Safety assessment of copper- and zinc-based metal-organic frameworks (MOFs) for embryonic development and adult fish of Oryzias melastigma.

The increasing prevalence of harmful algal blooms (HABs), specifically those resulted by toxigenic Alexandrium spp., notably threats human health and aquatic ecosystem. Metal organic frameworks (MOFs), particularly copper- and zinc-based MOFs have emerged as promising materials to control HABs. However, their application safety needs to be assessed because of poor knowledge of their ecotoxicity to marine organisms. In this study, the toxicity of Cu-MOF and Zn-MOF was evaluated to Oryzias melastigma at embryonic and adult stages. The Cu-MOF exhibited a concentration-dependent mortality and hatching rate at concentrations ≥ 2.0 mg L^-1. The Zn-MOF exhibited similar effects when the exposure doses ≥ 80 mg L^-1. Additionally, adult fish after exposure to Cu-MOF showed significant mortality rate at higher concentrations (≥ 4.0 mg L^-1), beside elevated oxidative stress markers. In contrast, Zn-MOF did not show mortality and oxidative stress although bioaccumulation of Zn²⁺ occurred in tissues. Based on the safety assessment of MOFs to marine medaka, the dosages for application of Cu-MOF (≤ 1.0 mg L^-1) and Zn-MOF (≤ 20 mg L^-1) are safe for controlling A. minutum-forming HABs. This study hints that the application of MOFs in mitigation of HABs should be carefully evaluated to balance their benefits in contrast to ecological risks.