Periphyton density influences organochlorine accumulation in rivers

To investigate the influence of eutrophication on organochlorine dynamics in lotic systems, we related polychlorinated biphenyl (PCB) concentrations in brown trout (Salmo trutta) to the periphyton density and total phosphorus concentrations (Tot-P) in 10 Swedish rivers. Tot-P concentrations in the water ranged from 37 6 4 to 156 6 51 mg L21. Periphyton density in the rivers during the experiment ranged from 6 to 199 mg carbon (C) m22 and was not related to the Tot-P concentration. The concentrations of PCB 52, PCB 66/95, PCB 90/101, PCB 132/153/105, PCB 160/138/158, PCB 180, and PCB 194 in brown trout were positively related to both periphyton density and Tot-P concentration, with periphyton density having the highest degree of correlation, 40–58%, compared to 6– 44% for Tot-P. All seven PCB concentrations in brown trout were significantly, positively related to the areal mass (ng m22) of the PCB in periphyton (r2 5 0.69–0.86). Contrary to what has been found for lakes, eutrophication and organochlorine accumulations are positively related in rivers. Thus, an increase in primary production should increase the exposure of the local biota but lead to a decrease of the downstream transport of these pollutants to coastal areas and oceans. The interactions between two major environmental issues, eutrophication of aquatic environments and organochlorine pollution, have received increased attention during the past decade (Larsson et al. 1992; Jeremiason et al. 1999; Dachs et al. 2000). These two environmental problems are both concerns in their own right, but because they tend to cooccur, interactions are important for predicting organochlorine transport and accumulation in aquatic systems. Changes in the primary production, the primary effect of eutrophication, may alter the behavior of organochlorines in the systems. Earlier, it was suggested that increased primary production in lakes had the effect of lowering the concentrations of organochlorines in lake biota (i.e., there is a negative relationship between trophic status and organochlorine concentrations) (Taylor et al. 1991; Berglund et al. 2001a). This relationship may lead to conflicting environmental effects because trying to remedy eutrophication by reducing nutrient loads to lakes may further increase organochlorine concentrations in already contaminated ecosystems. One proposed theory to explain the established negative relationship between eutrophication and organochlorines in lakes is that the increased sedimentation rate causes the sediment burial of organochlorine compounds while the primary producer biomass increases (Berglund et al. 2001b). The lipophilic organochlorines associate mainly with organic particles in the water. When algae die and start to settle to the bottom, organochlorines are withdrawn from the water column. Hence, the pelagic food webs receive less exposure in eutrophic lakes, where the organochlorines instead will accumulate in the benthic sediment (Berglund et al. 2001b). The interactions between eutrophication and organochlo1 To whom correspondence should be addressed. Present address: Limnology, Department of Ecology, Lund University, S-223 62, Lund, Sweden ([email protected]).