Determination And Risk Assessment Of Cumulative Efficiency Of Heavy Metals In Crassostrea Gigas

In recent years,with the rapid development of the economy,the pollution of heavy metals to the marine environment has become more and more serious due to human factors such as exhaust gas emission,sewage irrigation and the use of heavy metal over-standard products.Shellfish have high protein,high trace elements,less fat and other nutritional characteristics,and have long been favored by most consumers.Most bivalve molluscs are benthic and filter-feeding.The quality of their products is affected by the environment of the cultured seas.The accumulation of heavy metals through the food chain and the enrichment of organisms,human consumption of these shellfish containing heavy metals will cause Different degrees of poisoning.In this study,the oyster culture area was selected to monitor the marine environment in different seasons.According to the monitoring data,the environmental conditions of the sea area were artificially simulated.The improved shellfish water filtration rate measuring device was used to determine the addition of 10 times concentration of heavy metal Cu,Pb,Zn and Cd in natural environment water in different seasons.Under cadmium conditions,the accumulation and accumulation efficiency of heavy metals in Crassostrea gigas is intended to provide a scientific basis for the safety assessment of heavy metals in shellfish.The main contents and results of this study are as follows:(1)From June 2018 to March 2019,monitor the marine environment of the Shenhu Bay(118°40'~118°41'E,24°38'~24°40'N)aquaculture area in Fujian Province,select eight Monitoring points,respectively,determining the water temperature,salinity,pH,dissolved oxygen,TPM,POM,nitrate nitrogen,nitrite nitrogen,ammonia nitrogen,active phosphate,active silicate,Cu,Pb,Zn and Cd,in the four quarters(spring,summer,autumn,winter)of the culture area.15 marine environmental indicators.All the indicators of the test results did not exceed the standard.(2)In this study,Crassostrea gigas were used as experimental objects.The water tank method was used to test the shellfish water filtration rate,and the self-made water filtration rate measuring device was used to conduct experiments in the Shenhu Bay culture area of Fujian Province.By measuring the concentration of chlorophyll a in the seawater of the culture area and calculating the water filtration rate,the water filtration rates of the four quarters(spring,summer,autumn,winter)were 2.09 L/h,1.70 L/h,1.22 L/h,3.42 L/h.The results showed that the oysters in the sea had the highest water filtration rate in winter and the lowest in autumn,and the energy metabolism of oysters was normal..(3)In this study,Crassostrea gigas were used as experimental objects.According to the flow tank method,the integrated steady-state model and the characteristics of the two-box model,the filtration rate measurement device was used to measure the cumulative efficiency of shellfish.This experiment was conducted to determine the accumulation and accumulation efficiency of heavy metals in Crassostrea gigas under the conditions of adding 10 times of heavy metal,Cu,Pb,Zn and Cd in natural environment waters in different seasons.The Crassostrea gigas were placed in the simulated environment for a cumulative period of 7 days.After calculation,the results showed that the results of four seasons(spring,summer,autumn and winter)of Pacific oysters were Cu: 4.85%,8.18%,5.86%,5.26%,Pb: 32.0%,42.3%,34.1%,27.8%,Zn: 10.6%,15.6%,13.3%,10.3%,Cd: 17.1%,36.7%,24.6%,12.8%.(4)In this study,Crassostrea gigas were used as assessment targets for risk assessment of heavy metal content in four seasons.Through the correlation calculation of the measured content,the four heavy metal pollution indexes(Pi),weekly exposure(EWI)and target hazard coefficient(THQ)of Cu,Pb,Zn and Cd were obtained for risk assessment.The single-factor pollution index method was used to evaluate the safety risk of Cu,Pb,Zn and Cd in the oyster samples before and after accumulation.The results showed that the Pi without cumulative experiments were less than 1,which was in line with the standard of pollution-free food in China.Safe to eat;after the cumulative experiment,in addition to Pb and spring and autumn and winter Zn are in line with China's pollution-free food standard limit,but because Pb has exceeded,it has an food safety risk.The exposure evaluation method and the target hazard coefficient method were used to evaluate the exposure.The results showed that the four heavy metal EWI of the samples that were not accumulated in the four seasons were lower than the recommended values,and the THQ was lower than 1 except for the winter Cd.The risk caused by the human body is low;after the cumulative experiment,the EWI is less than the recommended value except for the Pb in summer only less than the recommended value,THQ is divided by Cu in four seasons,Pb is in summer,and Zn is less than 1 in spring,summer and autumn.More than 1 at this level,there is an excessive risk of consumption of Cd in each season.The risk to the human body at this level was Lower;after the cumulative experiment,the EWI except Pb is less than the recommended value in summer,the rest is less than the recommended value,and THQ is lower than the threshold.At this level,except for summer,there is excessive consumption risk of Pb in other seasons.From the results of the risk assessment,this experiment basically closes or exceeds the food limit value after the cumulative experiment,and there is a risk of eating.The daily consumption in each season cannot exceed 25 g/d,58 g/d,30 g/d.23 g/d;the heavy metal content of Pacific oysters without cumulative experiments are in line with China's pollution-free food standard limit,no food risk,but the daily consumption of each season is less than 81 g/d,231 g/d,102 g /d,68 g/d.