Accumulation And Distribution Of Cr In Fish And The Health Risk Assessment

Fish constitutes an important part of human diet,thus,the safety of fish has been highly concerned.In recent years,with the rapid development of industry,agriculture and urbanization,the large number of industrial and agricultural wastewater discharged into the aquatic system,which induces serious pollution.It has been reported that 80.1%of the sediments of rivers and lakes in China are polluted by heavy metals.Heavy metals can not only damage aquatic organisms due to their characteristic of high toxicity and tendency to bioaccumulate,but also affect human health through drinking,eating and other ways.Thus,to understand the distribution and metabolism effects of heavy metals in fish and to evaluate the potential risk from consuming fish contaminated by heavy metals are of great significance to protect the health of consumers.Chromium（Cr）is a ubiquitous heavy metal pollutant in the environment.In the early invesitgation of this paper,it was found that compared to other metals,Cr pollution in fish was more common.The content of metals in fish is varied as it is affected by the processes of accumulation,distrubution and depuration.Therefore,to explore the distribution and metabolism effects of Cr⁶⁺in fish is helpful to understand the response of fish tissues to Cr⁶⁺under Cr⁶⁺pollution conditions,and to provide a theoretical basis for reducing the accumulation of Cr⁶⁺and promoting the excretion of Cr⁶⁺in fish,and to further protect the safety of fish consumption.Up to now,the researches on Cr⁶⁺in fish are mainly focused on toxicity.However,toxicokinetics of Cr⁶⁺in fish is rarely reported.In this study,the typical heavy metal pollutant Cr in fish was firstly identified by the investigation.Then,the mainly polluted form Cr⁶⁺was chosen as the pollutant,crucian carp（Carassius auratus）,which is easily polluted by Cr,was chosen as the model fish,then the dirstribution and metabolism effects of Cr⁶⁺in different tissues were studied.The results showed that compared to fish muscle,Cr⁶⁺content in fish head was always higher.Then,the content of Cr⁶⁺in different fish species was determined and it was found that it is common that the Cr⁶⁺content in fish head is significantly higher than that in fish muscle.To clarify the specific reason that high content of Cr⁶⁺in fish head,the bighead carp（Hypophthalmichthys nobilis）was chosen as the object,and the accumulation and distribution of Cr⁶⁺in fish muscle and head were further studied.The main contents and results are as follows:1.Identification of the typical heavy metal pollutant in fishChaohu Lake is the fifth largest freshwater lake in China.In recent years,studies have shown that Chaohu Lake is polluted by heavy metals in different degrees.In this study,to evaluate the degree of pollution in Chaohu Lake,the contents of heavy metals（Zn,Pb,Cr,Cu,Ni,As and Cd）in water and sediment of Chaohu Lake were determined,and the results showed that Chaohu Lake posed a low ecological risk.Then,the health risk from consuming fish（Carassius auratus,Cyprinus carpio,Culter alburnus,Mylopharyngodon piceus,Hypophthalmichthys molitrix,Hypophthalmichthys nobilis,Megalobrama amblycephala and Ctenopharyngodon idellus）collected from Chaohu Lake was assessed and it was found that the consumption of C.auratus in Chaohu Lake would cause potential non-carcinogenic risk to children,and cause potential carcinogenic risk to teenagers and adults.In the non-carcinogenic risk,the contribution of Cr and Pb is 45%and 43%,respectively,while in the carcinogenic risk,the contribution of Pb is 0.2%-6%,and the contribution of Cr is 94%-99.8%.These results indicated that even in a low polluted water body,the accumulation of heavy metals in fish could also pose a potential risk to consumers,and the pollution of Cr in fish must be paid more attention.2.Distrubition and metabolism of Cr⁶⁺in different tissues of Carassius auratusAccording to the results of field investigation,Cr was chosen as the typical heavy metal pollutant in fish.However,up to now,the metabolism of Cr⁶⁺in different tissues of fish is still unclear.In this study,Cr⁶⁺was selected as the pollutant and C.auratus（which is easily polluted by Cr in the early investigation）was selected as the research object.And then,a 28-day exposure experiment and a 20-day clearance experiment were conducted to study the toxicokinetics of Cr⁶⁺in tissues（liver,kidney,intestine,gill,muscle and fish head）of C.auratus under different waterborne Cr⁶⁺exposure（0,0.1,1 and 10 mg/L）by using a two-compartment model.The results showed that the metabolism of Cr⁶⁺was tissue-specific,for example,gill and intestine played a key role in the temporary storage of Cr⁶⁺,liver played an important role in the detoxification process of Cr⁶⁺,fish muscle and fish head could be used as the short-term storage tissues of Cr⁶⁺,while kidney could be the long-term storage organs of Cr⁶⁺.The results of kinetics showed that the depuration rate of Cr⁶⁺in fish muscle and fish head was similar,so the higher Cr⁶⁺content in fish head was attributed to the higher absorption rate of Cr⁶⁺.The results of health risk assessment showed that Cr⁶⁺accumulated in fish head would cause a higher potential risk to consumers compared to that in muscle under all the exposure concentration（0,0.1,1and 10 mg/L）.These results indicated that the metabolism of Cr⁶⁺in fish is tissues-specific,and for the edible parts of fish muscle and head,the depuration rate of Cr⁶⁺was similar,so the higher Cr⁶⁺absorption rate ws contributed to the higher Cr⁶⁺content in fish head.3.Distribution characteristics of Cr⁶⁺in the main edible parts（muscle and head）of different commercial fish species and the related health