ORGANOCHLORINES AND TRACE-ELEMENTS IN 4 COLONIAL WATERBIRD SPECIES NESTING IN THE LOWER LAGUNA-MADRE, TEXAS

Eggs from four aquatic bird species nesting on the National Audubon Sa nctuary Islands of the lower Laguna Madre were collected during 1993 a nd 1994 to determine concentrations of organochlorine compounds and tr ace metals and to evaluate their possible detrimental effects on birds nesting in this aquatic ecosystem. The only chlorinated hydrocarbons found above detection limits were p,p'-DDE (DDE), p,p'-DDT (DDT), HCB, HCH, chlordane, and polychlorinated biphenyls (PCBs). Median DDE and PCB levels in eggs of four species were below 1 mu g/g ww. Concentrati ons of DDE were much greater (6-70 fold) than the concentrations of ot her chlorinated pesticides which were present at or near detection lim its. One egg from a snowy egret contained 9.65 mu g/g DDE, 0.056 mu g/ g DDD, and 1.75 mu g/g DDT. Ten heavy metals and trace elements (Hg, S e, B, Cr, Cu, Fe, Mg, Mn, Sr, and Zn) were detected in 90% of the samp les but at levels that were not of concern. In 1993-1994, concentratio ns of DDE in eggs of aquatic birds of the lower Laguna Madre were much lower than levels detected in this area during the late 1970s and ear ly 1980s. Concentrations of DDE, PCBs, and trace metals in eggs detect ed in this study could not be associated with deformities or other det rimental effects on birds.