Nanoremediation: Information for Decision Makers from NanoRem
Thematic Page 7: Risk Benefit Appraisal
2. Risks from In Situ Remediation Technologies in General
3. Risks from the Use of nZVI
4. Benefits for the Use of nZVI
5. NanoRem Activities
6. Additional Resources on the NanoRem Web Site
8. Feedback and Opinion
nZVI is the dominant nanoparticle used in remediation to date. In common with many other technologies utilised for the in situ treatment of contaminated soils and groundwaters, nZVI can pose health and safety risks if improperly handled. The aim of this page is to place in context the relative risks associated with nZVI compared to other technologies, and to highlight the areas of research identified as being required to substantiate a better risk benefit assessment for nZVI.
This thematic page summarises information provided by a chapter of the NanoRem report: 'A Risk/Benefit Appraisal for the Application of Nano-Scale Zero Valent Iron (nZVI) for the Remediation of Contaminated Sites'. The full report including additional information, detail and referencing can be downloaded from: www.nanorem.eu/Displaynews.aspx?ID=525.
2 Risks from In Situ Remediation Technologies in General
All remediation technologies have associated risks. Barriers to the use of new technologies are generally high, but once information on performance is available, these risks are accepted and appropriate risk assessments put in place to allow the technology to be utilised. Examples include:
- The commonest remediation technique in use is excavation and removal. This carries risks to workers (and the wider public) from operating plant and machinery as well as road traffic, and is widely seen as a non-sustainable technology.
- Alternative in situ chemical reagents, such as permanganate, persulphate, and Fenton’s reagent are potentially harmful to the biological functioning of soil, and can be transported over significant distances in groundwater plumes (Nathanail et al. 2007). Additionally, the application of Fenton’s reagent was the cause of the only reported death from an in situ remediation operation (ITRC 2001). Other in situ technologies, such as thermal heating and the use of surfactant, have been documented to have considerable negative impacts on soil functionality.
- The application of in situ bioremediation may require the introduction of organic substrates, such as vegetable oils, into aquifers. These additives can be quite long lived and can be transported over significant distances in groundwater plumes.
These technologies are routinely permitted across Europe, with potential adverse effects controlled by permit conditions. It would appear disproportionate to regulate nanoremediation in a different way. The challenge is therefore to have available technologies that are capable of measuring and mitigating adverse effects.
3 Risks from the Use of nZVI
The general consensus on the fate of nZVI particles within the subsurface is that the particles do not penetrate far from the point of injection (from <1m to an unproven 100 m for some modified types) (Phenrat et al. 2008) and that their lifespan appears to be relatively short (<1- 2 years), producing a “halo” effect around the point of injection and the treatment zone. The use of nZVI causes perturbations in the subsurface environment, for example by altering oxidation-reduction potential and pH. However, this is no different from other licensed technologies which depend upon redox alterations to achieve contaminant remediation. Nonetheless, as the technology is a relatively recent development, there is little field observation data to categorically substantiate NP transport and impact on the aquifer, and indeed the analysis of nanoparticles within the subsurface has, to date, proved problematic. Additionally, a particular impediment for the use of nZVI is the “dread” associated with the use of nanotechnologies which appears to lead to a heightened perception of risk from the use of this technology (see: Thematic Page 5 : Risk Perception Issues).
Further information on deployment risks is available in Thematic Page 8: Managing Deployment Risks. Regulatory and permitting issues are discussed in FAQ: What affects regulatory acceptance for nanoremediation (nZVI).
4 Benefits for the Use of nZVI
The use of nZVI for the remediation of contaminated groundwater is a technology which is seen as having significant benefits both now and in the medium/long term by extending the range of treatable contamination problems in the saturated zone. The table below sets out a schematic timeframe for potential benefits from nZVI deployment, in the short, medium and long term.
||Medium term (circa up to 5 years) the NANOREM ambition
||Longer term (circa >5 years)|
||Reliable technology option for source and pathway management of NAPLs, claimed to be without release of process intermediates.
||Saturated zone treatment for persistent organic pollutants (POP).
