Where Arsenic Comes From
- Rock/soil: Earth’s crust contains (on average) 2-5 ppm arsenic, though some kinds of minerals have much higher concentrations of arsenic. Some examples of arsenic minerals are arsenopyrite, realgar, orpiment, arsenolite. Weathering of these minerals will result in some arsenic getting into water and air.
- Volcanic activity can release large amounts of arsenic to the environment
- Every year, natural sources contribute about 1/3 of the total annual release of arsenic to the atmosphere. Most of this comes from volcanoes.
- Groundwater in contact with rocks that are high in arsenic MAY contain high concentrations of arsenic – this is a natural source of arsenic. Many of the world’s most troublesome problem spots are due to naturally high in arsenic in groundwater.
- In the oceans, some animals and plants make organic arsenic compounds. These can become quite concentrated in an organism, but they are generally of low toxicity even though they contain arsenic.
Anthropogenic (caused by human activities) sources:
- Mining/smelting of copper, gold, lead and zinc ores. Arsenic is a by-product since most of these ores are relatively rich in As. Some of the arsenic is purified for other uses (see below) and some remains in the waste rock. Arsenic in waste rock is not a problem on its own, but bacteria can produce acid and start wearing away the rock. That causes arsenic to be released into the water. Smelting, which is metal purification at very high temperatures, can also release a large amount of arsenic to the atmosphere. This and burning of fuels that contain arsenic are the largest industrial contributors of arsenic to air, water and soil.
- Wood preservation (greenish CCA pressure treated wood is treated with chromated copper arsenate, an arsenic and chromium containing preservative, to prevent deterioration from fungal attack. Eventually the metals in the preservative may leach out of the wood). This accounts for about 70% of global arsenic use and may be a large source of arsenic to the environment. Due to potential toxicity and leaching, CCA treated lumber is no longer used for home construction in the USA.
- Agricultural (many older pesticides against insects and rodents, herbicides and fungicides contained arsenic – lead arsenate was a particularly bad one, since both lead and arsenic are toxic! These were widely used before organic pesticides were developed. Where I live in Maine, arsenical pesticides were used in blueberry, potato and apple cultivation. Organic compounds containing arsenic are still used on cotton crops and are added to chicken feed to promote growth, so their poop will also be high in arsenic). Agricultural uses account for about 22% of global arsenic use
- Burning materials with arsenic in them (coal can be high in As, and so can diesel fuel. When the fuel is burned, arsenic is released into the air, and may come back to earth in rain or attached to particles)
- Glass industry (As is used to decolorize glass)
- Electronics industry (in semiconductors and lasers). Semiconductors are used in computer chips, so there are probably arsenic-containing semi-conductors in the computer you are using now!
- Also used in smaller quantities in:
- Pigments (for paints, papers, ceramics, etc.)
- Bullets (improves the sphericity and structure of bullets) and other munitions, fireworks
- Medical use of arsenic – some pharmaceuticals contain arsenic. Now arsenic-containing drugs may be used to treat leukemia. They were used more widely before antibiotics were discovered and produced, and before the toxic effects of arsenic at lower than lethal doses were known. For a while, Fowler’s solution (which contains arsenic) was used to treat everything from skin problems to arthritis to bacterial infections.
Wastewater from any of these industries can contribute to arsenic contamination in the environment. The effect should be restricted to an area near the source, however, so these are usually indentifiable and can be avoided as sources of drinking water.
People who work in industries that use a lot of arsenic may be occupationally exposed to higher than normal levels of arsenic. This may cause health effects (some of which gave supporting evidence of the chronic or long-term effects of arsenic).