High level of methylmercury exposure causes persisted toxicity in Nauphoeta cinerea

Abstract

Methylmercury (MeHg⁺) is a neurotoxicant abundantly present in the environment. The long-term effects of MeHg⁺ have been investigated in rodents, yet data on the long-term or persisted toxicity of MeHg⁺ in invertebrates is scanty. Here, we examined the acute, intermediate, and chronic effects upon dietary administration of MeHg⁺ in nymphs of Nauphoeta cinerea. Besides, the potential reversibility of the toxic effects of MeHg⁺ after a detoxification period was evaluated. Nymphs were exposed to diets containing 0 (control), 2.5, 25, and 100 μg MeHg⁺/g of diet for 10, 30, and 90 days. Additional groups of nymphs were fed with the same dose of MeHg⁺ for 30 days and then were subjected to a detoxification period for 60 days. The nymphs exposed to 100 μg MeHg⁺/g succumbed to a high mortality rate, along with multiple biochemical (increase of reactive oxygen species production and glutathione S-transferase activity, as well as decrease in the acetylcholinesterase activity) and behavioral alterations. We observed delayed mortality rate and behavioral alterations in nymphs exposed to 100 μg MeHg⁺/g for 30 days and subsequently subjected to 60 days of detoxification. However, the biochemical alterations did not persist throughout the detoxification period. In conclusion, our results established the persistent toxic effect of MeHg⁺ even after a prolonged detoxification period and evidenced the use of N. cinerea as an alternative model to study the toxicity of MeHg⁺.

Keywords: Cockroach; Docking; Heavy metal; Methylmercury; Neuro-locomotor dysfunction; Toxicology.