||Vadose zone treatment for difficult / untreatable problems such as highly recalcitrant contaminant classes (e.g. PCBs, dioxins, etc.) |
|Scale of benefits
||Minor, there are a range of established in situ treatments for DNAPLs, each with their relative advantages and disadvantages. Choices are often highly dependent on site specific factors. Potential wider benefits from lower negative soil impacts and fewer process intermediates.
||Significant enhancement of POP reduction practices.
||Potentially huge, given the large areas contaminated by recalcitrant organic compounds in Europe and further afield (e.g. Vijgen 2006). |
|Level of certainty
||Relatively certain, based on the degree of market penetration for nZVI use in NAPL, problems worldwide, wider benefits need to be substantiated.
||Uncertain, as in the absence of a “critical mass” of well-studied field case studies, many stakeholders may be reluctant to use an approach with a limited track record and incomplete cost-benefit assessment.
|Certainty is a function of the outcomes of the major field studies and cost-effectiveness assessments conducted over the next 5 years. The nZVI technology is at a crossroads. If large, well-executed field studies demonstrate effective contaminant transformation while maintaining control of treatment area, nZVI could become a remediation staple. As it is now, it is a niche technology used primarily to support other remedial technologies. |
||The use of nZVI in remediation continues to be the subject of active research by multiple academic research groups in North America, Europe, and Asia-Pacific region. The development potential is strong but currently limited because of various factors cited elsewhere in this report e.g. regulatory concerns, implications-related issues (uncertain fate and transport, discharge to surface waters), and a lack of a driver from responsible parties/consultants due to cost concerns, regulatory hurdles, and uncertain cost-benefit.
|Research on nZVI use in remediation is likely to continue. The outcomes of NanoRem may help reduce some of the barriers to the use of nZVI technology in remediation.
|The long term development potential for nZVI is high due to steady advances in materials development, fate and transport understanding, and better experience in utilizing technology tandems with such approaches as anaerobic bioaugmentation or biostimulation. Highest development potential will be fulfilled if nZVI demonstrates cost effectiveness, comparable efficacy in field trials to laboratory results and if implications-related issues are lower than anticipated. |
5 NanoRem Activities
While this seems a relatively positive risk output for the environmental use of nZVI, there is insufficient field scale observational data to categorically substantiate a view of limited nZVI transport and persistence that would be seen as satisfactory by all regulatory authorities. A particular impediment for the use of nZVI is the “dread” associated with the use of nanotechnologies which appears to lead to a heightened perception of risk of this technology’s use amongst the public and other stakeholder groups including, importantly, landowners.
NanoRem’s research agenda directly addresses these concerns, for example by:
- Undertaking detailed fate and transport studies.
- Development of measurement and assessment tools for NP performance, transport and fate which can be deployed in the field.
- Carrying out large scale tank based nanoparticle deployment studies.
- Carrying out case study field scale tests with full attention paid to deployment risk assessment and management.
6 Additional Resources on the NanoRem Web Site
This thematic page summarises information provided by a chapter of the NanoRem report: A Risk/Benefit Appraisal for the Application of Nano-Scale Zero Valent Iron (nZVI) for the Remediation of Contaminated Sites. The full report including additional information, detail and referencing can be downloaded from: www.nanorem.eu/Displaynews.aspx?ID=525.
Additional summary information is also available on the following online pages:
ITRC (INTERSTATE TECHNOLOGY AND REGULATORY COUNCIL) 2001 ‘Technical and Regulatory Guidance for In Situ Chemical Oxidation of Contaminated Soil and Groundwater’, Interstate Technology and Regulatory Cooperation Work Group In Situ Chemical Oxidation Work Team. [Online] Available at: http://international.vrom.nl/Docs/internationaal/ENGELSE%20versie%20circulaire%20B odemsanering%202009.pdf
NATHANAIL, J., BARDOS, P. AND NATHANAIL, P. 2007 Contaminated Land Management Ready Reference, EPP Publications/ Land Quality Press, Nottingham.
PHENRAT, T., SALEH, N., SIRK, K., KIM, H-J., TILTON, R.D. AND LOWRY, G.V. 2008 ‘Stabilization of aqueous nanoscale zerovalent iron dispersions by anionic polyelectrolytes: adsorbed anionic polyelectrolyte layer properties and their effect on aggregation and sedimentation’, Journal of Nanoparticle Research, 10, 5, 795-814