A sedimentary core in Wulihu Bay in Lake Taihu, the third largest freshwater lake in China, was analysed to delineate the vertical variation of alkanes, polycyclic aromatic hydrocarbon compounds (PAHs) and organochlorine pesticide (OCP) residues. The measured PAH compounds are the 16 US Environmental Protection Agency (US EPA) priority contaminants. The distribution patterns of normal alkanes indicate that they originate mainly from terrestrial inputs and autochthonous organisms as well as petroleum residues. Total PAH levels are mainly in the range of 698–962 ng/g dry weight with 4-ring compounds dominant. Twenty organochlorine pesticides were quantitatively determined, of which α- HCH, β- HCH, p,p'-DDT and its degradation product p,p'-DDD and Dieldrin were dominant. Total organochlorine pesticides, HCH compounds and DDT compounds were in the range of 14–104 ng/g, 3.0–10.4 ng/g and 0.65–38 ng/g dry weight, respectively. The sum of DDT and HCH compounds represents 30–47% of total pesticides residues. Total OCP residues, DDT compounds and HCH compounds reach peak concentrations at the depth of 2–4 cm, which may be related to the serious flooding in the Yangzi River in 1998.Their sharp drop in the 0–2 cm interval may be due to the comprehensive control and treatment of pollution in Lake Taihu drainage area implemented by the Chinese Government since 1998.

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