Increased susceptibility of juvenile chinook salmon to infectious disease after exposure to chlorinated and aromatic compounds found in contaminated urban estuaries

Saltwater-adapted juvenile chinook salmon (Oncorhynchus tshawytscha) exposed in the laboratory to various aromatic and chlorinated hydrocarbons representative of those found in urban estuaries in Puget Sound have a higher susceptibility to infectious disease relative to carrier-exposed juveniles. Disease susceptibility was assessed by examining the temporal percent cumulative mortality in juvenile chinook salmon after exposure to the marine pathogen, Vibrio anguillarum. Aromatic and chlorinated compounds tested included a sediment extract from the Hylebos Waterway predominantly composed of butadiene-like compounds (CHWSE), a model mixture of polycyclic aromatic hydrocarbons (PAHs), hexachlorobutadiene (HCBD), a PCB mixture (Aroclor 1254), and a single PAH, dimethylbenz[a]anthracene (DMBA). The effect of these compounds on disease susceptibility was tested in two separate trials. In Trial I, the percent cumulative mortality in salmon exposed to bacteria after exposure to either CHWSE, HCBD, or the model mixture of PAHs ranged from 28 to 31%, as compared to 16% in the acetone:emulphor control group at 7 days after challenge. In Trial II, the cumulative mortality in salmon ranged from 46 to 49% after exposure to either DMBA or the PCB mixture compared to 25% in the acetone:emulphor control group at 9 days after challenge. These results suggest that juvenile chinook salmon migrating to the ocean through a contaminated estuary experience immunodysfunction, characterized by lowered resistance to disease, which potentially could affect survival of populations that are particularly threatened.