Environmental monitoring and remediation action strategies require accurate measurements of the impact of contaminants of concern on terrestrial and aquatic organisms. Discrete sampling of water and sediment followed by laboratory analysis is a standard practice. Total concentration data provided by discrete measurements provides a baseline understanding of contaminant distribution, but provides only limited information on toxicity potential since a total concentration value may not predict to what extent pollutants are accessible to organisms. Passive samplers provide an alternative option to discrete sampling. Typically passive samplers have targeted the collection of trace organic compounds (TOCs), such as PCBs and other non-polar analytes such as PAHs. The integrative nature of passive samplers is useful in obtaining time weighted averages in water streams and increasing concentrations above method detection limits by accumulation over time. Special emphasis has been placed on mimicking the uptake of PAHs and PCBs by benthic organisms in order to illuminate the potential for adverse impacts on aquatic ecosystems without having to use live organisms and tissue extractions. As such, significant research has been accomplished developing biomimetic models, equilibrium models, and devices to simulate bioaccumulation. It is important to understand where contaminants are found in sediments, how source location affects bioavailability, and why passive sample design is critical.
The goal of the project was to utilize ABS Materials, Inc. swellable organosilica media to build and evaluate a passive sampler design that would possess the following attributes:
- Be able to measure a wide range of analytes including high logKow species (dioxins and chlorobenzofurans) as well as more polar compounds (TNT and RDX) and metals (Cu, Zn, Ni, and Pb).
- Use the ability of the media to expand and contract to create sorbents that possess an adsorptive capacity that mimics benthic organisms to better inform remedial action decisions.
- Provide a design that has a significantly lower cost than current passive samplers.
- Create samplers that are easy to deploy and can be analyzed by major commercial testing labs using standard methods.
The technical approach taken to address the objectives was as follows:
- Passive samplers were developed and tested using three different versions of Osorb® media to determine the optimal formulation for capture of metals, chlorinated polyaromatic compounds, TNT, and RDX.
- The fundamental performance of the passive samplers was tested in water to determine (A) time to equilibrium for analyte absorption, (B) sampler response to absorption of varying analyte concentrations as a measure of sensitivity, and (C) resistance to back diffusion to determine if response is integrative.
- The use of the passive samplers in sediment was analyzed using artificial sediment doped with varying concentrations of analytes. Recovery of sequestered chemicals within the Osorb passive samplers was completed to determine the % capture of both metals and munitions.
The major findings of the project were the following:
- Three different versions of Osorb® media were synthesized and tested for adsorption of metals, chlorinated polyaromatic compounds, TNT, and RDX. The optimal media was able to measure chlorinated polyaromatics, munitions, and metals simultaneously with high capacity allowing the media to act as an infinite sink.
- Passive samplers using Osorb media demonstrated a fast response time (minutes-hours) due to the open mesh design. There was linear correlation between concentration in the environment and sampler response.
- The high capacity and affinity of the media acted as a sink allowing the measurement of analytes in both the pore water and those that are reversibly bound to sediment. As such, the sampler may be able to mimic the tissue of benthic organisms.
The unique aspects of the sampler as designed and tested (i.e. low cost, fast capture rate, wide specificity) could open up new possibilities in sampling to provide data sets to site managers that are currently unavailable. Two examples are the following:
- Data indicate that Osorb media acts as an adsorptive sink for contaminants. If the partition coefficients of contaminants to the media indeed mimic fish tissue, the sampler could be used as direct measure of ecological impact. Such data could eliminate the need of costly bioassays.
- The fast uptake kinetics and proportional response to analyte concentration make the Sentinel™ passive sampler ideal for measurement of contaminants in stormwater. An array of passive samplers could be deployed at many stormwater collection points across an installation or throughout a near-shore watershed to provide a geospatial mapping of contaminants from a storm event. Monitoring inputs of pollutants is vital to understanding the sources of potential future sediment contamination. Knowledge of inputs could prevent measures such a re-dredging a site or undertaking additional unanticipated remediation measures.
Additionally, the successful completion of this project has resulted in the development and commercialization of the Sentinel™ passive sampler.
- The cost of a single sampler is approximately $25 (and less in bulk), which is cost efficient compared to other designs currently on the market.
- Post-deployment extraction and analysis can be done in a user’s laboratory or the sampler can be sent to Alloway Environmental Testing.
- Third party validation has been performed with the U.S. Navy, Oklahoma State, U.S. Geological Survey, and U.S. Department of Energy. Some of these third-party findings have already been published in the peer reviewed literature.
- Patented media with technology transfer fully completed.