Neurotoxicity and biochemical responses in the earthworm Pheretima hawayana exposed to TiO2NPs

• TiO2 NPs have low toxic effects on the anceic earthworm Pheretima hawayana.
• TiO2 NPs is highly toxic than their bulk TiO2 counterparts.
• AChE inhibited in earthworms treated with high concentration of TiO2 NPs.
• Antioxidant enzymes and MDA accumulation significantly increased in treated P. hawayana.
• Energy reserves of treated earthworms were significantly (p<0.05) lower than that of untreated.

Serious concerns have been expressed about potential risks of manufactured TiO2NPs. In this research, toxicity of nanoparticulate and bulk TiO2 were examined to the earthworm Pheretima hawayana. The 24-h median lethal concentration (LC50) and sublethal endpoints were assessed. Both NPs and their bulk counterparts were toxic. The 24-h LC50 for TiO2NPs (145.36 mg kg−1) was highly toxic than that of bulk TiO2 (357.77 mg kg−1). The aim of the present work is to evaluate the suitability of P. hawayana and its biochemical responses to be used as a bioindicator organism and biomarkers of TiO2 toxicity. Earthworms were exposed to three sublethal concentrations of TiO2NPs (1, 10 and 100 µg kg−1) for 28 days to test acetylcholinesterase (AChE), antioxidant enzymes (superoxide dismutase: SOD and catalase: CAT) activities and MDA content. The response of the antioxidant enzymes combined with AChE inhibition and MDA accumulation indicated that TiO2NPs could induce significant impairments to the earthworms at the actual environment tested concentrations. The results pointed out the high sensitivity of the antioxidant and oxidative stress related responses to TiO2NPs exposure, demonstrating their usefulness in environmental monitoring and risk assessment. The study highlights also the usefulness of earthworm P. hawayana as potential bioindicator species for assessing the risk of nanoparticles environmental contamination.