Occurrence of emerging organic contaminants in a tropical urban catchment in Singapore.

Emerging organic contaminants (EOCs) occurring in urban runoff can negatively impact sensitive ecosystems and drinking water resources. The occurrence of 13 EOCs was characterized in the Marina Catchment, a large urban catchment approximately one-sixth the area of Singapore. The 13 EOCs included alkylphenol ethoxylate metabolites (APEMs), hormones, pharmaceuticals, bisphenol A, and a pesticide (fipronil). The APEMs were most prevalent with concentrations of nonylphenol ethoxyacetic acid (NP1EC) and nonlyphenol (NP) ranging from several ng L(-1) to 6 μg L(-1) and 4 μg L(-1), respectively, while concentrations of octylphenol ethoxyacetic acid (OP1EC), dicarboxylated alkylphenol ethoxyacetic acid (CA3P1EC, CA4P1EC) were as high as 0.9 μg L(-1). Other EOCs were present in the ng L(-1) range: chloramphenicol 1-15 ng L(-1), ibuprofen 2-76 ng L(-1), naproxen 8-108 ng L(-1), bisphenol A 30-625 ng L(-1), fipronil 1-72 ng L(-1), estrone 1-304 ng L(-1), estriol 3-451 ng L(-1). The APEMs and EOCs detected appear to enter canals and rivers from non-point sources, possibly from runoff and leaking sewer lines. The closure of Marina Bay with a barrage has resulted in significantly higher levels of APEMS compared to when the bay was open to the sea. Depth profiles show that NP1EC and OP1EC were notably lower in deep waters compared to surface waters. NP, estrone and estriol exceeded literature-based Predicted No Effect Concentration (PNEC) values.