Prevalence of multiple exposures to occupational hazards in some industries in China

It is widely known that many workers are exposed to more than one occupational hazard, but little is known about the prevalence of multiple exposures to occupational hazards in the real world. In most occupational hazard risk assessments and toxicological studies, only one single occupational hazard is targeted. Recent commentaries have underlined the massive challenges associated with the identification of combinations of occupational hazards.1, 2 Identification of exposure combinations is important for public health and epidemiology since it is hypothesized that exposures induce changes in phenotype, not as a single agent, but as a collection of agents acting in concert.3, 4 Compared to the hazard risk assessment of single hazards, coexposure risk assessment presents a greater challenge due to the common existence of many types and numbers of hazards. One way to deal with this challenge is to identify combinations that are prevalent, which, in turn, might help prioritize research and interventions.5 Therefore, this study describes the prevalence of coexposure to chemical and physical hazards in China-based industrial enterprises using the database of occupational health surveillance. According to China's mandatory regulations, enterprises must arrange an occupational examination for workers who are exposed to occupational hazards. Industrial workers who were exposed to occupational hazards and underwent occupational physical examinations in our institute were included. We defined occupational exposure as the process of workers' contact with occupational hazards through the respiratory tract, skin, and other organs during occupational activities. Multiple exposure was defined as when a worker is exposed to two or more occupational hazards in the same enterprise. Enterprises in China must employ a third-party organization to identify and detect the occupational hazards that workers have been exposed to. Based on the categories of occupational hazards workers are exposed to described in the report of the third-party organization, the physical examination institution conducted examinations for workers according to technical specifications for occupational health surveillance (GBZ 188-2014). We obtained data on occupational hazards, age, and gender from the occupational physical examination system. Enterprises are classified according to the industrial classification system used for China's national economic activities (GB/T 4754-2017). All procedures performed in the study coincided with the 1964 Declaration of Helsinki as well as its later amendments or comparable ethical standards. Categorical variable was described by frequency (percentage), and continuous variable was described by mean ± standard deviation or median (interquartile range, IQR). All statistical analyses were performed using the R version 4.1.1 software (R Core Team, 2021), with the pheatmap package for the heat-map procedure and the igraph package for the network procedure. The study focused on 10,363 workers (71.4% males) exposed to occupational hazards who came from 371 industrial enterprises. The average age of workers was 29.0 ± 6.5 years. The distribution of occupational hazards in various industries is shown in Figure 1. In most industries, benzene and its homologs (including toluene, xylene, and ethyl benzene, etc., BTXE) were the primary hazards for occupational exposure, accounting for 43.2% of the total. Exposure to noise, ionizing radiation, nonmetallic dust, alcohols, ketones, ester, acid, alkane, and alkaline also play an important role in several industries, accounting for about 10%−20% of occupational hazards. The median number of occupational hazards workers experienced was 3.0 (IQR: 3.0–5.0). The proportion of workers exposed to two or more hazards reached 75.2%, those exposed to five or more hazards reached 33.8%, and exposure to 10 hazards or more reached 7.2%. The cross and net analysis results of coexposure are shown in Figure 2. BTXE hazards were the most common partner in coexposures. Cross-combination analysis showed that the proportion of workers exposed to BTXE combined with noise reached 12.8%, with nonmetallic dust reached 10.6%, and with alcohols or ketones reached even 20%. BTXE combined with noise, nonmetallic dust, alcohols, ketones, esters, and acids formed a coexposure cluster. This clustering trend can also be seen in the tree in Figure 1. The proportion of workers exposed to any two or more of the seven hazards reached 37.4%, the proportion of any three or more reached 26.8%, and the proportion of any four or more reached 15.3%. The combined exposure frequency of alkane, alkaline, furan, and other hazards was also striking. This study has described the multiple, coexposures of workers to occupational hazards in the real world in China. Utilizing the monitoring database to analyze multiple exposures to occupational hazards has also been reported in other studies.2, 6 The group of workers analyzed in the study came from the largest industrial enterprises zone in China, where there are many types of industrial enterprises. To some extent, the results of this study can represent the current situation of workers' multiple occupational exposures. The prevalence of multiple exposures poses a more difficult challenge for industrial enterprises as they seek to provide effective protective measures for workers. For example, if a worker is exposed to splashing harmful chemicals and works in a high-temperature environment, wearing protective equipment to prevent splashing contact will inevitably make it more difficult for a worker to adapt to the high-temperature working environment. Industrial enterprises need to make more efforts in the design and improvement of protective equipment, shift work and rest, mechanized operation, and so on. Among the occupational hazards workers are exposed to in various industries, BTXE were the primary hazards, and they also cross-linked with noise, nonmetallic dust, alcohols, ketones, esters, and acids to form a significant coexposure cluster. The detrimental health effects on workers exposed to BTXE in combination with other occupational hazards has been observed by some researchers. For example, it was found that noise combined with benzene−toluene−xylene exposures in painting workshops of automobile manufacturing enterprises had a positive influence on the systolic blood pressure of workers.7 Male occupational exposures to multiple solvents (benzene, methylene chloride, toluene, trichloroethylene, perchloroethylene, and 1,1,1-trichloroethane) increased the risk of amyotrophic lateral sclerosis.8 Nevertheless, the current understanding of the health effects of multiple exposures is far from sufficient. When understanding this study, the following limitations should be noted. First, the health monitoring database used in this study recorded the categories of occupational hazards workers are exposed to and the results of occupational health examination parameters, but there were no data on the duration and dose of workers exposed to various occupational hazards. Hence, when analyzing multiple exposures, this study could not identify the weight of exposure time and dose of each hazard. Second, the sample selection of this study is nonrandom sampling, which may have potential bias. In conclusion, multiple exposures of industrial workers to occupational hazards are prevalent, and BTXE, noise, nonmetallic dust, alcohols, ketones, esters, and acids often cross-link to form a significant coexposure cluster in industrial workers. Conceptualization: Yan-mei Cao and Wen-yi Liu. Data collection: Wei-min Gao and Liang-bin Xie. Analysis and interpretation of data: Hua-qing Liu. Writing—original draft preparation: Hua-qing Liu, Wen-yi Liu, and Yan-mei Cao. Writing—review and editing: Hua-qing Liu and Yan-mei Cao. All authors have read and approved the final version of the manuscript. We would like to thank Wordvice (https://wordvice.cn/) for English language editing. This study was supported by the Health Commission of Suzhou (SZYJTD201904). The authors declare no conflicts of interest. The work was performed at the Fifth People's Hospital of Suzhou and was approved by the Medical Ethics Committee of the Fifth People's Hospital of Suzhou on June 11, 2021 (code: 2021016). The corresponding author confirms that the manuscript is an honest, accurate, and transparent account of the study being reported. The data supporting the findings of this study are available from the corresponding author upon reasonable request.