No abstract

A survey of 11 agricultural watersheds located in southern Ontario revealed 81 pesticides were applied on farms and rights‐of‐way during 1975. An average of 39% of the land surface in the 11 watersheds was treated with a mean rate of 8.27 kg ha−1 of fungicides, herbicides, insecticides, and nematocides. This was equivalent to an average of 3.25 kg ha−1 year−1 over the whole area, with application rates varying from 0.005 kg ha−1 on hay and pasture to 51 kg ha−1 on potatoes (Solanum tuberosum L.), tomatoes (Lycopersicon esculentum Mill.), and tobacco (Nicotiana tabacum L.). Between May 1975 and April 1977 stream water draining the 11 watersheds was analyzed for 61 parent pesticidal compounds (plus four isomers), 13 metabolites, and two industrial organic pollutants. Forty‐one pesticides were common to the list of compounds used in the watersheds and the list included in the analytical procedure. These 41 pesticides accounted for 73% of the weight of pesticides used. Eighteen parent compounds (plus three isomers), three metabolites, and one industrial organic pollutant were found in drainage waters. In addition, three pesticides, DOT (dichlorodiphenyltrichloroethane‐o,p′ and ‐p,p′), TDE (tetrachlorodiphenylethane‐o,p′ and ‐p,p′), and HEOD (1,2,3,4,10,10‐hexachloro‐6,7‐epoxy‐1,4,4a,5,6,7,8,8a‐oxtahydro‐exo‐1,4‐endo‐5,8‐dimethanonaphthalene), identified in water, had not been in current use for several years.Among the pesticides used, only atrazine (2 chloro‐5‐ethylamino‐6‐iso‐propropylamino‐1,3,5‐triazine), endosulfan (6,7,8,9,10,10‐hexachloro‐1,5,5a,6,9,9a‐hexahydro‐6,9‐methano‐2,4,3‐benzo[e]‐dioxathiepin‐3‐oxide [mixed isomers]), and simazine (2‐chloro‐4,6‐bis(ethylamino)‐1,3,5‐triazine) persisted long enough to appear in water throughout the year. The overall unit‐area loading or losses to streams of the pesticides was 2.18 g ha−1 year−1, of which 2.02 g ha−1 year−1 was accounted for by atrazine.The entrance of pesticides into stream water was determined to occur in three main ways: from storm runoff waters (60%), in base flow from internal soil drainage (18%), and from carelessness, termed “spills,” associated with operating equipment adjacent to streams (22%). Five of the chemicals exceeded the water quality criteria established by the International Joint Commission (IJC) for lake and stream waters entering the Great Lakes. These were PCB (polychlorobiphenyl) in 78% of the water samples, ΣDDT (TDE + DDT) in 41%; HEOD in 16%; endosulfan in 14%; and heptachlor epoxide (1,4,5,6,7,8,8‐heptachlor‐2,3‐epoxy‐3a,4,7,7a‐tetrahydro‐4,7‐methanoindan) in 14%. None of the remaining 58 parent chemical compounds sought in the screening program exceeded the IJC water quality criteria.

No abstract

Blocks of apples, grapes, and pears were treated with captan at 1.7,2.8, or 3.4 kg ha"1 for 1-15 applications. Captan residues were measured over a 14-day period following the last application. Residues declined significantly in seven of nine experiments. Correlations between rainfall and captan residues were observed in five experiments. No correlations were observed in four experiments in which little or no rain fell in the first 7 days. In four of the trials the captan residues immediately following the last application did not exceed the 5 mg kg"1 maximum residue limit permitted under the Canadian Food and Drug Act. The longest periods required for residues to decline below the 5 mg kg'1 tolerance were 5 days for grapes, 3 days for pears, and 7 days for apples.