Do historical sediments of pulp and paper industry contribute to the exposure of fish caged in receiving waters?

Field experiments were conducted in early summer 2004 by caging brown trout (Salmo trutta m. lacustris) in Southern Lake Saimaa (SE Finland) for 10 days. Cages were positioned into two depths at four distances (5 to 17 km) from the pulp and paper mill; one set with direct contact to the sediment and other locating at the three meters' depth from the water surface. Resin acids were measured from sediment, water, and fish bile. Possible toxicities were investigated by measuring liver EROD-activity, HSP70-protein, and gene expression profiles by microarray. The concentration of resin acids in the sediment showed clear gradient along the distance from the mill, and their concentrations in water ranged approximately from one to 30 microg L(-1). In the trout bile, concentrations were higher near the surface than on the bottom, indicating the role of current releases as sources of resin acids. When compared to trout held upstream from the effluent source, no differences were found in liver EROD nor HSP70 in bottom cages. However, near surface, a slight but statistically significant increase in EROD and HSP70 was found. Altogether 145 genes were found to be differentially regulated at downstream sites when compared 10 km upstream from the mill. The numbers of genes at each site varied from 5 to 45 without consistent differences between bottom and surface cages. Overall, neither expression profiles nor composition of the transcription signatures made possible to conclude an overt toxicity in exposed brown trout.