Occurrence of C10−C13 Polychlorinated n-Alkanes in Canadian Midlatitude and Arctic Lake Sediments

Sediment cores from six lakes in Canada ranging from 49°N to 81°N were analyzed for C10−C13 polychlorinated n-alkanes (PCAs) with the intent of (i) examining the depositional trends with increasing latitude, (ii) studying the historical profiles and fluxes of PCAs in dated sediment slices, and (iii) investigating possible in situ degradation. Sediment slices were dated using 210Pb and 137Cs, and extracts were analyzed for PCA concentrations by high resolution gas chromatography electron capture negative ion high resolution mass spectrometry (HRGC-ECNI/HRMS) in the selected ion monitoring (SIM) mode. Concentrations of total PCAs in surface sediments declined significantly from 135 ng/g (dry weight (dw)) in sediments from the southern basin of Lake Winnipeg (50°N/96°W, Manitoba) to 4.52 ng/g in Hazen Lake (81°N/71°W, high Arctic); corresponding surficial fluxes were 147 and 0.9 μg/m2 yr, respectively. The high flux of PCAs to the south Lake Winnipeg basin suggests local contamination. This was confirmed by analyzing water collected from the Red River, a river that discharges into the southern basin of Lake Winnipeg, in which elevated levels of PCAs were detected (0.02−0.05 μg/L). The surficial flux of PCAs to Fox Lake (61°N/135°W), a subarctic lake in the Yukon, was also high, 34 μg/m2 yr. Much lower fluxes were found in Lake Nipigon (49°N/89°W, N. Ontario), 3 μg/m2 yr, the northern basin of Lake Winnipeg (52°N/98°W, Manitoba), 4 μg/m2 yr, and to Ya Ya Lake (69°N/134°W, Arctic) 0.45 μg/m2 yr. The remote locations of Hazen and Ya Ya Lakes and the low levels of PCAs observed in their corresponding sediment slices are consistent with long-range atmospheric transport. The profiles of PCAs in the midcontinental lakes showed maxima in slices dated from the early 1980s to the 1990s while that of ΣDDT showed a maxima in the 1960s. The presence of PCAs in surface sediments over a wide geographic area, including the Canadian Arctic, suggests that these compounds, which are components of commercial short chain chlorinated paraffins, are regionally and globally distributed by long-range atmospheric transport.