Persistent organic pollutants in little egret eggs from selected wetlands in Pakistan

The main goal of the present work has been to study the use of egret eggs to assess environmental pollution by POPs (HCB, HCHs, cyclodienes, DDTs and PCBs) in three Pakistani wetlands that are presumed to be affected by different types of pollution. Taunsa Barrage, affected mainly by agricultural pollutants; Karachi Harbor because of the supposed exposure to industrial activity-related POPs; and Haleji Lake as a relatively pristine area because of its location in a stony desert. Taunsa Barrage and Haleji Lake are wetlands of international importance according to the Ramsar Convention, while the Karachi Harbor is of interest because of the large human population living there. Eggs of the white (Egretta garzetta garzetta) and dark (Egretta garzetta gularis) morphs of Little Egrets were used as monitoring tools. Concentrations were also determined in several prey in this species' diet and in the sediments collected in their foraging areas. Differences in egg pollutant content among the three localities were significant for all the compounds. Overall, the eggs from Haleji Lake and Karachi showed, respectively, the lowest and highest percentages of detection and organochlorine concentrations. Biomagnification from sediments to prey and then to eggs has been documented in the three areas studied and is accompanied by higher percentages of detection of different compounds through the compartments. Differences in the biomagnification factor among the areas were small, even when differences in pollutant concentrations were high, suggesting that eggs are reliable indicators of POPs in the environment. The values found were generally lower than those reported for the eggs of large herons from North America or the Mediterranean basin, and are about the same order of magnitude that those of other medium-sized egrets from other pans of the world.