Assessing the viability of pre-industrial sediment prior to remediation using primary producer (Zostera marina and Spartina alterniflora) growth and survival

Boat Harbour (BH), Nova Scotia, has served as a polishing pond for treated pulp and paper effluent since 1967. In 2020, the effluent flow ceased, and the site will be remediated. The focus of the remediation is the removal of a layer of contaminated sediment, shown to contain high levels of metals and dioxins and furans. Our primary objective was to test whether the underlying pre-industrial sediment could support growth and survival of estuarine plants. A large-diameter (15 cm) corer was used to extract cores from underneath the contaminated layer. These cores were inserted into a reference estuary, along with cores of reference estuarine sediment. Four 3 X 3 subtidal plots were used to test transplants of the estuarine plant Z. marina, and five 1 X 9 marsh edge plots were used to test S. alterniflora. No significant differences in plant growth or survival were observed between BH and reference sediment after 2 months. Post-experiment analysis of contaminants (metals and PCDD/F’s) in both types of sediment and plant tissues showed similarly low levels of contaminants.

Concentrations of trace elements in recent and preindustrial sediments from Norwegian and Russian Arctic lakes

Cu, Hg, Ni, Pb, Se, and Zn concentrations in surface and preindustrial freshwater sediments from 66 lakes in the Norwegian and Russian Arctic were used for studying modern atmospheric deposition of these elements. Statistical analysis showed that, after adjusting for the effects of scavenging factors in sediments (organic matter, Al, and Fe), there were, in general, significantly higher concentrations of Hg and Pb in surface sediments than preindustrial sediments. The differences decreased with increasing latitude and increasing longitude to the east, and in the lakes from arctic islands of Svalbard and along the the arctic coastline of Russia, only Hg concentrations were elevated in surface sediments. We attribute this pattern to modern anthropogenic atmospheric deposition. There were no such differences or regional gradients for the other trace metals. A multivariate analysis of the sediment data showed that Hg and Se were associated with organic matter, whereas Cu, Ni, and Zn were associated with inorganic matter (Al, Fe). There was a shift in Pb association from inorganic matter in the reference sediment to organic matter in the surface sediment, which we interpret as an historic change in importance of sources (from bedrock-derived to atmospheric deposition).

Use of the freshwater macroinvertebrate Chironomus riparius (diptera: chironomidae) in the assessment of sediment toxicity

The growth and emergence responses of the midge Chironomus riparius Meigen were used to evaluate the toxicity of natural and formulated reference sediments which were either obtained from polluted sites or spiked with copper in the laboratory. A significant reduction in larval growth was only observed in one of the two polluted field sediments tested. The reasons for this are discussed. However, copper spiking resulted in significant growth reductions of larvae exposed to the two formulated reference sediments at copper concentrations of 3 and 4 mg Cu2+ 1−1. Growth of larvae exposed in natural reference sediment was not significantly affected at equivalent concentrations. The emergence of adults was adversely affected in polluted field sediment compared to formulated reference sediment. Male, female and total adult median emergence times (EmT50) were significantly greater in the former treatment indicating a delay in emergence, attributable to sediment contamination. In addition, survivorship of the larvae in the polluted sediment was reduced, resulting in a lower percentage of adults emerging compared to the formulated reference sediment. The results of this study illustrate the usefulness of chronic response criteria, incorporating the more sensitive life-stages of C. riparius, in the assessment of sediment toxicity.