Eugenol-Loaded Nanocarriers Exert Particle-Specific Adverse Effects on Daphnia magna Populations

Nanocarriers provide promising prospects for the transition to more sustainable agrochemical practices. However, the unique release dynamics of their loaded chemicals raise concerns about potential adverse effects on nontarget organisms. To address this, we compared the toxicity of bentonite and sepiolite nanocarriers loaded with the anesthetic/antibacterial chemical eugenol to the toxicity of pure eugenol. Daphnia magna was exposed to loaded nanocarriers, pure eugenol, and bare nanocarriers. In acute immobilization tests, a 50% effect concentration (EC₅₀) of 0.14 ± 0.01 mg eugenol L^-1 was derived for pure eugenol. Loading eugenol onto bentonite and sepiolite nanocarriers mitigated this acute toxicity, as indicated by respective EC₅₀ values of 0.48 ± 0.02 and 0.57 ± 0.07 mg eugenol L^-1. In 12-day toxicity tests, similar concentrations of eugenol were released from both nanocarriers. For the first day of exposure, this temporarily reduced the swimming speed of the daphnids. Moreover, in contrast to sepiolite nanocarriers, bentonite nanocarriers induced marked decreases in population growth. This reveals that nanocarriers exert particle-specific adverse effects on daphnid populations that cannot be predicted based on the toxicity of their individual constituents. We therefore plead to assess nontarget effects of the complete nanocarrier system, including the carrier and its loading, before allowing these products on the market.