Research On Toxicity Of Typical Light And Heavy Rare Earth Elements To Daphnia Magna And Relevant Mechanisms Of Action

Due to the disturbance of human activities（rare earth mining and the wide application of rare earths in agriculture,industry,aquaculture,pharmaceutical industry and high-tech industry）,more and more rare earths inevitably enter the ecological environment and organisms through various channels,causing potential risks to environmental ecological security.In recent years,there have been many studies on the toxic effects of rare earths on aquatic ecology,involving a variety of biota representatives of different ecological niches,but most of them are limited to the behavioral changes or physiological and biochemical processes of organisms at the individual level,and there are few studies on the aquatic ecotoxicity of heavy rare earths.So far,the research on the effects of rare earth elements on the nutritional status of aquatic organisms is very limited,and there is a big gap in the study of the toxic effects of rare earth ions on aquatic organisms at different ammonia nitrogen levels,which cannot fully and deeply explore the risk of rare earth exposure to aquatic ecology.Based on this,this study used Daphnia magna as an experimental organism to conduct acute and chronic exposure experiments to explore the toxic effects of typical light/heavy rare earth lanthanum and ytterbium exposure on individual and population levels of D.magna,and to study the effects of lanthanum exposure on the nutritional status of D.magna offspring.In view of the widespread eutrophication and the phenomenon of excessive ammonia nitrogen in the water body of rare earth mining areas,this paper further explores the chronic toxic effects of ytterbium exposure on D.magna under different ammonia nitrogen levels,as well as the effects on the activities of antioxidant enzymes such as SOD,CAT,GST and MDA content in D.magna,and clarifies the toxic mechanism of ytterbium on D.magna at the physiological and biochemical level.The main research contents and conclusions are as follows:（1）The LC₅₀ and 95%confidence intervals（CIs）of La³⁺and Yb³⁺on D.magna were16.2（12.5-20.8）and 3.2（1.3-7.6）mg·L^-1,12.2（8.9-20.3）and 2.8（2.1-3.5）mg·L^-1,respectively.When the concentration of La³⁺was higher than 108.5μg·L^-1 and Yb³⁺was higher than 98.6μg·L^-1,the survival time and 21-day survival rate of D.magna were significantly decreased.When the concentration of La³⁺was 282.3μg·L^-1 and Yb³⁺was 297.3μg·L^-1,the reproduction of D.magna was completely inhibited and no offspring were produced.Lanthanum and ytterbium promoted the growth,development and reproduction of D.magna slightly at low exposure concentration,but it showed obvious inhibitory effect at high exposure concentration,and the intrinsic rate of natural increase at the population level was significantly reduced.In contrast,heavy rare earth element ytterbium was more toxic to D.magna than light rare earth element lanthanum.（2）In exploring the effect of lanthanum exposure on the nutritional level of D.magna offspring,it was found that the nutritional level and total calorie level of D.magna offspring were significantly higher than those of the control group under low concentration lanthanum exposure.Under the exposure of higher lanthanum concentration,the reproduction number and nutritional status of offspring of D.magna were significantly adversely affected,which may destroy the inter-generational biological energy balance of D.magna and damage the biological potential of D.magna population,thus further affecting the nutritional regeneration rate of aquatic ecosystem and reducing the nutritional resilience and nutritional safety of aquatic ecosystem.（3）In the study of the toxic mechanism of ytterbium on the physiological and biochemical level of D.magna,the results showed that low concentration of ytterbium exposure had a certain stimulating effect on the antioxidant system of D.magna,while high concentration of ytterbium exposure could significantly inhibit the activity of antioxidant enzymes,and the presence of ammonia nitrogen would reduce the inhibitory effect of ytterbium ions on the antioxidant system of D.magna.The change of MDA content in D.magna showed that the stimulation of ytterbium ions on the antioxidant system under low concentration exposure could offset the oxidative stress and did not cause obvious oxidative damage,but the oxidative stress caused by ytterbium ions could not be completely offset at higher exposure concentration.Lipid peroxidation occurred in D.magna,which caused oxidative damage to the body.In the presence of ammonia nitrogen,the oxidative damage caused by ytterbium ions would be weakened to a certain extent.（4）In the combined exposure of ammonia nitrogen and ytterbium,ammonia nitrogen and ytterbium ions will produce antagonistic effects and reduce the chronic toxic effects of ytterbium ions on D.magna.