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MP6 Landscape-Scale Ecological Risk Assessment
(138) Ecological Risk Assessment of DDTs and PCBs at the Palos Verdes Shelf: Birds and Marine Mammals.
Arenal, C.1, Byron, E.1, Karen, D.1, Sample, B.1, Hill, T.2, Barackman, M.2, 1 CH2M HILL, Inc., Sacramento, CA, United States2 CH2M HILL, Inc., Redding, CA, United States
ABSTRACT- An Ecological Risk Assessment was performed to characterize risk to birds and mammals inhabiting the Southern California Bight (SCB) from indirect exposure to Palos Verdes Shelf (PVS) sediments contaminated with DDTs and PCBs. Wildlife receptors included double-crested cormorants, brown pelicans, bald eagles, peregrine falcons, and California sea lions. Oral exposure to total DDT (tDDT) and total PCB (tPCB) was estimated using a GIS-based food web exposure model. These GIS-linked dietary exposures were overlaid onto the seasonal foraging ranges of each species to yield area-specific dietary dosages (mg tDDT or tPCB/kg body wt/day). A weight-of-evidence approach that included these oral exposure estimates, egg and blubber residue data for birds and sea lions, respectively, and reproduction field studies as lines of evidence was used to evaluate risk. Risks from oral exposure to tDDT and tPCB were low for pelicans and cormorants during the breeding season, but increased during the non-breeding season when their foraging range extends throughout the SCB and includes more of the PVS area. Furthermore, measured egg residues exceeded benchmarks, which indicates that risk to individual cormorants or pelicans is possible, despite increasing population trends. Eagles and falcons are also at risk from exposure to tDDT and tPCB, as evidenced by exceedances of both oral and egg residue benchmarks and continued reproductive failure in breeding pairs nesting in the Channel Islands. Although the sea lion population appears to be increasing, individual sea lions may still be at risk from tDDT and tPCB exposure as indicated by oral exposure estimates and measured blubber data. In particular, sea lions forage more heavily within the PVS area during the fall and are therefore at the greatest risk during this time.
Key words: organochlorines, ecological risk, marine mammals, birds
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