Prenatal Thallium Exposure And Poor Physical Growth In Early Childhood:A Prospective Birth Cohort Study

BackgroundThallium?Tl?pollution remains a public health issue with potential adverse impacts on humans.Studies have indicated that prenatal exposure to thallium may be related with poor fetal growth,but no studies are known have researched its association with infant growth.ObjectiveTo investigate the levels of thallium exposure in first and second trimester of pregnant women and in umbilical cord blood of infants,and explore the effects of prenatal thallium exposures on early child physical growth aged 0-2 years in a prospective birth cohort study.Methods3 080 pregnant women and their child participated in this study,which were recruited from Ma'anshan birth cohort?MABC?.Information of demographic characteristics such as age and weight,maternal health status,nutritional supplements during pregnancy was collected by using self-developed questionnaire.Serum samples gathered in the first and second trimester of pregnant subjects and in umbilical cord blood of infants were measured by inductively coupled plasma mass spectrometry.Infant length or standing height and weight were obtained from medical records and 2years planned visits.We used length/height and weight to calculate z-scores for weight-for-age?WAZ?,height-for-age?HAZ?,weight-for-height?WHZ?,and body mass index-for-age?BMIZ?based on child growth standards by World Health Organization?WHO?in 2006.As the distribution of thallium levels was right skewed,it appeared an approximating normal distribution after being log¹⁰-transformed.The differences of thallium concentrations at different period were compared applying Spearman's correlations and paired Mann-Whitney tests.Using one-way analysis of variance and t test to compare thallium levels in different variable groups.Using t test to compare the difference of infant growth in boys and girls.And linear mixed model was used to investigate the association between serum concentrations of thallium and the children's anthropometric growth?WAZ,HAZ,WHZ,and BMIZ?aged 0-2 years,and stratification analysis by sex was also examined.ResultsThallium was detected in 100%of the all samples,and the median(P₂₅-P₇₅)of thallium levels in the first trimester,second trimester and umbilical cord serum were 61.7?50.7-77.0?,60.1?50.9-74.8?and 38.4?33.6-43.9?ng/L,respectively.Paired Mann-Whitney tests found thallium concentrations in umbilical cord serum were significantly less than that in maternal serum during the first and second trimesters,but slightly decreased from first to second trimester?all P<0.01?.In one-way analysis of variance,the thallium concentrations in the first and second trimester were significant differences in different pre-pregnancy body mass index?BMI?groups,and the thallium concentrations in umbilical cord serum were significant differences in different maternal age groups?all P<0.05?.Using adjusted linear mixed model,no significant relationships were observed between thallium exposure in first and second trimester and child growth parameters?all P>0.05?.However,the umbilical cord serum thallium levels may contributed to decreased WAZ??=-0.382,95%confidence interval?CI?:-0.670,-0.095?and HAZ??=-0.427,95%CI:-0.702,-0.152?,and have no significantly associated with WHZ and BMIZ?all P>0.05?.When stratified by sex,the umbilical cord serum thallium levels were negatively related to WAZ??=-0.450,95%CI:-0.853,-0.048?and HAZ??=-0.775,95%CI:-1.160,-0.391?for girls.Among boys,overall thallium exposures were not significantly associated with early children anthropometric outcomes?all P>0.05?.ConclusionIn the present study,our results suggested that prenatal thallium exposures may have a sex specific effect on child anthropometric measurements in the first 2 years of life.Umbilical cord serum thallium levels tended to be reduced child's stature and weight in young girls.