Joint Toxicity Of PFOS And Zn²⁺/Cd²⁺ To Limnodrilus Hoffmeisteri Under Different PH Levels

Due to its high surface activity,good thermal and chemical stability,perfluorooctane sulfonate?PFOS?,a perfluorinated compound,is extensively used in various industrial processes and consumer products,including surfactants,surface treatment agents,lubricants,polymers,paints,fire-fighting foams,and so on.The widespread use and extreme stability of PFOS have contributed to its ubiquitous occurrence in the environment worldwide.In natural environments,PFOS has been found to co-occur with various chemicals such as organic compounds?e.g.,herbicides,pharmaceuticals,alkylphenols?and heavy metals?e.g.,Cd,Cu,Zn,Pb?,causing aquatic organisms to be exposed to complex mixtures of these environmental contaminants.Thus,to fully understand the true environmental impact of PFOS,it is necessary to evaluate the aquatic toxicity of PFOS applied in combination with other xenobiotics.Detailed studies consist of the following two aspects:?1?The single or joint acute toxicity of PFOS and Zn²⁺ to L.hoffmeisteri was evaluated.Firstly,we investigated the 24h-EC50 values of PFOS and Zn²⁺ for L.hoffmeisteri under different pH conditions for PFOS and Zn²⁺.The results showed that the pH values of exposed solutions had an important effect on the toxicity to L.hoffmeisteri.It's mainly due to changes in the existing forms of Zn at different pH.According to the toxic unit analysis,the joint effects of PFOS and Zn²⁺ in this test were mainly simple addition.In order to gain a deeper understanding on the joint toxicity effect,bioaccumulation and oxidative stress status?SOD,GSH,MDA?in L.hoffmeisteri after 1 d and 10 d of exposure to different concentrations of Zn²⁺ and PFOS were evaluated at pH 8.0.Interactions of Zn²⁺ and PFOS were observed in bioaccumulation.The IBR values decreased significantly after 10 d,confirming the speculations that long-term living in the polluted environment leads to an adaptation of test organisms.This test can provide some basic toxicity data for the joint exposure of PFOS and Zn²⁺,and supply a reference for assessing the environmental risk of the pollutants.?2?The single and joint toxicity of PFOS and Cd²⁺ to L.hoffmeisteri:was evaluated,including acute toxicity?48h-EC50?,bioaccumulation and oxidative stress effects.Firstly,acute toxicity of Cd²⁺ and PFOS to L.hoffmeisteri at pH 6.2,7.0 and 8.0 were studied.Addition of PFOS resulted in a decrease in 48h-EC50 values.The bioaccumulation of PFOS and Cd in L.hoffmeisteri and changes in oxidative stress biomarkers?SOD,GSH,MDA?at 0.02 mg/L Cd²⁺,0.1 mg/L Cd²⁺,0.2 mg/L PFOS,2.0 mg/L PFOS,0.02 mg/L Cd²⁺ + 0.2 mg/L PFOS and 0.1 mg/L Cd²⁺ + 2.0 mg/L PFOS were also observed under pH 6.2 and 8.0.It was shown that the bioaccumulations of PFOS and Cd in L.hoffmeisteri were hardly changed under acidic conditions.This experiment not only provided the latest toxicity data of PFOS and Cd²⁺ on aquatic organisms under different pH conditions,but also enhanced our understanding of the environmental risks of coexisting pollutants.These results collectively show that the pH values have a great effect on the joint toxicity of PFOS and Zn²⁺/Cd²⁺,which may be due to the different species of Zn and Cd at different pH conditions.The bioaccumulations and oxidative stresses in L.hoffmeisteri after exposed to PFOS and Zn²⁺/Cd²⁺ for a period of time were changed.The different exposure concentrations and pH values led to a different interaction of PFOS and Zn²⁺/Cd²⁺ for bioaccumulation.In general,high exposure concentrations could cause more serious damage to organisms,and L.hoffmeisteri can adapt to the polluted environments after a long time exposure.The results of this experiment can provide reference for evaluating the toxicity effects of multiple pollutants on aquatic organisms,which is very meaningful.