Improvement of protective facilities in vinyl chloride units on liver injury status of occupational exposed group

Abstract

To comprehensively evaluate the effectiveness of improvement of protective facilities in a vinyl chloride monomer(VCM) on promotion toward health status of occupational exposed group and safety production at poly-vinyl chloride(PVC) by comparing the liver function indicators and inspection result before and after the improvement, and to analyze the possible influential factors. The information collection concerning facilities improvement in 2013 and 2016, identification toward critical controlling points, data or detection result from occupational on-site survey and physical examination were originated in July 2020, and 227 VCM exposed workers and 179 others without chemical reagents exposure history from production factory with calcium carbide process in Tianjin City were selected as objects. The effectiveness toward improvement of protective facilities in critical controlling points that occupational exposed workers usually involve in were evaluated through comparison toward VCM concentration result, thiodiglycolic acid(TDGA) content in urine, indicators on liver function and biochemistry and liver ultrasound. At the mean time, both binary Logistic regression analysis was used to screen the possible factors that contributed to abnormal symptoms and single dependent variable general linear regression model was used to find out the mutual interaction among influential factors. Prior to improvement on protective facilities, the C_(TWA)of VCM exposed by all 8 positions in G had exceeded 1 to 2 folds of occupational exposure limit(OEL=10 mg/m~3) and the position of synthetic operator and field sampling man were ones exposed to 1, 2-DCE with the range from 50% to 1 OEL, others hazard factors were found to meet relative OELs. Next, the content of TDGA in urine of exposed group was found to correlate strongly to the average concentration of VCM(r=0.79, P<0.05), and result of TDGA content, alanine aminotransferase(ALT), γ-glutamyl transpeptidase(GGT) and abnormal rate toward liver ultrasound test in exposed group were much higher than ones in control group with significant differences(P<0.05 or P<0.001). By contrast, after the improvement, the exposure level toward all identified hazard factors were declined to meet OEL levels with significant differences in TDGA content, and result of ALT, GGT and abnormal rates toward symptoms in liver ultrasound test such as liver calcification with thickened liver echo, peripheral fibrosis of the liver, multiple hepatic cysts were markedly lower than ones before improvement and still were higher than ones in control group(P<0.05 or P<0.001). Further, parameters of gender, length of employment, weekly contact time, VCM exposed level, TDGA content were all important contributing factors to abnormal symptoms in liver ultrasound test before and after improvement on protective facilities(P<0.05 or P<0.001), in which a significant interaction effect between gender and length of employment(F=4.028, P=0.044), weekly contact time and TDGA content(F=2.183, P=0.046) in urine were found in contribution analysis to abnormal symptoms in liver ultrasound test(P<0.05). The improvement measure carried out in VCM facilities by this PVC production factories with calcium carbide process effectively reduced the ambient concentration of hazard factors mainly led by VCM, but workers might still be at risk of liver injury even under VCM exposure at relative lower level, which may referred to factors of long weekly contact time, long length of employment and high fat diet.