Trophic transfer of contaminants in tree swallows (Tachycineta bicolor) nesting near Lake Calumet, Illinois

摘要

Tree swallow (Tachycineta bicolor) nestlings, eggs, and diet and sediment grab samples were used to quantify risks of exposure to15 trace elements, 31 polychlorinated biphenyl (PCB) congeners, 15 polybrominated diphenyl ether (PBDE) congeners and 13 organochlorine pesticides in the Calumet area of northeastern Illinois, USA. Nesting success and clutch size were measured in tree swallows to determine whether local contaminants reduced tree swallow fitness. Overall nesting success was not reduced when compared among sites and to range averages; 71-90% of clutches started had at least one nestling fledge. Likewise there were no differences among sites in the proportion of eggs that hatched and nestlings that fledged. Generally, contaminant concentrations in the media were considered low or not elevated, although sediment concentrations of cadmium, chromium, and nickel at some sites were higher than the ???probable effects concentration??? or the ???probable effects level??? for sediment dwelling organisms, and lead, manganese, and zinc were above the ???severe effects levels??? at some sites. Calumet nestlings in 2005 were fed between 51 and 64% aquatic insects by mass. Terrestrial insects in the nestling tree swallow diet contained significantly greater concentrations of lead than aquatic insects consumed by the nestling tree swallows. Mean mercury concentrations in nestlings ranged from 0.10 to 0.18 mg/kg dry weight (dw) and egg concentrations ranged from 0.11 to 0.23 mg/kg dw and approximately 5% of the total mercury mass in nestlings came from the eggs. Egg mercury concentrations, which are acquired directly from the mother, were positively correlated with the timing of nesting, and negatively correlated with brood size. Nestlings at Indian Ridge in 2004 and Powderhorn in 2005 accumulated the greatest mass of mercury. Mean sum PCB concentrations in tree swallow eggs ranged from 463 to 830 ng/g wet weight (ww) and from 105 to 208 ng/g ww in nestlings. Egg concentrations contributed approximately 48% of the total PCB mass in nestlings. Nestlings at Big Marsh in both years, and Indian Ridge in 2004 accumulated the greatest mass of PCBs. Nestlings from both Big Marsh and Indian Ridge in 2005 accumulated the most PBDEs, with approximately 21% of the total mass in nestlings coming from the eggs. Mean sum PBDE concentrations in eggs ranged from 47 to 78 ng/g ww and from 20 to 62 ng/g ww in nestlings, and these results appear to be among the first reported PBDE concentrations in tree swallows. Powderhorn had no record of sediment contamination that was found, however low levels of contaminants were in the sediment and biota there. Tree swallow nestlings accumulated a variety of contaminants from the Calumet sites though their diet, though eggs contributed significant amounts for some compounds like PCBs. Understanding contaminant presence and uptake in wetlands of the Calumet area is particularly useful due to the loss of wetland habitat in this region.