Oxidative Stress after Pollutant Exposure Depends Strongly on Experimental Design and Pollutant Properties in Annelids: A Meta-Analysis.

Measurements of oxidative stress are often performed to assess a species' general sublethal stress response to a pollutant. However, oxidative stress bioassays often produce seemingly ambiguous results, and the drivers that lead to these differences are largely unknown. To address this gap, we conducted a meta-analysis on reactive oxygen species (ROS) generation, ROS-associated damage products, enzyme activities, and gene expression levels in response to exposures to two groups of pollutants, nano- and microplastic particles (NMP) and neonicotinoid insecticides (neonics). Based on 2294 ROS-related measurements extracted from 45 studies, we show that measured effects vary substantially, with a strong overlap of measured effects with zero. As likely drivers of this variance, we identified multiple parameters of experimental design and pollutant properties. Finally, we performed data simulations and power analyses to investigate how well single experiments are able to detect oxidative stress-related effects. While most oxidative stress markers achieve sufficient power (80%) to demonstrate effects with sample sizes N < 20, conclusions derived from single studies with low sample sizes (N < 5) are at risk of being less informative than previously assumed. Our results highlight the importance of considering pollutant properties, experimental design, and sample size when measuring oxidative stress markers.