To the Editor: We examined the relationship between work in coke oven and by-product plants and serum activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in one of the largest steel companies of Taiwan in 1993 and 1994.1 During November 1992 and June 1993, the company measured monthly 16 respiratory polycyclic aromatic hydrocarbons (PAH) (<10 µm) on the top of the two coke ovens and around the administrative area. The mean total PAH exposure levels were ranked as follows (ng/m3): on the top of the older coke oven plant, 6.8 × 103; on the top of the newer coke oven plant, 2.1 × 103; around the administrative area, 6.5 × 101, respectively. The older coke oven plant is about 300 meters away from the newer one; the administrative area is approximately 2 kilometers away from these two coke oven plants. We found that workers(n = 91) in the older of the two coke oven plants had serum AST and ALT levels that were 17% and 37% (95% confidence intervals [CI], 1%-37% and 6%-77%), respectively, higher than those in the controls (n = 131) in 1994 after adjusting for appropriate confounders. We concluded that the commonly examined liver enzyme activities might be affected by coke oven emissions (COE), although only area samplings-rather than personal samplings-were available during the study. In August 1995 and February 1996, we conducted another study in this older coke oven plant to further investigate liver function profiles in coking workers.2 In this study, we recruited 88 workers working 3 months or more in the older coke oven plant and 59 referents, who had not visited coke operation areas in the last 3 months and who were from the administrative area in the same company. Personal breathing zone ambient benzene soluble fraction (BSF) of total particulates, as a surrogate of COE,3 were measured in each participant for 3 consecutive days. Serum liver function profiles, including AST, ALT, γ-glutamyl transpeptidase, alkaline phosphatase, bilirubin, hepatitis B surface antigen (HBsAg), and anti-hepatitis C antibodies, were examined in the morning after the exposure assessment in a fasting state. Exposure levels were categorized by exposure situations (high, medium, low) among coking workers. The high-exposure group (n = 23) worked topside of the oven. The medium-exposure group (n = 44) worked at the sideoven for more than 4 hours/day, whereas the low-exposure group(n = 21) worked at the sideoven for less than 4 hours/day and primarily remained in the control rooms. The median BSF concentrations for the various exposure situations were as follows: high-exposure group, 372µg/m3; medium-exposure group, 61 µg/m3; low-exposure group, 49 µg/m3; and referents, 10µg/m3.2 Although the coking workers(n = 88) did not significantly differ from the referents(n = 59) in any of the liver function profiles, we claimed that some biases were present in the referents. Therefore, we excluded the referents from further analysis and found that workers in the high-exposure group had a mean AST level that was 31% higher (95% CI = 9%-57%) and a mean ALT level that was 46% higher (95% CI = 7%-98%) than those in the low exposure group, after adjusting for appropriate confounders in multivariate models.
We were attempting to compute any hepatic aminotransferase changes over time between the first and second studies. However, only 56% and 25% of the coking workers and referents in the second study were subjects in the first study. Additionally, AST and ALT were analyzed by Hitachi Autoanalyzers 736(San Jose, CA) and 7050 (Tokyo, Japan) in the first and second studies, respectively. Since different methods were used to analyze AST and ALT in different places, we cannot examine the adverse liver function in these two studies simultaneously.2 An alternative approach is to further categorize the exposure status among coking workers working in the older coke oven plant in the first study, based on the exposure categories determined in the second study. The company installed two exhaust ventilation systems in larry cars before 1994 (January 1992 and March 1993)4 and had not renovated the engineering control between 1994 and 1996. Additionally, the coking process is quite constant over time. It is reasonable to assume that the intensity of COE exposure in 1994 was similar to that in 1995 and 1996. Therefore, we restricted the study subjects from the administrative area and the older coke oven plant in the first study and reanalyzed serum aminotransferase activities by exposure situations (high, medium, low, and referents). Figure 1 shows serum aminotransferase levels by exposure situations. We found that there was a positive trend from the referents to the high-exposure group for both AST and ALT (P = 0.0006 and 0.008, respectively). In the multiple linear regression analyses, workers in the high-, medium-, and low-exposure groups had ALT levels that were 54%, 44%, and 40% higher than those in the referents (95% CI, 4%-129%, 5%-98%, and 5%-87%, respectively) after controlling for the appropriate confounders (Quetelet's index, HBsAg, and educational level) (Table 1). Similar results were also found in AST.
Based on our studies,1,2 we conclude that current exposure to COE can affect serum aminotransferase levels in coking workers. After controlling for the possible effects of nonoccupational factors on serum aminotransferase levels, we propose that these adverse hepatic effects were caused by a mixture of hazards. Further study should include a longitudinal cohort study to investigate serum aminotransferase changes in coking workers.
Ming-Tsang Wu, MD, ScD
David C. Christiani, MD, MPH
Occupational Health Program; Department of Environmental Health; Harvard School of Public Health; Boston, Massachusetts
1. Wu MT, Kelsey KT, Mao IF, Wypij D, Liu HW, Christiani DC. Elevated serum liver enzymes in coke oven and by-product workers. J Occup Environ Med.
2. Wu MT, Mao IF, Wypij D, Ho CK, Chen JR, Christiani DC. Liver function profiles in coking workers. Am J Ind Med.
3. US Department of Labor, Occupational Safety and Health Administration. Final occupational safety and health standard for exposure to coke oven emissions. Fed Reg.
4. Wu MT. Characterization of coke oven exposures, urinary 1-hydroxypyrene concentrations, and liver function in steel workers.[Doctoral Thesis.] Boston, MA: Harvard School of Public Health; March 1997.
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