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Antibiotics are normally regarded as safe to aquatic ecosystems when their contamination concentrations are lower than the toxic threshold. This study observed the hazard of ciprofloxacin, sulphamethoxazole and their binary mixture to the aquatic environment at environmentally relevant concentrations lower than the toxic threshold, due to the stimulation on the bloom of Microcystis aeruginosa. The enhanced growth of M. aeruginosa, coupled with elevated photosynthesis activity, was exerted by 50-200 ng/L of ciprofloxacin, 100-200 ng/L of sulphamethoxazole and 20-100 ng/L of the binary antibiotic mixture. Stimulated production and release of microcystins were observed at even lower concentrations. The upregulation of transcription-related proteins, cell division-related proteins, a gas vesicle protein, a global nitrogen regulator (ntcA), two microcystin synthetases (mcyC and mcyH) and ATP-binding cassette transporters provided direct proteomic evidence for the regulation of target antibiotics on M. aeruginosa bloom. Cytochrome P450 was an essential component involved in stress responses and antibiotic biodegradation. Proteomic responses to antibiotic exposure presented a shift in the energy metabolism of M. aeruginosa towards the excitation of photosynthesis, an increase of carbohydrate biosynthesis and the inhibition of carbohydrate catabolism. Superoxide dismutase, enolase and D1 protein were candidate target proteins of different antibiotics in M. aeruginosa. The antibiotic mixture showed a greater hazard than single antibiotics, and a safe threshold of 5 ng/L was suggested for each target antibiotic under the coexistence condition.

Coexisting antibiotic contaminants have potential to regulate cyanobacterial bloom, and the regulation is likely affected by nitrogen supply. A typical cyanobaterium Microcystis aeruginosa was cultured with 0.05-50 mg L(-1) of nitrogen and exposed to 100-600 ng L(-1) of amoxicillin for 7 days. Algal growth was not significantly (p > 0.05) affected by amoxicillin at the lowest nitrogen level of 0.05 mg L(-1), stimulated by 600 ng L(-1) of amoxicillin at a moderate nitrogen level of 0.5 mg L(-1) and enhanced by 100-600 ng L(-1) of amoxicillin at higher nitrogen levels of 5-50 mg L(-1). Amoxicillin affected chlorophyll-a, psbA gene, and rbcL gene in a similar manner as algal growth, suggesting a regulation of algal growth via the photosynthesis system. At each nitrogen level, synthesis of protein and polysaccharides as well as production and release of microcystins (MCs) increased in response to environmental stress caused by amoxicillin. Expression of ntcA and mcyB showed a positive correlation with the total content of MCs under exposure to amoxicillin at nitrogen levels of 0.05-50 mg L(-1). Nitrogen and amoxicillin significantly (p < 0.05) interact with each other on the regulation of algal growth, synthesis of chlorophyll-a, production and release of MCs, and expression of ntcA and mcyB. The nitrogen-dependent stimulation effect of coexisting amoxicillin contaminant on M. aeruginosa bloom should be fully considered during the combined pollution control of M. aeruginosa and amoxicillin.

The toxicity of seven phthalate esters (PAEs), dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butylbenzyl phthalate (BBP), di-n-hexyl phthalate (DnHP), di-(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DOP) to embryogenesis and larval development of the marine univalve Haliotis diversicolor supertexta was examined by means of two-stage embryo toxicity test. At the blastula stage, the normal embryonic development of H. diversicolor supertexta showed a good dose-response decrease when exposed to DMP, DEP, DBP, BBP, and DnHP. 9-h EC(50) values of DMP, DEP, DBP, BBP, and DnHP were 55.71, 39.13, 8.37, 2.65, and 3.32 mg/l, respectively. 9-h EC(50) values of DEHP and DOP were not available due to their low solubility. The toxicity order of seven tested PAEs was BBP>DnHP>DBP>DEP>DMP>DOP>DEHP. With the completion of metamorphosis as an experimental endpoint, the 96-h no-observed effect concentration values of DBP, DEHP and the other five tested PAEs were 0.022, 0.021, and 0.020 mg/l, respectively. Due to simple obtainment, convenient stimulation to spawn in the lab, greater sensitivity than mature species, and short culture time, the embryos of H. diversicolor supertexta have the potential to be utilized in acute toxicity test for at least PAEs.

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