Bioaccumulation Characteristics Of Methylmercury In Daphnia Carinata Based On AIEgen

Methylmercury(MeHg)is one of the most recognized toxic heavy metal pollutants in the global human society.It is highly neurotoxic,easily bound to lipids,and difficult to metabolize from the body.This will eventually affect humans and have an impact on human brain development and related functions.Zooplankton is an important link between producers(phytoplankton and aquatic plants,etc.)and secondary consumers(fish,shrimp,shellfish,etc.)in aquatic food chains,and is also an important link in the enrichment and amplification of methylmercury in aquatic ecosystems.In this study,a new method for methylmercury detection was developed based on a new aggregation-induced emission fluorogen(AIEgen)probe,and the bioaccumulation process of methylmercury in Daphnia carinata was quantified and characterized by the AIEgen method.The quantitative measurement and qualitative analysis of methylmercury bioaccumulation in Daphnia carinata were carried out to investigate the enrichment of methylmercury in Daphnia carinata,in order to lay a theoretical foundation for future studies on the enrichment,transfer and amplification of methylmercury in the food chain of aquatic ecosystems.The results of the study are as follows:1.Establishment of a new method for detecting methylmercury using AIEgenThe aggregation-induced fluorescent probe AIEgen(m-TPE-RNS)dissolved in acetonitrile and methylmercury dissolved in pure water were able to bind specifically.At 60%water content of the reaction system,its specific binding product is able to fluoresce strongly under UV excitation.The aggregation-induced fluorescent probe m-TPE-RNS has a wave peak at 480 nm and the product m-TPE-RNO has a wave peak at 585 nm as detected by a fluorescence spectrophotometer.We analyzed the relationship between the luminescence(PL)intensity ratio(I585/I480)and methylmercury concentration(CMeHg)and generated a standard curve CMeHg = 1.14*ln(I585/I480)-0.333 for the determination of methylmercury concentration.2.Methylmercury enrichment level in Daphnia carinata: based on AIEgen assayThe uptake of methylmercury in Dahphia carinata in the 2.5 μmol/L group increased continuously to 0.123 μmol within 0-60 min after immersion,while that in the 5.0 μmol/L group was 0.218 μmol.After 60 min,the bioaccumulation of methylmercury began to level off gradually until 240 min when the experiment was completed.The end of the experiment.The results of methylmercury release by Dahphia carinata showed that in the 5.0 μmol/L group,Dahphia carinata released 0.061 μmol of methylmercury outward after 5 min of transferring the attacked Dahphia carinata into pure water,and then the amount of methylmercury release did not change much until the end of the experiment at 240 min when it stabilized,indicating that the methylmercury entering the body of Dahphia carinata was probably combined with the organism and thus enriched by Dahphia carinata.In the2.5 μmol/L group,Dahphia carinata released 0.076 μmol methylmercury after 5 min,and this release gradually stabilized within 60 min,and then the released methylmercury continued to decrease to 0.061 μmol until 240 min.By comparing the immersion group with the feeding group,we found that the uptake of methylmercury gradually increased with time in direct immersion until 150 In the feeding group,the accumulation of methylmercury increased continuously from 10 to 30 min at the beginning of timing,then decreased at 60 min,and finally leveled off.3.Enrichment sites of methylmercury in Daphnia carinata: based on AIEgen assayThe enrichment of methylmercury in zooplankton can be observed qualitatively using the AIEgen assay.Analysis of fluorescence tracer images under laser confocal fluorescence microscopy showed that methylmercury was mainly enriched in the compound eye of Dahphia carinata after direct immersion in methylmercury for 5 min,and the fluorescence at the compound eye became more intense over time and continued to move to the interior of the tissue.The red fluorescence was also found to have a weak emission at the optic nerve after 40 min of immersion.Although these red fluorescences were close to the compound eye and optic nerve,there was no fluorescence signal at the eye cells and brain,indicating that methylmercury could not reach the optic nerve cells through the compound eye.Comparative analysis between the immersed and fed groups showed that the enrichment of MeHg in zooplankton was more likely through direct contact than indirect food intake.And the accumulation of methylmercury in the visual organs and nervous system of D.ronin may be the cause of high mortality of D.ronin in the immersion group.