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: Included Uptake and internalisation: 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: Information shown in the overlying water layer includes:
Interface between the two sides measured as labile forms of dissolved metals.
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: 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.