Effects Of Fish Consumption During Pregnancy On Prenatal Exposure Levels To Mercury

BackgroundWith the development of science and progress of society,higher expectations and more researchs were requested for improving self-quality in human being. Improving the quality of the population and prepotency have become a common subject for human being.It is well documented that the reasons for birth defect effecting the quality of the population were divided into genetic factors and environmental factors.Birth defect and fetal abnormality which were caused environmental pollution have been main research contents in recent years.Prenatal exposure to mercury(Hg)causing fetal abnormality and the long-term damage of nervous system is one of the hot spots in academic circle in recent years.Three main forms of Hg are found in the environment:elemental mercury, or quicksilver(Hg~0),inorganic mercury,and organic mercury(mainly merthylmercury MeHg).Hg is a toxic element for the cell,and its most toxic form is MeHg.It is comparatively explicit that MeHg toxicity in human being was related to nephrotoxicity,immunotoxicity,reproductive toxicity and neurotoxicity so on.It is well documented that MeHg readily passed the placenta and blood-brain barrier during pregnancy,and can result in fetal abnormality and birth defect. Comparing with pregnant women,the fetus is particularly sensitive to MeHg,even at a concentration that results in few or no clinical signs of maternal toxicity. Prenatal MeHg exposure can induce mental retardation,low birth weight,and early sensorimotor dysfunction.Up to now,many results in toxic effect studies of MeHg mostly come from animal experiment,while data of studies about prenatal MeHg exposue in human being were chiefly come from epidemiological investigation.Numerous studies regarding the toxic effects of MeHg in humans have been performed and indicated that consumption of contaminated fish and seafood is the primary route of human exposure to MeHg.The environment of East China Sea has been under huge stresses posed by anthropogenic activities and population growth in the Yangtze River drainage basin and the areas along the coasts.The environmental degradation has now reached a level at which the health and well being of the coastal populations are threatened.Heavy metals are one of the main pollutants.Environmental Hg contamination from natural and anthropogenic sources has become a public health concern.However,few data are available on either Hg levels in fetus and their mothers or the effects of prenatal exposure to Hg in the Chinese population.Numerous studies suggested that more than 90%of total mercury(THg)in cord blood and cord tissue was MeHg.As a result,MeHg concentrateons in both cord blood and cord tissue were reflected by THg concentrations in cord blood and cord tissue,respectively.Objective:1.To seek for the biomarkers reflecting Hg exposure of fetus and their mothers in order to preventing the mother and fetus from excessively Hg exposure.2.To investigate Hg exposure levels of fetus and their mothers,and related characteristics factors according to making use of small sample survey,which could provide data and experience for the future's the epidemiological investigations and in-depth study.Methods:In total,from 2006 to 2008,77 paired samples were collected in two Chinese districts,Hangzhou city and Ninghai county.The recruited mothers(42 mothers coming from the obstetrical wards of Ninghai Women's and Children's Health Hospital and 35 mothers coming from Women's Hospital School of Medicine Zhejian University)filled in standard questionnaires(including Main characteristic of the parents and newborns).THg in the samples(cord tissues,maternal blood,and cord blood)was measured by cold vapor atomic absorption spectrophotometry (CVAAS)according to the method of Akagi et al.The relationships among all the samples(cord tissues,maternal blood,and cord blood)in THg concentrations were analyzed.SPSS13.0 for Windows(SPSS Inc.,Chicago,IL)was used for the statistical calculations.In view of the skewed data,THg concentration results in maternal blood,cord blood,and cord tissue were log-transformed to minimize the disproportional impact of extreme values.Statistical methods including Analysis of Variance(ANOVA),and t-test,pearson correlation,chisquared test and Multivariate linear regression analysis were used.A significance level of P＜0.05 (two tails)was used for all analyses.Results:1.In total,the mothers and their term newborns(40 males and 37 females)were recruited.No mother drank alcohol and smoked during pregnancy.No family members worked as dental doctors,thermometer or fluorometry makers.11 family members in Experimental group worked as fisher.We also found that there were higher Hg concentrations in cord blood among those who had been more than or equal 3 times of maternal dental amalgam fillings as compared with those who had been less than 3 times of maternal dental amalgam fillings(P＜0.05).Cord blood Hg concentrations in male newborn was obviously more than cord blood concentrations in female newborn(P＜0.05).Multivariate linear regression analysis included that maternal dental amalgam fillings and sex of newborn were influencing factors of cord blood THg concentrations.There was no statistically significant difference between Experimental group and Control group for the following factors: maternal age,gestation(weeks)and body weight for mothers and birth weight and body height for newborn.And there was no statistically significant difference in cord blood THg concentrations for the factors including maternal education and time live in Ninghai county or Hangzhou city for mothers,and the Apgar score for the newborn.2.There was statistically significant difference in constitute proportion of mothers with different frequencies of fish consumption(0～1 time/week 2 times/week,3 times/week and≥4 times/week)between Experimental group and Control group(P＜0.05).Constitute proportion of mothers who consumed fish more than or equal four times per week in Experimental group was more than constitute proportion of mothers who consumed fish more than or equal four times per week in Control group(P＜0.05).3.THg concentrations in maternal blood,cord blood and cord tissue in Experimental group were obviously more than THg concentrations in maternal blood,cord blood and cord tissue in Control group,respectively(P＜0.01).4.There was statistically significant difference in cord blood THg concentrations among groups with different frequencies of fish consumption(0～1 time/week,2 times/week,3times/week and≥4 times/week).Mothers who consumed fish more than or equal four times per week had much higher maternal blood,cord blood and cord tissue THg concentrations,which were nearly two times higher than those who rarely consumed fish.Making use of linear term in ANOVA,increasing Fish intake frequency showed significantly increased maternal(F=45.01 P＜0.01),cord blood(F=28.26 P＜0.01)and cord tissue(F=33.03 P＜0.01)THg concentrations.5.Of the 42 cord blood samples in Experimental group collected,about 35.7%had THg concentrations more than 5.8μg/L.But Of the 35 cord blood samples in Control group collected,about 14.3%had THg concentrations more than 5.8μg/L.6.Our study indicated that individual cord blood /maternal blood THg concentrations varied from 1.11 to 2.98 in mother-infant 77 pairs at parturition. THg concentrations in cord tissue showed strong correlations with THg concentrations in maternal blood(R~2=0.581 P＜0.01).THg concentrations in matemal blood showed strong correlations with THg concentrations in cord blood (R~2= 0.805,P＜0.01).THg concentrations in cord tissue showed strong correlations with THg concentrations in cord blood(R~2=0.739,P＜0.01).Conclusion:1.The findings of this study indicated that the frequency of fish consumption during pregnancy was the predictor of Hg concentrations.2.Of the 42 cord blood samples in Experimental group collected,about 35.7%had THg concentrations more than 5.8μg/L,which indicated that some fetuses because of excessive Hg exposure were still to remain in danger.3.The difference of sex and maternal dental amalgam fillings was the risk factors affecting fetus exposure concentrations to Hg.4.THg concentrations in both cord blood and cord tissue(dry)which were the important biomarkers reflecting Hg exposure of fetus,which was together analyzed, can understand the status of fetus Hg exposure during third term pregnancy.