The levels of organochlorine compounds in eggs of water birds from the colony on Tai Lake in China were studied. The eggs were collected in 2000 and belonged to the following species: 65 samples of black-crowned night heron (Nycticorax nycticorax), 36 samples of little egret (Egretta garzetta), 26 samples of cattle egret (Bubulcus ibis) from 13 clutches and 43 samples of Chinese pond heron (Ardeola bacchus) from 17 clutches. Dichlorodiphenyltrichloroethane (DDT) and its derivates (DDE and DDD), hexachlorocyclohexane (HCH) and its isomers (alpha-HCH, beta-HCH, gamma-HCH, delta-HCH), heptachlor, heptachlor epoxide, aldrin, dieldrin, endrin, endrin aldehyde, alpha-endosulfan, beta-endosulfan, and endosulfan sulfate were determined in the laboratory by gas chromatography. The data showed that DDE had the highest levels in all the samples, followed by beta-HCH. The mean levels of DDE among the water bird species were in the order as follows: black-crowned night heron (5464.26 ng/g, dry weight) > Chinese pond heron (2791.12 ng/g, dry weight) > little egret (1979.97 ng/g, dry weight) > cattle egret (660.11 ng/g, dry weight). DDT and its metabolites accounted for 90% of the total organochlorines, except that it was only 73% for cattle egret. The differences of the residue among the bird species were statistically significant and could be attributed to their variations in prey and habitat. Although the DDE burdens in Tai Lake were much lower than 8 microg/g (wet weight) which are thought to have significant adverse effects on black-crowned night herons, they would be expected to increase the risk of adverse effects on survival of chicks of herons and egrets, particularly black-crowned night heron, based on the critical value of 1 microg/g (wet weight) DDE. The burdens of HCHs in this study were higher and the cyclodienes were lower than those found elsewhere.
This research studied the six heavy metal contents, their distribution and the level of pollution in sediments at Haizhou Bay in 2009 and 2014. It was found that the content of cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu) accounted for the major factors in the sediments at Haizhou Bay. The content of major pollutants presented a declining trend from south to north, and the Pb-intensive area moved from the southern waters of the study area in 2009 to the northern waters of Ganyu Port in 2014. Analysis of the pollution load index shows that the study area suffers from medium-level pollution; the most polluted area was the waters around the estuary of Dragon-King River in 2009 and Ganyu Port in 2014, which meant that development of the port had significant impact on the heavy metal contents. Assessment based on the geo-accumulation index shows that Pb pollution deteriorated and Cd pollution abated slightly over the past 5 years. Analysis of comprehensive potential risk index indicates that the ecological risk of the study area from 2009 to 2014 was at the low-medium level, with Cd being the major contributor to the risks.
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