Heavy Metal Pollution In Crayfish (Procambarus Clarkiclarkii) And Assessment Of Health Risk Associated With Crayfish Consumption In China

Red swamp crayfish(Procambarus clarkii)is the third largest shellfish in the world and has been widely consumed,especially in Asia,Europe and North America.China is the world largest producer and consumer of crayfish.International concerns about elevated metal levels in aquatic organisms have been evoked.Crayfish has been reported to accumulate high levels of heavy metals due to omnivory and necrophagia.However,the current knowledge of potential risk associated with crayfish consumption has lagged behind that of fish.This was partly due to the lack of data regarding metal concentrations,consumption rates,and bioaccessibility.The present study provides the first national survey on heavy metal levels in crayfish in China and our survey of 217 cooked crayfish samples were collected from restaurants in 23 cities encompassing 12 provinces.The recorded mean valuess±SD were arsenic(As):253.3±142.4 ?g/kg,cadmium(Cd):29.88±39.2 ?g/kg,copper(Cu):9.2±5.8 mg/g,mercury(Hg):51.8 ± 29.2 ng/g,nickel(Ni):171±141 ?g/kg,lead(Pb):23.3±29.5 ?g/kg,selenium(Se):294.4±154.1 ?g/kg and zinc(Zn):20.1±6.3 mg/kg,respectively.There were no crayfish samples exceeding the national standard limits(GB2672-2012),but the Hg and As levels in crayfish were generally higher than those reported in other freshwater aquatic products.Our results also indicated that MeHg constituted 99.1%of total mercury(THg)in crayfish tail muscle and MeHg was mainly distributed in cellular debris(56.9±3.7%)as well as heat stable protein(34.3±3.2%).Besides,a good relationship was found between MeHg and THg(R2=0.96,p<0.001).Concentrations of some examined metals(e.g.,Hg and Ni)were affected by body size and sampling sites.In order to better assess risk of metals in crayfish,the bioaccessibility of heavy metals in crayfish were measured with an in vitro digestion model.Large differences in bioaccessibilities were found:As(94.3±8.2%),Cd(78.7±6.1%),Cu(93.0±19.37%),MeHg(9.3±5.5%),Ni(94.9±20.2%),Se(81.6±13.1%)and Zn(68.1 ±22.4%).The highest bioaccessibility was found for Ni(94.9±20.2%),followed by As(94.3±8.2%)and Cu(93.0±9.37%),while the lowest value at 9.3%was found for MeHg.Especially,bioaccessibility of MeHg in crayfish was much lower than that in other freshwater aquatic products(e.g.,rabbitfish and grouper),as well as bioaccessibilities of other metals in crayfish.In view of the differences in bioaccessibility among elements,bioaccessibility should be considered in the risk assessment.To explore the underlying mechanisms of the relatively low MeHg bioaccessibility in crayfish,the antagonistic effects of Se,subcellular fractionation as well as amino acid concentrations in crayfish,blackfish(Channa argus)andyellowcroaker(Larimichthyspolyactis)were compared.The results indicated that all the examined aquatic products had comparable subcellular distribution but relatively lower bioaccessibility of MeHg was found in the purified subcellular fraction of crayfish.This was probably because of the higher levels of functional groups in crayfish tissues(e.g.,thiol groups).Concentrations of some amino acids in crayfish were higher or comparable with those in blackfish and yellowcroaker.Especially for Cysteine,with the highest affinity to MeHg among all amino acids,its concentrationwas higher in crayfish(0.67%)than that in blackfish(0.58%)or yellowcroaker(0.45%).By using questionnaire survey,risk calculation,and probabilistic models,we estimated ingestion rates of crayfish,in order to assess health risk associated with crayfish consumption.Our results indicated low risk of metals in crayfish for the general populations in China.However,there could be risk for high consumption individuals in the middle and lower reaches of Yangtze River(MLYR).For example in Nanjing,a typical city in MLYR,crayfish consumption could pose high risk to around 0.5%of populations(Hazard index or HI>6).And for HI value,As HQ was a great contributor(nearly 70%),suggesting that As may be the main hazard when talking about heavy metals health risk via crayfish consumption.The cancer risk of As was already above the acceptable level of 1 per 100,000 recommended by USEPA,for the median value(2.46×10-5).Thus,for high crayfish-consuming populations(e.g.,in China,USA and Sweden),heavy metals in crayfish could still pose potential hazard and crayfish should be considered when assessing heavy metal exposure from food consumption.