Occurrence and mass loadings of n-alkanes in riverine runoff of the Pearl River Delta, South China: global implications for levels and inputs.

Riverine runoff samples were collected monthly from March 2005 to February 2006 from the eight major outlets of the Pearl River Delta (PRD), South China, and analyzed to obtain the concentrations of n-alkanes in both the filtrate and particulate phases. The average concentrations of Sigma(C15-C34) (i.e., sum of C15 to C34 normal alkanes) ranged from 0.06 to 2.97 microg/L (mean, 0.64 microg/L) in filtrate samples and from 1.00 to 98.8 microg/g (average, 19.8 microg/g dry weight) in particulate samples. Compared to results from around the world, the levels of hydrocarbon compounds in the PRD were at the high end of the global range. Evaluation of compositional indices of n-alkanes indicated that petroleum-related sources are the main contributor of n-alkanes found in the PRD, with minor contributions from high plant wax. Regression analyses appeared to suggest that n-alkanes are transported into the aquatic environment of the PRD via various pathways, and the transport mechanisms also are considerably influenced by the complex hydrologic conditions in the PRD. The annual riverine input of Sigma(C15-C34) from the PRD to the coastal ocean was 360 tons/year, or the equivalent of approximately 8,800 tons/year of petroleum hydrocarbons. The emission of Sigma(C15-C34) from all sources in the PRD was estimated at 39,000 tons/year, or 2.4 g/day per capita. Overall, the PRD contributes approximately 0.2% of the annual global input of n-alkanes to the coastal oceans, similar to the contributions of polycyclic aromatic hydrocarbons, further indicating that the PRD has been a significant source of hydrocarbon contamination to the global coastal marine environment.