Investigating Toxicological Effects of Short-Term Resuspension of Metal-Contained Freshwater and Marine Sediments

Abstract

Sediments in navigation-dominated waterways are frequently contaminated with a wide range of chemicals and are subject to resuspension events. There is little information documenting whether adverse ecological effects result from these resuspension of contaminated sediments. I studied the mobilization of metals (Zn, Cu, Cd, Pb, Ni and Cr) during resuspensions of freshwater and marine sediments and whether or not this resulted in toxicity to organisms. Sediment resuspension events were simulated using sediment flux exposure chambers (SeFEC) to resuspend metal-contaminated sediments from Lake DePue (IL) and two Portsmouth (ME) Naval Shipyard sites. Various resuspension events of environmentally relevant suspended particulate matter concentrations (200-1,000 mg/L) were performed. Short-term resuspension events (4 h) resulted in metal- and sediment-specific mobilization. Toxic effects on organisms were limited (Hyalella azteca and Daphnia magna survival, Neanthes arenaceodentata survival, growth and body burden, Pyrocystis lunula bioluminescence) over both the time period of the exposure and during a 4 to 10-d post-recovery period. I conclude that sediment resuspension events at relevant suspended particulate matter concentrations do not release large amounts of dissolved metals, most likely due to the oxidation of reduced iron, manganese and amorphous sulfide species and subsequent readsorption to iron and manganese oxides and organic matter, therefore limiting organisms’ exposure and effects. The redeposition of suspended sediments and associated metal speciation changes, from sulfides to oxides, has the potential to increase metal bioavailability and toxicity to sensitive benthic organisms. While the release of dissolved metals are low, resuspension events still pose the risk of causing toxic responses due to mobilization of contaminated sediments.