SPATIAL TRENDS AND HISTORICAL PROFILES OF ORGANOCHLORINE PESTICIDES IN ARCTIC LAKE-SEDIMENTS

Sediment cores were collected from eight remote lakes in Canada, along a mid-continental transect from 49 degrees N to 82 degrees N, with th e objective of examining latitudinal and temporal differences in depos ition of a wide range of persistent, semi-volatile, organochlorine (OC ) pesticides such as DDT, dieldrin, hexachlorobenzene (HCB), hexachlor ocyclohexane (HCH), and toxaphene. Samples were collected with a speci ally constructed box corer (30 x 30 cm), or with large (10-cm) KB core rs, from the deep basins of lakes at the Experimental Lakes Area (ELA) (49 degrees 30'N), Saqvacjuaq (63 degrees 39'N), Cornwallis Island (7 5 degrees 07'N), Axel Heiberg Island (79 degrees N), and Northern Elle smere Island (Lake Hazen; 82 degrees N). Sediment slices were dated us ing Pb-210 and Cs-137. Sediment extracts were analyzed by high-resolut ion GC-ECD with confirmation by GC-MS. Concentrations of total DDT (Si gma DDT) in surface sediments (0-1.3 cm depth) declined significantly with latitude from 9.7 ng/g (dry wt.) in ELA sediments to 0.10 ng/g in Lake Hazen. HCB levels showed a reverse trend; organic carbon normali zed concentrations increased with latitude. Concentrations of other OC pesticides (total HCH, total chlordane, toxaphene, and dieldrin) were generally in the range of 0.1-3 ng/g, with the sites at 63 degrees N and 75 degrees N generally having the highest levels. The profiles of Sigma DDT and total chlorobenzenes in all the mid-continental lakes sh owed maxima in slices dated from the late 1970s to the 1980s, which is about 5-10 years later than maxima reported for Lake Ontario. The res ults generally support several of the predictions of the cold condensa tion hypothesis.