Low-level occupational exposure to BTEX and dyschromatopsia: a systematic review and meta-analysis

<i>Objectives.</i> The present study aimed to assess whether occupational exposure to low concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) is associated with color vision impairment. <i>Methods.</i> We queried PubMed, Scopus, Embase, Web of Science and ProQuest as the main databases, as well as gray literature such as Google Scholar. A random-effects model was used to assess relative risk. A funnel plot was created to assess publication bias. Meta-regression analysis was applied to identify variables that explain the between-study variation in the reported risk estimate. <i>Results.</i> An overall standardized mean difference of 0.529 (95% confidence interval [0.269, 0.788]; <i>p</i> &lt; 0.0001) was obtained in the random-effects model, which corresponded to a medium-size effect. Duration and the levels of exposure to benzene, toluene and xylene were the significant predictors of the magnitude of the combined risk estimate. Chronic exposure to low levels of BTEX was associated with dyschromatopsia determined by the color confusion index. <i>Conclusions</i>. The impairments can occur even at exposures lower than the occupational exposure limits of BTEX. However, there are several flaws in the determination of workers’ exposure, which did not allow to establish how low a level of these chemicals can cause color vision impairment.研究目的。本研究旨在评估低浓度苯、甲苯、乙苯和二甲苯（benzene, toluene, ethylbenzene and xylene，BTEX）的职业暴露与色觉损害之间的相关性。 方法。本研究以PubMed、Scopus、Embase、Web of Science及ProQuest为核心数据库，同时检索Google Scholar等灰色文献。采用随机效应模型评估相对风险，绘制漏斗图以评价发表偏倚，并通过元回归分析识别可解释研究间风险估计值异质性的变量。 结果。随机效应模型分析得到合并标准化均数差为0.529（95%置信区间[0.269, 0.788]；*p*<0.0001），对应中等效应量。暴露时长以及苯、甲苯、二甲苯的暴露水平是合并风险估计值大小的显著预测因子。低浓度BTEX的慢性暴露与通过色混淆指数检测到的色觉障碍存在显著关联。 结论。即使暴露水平低于BTEX的职业接触限值，仍可能发生色觉损害。但当前在工人暴露水平的测定环节存在若干缺陷，无法明确此类化学物质达到何种低浓度时会引发色觉损害。