Metal Exposure, Bioaccumulation, and Toxicity Assessment in Sediments from the St. Lawrence River Before and After Remediation Using a Resuspension Technique

Abstract

This study, using Hyalella azteca and Chironomus riparius, evaluated the effects of exposure to heavy metal-contaminated sediments collected from the study area under three conditions: before remediation, after remediation, and suspended particulate matter (SPM). The selected toxicity tests allowed for the evaluation of biological responses across varying concentrations of heavy metals. Statistical analysis revealed no significant differences in survival or growth between sediment-exposed organisms and controls for either species. In addition, bioaccumulation of Cr, Ni, Cu, Zn, As, Cd, and Pb in both organisms was assessed and compared among the sediment conditions and the control. No statistically significant differences in tissue metal concentrations were found between organisms exposed to sediments from the study area and those in control conditions. Sequential extraction analysis indicated that a substantial proportion of metals in the sediments were bound in stable, non-bioavailable forms. These findings are consistent with the observed biological responses, as low levels of bioavailable metals corresponded with the absence of toxic effects. Together, the data confirm that the sediments, regardless of remediation stage or particle fraction, posed no significant biological risk under the conditions tested.

Keywords: Chironomus riparius; Hyalella azteca; bioaccumulation; heavy metals; toxicity.

Figure 1

Study area with the selected numbered sampling stations, which were potential locations for dredging.

Figure 2

Photo and schematic of the reactor with a Plexiglas cylinder and air jet arm connected to the central air compressor in the laboratory.

Figure 3

Schematic of the resuspension process in the laboratory.

Figure 4

Total concentration of heavy metals in (A) before the remediation test (mg/kg), in (B1) after the resuspension test (mg/kg), and (B2) in SPMs (mg/kg).

Figure 5

Comparison of the survival percentage of Hyalella azteca between the controls of the different tests (batch) with before-remediation samples at various stations.

Figure 6

Comparison of the RGR percentage of Hyalella azteca between the controls of the different tests (batch) and stations for before remediation samples at various stations.

Figure 7

Comparison of the survival percentage of Chironomus riparius between the controls and before remediation samples at various stations.

Figure 8

Comparison of the RGR percentage of Chironomus riparius between the controls and before remediation samples at various stations.