Study On The Photosynthesis And Toxic Effects Of Organophosphorus Flame Retardants On Microcystis Aeruginosa

As a high-efficiency,low-smoke,low-toxicity,the organophosphorus flame retardants,are increasingly used in life.Tris(2-chloroethyl)phosphate(TCEP)and Tris(1,3-dichloroisopropyl)phosphate(TDCPP),as typical and common chlorinated organophosphorus flame retardants(Cl-OPFRs),have been frequently detected in the aqueous environment in recent years,which bring ecological,environmental and health safety The problem of ecological,environmental and health safety has become a growing concern.The biological toxicity of Cl-OPFRs has been reported in the literature,but the ecological risk assessment of Cl-OPFRs in the aquatic environment is still inadequate.Microcystis aeruginosa plays a crucial role in maintaining the balance and stability of aquatic ecosystems and is closely related to the occurrence of cyanobacterial blooms.In this experiment,TCEP and TDCPP were selected as model compounds,and the Microcystis aeruginosa PCC7806 was used as the research object to explore the mechanism of Cl-OPFRs on the occurrence and inhibition of cyanobacterial blooms in terms of oxidative stress level and photosynthetic activity response,and also to detect and predict the release of microcystins,and the following conclusions were obtained:1.The effects of both TCEP and TDCPP on the growth of Microcystis aeruginosa showed significant Hormesis effect characteristics,growth was stimulated at low concentrations(TCEP 0.05～0.5 mg/L;TDCPP 0.5～1 mg/L)and inhibited at high concentrations(TCEP 50～250 mg/L;TDCPP 5～10 mg/L).And photosynthetic pigments(chlorophyll,carotenoids and phycocyanin,etc.)and photosynthetic oxygen release rate had similar trends with cell growth under different concentrations of TCEP and TDCPP exposure.2.The mechanism of the effect of two Cl-OPFRs on algal cell growth was initially investigated from the changes of reactive oxygen species(ROS)levels and antioxidant system-related enzyme activities in Microcystis aeruginosa.The results showed that under the exposure conditions of low concentrations of TCEP and TDCPP,the intracellular ROS and malondialdehyde(MDA)levels of Microcystis aeruginosa were slightly reduced and the antioxidant system was in a stable state;however,when the concentrations of TCEP and TDCPP were above 5 mg/L and 50 mg/L,respectively,the intracellular ROS increased significantly(P < 0.05),at which time the membrane lipid peroxidation levels of MDA and At this stage,the antioxidant systems superoxide dismutase(SOD)and peroxidase(POD)were active and played an active role in scavenging excess ROS in the organism,but did not alleviate the oxidative stress response.3.The mechanism of the effect of TCEP and TDCPP on photosynthesis in Microcystis aeruginosa was analyzed by studying the effect of two Cl-OPFRs on the photosynthetic activity of the cells.Low concentrations of TCEP and TDCPP promoted the pigment content,photosystem I(PS I)cyclic electron transfer activity,and photosynthetic oxygen release rate of Microcystis aeruginosa,and this stage of photosynthesis converts light into energy,thus promoting the growth of microalgae.Stimulation of NAD(P)H dehydrogenase(NDH-1)activity by low doses of Cl-OPFRs using fluorescence quantification and protein immunoblotting.The elevation of its mediated cyclic electron transfer activity worked in coordination with photosynthetic pigments such as carotenoids,which together reduced intracellular ROS production and promoted the growth of Microcystis aeruginosa.However,high concentrations of TCEP and TDCPP caused severe inhibition of growth and photosynthetic oxygen release activity through the imbalance between photosystem II(PS II)and PS I.Chlorophyll fluorescence induction,77 K fluorescence emission spectroscopy and photosystem stoichiometry results indicated that high concentrations of TCEP and TDCPP inhibited state transitions,excited cells into state I,and increased the PS II/PS I ratio.The elevated PS II/PS I ratio caused an imbalance between the two photosystems,which ultimately led to excessive production of reactive oxygen species,thus adversely influencing cell growth effects.4.TCEP and TDCPP promoted the secretion of Microcystis aeruginosa microcystin-LR(MC-LR),and the promotion effect was more visible with the increase of TCEP and TDCPP concentration.At the same time,TDCPP also promoted the release of tryptophan-like substances and tyrosine-like substances from Microcystis aeruginosa,and the dynamic release pattern of these substances may be one of the predictive parameters of MC-LR release from Microcystis aeruginosa.