The Effect of Sediment Type and pH-Adjustment on the Porewater Chemistry of Copper- and Zinc-Spiked Sediments

Abstract

The spiking of metals into sediments lowers pH, raises the oxidative state, and exacerbates the partitioning of Fe, Mn, and spiked metal to the porewater. This study reports the geochemical response of three sediments of varying metal-binding capacity to Cu-/Zn-additions and the influence of pH-adjustment on the major metal-partitioning processes. The increase in redox potential and porewater metal concentrations observed in metal-spiked sediment was minimized by sediment neutralization to pH 7 irrespective of sediment type. In the presence of minimal sulfide concentrations, porewater metal concentrations suggested a greater affinity of copper for organic carbon than zinc, which was thought more dependent on iron oxyhydroxide phases. The amount of iron in the porewater of metal-spiked pH adjusted sediment was, in turn, affected by the type and concentration of spiked metal in the porewater. Increasing porewater concentrations of copper and zinc corresponded to decreasing and increasing porewater iron concentrations, respectively. Porewater copper appeared to act as a toxicant of Fe(III) reducing bacteria, while porewater zinc is thought to have had a stimulatory effect. The present study provides further insight on geochemical changes occurring to metal-spiked sediments and their implications for the interpretation of toxicity tests.

Whole Sediment Toxicity Tests for Metal Risk Assessments: On the Importance of Equilibration and Test Design to Increase Ecological Relevance

“…Direct spiking of sediments with metals substantially alters the sediment geochemistry, particularly the sediment pH, redox potential, and partitioning of metals between dissolved and particulate phases, with potential effects on toxicity . Iron(II) and other cations in the porewater are typically displaced by the added metals . Those ions enter the overlying water via the porewater, which increases conductivity in the overlying water of the sediments with higher spiked metal concentrations, as our results clearly demonstrate (Fig.…”

Hitting Reset on Sediment Toxicity: Sediment Homogenization Alters the Toxicity of Metal‐Amended Sediments

“…Consequently, AVS was either stable (Zn experiments) or only slightly lower in freshly spiked than aged treatments (Raisin sediment in Ni experiments). These data add to the evidence showing that regulation of pH during metal amendment is of critical importance for producing sediments with a stable geochemistry that mirrors field‐contaminated ecosystems (Hutchins et al ; Brumbaugh et al ).…”

“…Recent advances in methods for adding metal to sediment (Simpson et al 2004;Hutchins et al 2009;Brumbaugh et al 2013) have maintained natural physicochemical conditions, particularly anoxia. Estimates for porewater equilibration times for various metals range from 10 to 70 d (Simpson et al 2004) if amendments are done under proper pH-buffered conditions (Hutchins et al 2008).…”

A novel method to assess effects of chemical stressors on natural biofilm structure and function

“…For certain pollutants (e.g. non-ferrous metals), there are established procedures for introducing the chemicals into sediments with minimal physical and chemical disruption (Simpson, Angel & Jolley, 2004;Hutchins et al, 2009). For both agar and sediment matrices, the chemical dose can be varied by altering the mass of pollutant added to the matrix.…”