The impact of neonicotinoid insecticides on amphibians: A comprehensive review and future research challenges

Neonicotinoid insecticides (NNIs) are widely used in agriculture; however, their effects on anuran amphibians remain poorly explored. This global review critically examines the existing literature, with data obtained from Web of Science and Scopus databases. A total thirty-seven studies were published from 2004 to 2023. Most studies originate from countries with significant scientific investment, with a notable absence of research from Europe, likely due to European Union restrictions on NNIs. Despite these restrictions, NNIs continue to be produced and exported from Europe. Since 1990, four generations of NNIs have been developed, generally characterized by high water solubility and environmental persistence, which increases the risks of groundwater contamination. Imidacloprid (46%), Clothianidin (22%) and Thiamethoxam (20%) were the most studied NNIs. The research predominantly focused on species such as Lithobates sylvaticus, Xenopus laevis, Lithobates pipiens and Pelophylax nigromaculatus. A significant 71.43% of the studies involved tadpoles, due to their vulnerability during early development and importance for population survival. L. sylvaticus, L. pipiens and P. nigromaculatus were extensively studied due to their distribution and X. laevis due to its ease of laboratory handling. The most common experimental approaches included survival tests, which assessed mortality rates, and biochemical tests that revealed cellular damage and concerns regarding lipid peroxidation. Developmental studies indicated both physical and physiological impacts, while genotoxic tests demonstrated damage to genetic material. Notable variability in responses was observed between species and compounds. The biomarkers investigated employed diverse methodologies, suggesting the need for more effective techniques. In the concluding remarks and future perspectives, the study presents the main findings, identifies important gaps in current research, emphasizes key challenges, and outlines strategic directions for future investigations.