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Aquatic ecology

Delivery of pollutants by spawning salmon

Fish dump toxic industrial compounds in Alaskan lakes on their return from the ocean.


Pollutants are widely distributed by the atmosphere and the oceans1. Contaminants can also be transported by salmon and amplified through the food chain. Here we show that groups of migrating sockeye salmon (Oncorhynchus nerka) can act as bulk-transport vectors of persistent industrial pollutants known as polychlorinated biphenyls (PCBs), which they assimilate from the ocean and then convey over vast distances back to their natal spawning lakes. After spawning, the fish die in their thousands — delivering their toxic cargo to the lake sediment and increasing its PCB content by more than sevenfold when the density of returning salmon is high.

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Correspondence to E. M. Krümmel.

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The authors declare no competing financial interests.

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Figure 1
Figure 2: Surface sediments in Alaskan lakes show a similar pattern of polychlorinated biphenyl (PCB) congeners to that found in salmon returning to spawn, and sedimentary PCB concentrations are strongly correlated with the density of salmon returning.


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