CONTAMINANT CONCENTRATIONS AND BIOMARKER RESPONSE IN GREAT BLUE HERONEGGS FROM 10 COLONIES ON THE UPPER MISSISSIPPI RIVER, USA

In 1993, great blue heron (Ardea herodias: GBH) eggs were collected fr om 10 colonies on the upper Mississippi River (UMR). They were then ar tificially incubated until pipping and analyzed for mercury, selenium, and organochlorines. Livers of embryos were analyzed for hepatic micr osomal ethoxyresorufin-O-dealkylase (EROD) activity and four measures of oxidative stress. Brains were measured for asymmetry and blood was measured for the coefficient of variation of DNA (DNA CV). Organochlor ine concentrations were generally low (geometric mean DDE = 1.3 mu g/g wet weight; polychlorinated biphenyl [PCB] = 3.0 mu g/g; 2,3,7,8-tetr achlorodibenzo-p-dioxin [TCDD] = 11.5 pg/g). Eggshell thickness was ne gatively correlated with DDE concentrations. Mercury (geometric mean = 0.8 mu g/g dry weight) and selenium (3.1 mu g/g dry weight) concentra tions in GBH eggs were within background levels. EROD activity was not correlated with total PCBs, TCDD, or toxic equivalents (TEQs), based on the relative contribution of individual PCB congeners, dibenzodioxi ns (PCDDs), and dibenzofurans (PCDFs) to total calculated TEQs. Three of the four measures of oxidative stress were correlated with mercury concentrations. Twenty of 43 (47%) embryo brains were asymmetrical and the embryos with asymmetrical brains had higher EROD concentrations i n the liver and higher DNA CV in the blood than embryos with symmetric al brains.