Benthic invertebrates can uptake metals through diffusion of free ion solutes, or ingestion of sediment-bound forms. This study investigated the efficacy of the metal chelating resin SIR 300™ in adsorbing porewater metals and isolating pathways of metal exposure. A field experiment (Botany Bay, Sydney, Australia) and a laboratory toxicity test each manipulated the availability of porewater metals within contaminated and uncontaminated sediments. It was predicted that within contaminated sediments, the resin would adsorb porewater metals and reduce toxicity to invertebrates, but in uncontaminated sediments, the resin would not significantly affect these variables. Whereas in the laboratory, the resin produced the predicted results, in the field the resin increased porewater metal concentrations of contaminated sediments for at least 34 days and decreased abundances of four macroinvertebrate groups, and richness in all sediments. These contrasting findings highlight the limits of extrapolating the results of laboratory experiments to the field environment.

Eisenia fetida earthworms were exposed to phenanthrene for thirty days to compare hydroxypropyl-β-cyclodextrin (HPCD) extraction of soil and 1H NMR earthworm metabolomics as indicators of bioavailability. The phenanthrene 28-d LC50 value was 750 mg/kg (632–891, 95% confidence intervals) for the peat soil tested. The initial phenanthrene concentration was 319 mg/kg, which biodegraded to 16 mg/kg within 15 days, at which time HPCD extraction suggested that phenanthrene was no longer bioavailable. Multivariate statistical analysis of 1H NMR spectra for E. fetida tissue extracts indicated that phenanthrene exposed and control earthworms differed throughout the 30 day experiment despite the low phenanthrene concentrations present after 15 days. This metabolic response was better correlated to total phenanthrene concentrations (Q2 = 0.59) than HPCD-extractable phenanthrene concentrations (Q2 = 0.46) suggesting that 1H NMR metabolomics offers considerable promise as a novel, molecular-level method to directly monitor the bioavailability of contaminants to earthworms in the environment.

In the context of the European Water Framework Directive, controlled flooding of lowlands is considered as a potential water management strategy to minimise the risk of flooding of inhabited areas. However, due to historical pollution and overbank sedimentation, metal levels are elevated in most wetlands, which can cause adverse effects on the ecosystem's dynamics. Additionally, salinity affects the bioavailability of metals present or imported into these systems. The effect of different flooding regimes and salinity exposure scenarios (fresh- and brackish water conditions) on Cu and Zn accumulation in the oligochaete Tubifex tubifex (Müller, 1774) was examined. Metal mobility was closely linked to redox potential, which is directly related to the prevalent hydrological regime. Flooded, and thus more reduced, conditions minimized the availability of metals, while oxidation of the substrates during a drier period was associated with a rapid increase of metal availability and accumulation in the oligochaetes.

Laboratory experiments were conducted to assess the effects of soil sterilization on the bioavailability of spiked p,p'-DDE and anthracene to the earthworms Eisenia fetida and Lumbricus terrestris. Physical and chemical changes to soil organic matter (SOM) induced by sterilization were also studied. Uptake of both compounds added after soil was autoclaved or gamma irradiated increased for E. fetida. Sterilization had no effect on bioaccumulation of p,p′-DDE by L. terrestris, and anthracene uptake increased only in gamma-irradiated soils. Analyses by FT-IR and DSC indicate sterilization alters SOM chemistry and may reduce pollutant sorption. Chemical changes to SOM were tentatively linked to changes in bioaccumulation, although the effects were compound and species specific. Artifacts produced by sterilization could lead to inaccurate risk assessments of contaminated sites if assumptions derived from studies carried out in sterilized soil are used. Ultimately, knowledge of SOM chemistry could aid predictions of bioaccumulation of organic pollutants.

The impact of residual PAHs (2250 ± 71 μg total PAHs g−1) following enhanced natural attenuation (ENA) of creosote-contaminated soil (7767 ± 1286 μg total PAHs g−1) was assessed using a variety of ecological assays. Microtox™ results for aqueous soil extracts indicated that there was no significant difference in EC50 values for uncontaminated, pre- and post-remediated soil. However, in studies conducted with Eisenia fetida, PAH bioaccumulation was reduced by up to 6.5-fold as a result of ENA. Similarly, Beta vulgaris L. biomass yields were increased 2.1-fold following ENA of creosote-contaminated soil. While earthworm and plant assays indicated that PAH bioavailability was reduced following ENA, the residual PAH fraction still exerted toxicological impacts on both receptors. Results from this study highlight that residual PAHs following ENA (presumably non-bioavailable to bioremediation) may still be bioavailable to important receptor organisms such as earthworms and plants. Residual PAHs in creosote-contaminated soil following enhanced natural attenuation impacted negatively on ecological receptors.

Soil amendments previously shown to be effective in reducing metal bioavailability and/or mobility in calcareous metal-polluted soils were tested on a calcareous dredged sediment-derived soil with 26 mg Cd/kg dry soil, 2200 mg Cr/kg dry soil, 220 mg Pb/kg dry soil, and 3000 mg Zn/kg dry soil. The amendments were 5% modified aluminosilicate (AS), 10% w/w lignin, 1% w/w diammonium phosphate (DAP, (NH4)2HPO4), 1% w/w MnO, and 5% w/w CaSO4. In an additional treatment, the contaminated soil was submerged. Endpoints were metal uptake in Salix cinerea and Lumbricus terrestris, and effect on oxidation-reduction potential (ORP) in submerged soils. Results illustrated that the selected soil amendments were not effective in reducing ecological risk to vegetation or soil inhabiting invertebrates, as metal uptake in willows and earthworms did not significantly decrease following their application. Flooding the polluted soil resulted in metal uptake in S. cinerea comparable with concentrations for an uncontaminated soil.

1H NMR metabolomics was used to monitor earthworm responses to sub-lethal (50-1500 mg/kg) phenanthrene exposure in soil. Total phenanthrene was analyzed via soxhlet extraction, bioavailable phenanthrene was estimated by hydroxypropyl-β-cyclodextrin (HPCD) and 1-butanol extractions and sorption to soil was assessed by batch equilibration. Bioavailable phenanthrene (HPCD-extracted) comprised ∼65-97% of total phenanthrene added to the soil. Principal component analysis (PCA) showed differences in responses between exposed earthworms and controls after 48 h exposure. The metabolites that varied with exposure included amino acids (isoleucine, alanine and glutamine) and maltose. PLS models indicated that earthworm response is positively correlated to both total phenanthrene concentration and bioavailable (HPCD-extracted) phenanthrene in a freshly spiked, unaged soil. These results show that metabolomics is a powerful, direct technique that may be used to monitor contaminant bioavailability and toxicity of sub-lethal concentrations of contaminants in the environment. These initial findings warrant further metabolomic studies with aged contaminated soils.

Applying amendments to multi-element contaminated soils can have contradictory effects on the mobility, bioavailability and toxicity of specific elements, depending on the amendment. Trace elements and PAHs were monitored in a contaminated soil amended with biochar and greenwaste compost over 60 days field exposure, after which phytotoxicity was assessed by a simple bio-indicator test. Copper and As concentrations in soil pore water increased more than 30 fold after adding both amendments, associated with significant increases in dissolved organic carbon and pH, whereas Zn and Cd significantly decreased. Biochar was most effective, resulting in a 10 fold decrease of Cd in pore water and a resultant reduction in phytotoxicity. Concentrations of PAHs were also reduced by biochar, with greater than 50% decreases of the heavier, more toxicologically relevant PAHs. The results highlight the potential of biochar for contaminated land remediation.