The never-ending story of dangerous ubiquitous particles: A meta-analysis of microplastics

Globally, most studies on microplastic (MP) contamination have focused on marine environments, while freshwater and estuarine environments have received little attention, overlooking the connectivity between these systems and the influence of the continent on the marine zone. This study evaluates the abundance and distribution of MP in marine water, estuarine water, freshwater, beach sand, marine sediment, estuarine sediment, and riverine sediment. Through a systematic review of 93 publications comprising 1542 data points, the proportion of MP was assessed, and a meta-analysis of proportions was conducted to determine the global prevalence of MP. The meta-analysis revealed that filaments (42 %) and fragments (37 %) were the dominant types across all environments. A random-effects model was used to assess the proportion of MP in each study, as well as the overall proportion. The effect size was P = .16 (95% CI: 0.15 to 0.17), with high heterogeneity (Q_T = 160,759.82, df = 1541, p < .001; I² = 99.04%). Mixed-effect models were used to assess the influence of moderator (country, environment, and region) on the prevalence of MP types. The analysis revealed that all moderators contributed to significant differences between MP types, with high heterogeneity (≥ 99 %). The most relevant finding of this study was that the best moderator, according to the AIC criterion (Q_M = 3.02, df = 6, p = .81, I² = 99.04%), was the environment, indicating that this moderator has the strongest influence on the prevalence of MP.