Hazard assessment of nickel nanoparticles in soilThe use of a full life cycle test with Enchytraeus crypticus

Nanoparticles (NPs) such as nickel (Ni) are widely used in several applications. Nevertheless, the environmental effects of Ni NPs are still poorly understood. In the present study, the toxicity of Ni NPs and nickel nitrate (NiNO3) was assessed using the standard test species in soil ecotoxicology, Enchytraeus crypticus (Oligochaeta), in a full life cycle test, adding the endpoints hatching, growth, and time to reach maturity, besides survival and reproduction as in the standard Organisation for Economic Co-operation and Development Guideline 220 and/or International Organization for Standardization 16387. For Ni NPs, the Ni in soil and in soil solution was concentration- and time-dependent, with a relatively higher soil solution content in the lower and shorter exposure concentrations and times. Overall, NiNO3 was more toxic than Ni NPs, and toxicity seemed to occur via different mechanisms. The former caused reduced hatching (50% effect concentration [EC50]=39mg Ni/kg soil), and the negative effects remained throughout the life cycle, in all measured endpoints (growth, maturation, survival, and reproduction). For Ni NPs, hatching was the most sensitive endpoint (EC50=870mg Ni/kg soil), although the organisms recovered; that is, additional endpoints across the life cycle showed that this effect corresponded to a delay in hatching because organisms survived and reproduced at concentrations up to 1800mg Ni/kg soil. On the other hand, the lowest tested concentration of Ni NPs (100mg Ni/kg soil) caused reproduction effects similar to those at higher concentrations (1000 and 1800mg Ni/kg soil). The present results show that the potential implications of a nonmonotonic dose response should be considered when assessing the risks of Ni NP exposure in soil. Environ Toxicol Chem 2017;36:2934-2941. (c) 2017 SETAC