Exploring the bioavailability of nickel in a soil system: Physiological and histopathological toxicity study to the earthworms (Eisenia fetida).

Nickel (Ni) contamination in soils, at high concentrations, is considered to be very common. Knowledge of the total content of Ni is frequently insufficient to estimate environmental risk. Our explored findings showed that the earthworms adding reduced the available Ni, along with the superior performance of HCl than CaCl2. The bioaccumulation of Ni in earthworms was aggravated with increasing Ni dosage and exposure time. Bioaccumulation factor was significantly correlated with the extractable Ni, which was the most suitable predicting the variations of Ni bioavailability. LC50 of earthworms on 7 and 14 days were 1202.444 mg kg-1 and 1069.324 mg kg-1, respectively along with the recovery rate in 500 mg kg-1 Ni polluted soil reached up to 92.5%. Earthworms' respiration was sensitive presenting a significant dose-effect relationship with the Ni concentration. Five biochemical indices in earthworms were induced along with the relevance of a dose- and time-response pattern. Additionally, histological damage in earthworm's body wall, intestine and seminal vesicles were observed under high level of Ni exposure. Overall, we believe that our current study will open a new window for deeper insights into the potential availability of Ni along with other associated metals on the function of soil ecosystem.