ARSENIC, MERCURY, AND LEAD AS HYDROPHILE AND BIOPHILE ELEMENTS: IMPLICATIONS FOR HEALTHY WATERSHEDS AND HUMANS

Arsenic, mercury, and lead are toxic substances that can be widespread and tend to accumulate in the biosphere and hydrosphere. Their occurrence in fish (mercury) and drinking water (arsenic and lead) are principal pathways into humans. In Bangladesh an estimated 9,000 deaths per year are arsenic related and world wide an estimated 100 million people are chronically exposed to arsenic in drinking water. In the U.S. an estimated 434,000 children have their intellectual development threatened by elevated blood lead levels and 350,000 people may drink water with high arsenic concentrations. Mercury from fish consumption in the U.S. threatens the neurodevelopment of an estimated 300,000 newborns each year.

Arsenic is a threat in rural watersheds because its hydrophile nature can cause high concentrations in well water. Arsenic may be a future threat in rural and suburban watersheds because of past practices. From 1960 to 2003 an estimated 420,000 tons of arsenic was used in the manufacture of pressure treated wood and another 115,000 tons was used in agriculture. From 1910 to 1970 the largest usage of arsenic was in agriculture.

Mercury is biophile because it readily forms methylmercury that bioconcentrates up the food chain. Because of burning fossil fuels, usage in gold mining and industry usage, mercury is deposited in watersheds. Fish consumption is the major source of mercury for most people. About 30% of atmospheric deposition of mercury is from natural sources. The distribution of mercury is international; the USEPA estimates that 83% of atmospheric deposition of mercury in the U.S. originates from international sources. The future of atmospheric deposition of mercury is mixed with man-made mercury emissions declining for Europe and North America but increasing elsewhere. In 2005 the Asia Pacific countries consumed 3.2 billion tons of coal (56% of world total) often without emission controls, and are increasing production by 8.2% per year.

Lead is biophile because of its identical charge and similar size to calcium. Within urban watershed man-made areas of high lead concentrations are the result of lead's prior usage in gasoline, paint, lead pipes and solder on copper pipes. In the U.S. 4 million tons of lead used in gasoline remains in dust and soil. Three million tons of lead is found in lead paint on 60 million private homes.