Toxic Effects And Gene Expression Of Zebrafish Embryos Exposed To Methylmercury,Cadmium And Arsenic And The Mixture

Heavy metals released by industrial process and natural disasters have caused severely environmental pollution and health damage.Anthropogenic heavy metals are the main source of heavy metal pollution.The adverse health outcomes of heavy metal exposure have been intensively studied,but most studies mainly focus on elucidating the toxic effects and mechanisms of single metal.In the environment,many heavy metals simultaneously exist.Human and wildlife are facing to exposure of multiple heavy metals.Therefore,it is urgent to assess the health risk associated with mixture of heavy metals exposure and reveal mechanisms of toxic effects.In this study,methylmercury,cadmium and arsenic,which are widely distributed in the environment with highly toxic effects,were selected to study the toxic effects of single and the mixture exposure on the development of zebrafish embryos.The toxic effects of the three heavy metals were analyzed;the expression patterns of the selected genes were screened by employing in situ hybridization;the relative expression levels of the selected genes were measured by using quantitative PCR.The main results are as follows:（1）Concentration response curve associated with exposure of zebrafish embryos to single and mixture of methylmercury,cadmium and arsenic.The LC₅₀of arsenic was 193.80 mg/L,and the LC₅₀of mixture of methylmercury,cadmium and arsenic ranged from 1/4 LC₅₀（10.00μg/L,4.00 mg/L,and 48.00 mg/L for methylmercury,cadmium,and arsenic,respectively）to 1/2 LC₅₀（20.00μg/L,8.00 mg/L and 96.00mg/L for methylmercury,cadmium,and arsenic,respectively）.Both arsenic and the mixture exposure resulted in reduced hatchability of zebrafish embryos.（2）Gene expression patterns of markers associated with exposure of embryos to single and mixture of methylmercury,cadmium and arsenic.Embryos exposed to single heavy metal showed genes abnormal expressing in the olfactory bulb,lens,lateral line,skin and muscle,which may link the deficiency of functions of olfactory bulb,eye,lateral line,skin and muscle.Embryos exposed to mixture of methylmercury,cadmium and arsenic showed abnormal expression of genes in the olfactory bulb,skin,and the boundaries of mid-hindbrain,which may affect the development of the olfactory bulb,skin,and brain.（3）Changes in expression of marker genes related to exposure of embryos to single and the mixture of methylmercury,cadmium and arsenic.Both single and their mixture exposed embryos showed changes in expression of genes involving in oxidative stress,substance transport,DNA synthesis and repair,transcriptional regulation and genes related to early development.The effects of single high-concentration heavy metal exposure and combined low-concentration exposure on the expression of marker genes were partially similar.The toxic effects of combined heavy metal exposure were not only additive,but also antagonistic and synergistic.To sum up:this study uses zebrafish embryos as model organisms,and finds that methylmercury,cadmium,arsenic and their mixture affect development of zebrafish embryos.The ectopic expression of genes are found in embryos exposed to methylmercury,cadmium and arsenic and their mixtures,such as olfactory bulb,eye,lateral line,skin,muscle and nerve.Expression of genes related to oxidative stress,material transport,DNA synthesis and repair,transcriptional regulation and early development is affected in embryos exposed to either single or mixture of heavy metals.This study preliminarily determined the similarities and differences of the marker genes expression related to single and mixture exposure,laying a foundation for further elucidating the causal relationship between key molecular events caused by combined exposure and abnormal early development of organisms.