Organic chlorine compounds in lake sediments. VI. Two bottom sites of Lake Ladoga near pulp mills

Abstract Chloride, total and extractable organically bound chlorine, chlorohydrocarbons, polychlorodibenzo-p-dioxins (PCDD) and polychlorodibenzofurans (PCDF) were measured in dated bottom sediment layers of two sites of the northern Lake Ladoga near pulp mills. Concentrations and annual depositions of pulp chlorobleaching products in Ladoga sediments were significantly lower than those in pulp mill recipient bottoms in Central Finland. However, typical chlorobleaching traces bound chlorophenolics, chlorocymenes and chlororetenes were readily identified. HCBz, HCHs and chlordanes occurred at low background levels like in Central Finland. In contrary, depositions of the DDT residues (4–16 μg m −2 a −1 ) and PCBs (7–19 μg m −2 a −1 ) at Ladoga were higher than the background levels in Finland (1 and 2 μg m −2 a −1 , respectively). PCB isomer pattern in Ladoga indicated a Russian origin. PCDD and PCDF were at low background levels. Their isomer patterns deviated from those of pulp mill effluent or common background. ECOTOXICITY of the sediments studied can be only very preliminarly estimated from the TEQ values (Tables 2 and 3). Bioaccumulation ratio from sediment to (zoobenthos) mussels (dw/fw) have been observed to be about one for PCDD/Fs and about ten for PCBs /21/. Consequently, the maximal TEQ level in exposed mussels from the surface sediment could be 37 and 35 pg/g (fresh weight). These levels have not been observed to cause any toxic effects to the animals, but they are of concern in food due to biomagnification. PCDDs and PCDFs are not, but PCBs are significant contributors to this concern.