Emerging and persistent organic pollutants in sediment cores from the Singapore Straits: Rising pharmaceuticals, variable caffeine and static PAHs

Five sediment cores of 40 cm length were collected from the Singapore Strait and analysed for emerging and persistent contaminants to assess changing pollutant trends and risk to benthic ecology. Data on the sedimentary accumulation of pharmaceuticals are currently lacking and yet present a potential threat to Singapore's coastal ecosystem. Pharmaceuticals occurred in the order hormones>non-steroidal anti-inflammatory>antibiotics and were highest at the sediment surface then decreased down-core. Similar trends were observed for individual antibiotics, azithromycin 0.18–0.51 ng/g⁻¹, clarithromycin 0.02–0.44 ng/g⁻¹ and erythromycin-H₂O 0.01–0.04 ng/g⁻¹ as well as anti-inflammatory drug ibuprofen 0.19–8.59 ng/g⁻¹. The non-systematic variation in the hormone estradiol (E2) 3.41–13.83 ng/g⁻¹ and drink/food ingredient caffeine 1.27–9.19 ng/g⁻¹ was attributed to greater mobility and or post depositional degradation. In contrast, polyaromatic hydrocarbons (∑¹⁶PAH) 0.322–32.569 mg/kg⁻¹ as well as trace metal mercury (Hg) 0.039–1.022 mg/kg⁻¹ were invariant, except for one core which showed a clear-rise and near surface fall tracking TOC% and clay-silt particles. PAH source ratios and parent to alkylated profiles conferred mainly petroleum combustion sources with minor petroleum inputs. Sedimentary PAH and Hg were mostly below established non-statutory sediment quality benchmarks and deemed unlikely to negatively impact benthic ecology. Together PCA and HCA evaluation confirmed similar physico-chemical association for pharmaceuticals and persistent contaminants except for antibiotics. Sediments from Singapore Strait record a recent shift from predominantly hydrocarbon pollution to more complex mixtures spanning pharmaceuticals and caffeine that are suggested but not unequivocally proven to be from on-shore industrial or waste-water discharge sources.