Field measurement of nickel sediment toxicity: role of acid volatile sulfide.

A field experiment was performed in four freshwater systems to assess the effects of Ni on the benthic macroinvertebrate communities. Sediments were collected from the sites (in Belgium, Germany, and Italy), spiked with Ni, and returned to the respective field sites. The colonization process of the benthic communities was monitored during a nine-month period. Nickel effect on the benthos was also assessed in the context of equilibrium partitioning model based on acid volatile sulfides (AVS) and simultaneously extracted metals (SEM). Benthic communities were not affected at (SEM - AVS) ≤ 0.4 µmol/g, (SEM - AVS)/fraction of organic carbon (f(OC)) < 21 µmol/g organic carbon (OC). Sediments with (SEM - AVS) > 2 µmol/g, (SEM - AVS)/f(OC) > 700 µmol/g OC resulted in clear adverse effects. Uncertainty about the presence and absence of Ni toxicity occurred at (SEM - AVS) and (SEM - AVS)/f(OC) between 0.4 to 2 µmol/g and 21 to 700 µmol/g OC, respectively. The results of our study also indicate that when applying the SEM:AVS concept for predicting metal toxicity in the field study, stressors other than sediment characteristics (e.g., sorption capacity), such as environmental disturbances, should be considered, and the results should be carefully interpreted.