Direct toxicity of environmentally persistent free radicals to nematode Caenorhabditis elegans after excluding the concomitant chemicals

Environmentally persistent free radicals (EPFRs) have attracted extensive attention due to their potential toxicity. However, EPFRs-containing particles always coexist with their parent organic contaminants and intermediate degradation products (IM), which may have hindered the toxicity assessment of EPFRs. In this study, the toxicity of EFFRs was specifically verified after comparing the systems without EPFRs, such as the immediate mixture of catechol (CT) and particles, solutions of CT only, IM extracted from the particles, as well as particles after EPFRs quenching. Caenorhabditis elegans (C. elegans) were used as model organisms. Our results showed that EPFRs-containing particles (Si-Al-CT) exhibited significant toxicity to C. elegans, but not for the parent chemical CT and IM on the particles. Higher levels of reactive oxygen species (ROS) and malondialdehyde (MDA) in the Si-Al-CT system were attributed to the mediated generation of center dot O-2(-) and center dot OH via EPFRs. EPFRs could increase gene expressions related not only to oxidative stress and biotransformation in C. elegans, but also to indications of disturbances in energy homeostasis, survival, proliferation, cell and embryonic development. Overall, these results confirmed the direct toxicity of EPFRs and highlighted the key role of EPFRs which may be neglected in assessing the environmental risks of organic contaminants.