[Fecal Contamination in Laolongdong Underground River as Measured by the Sterol Biomarkers]

To investigate whether the underground river was polluted or not, and trace the source of fecal sterols, the particulate water samples were collected from typical karst underground river named Laolongdong in Nan'an District, Chongqing Municipality in October, 2014, January, March and May, 2015. Ten prior steroids in the underground river were quantitatively analyzed by the gas chromatography-mass spectrometer (GC-MS). The results showed ten steroids including 9 sterols and 1 ketone were detected. During the sampling period, the mass concentrations of particulate steroids (ranging between 1573 and 5007 ng·L^-1) in March and May were higher than those in October and January. The 3 principal steroids-cholesterol, β-sitosterol and coprosterol-in the river accounted for 50.8%-80.4% of the total steroids. The ratios of (epicoprostanol+coprostanol) to (coprostanol+epicoprostanol+cholestanol) of three samples were greater than 0.7, which indicated the river was contaminated in sampling months. The ratio of epicoprostanol to coprostanol was less than 0.2 in October, which indicated the wastewater came from the upstream sewage treatment plant. The ratios of coprostanol to ΣSteroids and coprostanol to 24-ethylcoprostanol in January, March and May were respectively 0.109-0.254 and 6.3-10.3, which indicated that Laolongdong underground river was mainly polluted by human feces. The ratio of 24-ethylcoprostanol to 24-ethylcholestanol in March (0.86) was less than those in January (5.4) and May (2.3), which showed the river was polluted more severely in March than in January and May by poultry dung.