Application of sedimentary fecal stanols and sterols in tracing sewage pollution in coastal waters

A coastal water disposal site for municipal wastewater sludge was established in the southeastern waters of Hong Kong in 1991. Although the assimilating capacity of such a disposal site was expected to be high, some accumulation of dumped sewage sludge on the nearby bottom sediments was considered inevitable. In this study, sedimentary fecal stanols and sterols, such as coprostanol (5 beta(H)-cholestan-3 beta-ol), cholestanol (5 alpha(H)-cholestan-3 beta-ol) and cholesterol, were chosen as molecular markers for the tracing of deposited sewage contaminants in the vicinity of the disposal site. Sediment samples from eleven locations ranging from the centre of the disposal site to up to 20 km from the site were sampled in 1994. All sediment samples were shown to contain the molecular markers, with concentration ranges as follows (in mu g/g of dry sediment): coprostanol 0.34-5.09; cholestanol 0.65-3.87; cholesterol 0.64-3.92. The fecal stanol/sterol ratio 5 beta/(5 alpha + cholesterol) was found to be a suitable parameter for the comparison of sewage contamination in sediments. Non-parametric Kruskal-Wallis ANOVA and Student-Newman-Keuls pairwise multiple comparison analyses revealed that stations in the northeast and southwest of the disposal site were more polluted. Such anisotropic distribution of sewage markers was consistent with the directions of currents flowing through the disposal site. A mass balance model was developed to provide rough estimation of the sewage sludge loading in the sediments from the observed stanol/sterol ratio. (C) 1998 Elsevier Science Ltd. All rights reserved.