Negative effects of polyvinyl chloride microplastics and the plasticizer DnOP on earthworms: Co-exposure enhances oxidative stress and immune system damage in earthworms

Polyvinyl chloride microplastics (PVC-MPs) are the most used plastics in agriculture. Di-n-octyl phthalate (DnOP), a commonly used plasticizer in PVC-MPs, may be released from plastic and coexist with PVC-MPs. The effects of DnOP alone and coexisting with PVC-MPs are not known. We evaluated the effects of DnOP or/and PVC-MPs on earthworms, and used integrated biomarker response (IBR) to assess the combined toxicity. Molecular docking and transcriptomics were employed for further interpretation of possible toxicity mechanisms. The results showed that exposure to DnOP or/and PVC-MPs caused oxidative damage and interfered with reproduction, adversely affecting the growth and reproduction of earthworms. IBR results showed that toxicity of DnOP+PVC-MPs exposure was greater than that of DnOP and PVC-MPs exposure alone. DnOP has the ability to directly bind to proteins that are associated with antioxidant enzymes and alter their structure. The transcriptomics results indicated that DnOP and PVC-MPs exposure alone mainly affected growth and development-related pathways, while co-exposure affected apoptosis and immune system-related pathways more. To the best of our knowledge, this is the first comprehensive investigation of the combined toxicity of DnOP or/and PVC-MPs to earthworms from different perspectives, which gives scientifically sound evidence for the rational use of plasticizers DnOP and PVC-MPs.