Toxic Effects Of Metolachlor And Simetryn On Mactra Veneriformis

The impact of herbicide pollution on the marine environment and the quality and safety of aquatic products has attracted widespread attention.Amide herbicides and triazine herbicides are two types of herbicides with a wide range of use and a high amount of use.In this study,two herbicides,metolachlor and simetryn,were selected,and Mactra veneriformis were used as the research objects,to explore the effects of herbicide pollution on shellfish culture in tidal flats in the Yellow River Delta.The semi-static water quality contact poisoning method was used,and the experimental group with the herbicide concentration close to the environment was set up to study the effects of different concentrations of metolachlor and simetryn on the meat condition,ingestion rate and filtration rate of Mactra veneriformis,as well as effects on antioxidative enzyme activity and tissue structure in gills and hepatopancreas.From the perspectives of physiology,histopathology and enzymology,this paper analyzes the toxic effects of metolachlor and simetryn on Mactra veneriformis,and expounds the correlation of drug dosage,stress time and the degree of damage to shellfish.Meanwhile,a gas chromatography-mass spectrometry(GC-MS)method was established for the determination of five amide herbicides(Acetochlor,Alachlor,Metolachlor,Butachlor,Pretilachlor)and their metabolites(2-Ethyl-6-methylaniline,MEA;2,6-Diethylaniline,DEA)in aquatic products,providing experimental support and analytical basis for the determination of herbicide residues in aquatic products.The purpose of this study is to explore the impact of herbicide pollution on the safety of aquatic products,and to provide reference data for promoting the healthy and sustainable development of delta tidal flat shellfish aquaculture.A gas chromatography-mass spectrometry method for the detection of amide herbicides and their metabolites was established.The homogeneous sample after adding the standard was extracted with ethyl acetate-dichloromethane mixed solvent(3:2,v/v),concentrated by nitrogen blowing,purified by HLB solid phase extraction column,eluted with 3 m L of n-hexane,and eluted with GC-MS for quantification.After optimizing the detection conditions,the results show that MEA,DEA,and Metolachlor are within the mass concentration range of 1.0-25μg/L,and the other four herbicides have good response values within the mass concentration range of 2.0-50μg/L.The correlation coefficient(r~2)were greater than 0.998 8.In the recovery test of low,medium and high spike levels,the recovery rate of Mactra veneriformis ranged from 69.7%to 111%,and the relative standard deviation(RSD)was between 0.40%to 7.6%.The limit of detection and quantification for MEA,DEA and Metolachlor is 0.5,1.5μg/kg;the limit of detection and quantification for the remaining four herbicides is1.0,3.0μg/kg.This method is suitable for the residue detection of five amide herbicides and their metabolites in aquatic products.To study the toxic effects of metolachlor stress on Mactra veneriformis and its bioaccumulation and elimination law.The results showed that metolachlor induced or inhibited anti-oxidase activity under differing metolachlor concentrations.It was found that 10μg/L of metolachlor significantly increased SOD activity in gill tissue,and different concentrations of metolachlor inhibited CAT activity in the gill and hepatopancreas.Metolachlor at 0.5 and 2.5μg/L caused irreversible oxidative damage to SOD and CAT in the gills;the SOD and CAT activities in the gills of the 10μg/L metolachlor concentration group was restored to the level of the control group during the elimination phase.The SOD and CAT activities in the hepatopancreas of the three concentrations groups were restored to or close to the level of the control group during elimination phase.Compared with SOD,the CAT activity was more susceptible to exogenous stimulation and was inhibited;this may be related to the sensitivity and mechanism of action of the two enzymes.After eliminating drug stress,the MDA content in the gills and hepatopancreas of all concentration groups had returned to or was lower than that of the control group.This suggests that the effects of metolachlor stress on lipid peroxidation in the gills and hepatopancreas of Mactra veneriformis may be reversible.Metolachlor stress induced gill filament enlargement,ciliary shedding,epithelial cell damage,and digestive canal damage;the dose-time effect of two types of tissue damage was evident.After 21 d of metolachlor stress experiment and 14 d of elimination,there was no significant difference in shellfish plumpness in each group compared with the control group,and all of them decreased slightly.The ingestion rate and filtration rate of the low and medium concentration groups were significantly lower than those of the control group on the 14th day of enrichment,and the high concentration group was significantly lower than that of the control group on the 7th day of enrichment,showing a certain dose effect.In the high concentration group,the ingestion rate and filtration rate decreased to the lowest value on the 21st day,showing a time effect.After being kept in purified water for a while,the ingestion rate and filtration rate of the experimental group could all return to normal levels.The residues of metolachlor and its metabolite MEA in Mactra veneriformis reached the maximum value on the 2nd and 10th days,at the second day of enrichment,the content of metolachlor in high concentration group exceeded the"uniform standard"of 10μg/kg,the residues of metolachlor decreased after 4 days of elimination,the high concentration group decreased by 24.4%,the medium concentration group decreased by 76.8%,the content of the low concentration group was below the detection limit,and the decrease of MEA was relatively small.To study the toxic effects of simetryn stress on Mactra veneriformis and its bioaccumulation and elimination law.The results showed that the enzyme activity of gills was inhibited under 0.2μg/L、10μg/L concentrations of drug stress,while the enzyme activity of hepatopancreas was induced at 0.2μg/L concentration and inhibited at 10μg/L concentration.The SOD,CAT activity and MDA content of the two tissues in all experimental groups could return to normal levels during the elimination phase.The mesh structure of the gills melted,the gill filaments became loose,and diseased structure appeared;the hepatopancreatic digestive tract was damaged,the structure fell off,and small cavity appeared.The drug content of the tissues reached the maximum on the 10th day of the enrichment stage,in the high-concentration group,the content of simetryn in the enrichment stage all exceeded the"uniform standard"of 10μg/kg,and the residual drugs could be eliminated by the water purification.The shellfish plumpness of the control group and the experimental group decreased gradually with time,and there was no significant difference between the experimental group and the control group.The change trend of shellfish ingestion rate and filtration rate was similar.The feeding ability of the experimental group increased significantly on the 7th day of enrichment,and the difference between the low concentration group and the high concentration group was significant,showing physiological compensation.In other time periods,the feeding ability of the experimental group was not significantly different from that of the control group.