Accumulation Of Tri(1,3-dichloroisopropyl) Phosphate In Marine Organisms In Liaodong Bay And Its Toxicity And Ecological Risk

With the regulation and phase-out of brominated flame retardants,the production and use of organophosphate flame retardants（OPFRs）has rapidly increased.OPFRs are often added as additives to various products and can easily released into different environments.Eventually they enter natural water bodies through various pathways and pose a threat to aquatic ecosystems.OPFRs have certain persistence in water environment,bioaccumulation potential and toxicity to organisms.Therefore it is important to conduct bioaccumulation and toxicological studies of OPFRs in aquatic ecosystems and to assess the environmental and health risks of OPFRs.In this study,the concentration and distribution characteristics of OPFRs in the Marine biota of Liaodong Bay were investigated.On this basis,four typical OPFRs were selected,namely triisooctyl phosphate（TEHP）,tri（2-chloroethyl）phosphate（TCEP）,tri（1,3-dichloroisopropyl）phosphate（TDCIPP）and triphenyl phosphate（TPHP）.A subacute exposure experiment was conducted on embryos of marine medaka（Oryzias melastigma）for 20 days.After comprehensive consideration of its biotoxicity,current use and research progress,this study carried out a life cycle exposure experiment on TDCIPP as the target pollutant,and the toxic effects and potential mechanism of long-term exposure to TDCIPP on marine medaka were explored.Finally,the potential ecological risk of TDCIPP to marine organisms was evaluated.The results of this study provide theoretical data for ecological risk assessment of OPFRs.The main research contents and conclusions are as follows:（1）The bioaccumulation and distribution of OPFRs in marine organisms in the Liaodong Bay,China were investigated,and the median lethal concentration(LC₅₀)of four OPFRs were evaluted.OPFRs were detected in 24 marine organisms（14 fish species and 8 invertebrate species）,indicating their widespread presence in the Liaodong Bay.The total OPFRs ranged from 2.60 to 776 ng/g ww.TEHP and TCPP were the most commonly detected OPFRs compounds in marine organisms,but TCEP was dominant in most marine species（16/24）.Chlorinated OPFRs had the highest content,and alkyl OPFRs and aryl OPFRs accounted for a similar proportion.Lipid is one of the important factors affecting the concentration of OPFRs but not feeding habit.No biomagnification potential of OPFRs was found in the Liaodong Bay biota.Subacute exposure of marine medaka embryos showed that the 20d LC₅₀order of the four typical OPFRs is TPHP（190.6μg/L）>TDCIPP（724.4μg/L）>TEHP（24.5mg/L）>TCEP（55.0 mg/L）.（2）The toxicity of chronic TDCIPP exposure to embryos and heart development in marine medaka was studied.The results showed that chronic exposure to environmental concentrations（0.05、0.5、5和50μg/L）of TDCIPP could induce developmental toxicity in the early life stages of marine medaka,including accelerated heart rate,reduced hatching rate and increased malformation rate.This study found that the expression levels of key genes regulating heart development changed with exposure time during embryonic development,suggesting that the heart may be an important target organ of TDCIPP.Therefore,TDCIPP exposure has toxic effects on the heart by inducing cardiac malformations in the early stage and promoting cardiac defects by amplifying inflammatory responses in the late stage.In addition,TDCIPP exposure could lead to oxidative stress,but the antioxidant enzyme system is activated to counteract the production of reactive oxygen species,preventing significant lipid peroxidation damage.Finally,the observation of reduced vitelline protein（VTG）content in newly hatched fish confirms the inflammatory response,oxidative stress,and consequent cardiac developmental toxicity induced by TDCIPP.（3）The effects of TDCIPP exposure on the time-dependent growth of juvenile marine medaka and its mechanism were explored.After hatching in artificial seawater containing different concentrations of TDCIPP,marine medaka embryos continued to be exposed to the corresponding concentrations of exposure solution up to 90 dph.Phenotypic indicators（body length and body weight）were observed to be time-dependent and dose-dependent in growth inhibition during this growth and development,with 30-90dph being the most sensitive window period of TDCIPP exposure in marine medaka,but phenotypic changes began at 60 dph.TDCIPP exposure caused significant changes in the contents of THs,GH and IGF hormones as well as the transcription levels of genes involved in the hypothalamic-pituitary-thyroid（HPT）axis and the growth hormone/insulin growth factor（GH/IGF）axis,ultimately leading to growth inhibition.However,this change at the molecular level did not have a time-or dose-dependent effect,but was a dynamic,multi-component coordinated complex regulatory process.（4）The effects of TDCIPP on reproductive inhibition of female marine medaka and the development of offspring were explored.Chronic exposure to TDCIPP did not change the phenotype of female marine medaka,but changed the transcription levels of related genes on the hypothalamic-pituitary-gonadal（HPG）axis and the levels of sex hormones,resulting in the imbalance of sex hormone secretion,inducing pathological damage to the ovary and shifting the follicle development stage to immature stage,thus reducing the fecundity.Furthermore,after long-term exposure to TDCIPP,although there were no significant change in the levels of VTG in the liver and eggs of female marine medaka,the quality of eggs decreased,leading to a significant decrease in hatching rate and body length,as well as an increase in the rate of malformations in their offspring.Using the species sensitivity distribution（SSD）method,a optimal SSD curve can be fitted based on the lowest observed no-effect concentration（LOEC）of the reproductive toxicity endpoint in this study.The long-term water quality benchmark derived from the SSD curve is 1μg/L.The risk quotient（RQ）value calculated using the highest TDCIPP concentration detected in Chinese seawater is 0.109,indicating that TDCIPP poses a moderate risk to marine ecosystem.