The natural distribution of vegetation is mainly regulated by the amount and seasonality of rainfall, temperature and soil fertility. The clearing of native vegetation from 1983 to 1993 has been most pronounced in Queensland and New South Wales, where it is estimated that 300,000 and 150,000 hectares respectively have been cleared annually. Livestock grazing activity, mainly sheep and cattle, is the largest land-user in Australian agriculture. About 2,500 farm chemicals and 2,000 animal health products containing around 400 active ingredients are used in Australia to control over 5,000 economically significant pests. MPCs are set out in Standard A12 of the food standards code.
Insecticides are more toxic than herbicides, and are predominantly used in developing countries.
Pesticides are heavily used on export crops like cotton, bananas, coffee, vegetables and flowers. Nitrate is one of the most common chemical contaminants found in drinking water, presumably mainly from over application of nitrogen fertiliser. Qld SA WA Tas. NT ACT Aust. The amount of nitrogen for uptake at any given time has more than doubled since the 1940s, as a result of human activities.