In 1993, 20 great blue heron (Ardea herodias; GBH) eggs (one per nest) were collected from a colony at the Indiana Dunes National Lakeshore, Indiana (INDU). The eggs were artificially incubated until pipping and were then analyzed for organochlorines, mercury and selenium. Livers of embryos were analyzed for hepatic microsomal ethoxyresorufin-O-dealkylase (EROD) activity. Brains were measured for asymmetry. Egg-laying began in early April and the mean clutch size was 4.2 eggs per clutch. Organochlorine concentrations were generally low (geometric mean p,p'DDE = 1.6 ?g/g wet weight; polychlorinated biphenyl [PCB] = 4.9 ?g/g); however, one egg had elevated concentrations of p,p'DDE (13 ?g/g) and PCBs (56 ?g/g). EROD activity in the embryos analyzed from INDU was not elevated. The frequency (11%) of brain asymmetry was low. Eggshells on the average were 3.4% thinner than eggshells collected prior to the use of DDT. Mercury (geometric mean = 0.9 ?g/g dry weight) concentrations in GBH eggs were within background levels. Selenium (4.0 ?g/g dry weight) concentrations in eggs were above background levels, but below a concentration threshold associated with reproductive impairment.
Additional publication details
Organochlorines, mercury, and selenium in great blue heron eggs from Indiana Dunes National Lakeshore, Indiana