A systematic review and meta-analysis of pollutants in environmental media

Environmental pollutants are ubiquitous in our environmental media, resulting in detrimental impacts on both humans and the environment. An evidence-based review, particularly a systematic review and meta-analysis, performs a crucial function in assessing the pollution status of pollutants in environmental media at national and global scales. We selected and thoroughly investigated 76 papers focusing on systematic reviews and meta-analyses of contaminants in environmental media. The need to broaden the scope of studies was observed with an increase in the total number of publications, and there were greater focuses on food safety, water pollution, biological pollution, and environmental risks. Furthermore, this review outlined the fundamental procedures involved in a systematic review and meta-analysis, including literature searching, screening of articles, study quality analysis, data extraction and synthesis, and meta-analysis. A meta-analysis typically comprises fixed- and/or random-effects meta-analysis, identifying and measuring heterogeneity, sensitivity analysis, publication bias, subgroup analysis, and meta-regression. We specifically explored the application of meta-analysis to assess the presence of contaminants in environmental media based on two different pollutant categories, namely, non-biological and biological pollutants. The mean value is commonly utilized to assess the pooled concentration of non-biological pollutants, while the prevalence serves as the effect size of biological pollutants. Additionally, we summarized the innovative applications, frequent misuses, and problems encountered in systematic reviews and meta-analyses. Finally, we proposed several suggestions for future research endeavors.