| Pesticides are widely used in the production of agricultural products,and playing a vital role in ensuring China’s food security.Although rarely used pesticides occurred in the production of aquatic products,pesticides also entering into aquaculture environment by runoff and background exposure,and were found in edible parts,further influencing human health and posing dietary risk.Thus,for the purpose of the protection of dietary safety of residents,pesticides are imperative to be involved into national routine monitoring plan of quality and safety of aquatic products.However,when local government would conduct monitoring plan,efficient allocation of resources of quality and safety supervision achieved by the model of risk ranking is essential,that is,precision problem of quality and safety supervision of aquatic products needs to be addressed.Taken Chinese mitten crab（Eriocheir sisensis）cultured in China as an example,the present thesis tried to estimate the route of pesticide entering into aquaculture environment,identify and quantify the types of residual pesticides in the edible part of Chinese mitten crab.Moreover,by the model of dietary risk ranking and the method of ecological risk assessing,the impact of dietary safety and survival safety of Chinese mitten crab when exposed to different aquaculture modes and procedures were explicated.The results of the present thesis were supposed to provide technical support in the national quality and safety supervision of aquatic products,especially Chinese mitten crab.The main research contents and conclusions were as following:（1）The organochlorine pesticides（OCPs）were widely found in cultured Chinese mitten crabs in China.Seventy Chinese mitten crab samples,consisted by a total of2100 individuals（half male and half female）,were collected in main production areas（Jiangsu Province）in China.The objective was to reveal occurrences and patterns of23 selected organochlorine pesticides（OCPs）in edible tissues.The results showed that,Among all collected samples,98.75%of total OCPs（69 out of 70）were detected.Concentrations of total residual OCPs in mitten crabs ranged from 0.72 to51.51μg·kg-1.Dichlorodiphenyl trichloroethanes（DDTs）and hexachlorocyclohexanes（HCHs）were the two main contributors of total OCPs,with the detected values ranged from 0.14 to 30.89μg·kg-1 and 0.23 to 4.04μg·kg-1 respectively.p,p’-DDE accounted most for DDTs with the mean value of 61.19%,indicating that aerobic ageing is the main contributor of the degradation of DDTs.Additionally,High majority of DDTs were found in few samples,meaning that aged pollution and recent input of DDTs coexisted.The source analysis also indicated that no usage of HCHs in the main production area of mitten crab.For dietary risk,at least 8 individuals of mitten crabs per day were allowed for local residents,showing low risk for consumption.（2）In terms of identifying and quantifying potential residual pesticides,a suit of effective non-target screening strategy was developed.In the present thesis,the custom non-target strategy was applied to screen potential residual pesticides in Chinese mitten crab cultured in high intensive pond and rice-crab coculture system.The results showed that,there were total of 11 types of residual pesticides,that is Aldicarb,Bioresmethrin,Buprofezin,Cyromazine,Dinotefuran,Isoprocarb,Oxamyl,Pendimethalin,Pirimicarb,Methomyl,and Trichlorfon,in the edible part of Chinese mitten crab,caused by runoff entering into aquaculture environment.Firstly,UHPLC-HRMS was used to construct a local mass spectrum database of pesticides maybe entering into aquaculture environment by runoff.There were a total of 198 types of pesticides involved in the self-constructed database.By the analysis of non-target screening for Chinese mitten crab cultured all over the China,11 types of residual pesticides were found,10 out of 81 types of involved insecticides,1 out of 59 types of involved herbicides,and none of 58 types of involved fungicides.Carbamate pesticides were most frequently detected,while Bioresmethrin had the highest residual content,with the value of 113.01μg·kg-1,due to high coefficient of bioconcentration factor（BCF）.In conclusion,the residue of pesticides in Chinese mitten crab was caused by indirectly entering into aquaculture environment,and posing low dietary risk.（3）Assembled the two categories of pesticides,that is OCPs and screened types in previous study,a local potential residual pesticides database was constructed,consisting of 24 types.On the basis,using the principle of dietary risk superimposed by exposure route and hazard identification,a model of dietary risk ranking was developed.Calculated by the model,the total dietary risk scores in North and South China ranged from 0 to 28,and 3 to 36 respectively.Regions in the south scored 1 to7 points higher than those in the north.In conclusion,some DDTs,such as p,p’-DDD、o,p’-DDT,p,p’-DDT,and Bioresmethrin were finally recognized as the most residual dietary risk types of pesticides.National monitoring plan of Chinese mitten crab would focus on these types preferentially.In the advocating of the pesticide reduction policy,these types are also starting with the first.The effective measures to control or remove these types of pesticides were dredging silt and cutting off non-point runoff.（4）To limit the growth of insects and weeds and to maximize the yield of rice,various pesticides,including chlorantraniliprole（CAP）,are frequently being used in rice farming,and directly entering into aquaculture environment by runoff.Although no residual content were detected in non-target screening experiment,its exposure levels in surrounding environment may cause acute and chronic toxicity effects of aquaculture animals.The effect of CAP usage on the survival and edible safety of crab species living in the coculture system has not been investigated.In the present thesis,we created a field simulation experiment and discovered that the amount of CAP entering the rice-crab coculture system accounted for 82.22%of the total CAP content present in the spray barrel.Moreover,when CAP residues found in the soil leached into nearby areas,we observed an increase in the CAP concentration in the water and sediment.Specifically,peak CAP concentration(1.35μg·L-1)was detected in water within 1 day,and a steady CAP concentration in the sediment(2.55μg·kg-1)was detected within 3 days.Moreover,an extensive field sampling experiment conducted in the basin of the lower reaches of the Yangtze River revealed that CAP was routinely used in rice-crab coculture systems.Although detected CAP concentrations were below 1μg·L-1 in ditch water and below 1μg·kg-1 in ditch sediment,there was still a potential risk associated with the crab growth.Importantly,there was no risk associated with crab consumption,given the low detection frequency of CAP in the collected samples,the results were according with the previous results obtained from non-target screening experiment.Our analysis suggests that an increase in usage ratio and a decrease in the total CAP content will likely promote safe application of CAP in the rice-crab coculture systems. |
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