Fecal steroids in riverine runoff of the Pearl River Delta, South China: Levels, potential sources and inputs to the coastal ocean

Domestic sewage is a potential source of contamination deteriorating water quality in rivers and coastal environments. The present study determined the concentrations of eight steroids in both filtrate and suspended particulate matter (SPM) samples collected monthly at the eight major riverine runoff outlets of the Pearl River Delta (PRD), South China, from March 2005 to February 2006. The concentration of the eight steroids (sum of which is defined as Σ₈steroid) in the filtrate and SPM samples ranged 16.7 – 1340 ng L⁻¹ and 0.44 – 240 µg g⁻¹, respectively. The filtrate samples contained the highest levels of cholesterol (CHOE) and stigmasterol (STIG) on average, whereas the SPM samples had the largest relative abundances of CHOE and coprostanol (COP). In general, larger proportions of the steroids were associated with SPM than with the filtrate phase. The combined (filtrate plus SPM) concentrations of COP in riverine runoff of the PRD were at the midpoint of the global range in surface water. The concentrations of Σ₈steroid and COP in SPM were not significantly correlated with particulate organic carbon (POC), riverine runoff, or SPM concentrations, which indicates the dominance of nonpoint input sources for the occurrence of steroids in the PRD. The annual riverine inputs of Σ₈steroid and COP were estimated at 360 and 31.6 tons yr⁻¹, respectively, and the monthly inputs of both Σ₈steroid and COP were positively correlated with monthly runoff discharge. Furthermore, the concentrations of Σ₈steroid, COP, and CHOE showed significant temporal and spatial variability. These results can be explained by a combination of climatic characteristics, socioeconomic conditions, and steroid sources. Analyses of the diagnostic indices of COP and background information suggested that riverine runoff from the PRD may have been affected by domestic wastewater, which appeared to be a major COP source to the Pearl River Estuary and South China Sea.