Effect of sublethal concentrations of agrochemicals on zooplankton populations: A meta-analysis study

Intensive agricultural practices associated with population growth have significantly increased agrochemical discharge into aquatic systems, adversely impacting aquatic biota. Numerous studies have established the lethal effects of agrochemicals on zooplankton populations, which inform environmental risk assessment programs. However, limited attention has been given to the effects that sublethal agrochemical concentrations-within legally permitted ranges-may have on zooplankton. This study aims to analyze the impact of sublethal agrochemical concentrations on zooplankton abundance through a meta-analysis. A comprehensive search was conducted in digital databases, and study selection and data extraction were performed independently by three authors. Using a random-effects model, the effect size (g) of the standardized mean difference was calculated, and heterogeneity was assessed with the Q statistic and I² index. Twenty-four studies met the inclusion criteria, yielding 1036 data points after removing records with zero variability. Following outlier exclusion, the global meta-analysis estimated a large and significant negative effect of sublethal agrochemical exposure on zooplankton abundance (g = -1.42; p < .0001). This effect remained robust despite the reduction of heterogeneity (Q test significant; I² decreased from 74 % to 26 % after outlier removal). Moderator analyses revealed that the impact varied significantly depending on several factors, including study location, agrochemical type and composition, concentration range, experimental setup, taxonomic order, and species, while exposure time did not explain variability in effect sizes. The results underscore the importance of considering sublethal agrochemical effects on zooplankton abundance in toxicological risk assessments, given their potential impact on zooplankton communities and, consequently, the functioning of aquatic ecosystems.