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 the objective of examining latitudinal and temporal differences in deposition of a wide range of persistent, semi-volatile, organochlorine (OC) pesticides such as DDT, dieldrin, hexachlorobenzene (HCB), hexachlorocyclohexane (HCH), and toxaphene. Samples were collected with a specially constructed box corer (30 x 30 cm), or with large (10-cm) KB corers, from the deep basins of lakes at the Experimental Lakes Area (ELA) (49 degrees 30'N), Saqvacjuaq (63 degrees 39'N), Cornwallis Island (75 degrees 07'N), Axel Heiberg Island (79 degrees N), and Northern Ellesmere Island (Lake Hazen; 82 degrees N). Sediment slices were dated using Pb-210 and Cs-137. Sediment extracts were analyzed by high-resolution GC-ECD with confirmation by GC-MS. Concentrations of total DDT (Sigma 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 normalized 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 showed 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 results generally support several of the predictions of the cold condensation hypothesis.