Assessing the potential toxicity of resuspended sediment

Abstract

Abstract-Two moderately contaminated freshwater sediments (Sorel Harbour, St. Lawrence River, Canada) were subjected to a suspension event. The objective was to assess the environmental impact of the disposal of dredged material in water, in particular, the short-term effects of dumping on the water column and the long-term effects of dredged sediment deposits. In a series of microcosms, the sediments were left to stand for 25 d under flow-through conditions (reference conditions). In a second series of microcosms, sediments were vigorously suspended for 15 min before being left to settle and were submitted to the same treatment as reference sediments during the following 25 d. Physicochemical and biological parameters (Daphnia magna and Hydra attenuata survival) were measured in overlying water throughout the experiment. Sediment toxicity was assessed with Chironomus tentans and Hyalella azteca exposed to sediments collected at both the beginning and end of the 25-d period. Pore-water toxicity was evaluated with D. magna. During the suspension process, in the Sorel Harbour mixed sediment overlying water, we observed effects on H. attenuata survival and ammonia and metals (chromium, copper, and zinc) releases. Meanwhile, in reference (nonmixed) and mixed sediments as well as in associated pore waters, there were no significant chemical modifications nor biological effects after the 25-d experiments. The developed approach, which attempts to simulate a dumping process, aims at allowing the assessment of the short-and long-term hazards resulting from a resuspension process in overlying water and in resettled sediments using both chemical and biological measurements.

Assessment of contaminated sediments with an indoor freshwater/sediment microcosm assay

“…The concentrations of unionized ammonia, which is an important sediment‐associated toxicant, were below toxicity levels for the freshwater species introduced in microcosm: 5‐d 50% inhibitory concentration (IC50) of 7.16 mg NH 3 /L for L. minor [31], 48‐h 50% lethal concentration (LC50) of 3.5 mg NH/L for D. magna [32], four‐week LC50 of 1.1 mg NH 3 /L for H. azteca [33], and 96‐h LC50 of 2.0 mg NH 3 /L for C. riparius [5].…”

“…One solution for the management of dredged sediments is their relocation or deposit in the water, such as in open gravel quarries [2,5]. These systems tend to be used as disposal sites due to the lack of any other disposal site, their proximity to waterways, and economic considerations.…”

“…The intensity of impacts depends on pollutant concentration and bioavailability that condition pollutant toxicity. Suspended sediments may induce numerous physical impacts, e.g., an increase of turbidity associated with a decrease of dissolved oxygen content and a reduction of feeding and spawning habitats for benthic organisms [5]. Pollutants can be mobilized and released from sediments to the overlying water [4] and become bioavailable for pelagic organisms (fishes and invertebrates).…”

“…Sediment potential for toxicity usually is assessed by using chemical characterization and short‐term single bioassays on whole sediment and pore water. The tests usually used are the Microtox™ (Azur Environmental, Carlsbad, CA, USA) assay on Vibrio fisheri , the cladoceran Daphnia magna (neonates) immobilization assay, the amphipod Hyalella azteca survival and growth assay, and the midge Chironomus riparius survival and growth assay [5,7–9]. These bioassays are characterized by their simplicity, rapidity, sensitivity, replicability, reproductibility, and low cost.…”

Sediments, porewaters and diagenesis in an urban water body, Salford, UK: impacts of remediation

“…Therefore, any physical and chemical changes acting upon the sediment exert a major potential role on short-to long-term contaminant mobility. Physical changes having a major impact upon contaminant mobility include resuspension of sediment, through sediment disturbance or dredging, which can lead to both the desorption and oxidation of contaminant and nutrient species (Morin and Morse, 1999;Bonnet et al, 2000;Saulnier and Mucci, 2000). Chemical changes are dominated by early diagenesis, which is a series of bacterially mediated organic matter oxidation reactions taking place within the sediment.…”