Studies Of Heavy Metal Pollution And Cadmium Species In Shellfish Collected From Some Coastal Areas Of Fujian

Shellfish are easily enriched with heavy metals,which is harmful to human health.However,different species of heavy metals may have different toxicological characteristics.The total amount of heavy metals cannot truly reflect their hazards.Based on this,on the basis of investigating and analyzing the pollution of heavy metals in several types of seawater shellfish,this dissertation has carried out Cd species detection methods and species changes of Cd during the simulated digestion process for cadmium(Cd)pollution characteristics.It is important for understanding the shellfish Cd pollution to human health risks.The main content of the paper is as follows:Section 1,To conduct research and assessment of shellfish heavy metal pollution and health risks in some coastal areas of Fujian.Analysis of the pollution levels of 10 elements(As,Cr,Mn,Ni,Cu,Zn,Cd,Sn,Sb,Pb)in the five main edible shellfish(short-necked clam,scallop,mussel,razor clam,and oyster).And use target hazard coefficients(THQs)to conduct risk assessments of shellfish heavy metal pollution.The results show that in the 240 shellfish samples collected,the average level of heavy metals is Zn> Sn> Cu> Mn> As> Cr> Ni> Cd> Pb> Sb,among them,the exceeding rate of Cd,As and Cu are 27%,33% and 2% respectively.Except for the THQ value of As in razor clams is 1.148,the THQ values of the other elements are far below 1.Based on the calculation results of the HI value,the shellfish in the collection area has no obvious risk to human health.Section 2,The size exclusion chromatography(SEC)was used in combination with inductively coupled plasma mass spectrometry(ICP-MS)and electrospray ionization quadrupole time-of-flight mass spectrometry(ESI-QTOF-MS)to study the Cd species of shellfish.Taking Cd in short-necked clam as an example,three different sizes Cd-binding species were found in short-necked clam by SEC-ICP-MS.Further analysis by SEC-ESI-QTOF-MS revealed that the high molecular Cd species may be a Cd-binding protein with a molecular weight of 32695 Da.The molecular weights of Cd homologous species including 10764 Da,17984 Da,18156 Da,19236 Da and 20978 Da may be attributed to Cd-binding like-metallothionein.In addition,some small molecules of Cd species may be the product of the combination of Cd and amino acids.The analysis results of Cd species show that the Cd entering the shellfish body does not exist in the free state,but combines different proteins and amino acids.Using these two combined analysis methods of SEC-ICP-MS and SEC-ESI-QTOF-MS,the combined species of heavy metals in shellfish can be obtained.Section 3,Taking the Cd pollution of short-necked clam as an example,through using these two combined analysis methods of SEC-ICP-MS and SEC-ESI-QTOF-MS and a simulated digestion model to study the main species and transformation of Cd in shellfish at different digestion stages.The results of SEC-ICP-MS showed that 4 and 3 Cd-binding species were found in the stomach and intestine digestive juice,respectively.These Cd-binding species were further characterized by SEC-ESI-QTOF-MS,it was found that both the stomach and intestine digestive juice contained 32695 Da Cd-binding species.However,compared with the undigested sample,the content in the gastric digestive juice decreases,and the content in the intestinal digestive fluid increases.The small molecule Cd-binding species were also found in the stomach and intestine digestive juice,indicating that during the process of stomach digestion,the large molecule Cd-binding species may be partially degraded.At the gastric stage,the species of Cd binding to metallothionein disappears.This may be due to the bound metal(Cd)is removed from the metallothionein under acidic conditions of gastric juice,Cd binds to like-metallothionein again at the intestinal stage,and its species molecular weight is mainly 19236 Da.In addition,in the intestinal juice,the content of small molecule Cd-binding species decreases,and the Cd-binding species mainly exists in the form of macromolecules and like-metallothionein,which shows that the small molecule Cd species is easily absorbed in the intestinal juice,while the macromolecules species of Cd-binding protein and like-metallothionein can protect the body and reduce the harm of Cd,but the physiological and biochemical effects of Cd species still need further study.