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The efficiency of seven microalgal species, namely, Chlamydomonas sp., Chlorella miniata, Chlorella vulgaris, Scenedesmus platydiscus, Scenedesmus quadricauda, Selenastrum capricornutum, and Synechosystis sp. to remove pyrene from solution varied from species to species. According to the 6-hour, 12-hour, and 7-day exposure data, S. capricornutum was the most efficient species in the removal of pyrene, followed by S. platydiscus (a local isolate), and the least effective species was C. vulgaris. For all species, the removal was very rapid in the first 3 to 6 hours of treatment, and no significant difference was found between live and dead cells of C. miniata, C. vulgaris and S. capricornutum, indicating that the initial removal was due to passive physico-chemical biosorption. More than 65% of the pyrene adsorbed was bound on cell wall materials of S. capricornutum, suggesting the major binding sites were on cell walls. The pyrene removal was also dependent on the concentration of algal biomass used, the more the biomass the higher the removal percentages. In addition to biosorption, pyrene was accumulated and transformed inside live cells. In 7-day S. capricornutum culture, pyrene was not detected in either culture medium or algal pellets, and pyrene might have been completely transformed by this species. The degree of bioaccumulation and biotransformation was species specific.

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The present three-year field investigation on sediment in the eutrophic Pearl River in South China showed that concentrations of sulfonamides (SAs), fluoroquinolones (FQs), and macrolides (MLs) in the river areas where blooms occurred were 4.6, 2.4, and 3.4 times higher than those without blooms, respectively, but the respective concentrations of tetracycline (TC) and oxytetracycline (OTC) in the areas with blooms were 2.6 and 3.8 times lower than those without. Significant positive correlations were found between concentrations of chlorophyll a in water and most antibiotics in sediment. Further investigation in each season suggested that lower diffusion but higher sinking were possible reasons driving the burial of sulfapyridine (SPD), sulfamethoxazole (SMX), and trimethoprim (TMP) in sediment from areas where blooms occurred, with burial rates up to 14.86, 48.58, and 52.19 g month–1, respectively. Concentrations of TCs in both water and sediment were inversely correlated with phytoplankton biomass, which might be related to the enhanced biodegradation capacity of bacteria caused by phytoplankton blooms. Phytoplankton also affected concentrations of antibiotics in the snail, Bellamya purificata, with higher values in March but lower values in September. The concentration of antibiotics in snails positively correlated with that in sediment when snails were dormant but with antibiotics in water after dormancy.

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