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Avian and fish botulism outbreaks have been recorded since 1999 in eastern Lake Erie. These outbreaks are caused by Clostridium botulinum type E, a toxin-producing bacteria that is found in anoxic substrates rich in organic material. We studied the environmental conditions present in eastern Lake Erie during 2002, a year when several botulism outbreaks were observed. We also tested for the presence of C. botulinum type E in lake sediments. Samples were taken at six stations from two sites of different depths in the Dunkirk (New York, USA) area. The depth of the sampling sites influenced physico-chemical and biological processes in the sediments. We used the quantitative polymerase chain reaction (Q-PCR) to quantify the levels of C. botulinum type E in the samples. Sediment samples contained a patchy distribution of type E spore concentrations (from not detectable to 5520 DNA copies/mg). Samples of benthic invertebrates tested positive for C. botulinum type E spores in tissues (Gammarus 2028 DNA copies/mg, oligochaetes 428 DNA copies/mg, chironomids 148 DNA copies/mg and dreissenid mussels 715 DNA copies/mg). Principal components analysis (PCA) from inshore stations indicated that a decrease in dissolved oxygen, pH and redox potential near the sediment was associated to an increase in specific conductance and the type E toxin gene in sediments. We also found that C. botulinum type E spores are present in sediments at different depths and at different times through the ice-free season.

We studied the occurrence, bioaccumulation, and biomagnification of polybrominated diphenyl ethers (PBDEs) in a mixed food web of native and non-native species in Lake Erie. Non-native species were found at the basal level of the web (dreissenid mussels), at the intermediate level (round gobies, rainbow smelt), and at the top predator rung (steelhead trout). Mean concentrations of total PBDEs in biota (wet mass) ranged from 1.03 ng·g–1 in dreissenid mussels to 31.5 ng·g–1 in walleye. Large piscivores (smallmouth bass, steelhead trout, walleye, and lake trout) had PBDE concentrations three to seven times higher than prey fish (emerald shiners, round gobies, rainbow smelt, and yellow perch). Walleye had the highest concentration of PBDEs among all of the fish species analyzed. BDE 47 was the dominant congener found in biota. Biomagnification factors (corrected for trophic level) indicated that total PBDEs were biomagnified in three fish species: rainbow smelt, smallmouth bass, and steelhead trout. Overall, BDEs 47 and 100 had the highest level of trophic magnification (TMF) from invertebrates to top predators. For fish species, the highest TMF was for BDEs 47 and 49+71. We found that dreissenid mussels and round gobies had the lowest PBDE contamination of the organisms analyzed; however, other non-native prey species such as rainbow smelt contributed significantly to the biomagnification of PBDEs.