Tracing anthropogenic contamination in the Pearl River estuarine and marine environment of South China Sea using sterols and other organic molecular markers

5β-Coprostanol together with eight other sterols and unresolved complex mixtures (UCMs) were quantitatively investigated for surficial sediments and surface waters to assess the impacts of anthropogenic activities on the Pearl River estuarine and marine environment of South China Sea. The studied area extends from the Pearl River Estuary southward to the open sea. 5β-Coprostanol concentrations ranged from trace amounts to 53 μg g−1 TOC in surficial sediments. The highest levels and highest percentages of coprostanol were found in the Pearl River estuary, especially in the inner estuary and those sites close to the submarine outfalls of Hong Kong. For waters, only in estuarine samples was coprostanol quantitatively detected, ranging from 11 to 299 ng L−1. Bimodal UCM “humps” were observed for most sediment samples, with concentrations ranging from 215 to 10,491 μg g−1 TOC in sediments and from 2 to 26 μg L−1 in waters, respectively. Progressive seaward declines in concentrations were found for both 5β-coprostanol and UCM in surficial sediments. Trace or no 5β-coprostanol was found in open-sea samples. Concentrations of coprostanol and UCM in surficial sediments are correlated. These results imply that there are obvious anthropogenic contaminations in the Pearl River estuary. The submarine outfalls in Hong Kong represent important sources of the sewage pollution to the Pearl River estuarine sediments evidenced by a combination of coprostanol concentration, diagnostic indices, sterol profiles and UCM. No obvious dispersion or transport of the sewage contamination occurred from the Pearl River estuary to the open South China Sea indicated by fecal sterol biomarkers.