Assessment of effects of PCB-contaminated floodplan soils on reproductive success of insectivorous songbirds

Abstract

From the 1930s through 1977, polychlorinated biphenyls (PCBs) were used in manufacturing processes at an industrial facility in Pittsfield, Massachusetts (USA). While use of PCBs was discontinued in 1977, inadvertent releases prior to that time were conveyed to the Housatonic River and deposited in river sediments downstrean of the facility. During periodic flooding, river sediments containing PCBs were deposited on soils of the 10-year floodpain within an area managed for wildlife conservation. Based on investigate reports of the study area, concentrations of PCBs in surficial floodplain soil (top 15 cm) in the river reach containing that area range from non-detect to 75 mg/kg, with a mean of 12 mg/kg, while PCB concentrations in the surficial sediments in this reach of the river range from 0.04 mg/kg, with a mean of 33 mg/kg. Pursuant to the Massachusetts Contingency Plan and the Resource Conservation and Recovery Act, an ecological risk assessment was designed to evaluate the potential risk of harm posed to the ecosystem by the contaminated floodplain soils. Some of the studies included in this risk assessment have been completed. One such study focused on reproductve success of passerine (i.e., songbird) populations. This assessment endpoint was evaluated based on comparisons of clutch sizes, numbers of eggs hatched, and hatching success of eight species of songbirds living within the floodplain (target population) to those of reference populations nesting outside of the floodplain and to ranges reported in the scientific literature. Approximately 300 natural nests were monitored throughout the 1993 breeding season and reproductive outcome was evaluated on both an overall basis and a species-specific basis. Clutch sizes and numbers of young hatched were not significantly different between target and reference groups for individual species, although sample sizes were generally small. Mean clutch sizes plus or minus one standard deviation were well within normal ranges reported in the literature for all species considered and for both target and reference groups. Hatching success of reference and target nests was 88.4 percent and 87.4 percent, respectively, a difference that is not statistically significant (p=0.77). This endpoint was examined for the target and reference communities rather than individual species, and sample sizes were 45 and 60 for reference and target groups, respectively. Overall, PCBs in the Housatonic River system do not appear to be adversely affecting reproduction in songbirdgs at the community level.