Nickel phase partitioning and toxicity in field-deployed sediments.

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• Sediment Geochemistry

Background:

• Bioavailable metals in sediments are often less than total concentration due to complexation.
• Simultaneous extracted metal and acid volatile sulfide (SEM-AVS) models predict metal bioavailability and toxicity.
• Previous SEM-AVS model studies for nickel (Ni) contamination were mainly lab-based.

Purpose of the Study:

• To evaluate the field applicability of SEM-AVS models for Ni-contaminated sediments.
• To assess the relationship between Ni bioavailability, sediment geochemistry, and macroinvertebrate colonization.
• To investigate the influence of sediment characteristics on Ni partitioning and toxicity.

Main Methods:

• Five lotic sediments with varying sulfide and organic carbon were amended with Ni.
• Sediments were deployed in streams for eight weeks to assess colonizing macroinvertebrates.
• Geochemical analyses tracked Ni partitioning and associations with sediment components over time.

Main Results:

• Macroinvertebrates showed negative responses to Ni-treated sediments, with SEM-AVS models initially predicting toxicity.
• Model predictions and macroinvertebrate responses diverged by week 8.
• Ni partitioning shifted from organic carbon to Fe and Mn oxides, reducing bioavailability.

Conclusions:

• SEM-AVS models may overestimate Ni bioavailability in sediments with oxic surface layers and Fe/Mn oxides.
• Fe and Mn oxides play a significant role in reducing Ni availability to aquatic biota in field conditions.
• Sediment geochemistry, particularly Fe and Mn oxides, influences the accuracy of bioavailability models over time.