Please direct all questions and comments to Dr. Christian De Kimpe Pesticides Surface runoff from agricultural lands is an important pathway for introducing pesticides to surface waters. Much less is known about atmospheric deposition of the current generation of pesticides. Pesticide concentrations in surface waters vary considerably both regionally and across Canada. Effect of atmospheric deposition on surface water quality Many chemicals, including acids, metals, and organic contaminants, are deposited from the atmosphere onto the land or water. Much of this atmospherically transported material originates outside Canada's borders.
Acid rain is caused by the emission and atmospheric transport of sulfur and nitrogen pollutants.
Thus, surface water acidification almost never occurs in areas of major agricultural activity. Even if the soil gradually loses its capacity to neutralize acidity by leaching of base cations, it is likely that liming or other soil amendment to increase crop yield will occur long before there is any sign of increased acidity in runoff waters. Metal concentrations in atmospheric deposition are much smaller than those in several common soil amendments such as superphosphate, sewage sludge, or cow manure. As long as soil conditions do not yield acidified runoff, metals added to soil will be largely retained. If the soil acidifies, however, the stored metal burden may be mobilized and leach into surface water or groundwater.