| Arsenic（As）is a metalloid element that exists in the natural environment and is carcinogenic.With the continuous development of the economy,human activities have caused water pollution in As.Freshwater shellfish and fish have a strong ability to enrich arsenic,and As can be passed to humans through the food chain,and the As pollution of freshwater products poses a threat to human health.Aquatic organisms can absorb As in the environment and carry out biotransformation in the body,resulting in different As forms in fish.In the past,seawater products are more studied than freshwater products.Therefore,The article studied the enrichment mechanism and transformation of as in freshwater products,which provided basic data for the edible risk assessment of freshwater products.（1）Total arsenic and Arsenic Species in Environmental Freshwater ShellfishThe Xiangjiang River,which is typical of mining pollution,was selected as the research water area,and shellfish（P.eximius）were collected for total arsenic（t As）research,the As pollution of shellfish in the Xiangjiang River Basin was significantly higher than that of other water.The t As concentrations of the edible,non-edible,and whole giant snails were2.802～6.956 mg·kg-1 dw,6.715～28.814 mg·kg-1 dw,and 4.758～17.117 mg·kg-1 dw,respectively.The t As concentrations of the edible were significantly lower than in the non-edible portion.Through As speciation analysis,it was found that the concentrations of As B and As（V）were high,and the concentrations of As C,DMA,and MMA were low.The proportion of As B in the edible part was 23.6%～43.0%,and the proportion of As B in the non-edible part was 5.6%～31.7%,which was much lower than that reported in marine fish and marine shellfish.Through correlation analysis,it was found that there was a significant correlation between As（V）and As（III）in edible and non-edible parts,indicating that As（V）was converted to As（III）in P.eximius.There was a significant correlation between DMA and As B in the edible portion,indicating that the conversion of DMA to As B occurred in the shellfish muscle.Through the health risk evaluation,the results show that the non-carcinogenic health risk evaluation value（THQ）of P.eximius is 0.31,and the THQ value is lower than 1,indicating that there is no non-carcinogenic health risk to consumers;the potential carcinogenic health risk value（CR）is 1.40×10-4,the acceptable CR values ranged from 1×10-6 to 1×10-4,indicating that the continuous consumption of P.eximius would pose considerable potential carcinogenic health risks to local consumers.（2）Enrichment and transformation of arsenic in freshwater fishBy designing an indoor inorganic arsenic exposure experiment,the effects of exposure time and exposure concentration on total arsenic and arsenic species in benthic carp were discussed.With the increase in exposure time,it will cause obvious arsenic enrichment.When exposed to As（III）,the total arsenic concentration in meat increases with time,and the total arsenic concentration in the liver and gills first increases and then decreases with time.When exposed to As（V）,the total arsenic concentration in meat and liver first increased and then decreased with time,and the total arsenic concentration in gills increased with time.The concentration of As B in meat,liver,and gills increased with exposure time,converting inorganic arsenic into almost non-toxic As B for storage in the body.Through correlation analysis,it was found that there may be a mutual transformation between different arsenic forms in various tissues of carp,including the redox reaction of inorganic arsenic,the methylation process of inorganic arsenic,and the conversion of DMA to As B.At different exposure concentrations,it was found that the total arsenic concentration in the meat,the liver,and the gill tissue of carp increased with the increase of the exposure concentration,indicating that the concentration of total arsenic in carp was dose-dependent.Through the calculation of the enrichment factor of inorganic arsenic,it was found that the enrichment factor of various arsenic species in fish meat,liver,and fish gill tissues decreased with the increase of dissolved As（III）concentration in water when exposed to As（III）;while the enrichment factor of each arsenic species in fish meat,liver,and fish gills tissues increase with the increases of dissolved As（V）concentration in water when exposed to As（V）.（3）Effects of different exposure pathways on the enrichment and transformation of arsenic in freshwater fishBy designing an indoor inorganic arsenic exposure experiment,the effects of different exposure pathways,the mechanism of different tissue enrichment,purification rules,and biotransformation of the benthic fish crucian carp were discussed.Through the study of different exposure pathways,it was found that the total arsenic accumulation of crucian carp caused by water exposure was much higher than that of food exposure,indicating that arsenic pollution in water was a greater threat to fish than food arsenic pollution.The concentration of total arsenic in different tissues was different.The concentration of total arsenic in gills increased with time;the concentration of total arsenic in back muscles was slightly higher than that in abdominal muscles;in the liver,the concentration of total arsenic was significantly increased on the 30th day after As（III）exposure,However,the total arsenic concentration in the As（V）exposure decreased significantly on the 30th day;the total arsenic concentration in the kidney first increased and then decreased with time;in the intestine,the total arsenic concentration increased significantly on the 1st day,it was significantly decreased on the 3rd day in inorganic arsenic exposure,and the total arsenic concentration first increased and then decreased with time in the later period;the chang trend in the skin was similar to that in the intestine.The mechanism of arsenic enrichment was further discussed through oxidative stress experiments.Gills were directly exposed to arsenic-containing water,and it was difficult to initiate an antioxidant enzyme strategy to combat the invasion of inorganic arsenic;In the liver,the glutathione（GSH）concentration was significantly positively correlated with the total arsenic concentration,which decreased with time in As（III）exposure and increased with time in As（V）exposure,indicating that different forms of arsenic exposure lead to different oxidative stress responses in the liver;The kidney can resist oxidative stress caused by exposure to ambient concentrations of inorganic arsenic by regulating total superoxide dismutase（T-SOD）levels.After repurifying the crucian carp exposed to inorganic arsenic,it was found that the total arsenic concentration in the fish could be restored to the concentration of the initial inorganic arsenic exposure and even the concentration of the control fish,indicating that the freshwater crucian carp has a strong self-purification ability.Through the study on the distribution of arsenic forms,after 30 days of exposure to inorganic arsenic,it was found that the main arsenic form in muscle,liver,and kidney of crucian carp was As B,which accounted for about 85%in muscle,76%in liver,and 89%in kidney,but the main arsenic form in gill was as（V）（about 62%）. |
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