Occurrence and distribution of synthetic musks, triclosan and methyl triclosan in a tropical urban catchment: Influence of land-use proximity, rainfall and physicochemical properties

Abstract

This study involved a comprehensive thirteen month survey of synthetic musks, triclosan (TCS) and methyl triclosan (MTCS) in surface water, as well as suspended particular matter (SPM) and bottom sediments in a tropical urban catchment in Singapore. The polycyclic musk, Galaxolide (HHCB), exhibited the highest concentration among musk compounds, ranging from 5.16 to 42.9ng/L in surface water, 11.0 to 108ng/g dry wt. in sediments and 44.1 to 81.3ng/g dry wt. in SPM. Concentrations of musk ketone, the dominant nitroaromatic musk, ranged from 0.08 to 6.45ng/L in water, 0.082 to 0.72ng/g dry wt. in sediments and 1.75 to 5.50ng/g dry wt. in SPM. Concentrations of MTCS ranged from 0.0056 to 5.6ng/L in water, 0.01 to 0.17ng/g dry wt. in bottom sediments and 0.75 to 2.81ng/g dry wt. in SPM. These concentrations are below predicted no-effect concentrations (PNEC). Principal components analysis (PCA) results showed that synthetic musk concentrations were positively correlated, indicating common source emissions. Rainfall amount and land-use index were found to be key determinants of hydrophobic organic contaminant concentrations in this catchment. Concentrations of TCS and its methylated degradation product, MTCS, were also positively correlated. However, the relative composition of MTCS to total triclosans was relatively low in water (2.8±2.5%) and bottom sediments (0.3±0.1%), suggesting only minor transformation of TCS to MTCS. The organic carbon-water distribution ratio, log Koc (observed), ranged between 3.8 and 5.4 for musks, TCS and MTCS, indicating relatively strong partitioning from dissolved to solid phases. These field-derived log Koc (observed) values are comparable to estimated values based on physicochemical properties. The results provide insight into the occurrence, transport pathways and exposure risks of synthetic musks, triclosan and methyl triclosan in this tropical catchment.