A microcosm study to support aquatic risk assessment of nickel: Community-level effects and comparison with bioavailability-normalized species sensitivity distributions

The aquatic risk assessment for nickel in the European Union is based on chronic Species Sensitivity Distributions (SSD) and the use of bioavailability models. To test if a bioavailability-based safe threshold of nickel (the Hazardous Concentration for 5% of the species, HC5) is protective for aquatic communities, microcosms were exposed to 5 stable nickel treatments (6-96 mikrog/L) and a control for 4 mo to assess bioaccumulation and effects on phytoplankton, periphyton, zooplankton and snails. Ni concentrations in the periphyton, macrophytes and snails measured at the end of the exposure period increased in a dose-dependent manner, but did not indicate biomagnification. Abundance of phytoplankton and snails decreased in 48 and 96 mikrog Ni/L treatments, which may have indirectly affected the abundance of zooplankton and periphyton. Exposure up to 24 mikrog Ni/L had no adverse effects on algae and zooplankton while the rate of population decline of the snails at 24 mikrog Ni/L was significantly higher than in the controls. Therefore, the study-specific overall no observed adverse effect concentration (NOAEC) is 12 mikrog Ni/L. This NOAEC is approximately twice the HC5 derived from a chronic SSD considering the specific water chemistry of the microcosm by means of bioavailability models. Thus, the study provides support to the protectiveness of the bioavailability-normalized HC5 for freshwater communities.