Monitoring Temporal and Spatial Trends in Polychlorinated Dibenzo-p-dioxins (PCDDs) and Dibenzofurans (PCDFs) in Eggs of Great Blue Heron (Ardea herodias) on the Coast of British Columbia, Canada, 1983–1998

Eggs from 21 resident great blue heron (Ardea herodias) rookeries were monitored from 1983 to 1998 along the coast of British Columbia, Canada, for contamination with polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). Dominant congeners (1,2,3,7,8-PnCDD, 1,2,3,6,7,8-HxCDD, 2,3,7,8-TCDD, 2,3,7,8-TCDF, 1,2,3,7,8,9-HxCDD and 2,3,4,7,8-PnCDF) fell markedly in the early 1990s after pulp mills changed from molecular chlorine bleaching to alternative bleaching technologies, and the use of chlorophenolic wood preservatives and anti-sapstains was severely restricted. Strong positive linear regressions between prey fish and heron egg contaminant levels suggested that local dietary uptake was an important route of exposure for herons. Toxic equivalent concentrations (TEQs) sufficient to produce embryotoxicity in great blue heron chicks were measured in eggs from 1985 to 1991 at some colonies. Despite reduction in PCDD/Fs, estimated TEQs remained elevated throughout the 1980s at some urban colonies due to contributions from PCBs.