Estimation of the load of cyclic organochlorines in North Sea zooplankton

During a North Sea survey in late spring 1986, zooplankton biomass (g dry weight/m²) as well as pollutant concentrations in zooplankton (ng/g dry weight) were determined at 127 stations. On the basis of these data, the load of several cyclic organochlorines in zooplankton (ng/m²) was estimated. It appeared that the highest loads of these pollutants were incorporated in the large zooplankton stocks of the northern and central North Sea, north of 56°N, whereas the highest concentrations were found in zooplankton of the southern North Sea. An explanation for the accumulation of pollutants in sediments as well as in benthos organisms of the central and northern North Sea as found by several authors is discussed in connection with the assumption of a considerably high vertical flux of organic material in these areas. The calculation of total zooplankton content in the North Sea during the late spring survey amounted to about 5 million tons dry weight. This biomass was estimated to contain about 2.6 t PCBs, 19.3 kg p,p′-DDE, 12 kg τ-HCH, 6.4 kg HCB und 5.6 kg α-HCH. These results agree with those on other compartments of the North Sea ecosystem (benthos, fish) found in recent literature. The estimated annual turnover of PCBs in zooplankton (15.2 t) is of the same order of magnitude as the estimated amount transported yearly into the North Sea by rivers and the atmosphere (6–13 t).