Toxic Effects Of Binary Mixtures Of Sulfamethoxazole And Deethyl Atrazine On Phytoplankton

In recent years,the ecological risks associated with the use of chemical products like antibiotics and pesticides are widely acknowledged.Metabolites of these products may enter the water environment through the food chain and other pathways.Through the process of bioconcentration,phytoplankton and other aquatic organisms can enrich the water body with pesticides,heavy metals,antibiotics,and other substances.They serve as the carriers and receptors for the migration and transformation of these pollutants in the water body.Antibiotic and other drug residues left behind by pollutants can harm water bodies in a number of ways.Numerous national and international studies have shown that pollutant residues can have an impact on phytoplankton and even pose risks to organisms at higher trophic levels.In addition,most of the current studies on the toxic effects of pollutants on phytoplankton have focused on single pollutants,and it is challenging to study the combined effects of pollutants.Therefore,this paper was carried out to investigate the toxic effects of the antibiotic sulfamethoxazole（SMX）and the pesticide metabolite deethyl atrazine（DEA）under interactive stress on phytoplankton.In order to reveal the mechanism of toxic effects of phytoplankton under the interaction of typical exogenous antibiotics and bulk pesticide metabolites,and to provide some data basis for the risk assessment of pollutants in water bodies.（1）Two phytoplankton species（Chlorella vulgaris and Synedra ulna）were selected as indicator organisms and simulated in the laboratory with the help of an artificial climate chamber to investigate the changes of phytoplankton cell density and physiological and biochemical characteristics under the interactive stress of SMX and DEA based on the half-effect concentration(EC₅₀)of SMX and DEA on the two phytoplankton species.The results showed that both single exposure and combined exposure to DEA were not sufficient.The results showed that both phytoplankton and(Chlorella vulgaris exhibited a"low-promoted-high-inhibited"phenomenon（low concentration promoted and high concentration inhibited）in both single and combined exposures,and the changes in chlorophyll a content of Chlorella vulgaris were proportional to the changes in their cell growth.Two antioxidant enzymes,SOD and CAT,as well as the MDA content essentially displayed a trend of first increasing and then decreasing with the increase of the treatment group concentration in both single-treatment and combined-treatment systems.TU analysis showed that the combined toxicity of SMX and DEA on Chlorella vulgaris was synergistic at the beginning of the incubation period,but at the end of the experiment,the combined toxicity changed to antagonistic effect.The combined toxicity of Synedra ulna showed a synergistic effect at 4,7 and 14 days of combined SMX and DEA exposure.（2）A study was done on the effects of various combined SMX and DEA exposures on the phytoplankton communities based on the ratio of SMX and DEA concentrations in the actual water column.Natural phytoplankton communities were collected and cultured in the surface water of a lake in Shandong Province.The findings showed:At the start of the experiment,44species of phytoplankton were counted,including 7 cyanobacteria,28 green algae,4 diatoms,1 cryptophyte,and 4 nudibranchs.The blank control group showed a significantly higher biological density of green algae and diatoms after 9 days of incubation compared to the initial incubation period,while the biological density of cyanobacteria,cryptophytes,and nudibacteria increased to a lesser extent;the biological density of cyanobacteria and cryptophytes in the treatment group increased to a greater extent,while that of green algae and nudibacteria increased to a lesser extent,and that of diatoms remained almost unchanged.The changes in chlorophyll content indicated that the combined exposure of SMX and DEA may have inhibited the growth of some algal species.