Arsenic is a naturally occurring element in the earth's crust, and is found throughout the environment. It is important to maintain a distinction between inorganic and organic arsenic, since the organic forms are usually less toxic than the inorganic forms.
Pure arsenic is a gray-colored metal, but this form is not common in the environment. Rather, arsenic is usually found combined with one or more other elements such as oxygen, chlorine or sulphur. Combined with these elements it is referred to as inorganic arsenic, whereas, combined with carbon and hydrogen, it is referred to as organic arsenic. Many arsenic-containing substances, both inorganic and organic, are naturally occurring, while others are man-made.
All soil contains some amount of arsenic. In Ontario, background arsenic concentrations in old urban parkland range up to 17 parts per million (ppm), while concentrations in rural parkland can reach 11 ppm.
Although significant amounts of arsenic can be released from natural ore bodies, human activity accounts for most arsenic contamination in soil. In Ontario, many gold, silver, nickel, copper and zinc ores are contaminated with arsenic. As a result, the areas of highest contamination are in the vicinity of mining and smelting operations. Arsenic concentrations in soils around mine sites have been reported as high as 4,700 ppm.
Because arsenic occurs naturally in the environment, everyone is exposed to low levels. The greatest, most common source of exposure to organic arsenic is from food, particularly shellfish, meat, poultry, grain and dairy products. Food and drinking water together account for 99 per cent of total daily intake of arsenic through ingestion. The breakdown is roughly 84 per cent from food, 15 per cent from drinking water, less than one per cent from soil/dusts (emphasis, SmoothingPlane) and a negligible amount from skin contact. Although most areas in Ontario have low levels of arsenic in drinking water supplies, there are places in Northern Ontario where arsenic concentrations in drinking water supplies are relatively high. People living near mining or smelting operations that have been historically contaminated with arsenic may be exposed to higher arsenic concentrations through ingestion of soil or through inhalation of arsenic-contaminated dust.
Edible portions of plants seldom accumulate high concentrations of arsenic. This is because most backyard vegetable plants are sensitive to arsenic in soil and will either be killed or severely stunted long before the arsenic concentrations in their tissues reach concentrations that pose a health risk. The extent of arsenic uptake into plants not only depends on the degree of arsenic contamination in the soil but also on soil properties. In general, the sandier or wetter the soil, the greater the potential for arsenic toxicity. Toxicity symptoms in plants include stunted, blackened roots and blackened leaf margins.
The highest arsenic concentrations tend to be in root crops, particularly beets and radishes. Fruit crops, such as tomatoes, berries and apples, present a much lower risk because they take up and store very little arsenic.
Green beans are good indicators of arsenic in soil, since bean plants are particularly sensitive to arsenic. If green beans grow well in a garden, it is unlikely that the uptake of arsenic into other vegetables will be high enough to pose a health risk.
A person can take very simple steps to reduce their personal exposure to arsenic in soil or dusts, and because of arsenic's known toxicity, such measures are generally advised. These steps apply to reducing exposures to any metal in soil, in any location.
Contaminated soil can be removed, or exposure can be reduced by covering the soil with clean soil or sod. Soil can also be paved over or covered with paving stones or decking. Other things you can do: