Joint Toxicity Of Microplastics And Dibutyl Phthalate(DBP) To Marine Organisms

As an emerging contaminant,microplastics?MPs?contamination in marine environment has caused a great burden in past few years and seriously threatened the safety of human beings and other living things.Phthalic acid esters are abundant as plasticizers in polymers and coexist with MPs extensively in marine ecosystems.They could interfere with the normal life activities of marine organisms as an environmental endocrine disruptor.However,there has been rarely available information on their combined toxic effect to aquatic organisms.Therefore,taking Chlorella pyrenoidosa and Tigriopus japonicus as the target species,this study aimed to investigate the combined toxicity of polystyrene microplastics?mPS?and dibutyl phthalate?DBP?on these species at individual and population levels.The interactions among mPS,DBP and the target species were studied to explore the potential toxic mechanisms.The 96 h-IC₅₀ value of DBP for C.pyrenoidosa was 2.41?mg/L.mPS exhibited size-dependent inhibitory effect to C.pyrenoidosa,with the 96 h-IC₅₀ at 6.90 and 7.19?mg/L for 0.1and 0.55??m mPS,respectively,but little toxicity was observed for 5??m mPS.The interaction parameter?based on the response additive response surface?RARS?model varied from-0.309to 5.845,indicating the interaction pattern varying with exposure concentrations of chemical mixtures.The interaction between mPS and DBP was antagonistic at low concentrations of DBP and synergistic at relatively high concentrations of DBP when the concentration of mPS was less than about 10 mg/L,but it was antagonistic across all concentrations of mPS above 10mg/L.A modified RARS model?taking?as a function of exposure concentration?was constructed and could well predict the combined toxicity of mPS and DBP.More than 20%reduction of DBP was observed at 20?mg/L mPS,while 1?mg/L mPS had no significant effect on the bioavailability of DBP at different sampling time points.Volume,morphological complexity and chlorophyll fluorescence intensity of microalgal cells were disturbed by both DBP and mPS.The antagonistic effect of high concentrations of mPS might be partially attributed to the combination of hetero-and homo-aggregation and the reduced bioavailability of DBP.The 96 h-IC₅₀ value of DBP for T.japonicus was 1.23?mg/L,while exposure to mPS didn't have significant lethal effect on the copepods.Adsorption to MPs led to decreased bioavailability of DBP,resulting in decreased toxicity of DBP.In contrast to acute toxicity test,DBP didn't affect the reproduction of the copepods at lower exposure concentrations,while mPS reduced the number of nauplii and extended the time to hatch.Similar as acute toxicity test,antagonistic interaction was observed for mPS and DBP in chronic reproduction test as well,which might be attributed to promoted aggregation of mPS at presence of DBP.The overall findings of the present study profiled the combined toxic effects of mPS and DBP on marine plankton species which will be helpful for further evaluation of ecological risks of mPS and DBP in marine environment.