From bacteria to fish: ecotoxicological insights into the bioinsecticide Spinosad

Background: Spinosad, a natural bioinsecticide derived from Saccharopolyspora spinosa, is widely used in agriculture due to its high selectivity toward target pests and low environmental persistence. However, its increasing application raises concerns about its potential toxic effects on non-target species, especially under environmentally relevant exposure scenarios. This study aimed to evaluate the acute toxicity and sublethal biochemical effects of Spinosad across multiple aquatic species, representing different trophic levels.

Methods: A multi-species ecotoxicological assessment was conducted to evaluate the sensitivity of model aquatic species to Spinosad. Standardized acute toxicity tests were performed with Aliivibrio fischeri (bacteria), Raphidocelis subcapitata (algae), Daphnia magna (crustacean), and Danio rerio embryos (fish). In addition, biochemical biomarkers were analyzed in D. magna and D. rerio to assess oxidative stress (catalase [CAT], glutathione S-transferase [GST] activities), lipid peroxidation (thiobarbituric acid reactive substances [TBARSs]), and neurotoxicity (acetylcholinesterase [AChE] inhibition) effects.

Results: Spinosad exhibited a wide range of toxicities among the tested species, with EC₅₀ values of 105.66 mg/L for A. fischeri, 3.93 mg/L for R. subcapitata, 0.018 mg/L for D. magna, and 1.37 mg/L for D. rerio embryos, indicating increasing sensitivity from prokaryotes to invertebrates. Biochemical assays revealed that even at environmentally relevant concentrations (~0.4 μg/L reported in surface waters), Spinosad induced significant oxidative stress, enhanced lipid peroxidation, and inhibited AChE activity in D. magna and D. rerio embryos, suggesting sublethal but ecologically relevant effects.

Conclusions: The ecotoxicological profile of Spinosad demonstrates its high toxicity to aquatic invertebrates and its potential to disrupt key physiological processes in fish at low concentrations. These findings highlight the need for more comprehensive environmental risk assessments that consider both acute and chronic toxicity and sublethal biomarker responses, particularly under realistic exposure scenarios. Monitoring Spinosad levels in freshwater ecosystems is crucial in order to safeguard aquatic biodiversity and guarantee the health status of aquatic ecosystems.