Environmental exposure to heavy metals has been linked to a w ide range of human health detected the levels of 15 metals in urine samples from 500 representative sub‐samples in an ongoing occupational cohort study(Jinchang Cohort)to directly evaluate metal exposure levels. Fifteen metals,namely As,Ba,Be,Cd,Cs,Cr,Co,Cu, Pb,Mn,Ni,Se,Tl,U,and Zn,were detected by inductively coupled plasma quadruple mass results showed that median creatinine adjustment and geometric mean urinary metal levels were higher in the heavy metal‐exposed group,except Se and Zn,than other reported general or occupational populations. Further studies should address the effects of heavy metals on human health.

China has become the largest producer and consumer of heavy metals in the world due to rapid industrialization and urbanization[1].A large quantity of metals has been released into the environment and has had significant health implications for occupational workers;however,lim ited urinary metal reference data are available for metal‐exposed have established a prospective cohort study among metal‐exposed workers called the China Metal‐exposed Workers Cohort Study (Jinchang Cohort)[2]for the purpose of evaluating the association between metal exposure and various health the present study,we detected levels of 15 metals in urine samples from a representative sub‐sample of 500 subjects in the Jinchang Cohort to evaluate metal exposure levels among occupational workers.

A total of 500 participants working in the Jinchang nonferrous metal industry for at least 1 year were selected from the Jinchang Cohort to participate in this were occupationally exposed to nickel,copper,cobalt,and other metals from various production processes,including m ining, concentrating,smelting and 500 workers were between the ages of 20 and 50 years and included three subgroups based on their occupation,including management and service workers,chem ical and metal products manufacturing workers,and m ining/smelting/ refining workers.

Spot urine specimens were collected in cryogenic tubes,stored at‐40°C,and then shipped on dry ice to the Public Health School of Lanzhou levels of 15 heavy metals were measured by inductively coupled plasma mass spectrometry(Thermo Scientific,Rockford,IL,USA): arsenic(As),barium(Ba),beryllium(Be),cadm ium (Cd),cesium(Cs),chrom ium(Cr),cobalt(Co),copper (Cu),lead(Pb),manganese(Mn),nickel(Ni), selenium(Se),thallium(Tl),uranium(U),and zinc (Zn).All urine samples were completely thawed at room temperature and 1 m L sample was m ixed w ith 3.0%HNO3to a final volume of 2.5 m L for overnight nitrification[3].The standard human urine reference(SRM 2670A;National Institute of Standards and Technology,Gaithersburg, MD,USA)was used as an external quality control, and sample spike recoveries were used to confirm analytical recovery,which was 95%.The intra‐day and inter‐day coefficients of variation were±5%.Urinary metal concentrations were log‐transformed prior to data statistical parameters were computed replaced the metal concentrations below the lim it of detection(LOD)with LOD/2.An agglomerative hierarchical cluster analysis based on the average linkage method and a correlation matrix were also analyses were conducted using SAS software ver.9.4(SAS Institute,Cary,NC,USA).

Table 1 shows the urinary metal levels of the 500 subsamples in the Jinchang Cohort table shows the LODs and the proportion of results below the LOD,arithmetic(AM)and geometric mean (GM)concentrations,and median and selected LODs were in the range of 0.0002 μg/L(for U)to 0.1391 μg/L(for Zn)calculated from undiluted urinary metal levels,except that of Be,were higher than the LODs.The GM,AM,and median levels of urinary As were 54.68,118.05,and 46.30μg/g creatinine, corresponding urinary Ni levels were 4.27,7.21,and 3.97 μg/g creatinine, GM values of urinary Cd,Cr,Co,Cu,Pb,Mn,and Zn were 0.53, 0.91,0.56,12.17,4.06,1.71,and 249.76 μg/g creatinine,respectively.

Inter‐metal relationships provide information on metal sources and results obtained by cluster analysis are also presented w ith a dendrogram where the distance axis represents the degree of association of the between‐group variables(Figure 1).Many of the metals,except Be, correlated w ith each positive correlations were found between Ba and Mn,Ni and Co,and Cr and Cu w ith Pb(P≤0.05).

We compared the urinary heavy metal levels among occupational workers in the cohort w ith Chinese,US,and Canadian general populations,as well as Chinese coke oven workers(Table 2).The median urinary As level in nonferrous metal workers was approximately two times higher than that of the Chinese general population(65.158 μg/L) and 10‐fold higher than levels in the Canada general population(65.158 vs.11.67 μg/L).Arsenic exposure from As dust was the largest source for metal‐exposed workers,which usually originates from copper and other metal creatinine adjusted median values for Pb were about 14 times higher than those in the US general GM value was also about eight‐fold higher than that in the US,Canadian,and German populations[3].Higher As and Pb levels have been found in metal‐exposed workers in the Jinchang Cohort,com pared w ith those of general and occupational populations.