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The challenge

Variations in contaminant toxicity

Contaminants are present in waters, sediments and soils in a range of different chemical and physical forms, which differ in the extent to which they are bioavailable and potentially toxic to aquatic and terrestrial organisms.  Measurement of total contaminant concentrations will include forms where the contaminants are inert (non-bioavailable forms) and so will overestimate the bioavailable fraction and hence the risks posed to ecosystem health.  

Graphic diagram depicting an ecosystem showing partitioning and speciation on one side and the uptake and internalisation on the other side and a variety of chemical processes (arrows showing directional processes) between the two.

Included under Partitioning - Speciation:

  • measured as non-labile forms of dissolved metals
  • non-bioavailable metal forms
  • strong complexes
  • colloidal forms
  • DOC forward and backwards movement between:
    • Ca2+, Mg2+, Na+,H+
    • Me2+ to:
      • weak complexes (X-L where L= hydroxide, carbonate, sulfate etc) back to:
        • colloids

Included Uptake and internalisation:

  • organism-water interface
  • toxic action or transport sites within the organism (represented by a fish graphic showing pathways for: active influx, passive efflux, renal excretion)
  • Me2+ forward and backwards movement between chemical on partitioning-speciation side as part of:
  • competition: Ca2+, Mg2+, Na+,H+
  • toxicity: Me2+
  • toxicity?: weak complexes (X-L where L= hydroxide, carbonate, sulfate etc)
Interface between the two sides measured as labile forms of dissolved metals.

An underwater ecosystem depicting the interplay between chemical and organic processes between the overlying water and sediment layer through the sediment-water interface.

Information shown in the sediment layer includes:

  • Porewater-Org: partitioning to pore water (arrow indicates upward movement from sediment to water layer)
  • MnO2-M, ≡ POC-Org, FeOOH-M; binding to sediment phases (close to the sediment-water interface)
  • ≡ POC-Org (present within the sediment layer)
  • H2S/FeS/FeS2 (sulfides) (present closer to the bottom of the sediment layer)
  • porewater-Mn+ (arrow indicates upward motion through the sediment-water interface)
  • MnO2, Fe3+/Fe(OH)3/FeOOH present in the oxic layer
  • Mn2+; oxidation/reduction (up/down arrow indicates movement between sub-oxic and anoxic sediment layer)
  • Fes + M2+ → MS ↓ +Fe2+: reactions with AVS (present in anoxic sediment layer)

Information shown in the overlying water layer includes:

  • Dissolved-Org: various directional arrows indicates outward movement into the following:
    • microbial degradation
    • hydrolysis
    • photolysis
    • colloidal-org
    • suspended particulates
  • Suspended Particulates; binding metals and organics downward to sediment-water interface taking the following:
    • ≡ POC-Org
    • FeOOH-M
    • MnO2-M
  • Mn+: arrow indicates upward motion from within sediment layer to dissolved M species with directional arrows to:
    • colloidal M
    • suspended particulates.

Our response

Developing methods for assessing contaminant bioavailability and incorporating these in assessments

For many years, we have been evaluating and developing methods for assessing the bioavailability of both metal and organic contaminants in the environment, and using these approaches to improve environmental risk assessments.

Bar graph showing a trend for stronger containment binding with increasing concentration of organic carbon, AVS and percentage-silt.

Arrow indicates an upward trend and includes the following details:

  • Lower bioavailability
  • Lower risk of adverse effects
  • Risk-based guideline concentration increases.

Hazard concentration / benchmark (mg/kg) along the Y axis with bar measurements at 100, 300 and 900 mg/kg. 

In waters, our Chelex-labile metals method provides a rapid assessment of metal concentrations in waters into labile and non-labile forms, where the latter are considered of low risk to the health of aquatic organisms. This method has now been adopted by commercial laboratories.

For sediment quality assessments, improved methods include equilibrium partitioning approaches and lability-based assessment methods based on contaminant extractability and fluxes using the techniques of diffusive equilibrium, and gradients, in thin films (DET-DGT).

We are also developing methods for predicting contaminant bioavailability based on water sediment and soil properties, and developing bioavailability-based guideline values.

Uptake and bioaccumulation of contaminants by organisms and toxicity to organisms confirms contaminant bioavailability, and we have developed and refined a range of bioaccumulation bioassays to measure a range of biological responses.

In soils, we have evaluated the impact of soil characteristics that modify contaminant sequestration, and have linked that to contaminant bioavailability.

The results

Providing assessment solutions for industry and government

We apply a range of chemical and biological tools to solve problems for industry and Government. When available assessment procedures are not fit for purpose we develop new ones.

For example, our bioavailability assessments for mining companies of downstream fresh waters have incorporated our novel Chelex-labile metal method and our purpose-developed ecotoxicity tests with a metal sensitive bacterium and local microalgal species.

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