risk assessmentThe results of Cr⁶⁺distribution in C.auratus showed that Cr⁶⁺content in fish head was higher than that in muscle.In order to verify whether there is a similarity about Cr⁶⁺content in fish head is higher than that in muscle of different fish species,Cr⁶⁺contents in muscle and head of 14 fish species（Ctenopharyngodon idellus,Megalobrama amblycephala,Hypophthalmichthys molitrix,Hypophthalmichthys nobilis,Carassius auratus,Cyprinus carpio,Culter alburnus,Micropterus salmoides,Siniperca chuatsi,Clarias fuscus,Tachysurus fulvidraco,Ictalurus punctatus,Mylopharyngodon piceus and Channa argus）were determined.The results showed that Cr⁶⁺content in fish head was always higher than that in muscle.Additionally,the health risk assessment showed that Cr⁶⁺contents in dorsal muscle and ventral muscle did not cause health risk to children,teenages and adults,however,Cr⁶⁺contents in fish head caused potential carcinogenic risk to adults.These results indicated that compared to fish muscle,a higher content of Cr⁶⁺was always found in fish head,which would pose a higher potential risk.Thus,the consumption of fish head must be paid more attention.4.The difference of of Cr⁶⁺accumulation in muscle and head of Hypophthalmichthys nobilisIt has been found that the content of Cr⁶⁺in fish head is higher than that in muscle.And the metabolic kinetic study showed that the higher Cr⁶⁺absorption rate ws contributed to the higher Cr⁶⁺content in fish head.However,the specific reason for the higher absorption rate of Cr⁶⁺in fish head is still unclear.In this study,H.nobilis,which were chosen as the object fish,were exposed to different waterborne Cr⁶⁺（0,0.01,0.1,1and 5 mg/L）,and the accumulation differences of Cr⁶⁺in fish muscle and head were studied.The results showed that Cr⁶⁺content in fish head was always higher than that in muscle during the whole experiment,which is in line with the results of C.auratus.Previous studies have shown that the accumulation of metals such as arsenic（As）and zinc（Zn）is associated with the fat content in fish tissues.To explore whether the accumulation of Cr⁶⁺in fish tissues is also related to the fat,the fat content in muscle and head was detected,and the highest content of fat was found in head.Besides,correlation analysis showed there was a significant positive correlation between Cr⁶⁺content and fat content in tissues.Subsequently,to further verify the direct relationship between Cr⁶⁺and fat in H.nobilis,fat in tissues were extracted by anhydrous ether,and then,Cr⁶⁺content in fat part and non-fat part were measured separately.The results showed that Cr⁶⁺was not mainly deposited in fat,as Cr⁶⁺content in fat part of muscle was less than 30%,and Cr⁶⁺content in fat part of head was less than 5%.In addition,a vitro adsorption experiment of oil（fish oil,soybean oil,peanut oil and flaxseed oil）and water also showed that Cr⁶⁺mainly existed in water phase,and the amount of Cr⁶⁺adsorbed by oil was less than 25%.These results indicated that the accumulation of Cr⁶⁺in fish head is higher than that in muscle,although a significant positive correlation was found in fat and Cr⁶⁺contents,the Cr⁶⁺accumulated in fish head was not mainly deposited in the fat,that is,the high content of fat in fish head is not the direct casue of the high content of Cr⁶⁺in fish head.5.Distribution of Cr⁶⁺in different parts of Hypophthalmichthys nobilis headTo further explore the specific reason for the high content of Cr⁶⁺in fish head,H.nobilis,which was chosen as the research object,was exposed to 1 mg/L Cr⁶⁺for 14 days.After accumulating a certain amount of Cr⁶⁺,the distribution of Cr⁶⁺in fish head was studied.The fish head was divided into seven parts:cerebrospinal fluid,fish brain,fish eye,fish lip,gill meat,other meat and fish bone.The results showed that the content of Cr⁶⁺in each part was as follows:fish bone>fish lip>other meat>gill meat>fish eye>fish brain>cerebrospinal fluid.It could be seen that the contents of Cr⁶⁺in fish bone and fish lip were extremely high in fish head,which indicated that Cr⁶⁺was mainly deposited in the bone of fish head,and the high content of bone was the main reason for the high content of Cr⁶⁺in fish head.The results of health risk assessment showed that except for fish lips and fish bones,other edible parts did not cause health risk to different populations.It is worth noting that although Cr⁶⁺in fish head is mainly deposited in the bone,the content in meat of fish head is still higher than that in dorsal muscle and ventral muscle.These results indicated that Cr⁶⁺in fish head is mainly deposited in the bone,and in the health risk assessment of fish head consumption,the influence of bone should be considered as the existence of bone would lead to overestimation of the risk.In conclusion,the typical heavy metal pollutant Cr was selected firstly by the investigation of heavy metals pollution in different fish species.Then,the toxicokinetics of Cr⁶⁺in fish tissues was studied and the specific metabolism of Cr⁶⁺in tissues was found.Compared to fish mucle,the higher uptake rate of Cr⁶⁺in head contributed to the high content of Cr⁶⁺in it.Furthermore,the reason for the high contant of Cr⁶⁺in fish head was explored,and it was found that the Cr⁶⁺in fish head was not deposited in fat,but mainly deposited in bone.The results of this study could enrich our understanding of the safety of fish consuming,especially for the consumption of fish head polluted by Cr⁶⁺.Moreover,this study could lay a foundation for the further study about the metabolism of Cr⁶⁺in fish,provide a theoretical basis for reducing the accumulation of Cr⁶⁺and promoting the excretion of Cr⁶⁺in fish,and play an important guiding role in ensuring the quality and safety of aquatic products.