Non-aromatic hydrocarbons in suspended matter from Changjiang (Yangtse River) estuary: Their characterization and variation in winter and summer (low- and high-flow) conditions

Abstract

A study of non-aromatic hydrocarbons in suspended particles from the Changjiang River mouth and adjacent East China Sea was carried out by gas chromatography and gas chromatography-mass spectrometry. The analysis of different hydrocarbon species indicated large differences between the two periods investigated (winter and summer 1986) corresponding to low and high runoff of the river. Non-aromatic hydrocarbon concentrations ranged from 1·02 to 25·55 μg 1 1in winter, and from 0·25 to 5·26 μg 1 1in summer. In winter, two features characterized non-aromatic hydrocarbons: n-alkane patterns maximizing at n-C 27, n-C 29 or n-C 31 and the presence of pentacyclic triterpenoids of the hopane-type which were present mainly in the α, β-hopane series. Other features appeared in summer such as large levels of n-C 17, n-C 19 and n-C 24 and alkenes characterized by a relatively high proportion of polyunsaturated C 21 species. Phytoplankton markers were present in high amounts at stations 1 (north-side), 6 (open-sea zone) and 5 (north of mixing zone), whereas zooplankton-related compounds were abundant at stations 1 (north-side), 6 and 12 (open-sea zone) in summer. An even carbon predominance in the low molecular range, C 18–22, was found in some samples for both seasons. According to several criteria such as n-alkane distribution pattern and ratio of unresolved to resolved compounds, the petroleum contamination of Changjiang estuary was low in 1986, for both low- and high-flow seasons.