POLYCHLORINATED BIPHENYL (PCB) LEVELS IN SEDIMENTS, AQUATIC EMERGENT INSECTS, AND MARSH WRENS IN A GREEN BAY, LAKE MICHIGAN COASTAL MARSH
Kevin A. Palmer
Aquatic emergent insects are an important food resource for wetland avifauna, providing a link between the aquatic and terrestrial ecosystem. Besides providing a source of energy and nutrients to insectivorous birds, aquatic emergent insects may also serve as a vector for contaminants from the sediments. To investigate the potential for aquatic emergent insects to provide a biotic pathway for organochlorine contaminants, sediments, aquatic emergent insects, and marsh wrens were collected from a coastal marsh on Green Bay, Lake Michigan and analyzed for Polychlorinated Biphenyls (PCBs).
During 1992 aquatic emergent insects were collected in floating box traps at Peters Marsh and Sensiba Wildlife Area and analyzed for total PCBs. Insects collected at Peters Marsh had a mean total PCB concentration of 0.189 ug/g wet wt., and insects collected at Sensiba Wildlife Area had mean total PCB concentrations of 0.116 ug/g. While insect PCB concentrations at Sensiba Wildlife Area are lower, the difference between the two marshes was not statistically significant.
In 1993, floating box traps were placed within active nesting/feeding territories of marsh wrens (Cistothorus palustris) nesting along two channels at Peters Marsh, and aquatic emergent insects were collected and analyzed for total PCBs. Sediments, marsh wren eggs, and marsh wren nestlings were also collected and analyzed. Total PCB concentrations in sediments sampled at Peters Marsh ranged from 0.011 to 0.265 ug/g dry wt. with a mean concentration for 24 samples of 0.100 ug/g dry wt. Aquatic emergent insects collected at Peters Marsh had a mean total PCB concentration of 0.172 ug/g wet wt. There was a significant difference between insects collected in June and July versus August and September. Marsh wren eggs from Peters Marsh had a mean total PCB concentration of 1.97 ug/g wet wt. Marsh wren nestling total PCB concentrations ranged from 0.360 to 1.80 ug/g wet wt., and the PCB concentration was dependent upon the age of the nestling. Younger nestlings (4 and 5 day old) had a higher PCB concentration than older nestlings (14 day old).
A marsh wren PCB bioenergetic model was developed for 1 to 15 day old nestlings and the model predicted PCB concentrations to within 0.1 to 0.2 ug/g wet weight for three of the four marsh wren nestlings collected.
The eight highest sediment samples exceeded the high range for 11 of 18 potential injury thresholds listed in the Assessment Plan for the Natural Resources Damage Assessment (1996), although none of the sediment samples exceeded the maximum benthic threshold of 1 ug/g total PCB. Furthermore, 19 of the 22 aquatic emergent insect samples collected in this study exceeded the International Joint Commission Aquatic Life PCB Guideline of 0.100 ug/g.