PCBs and organochlorine pesticides in phytoplankton and zooplankton in the Indian sector of the Southern Ocean

Abstract

Samples of phyto- and zooplankton were collected in the Indian sector of the Southern Ocean (38–67°S, 18–84°E) and analysed for organochlorine residues (PCBs and pesticides). The PCB concentration in particulate matter (mainly phytoplankton) appeared to be high and similar to that of temperate zones: 0.7 μg g⁻¹ dry weight. Contamination levels were more constant expressed per water volume than per dry weight, and seven times lower (1.2 μg m⁻³) than in northern temperate zones (8.8 μm⁻³ in the North Sea). The Antarctic ecosystems are thus less contaminated than temperate ones — as expected — but the very low phytoplankton biomass present cause high PCB levels per unit of biomass. These results confirm the necessity of using different systems of units in order to correctly express the contamination levels and to identify the main mechanisms responsible for the accumulation of stable pollutants. PCB levels in netplankton samples (mainly zooplankton) were comparable with phytoplankton on a dry weight basis (0.7 μm⁻³), lower on a lipid weight basis (5.8 μg g⁻¹ lw for netplankton, 16.3 for particulate matter) and were much higher per seawater volume (27.2 μg m⁻³ for netplankton, 1.2 for particulate matter). Netplankton contamination is comparable in the Antarctic (0.35 μg g⁻¹ dw) and the North Sea (0.70) since zooplankton feeding on phytoplankton has similar levels of contamination in both ecosystems. Lindane, heptachlor epoxide, dieldrin, DDE and DDT were observed in various samples at trace levels. The high DDE/DDT ratio reflects the more recent origin of Antarctic organochlorines.