Monitoring of persistent organic pollutants (POPs): Examples from Lake Vattern, Sweden

Lake Vattern in southern Sweden is a large oligotrophic lake with high surface to catchment area ratio (ca. 0.4) and a water residence time of 60 years. The lake combines sensitivity to atmospheric POP-pollution with general susceptibility for effects of POPs and slow concentration decline. Time series, from the 1960s until 1996, of PCBs and DDT in fish and data on TCDD in sediment of L. Vattern are presented and compared to other large lakes. The long time dataset of POPs in Arctic char (Salvelinus salvelinus) shows a significant annual decline of about 5% for PCBs and 13% for DDT. These rates are in agreement with other studies. Nutrients as well as biological effects and factors affecting the fate of POPs in oligotrophic lakes with long residence times are discussed. We propose that oligotrophic clear lakes are important ecosystems for monitoring POPs in biota

AMPEROMETRIC BIOSENSORS BASED ON IMMOBILIZED ENZYMES AND CHEMICALLY MODIFIED ELECTRODES

Amperometric biosensors based on two different reaction mechanisms are presented. Common to both types is the combination of a selective catalytic reaction that can be followed amperometrically at 0 mV vs SCE and below. One type is based on the chemical modification of carbon pastes with a dehydrogenase, the necessary cofactor NAD’, and a redox mediator. In the presence of the enzyme substrate NADH will be produced. The high overvoltage for the electrochemical oxidation of the NADH is decreased by the addition of the redox mediator to the paste. The redox mediators used are phenoxazine derivatives making the electrocatalytic oxidation of NADH possible at 0 mV vs SCE and below. A glucose sensor based on glucose dehydrogenase is described. Another type is based on the co-immobilization of a hydrogen peroxide producing oxidase with horse radish peroxidase on the surface of heat-treated graphite. The detection is based on an apparent direct electron transfer from the electrode to the immobilized peroxidase starting at +600 mV and reaching a maximum at about O mV vs SCE. The co-immobilized enzyme layer is stabilised by the addition of bovine serum albumin and glutaraldehyde to the reaction mixture. A glucose sensor based on glucose oxidase is presented