METALS IN AGRICULTURAL SOILS OF ONTARIO

Abstract

Farm fields (296) in all agricultural areas of Ontario were sampled to a depth of 15 cm and analyzed for 10 metals and one non-metal. Metal additions to soils in the form of pesticides, trace elements, fertilizers, feed additives and non-agricultural depositions were reviewed. Arsenic and lead levels were elevated in fruit orchard soils as a result of using lead and calcium arsenate over the past 65 yr. Apple orchard soils had higher As and Pb levels than cherry soils, and these were higher than peach soils, correlating with the length of usage and the annual rates of application. Arsenic levels were slightly increased in potato soils due to the use of sodium arsenite. Mercury content in apple orchard soils was slightly elevated by the use of phenyl mercuric acetate over a 20-year period. The treatment of seed grain with methyl mercurials over a 40-yr period was not reflected in the content of farm soils. Organic soils had higher levels of mercury than mineral soils. Copper levels in soils were highest in organic soils following several years' treatment with copper as both a trace element and a fungicide. Copper concentrations in orchard and vineyard soils were raised only slightly by the application of copper fungicides over an 80-yr period. Widespread application of manganese as a trace element and fungicide in the production of vegetables and bean crops was not detected in soils on which these crops were grown. A much smaller use of fungicide containing iron and zinc likewise was not evident in these soils where these fungicides were used in crop production. Cadmium, cobalt, chromium, iron, and nickel levies were not affected by agricultural practises, especially those involving the use of general fertilizers and barn yard manures; however, serious inputs were found on a small number of soils from industrial activities, especially near a nickel–cobalt smelter and the disposal of sludge. Mean natural background levels of metals in agricultural soils of Ontario in order of increasing magnitude were mercury, 0.08; cadmium, 0.56; cobalt, 4.4; arsenic, 6.3; lead, 14.1; chromium, 14.3; nickel, 15.9; copper, 25.4; zinc, 53.5; manganese, 530; and iron, 14.470 ppm. Most metals increased with increasing clay or organic matter content of the soil.