-derived plumes ascend, such as in Hawaii and Yellowstone National Park, US. Arsenic is an incompatible element (does not fit easily into the lattices of common rock-forming minerals). Concentrations of arsenic are high mainly in geothermal waters that leach continental rocks.
Biochemically, arsenic prevents use of thiamine resulting in a clinical picture resembling thiamine deficiency. Poisoning with arsenic can raise lactate levels and lead to lactic acidosis. Low potassium levels in the cells increases the risk of experiencing a life-threatening heart rhythm problem from arsenic trioxide. Arsenic in cells clearly stimulates the production of hydrogen peroxide (H2O2). When the H2O2 reacts with certain metals such as iron or manganese it produces a highly reactive hydroxyl radical. Inorganic arsenic trioxide found in ground water particularly affects voltage-gated potassium channels,
disrupting cellular electrolytic function resulting in neurological disturbances, cardiovascular episodes such as prolonged QT interval, neutropenia, high blood pressure,
central nervous system dysfunction, anemia, and death. Arsenic exposure plays a key role in the pathogenesis of vascular endothelial dysfunction as it inactivates endothelial nitric oxide synthase, leading to reduction in the generation and bioavailability of nitric oxide. In addition, the chronic arsenic exposure induces high oxidative stress, which may affect the structure and function of cardiovascular system. Further, the arsenic exposure has been noted to induce atherosclerosis by increasing the platelet aggregation and reducing fibrinolysis. Moreover, arsenic exposure may cause arrhythmia by increasing the QT interval and accelerating the cellular calcium overload. The chronic exposure to arsenic upregulates the expression of tumor necrosis factor-α, interleukin-1, vascular cell adhesion molecule and vascular endothelial growth factor to induce cardiovascular pathogenesis. Arsenic has also been shown to induce cardiac hypertrophy by activating certain transcription factors involved in pathologically remodeling the heart.