Nanoremediation: Information for Decision Makers from NanoRem
FAQ: Are there any risks from nZVI nanoparticles associated with the use of nanoremediation at contaminated sites?
This factsheet discusses only the potential risks from the deployment of Nanoparticles (NPs) as nanoremediation technique, i.e. the risks on human health and environment from the nanoparticles themselves. The risks from the contamination problem being treated, including as a result of failure of the nanoremediation process such as the delivery of nanoparticles to the contaminated media, or inadequate destruction of contaminants or of residual contamination are not discussed here:
Appropriate use of nanoremediation should have the same level of confidence and the same safety requirements as applied to any other in situ redox based remediation technique, some of which can depend on the introduction of potentially hazardous treatment reagents into the subsurface (for example hydrogen peroxide or permanganate). However, the general public’s concerns about nanotechnologies, and a lack of effective validated field performance data, mean that liable parties and / or regulators may pay particular scrutiny to nanoremediation use. As a project NanoRem will produce independent and objective large and field scale performance data to provide a more robust basis for decision-making in the future (see NANOREM project description). In the interim the following information has been prepared, on the basis of published information, to assist decision makers.
The introduction of NPs into the sub-surface may cause risks to human beings or the environment if:
1. The nanoparticles, including reactive and spent NPs, and associated coatings, modifiers or catalysts are harmful to human health or the environment, AND
2. The receptor is exposed to a harmful dose.
The first condition depends on the toxicity of the NPs, their mobility / stability, persistence and capacity to bio-accumulate which are closely linked with the NP physical properties (particle size, specific surface area) and its composition (FAQ: What are nano particles and how does remediation work?); The second condition is very much related to the site specific conditions (presence of NP source, pathway, receptor described in the conceptual site model), the remediation design and implementation (FAQ: What are nanoparticles and how does remediation work?); (injection method and quantity of injected reactive agent) and the propensity for the NPs to migrate to potential receptors (fate and transport of the NPs) (FAQ: What are nanoparticles and how does remediation work?).
Safety and environmental risks (to human health, ecosystems and /or natural resources) associated with nanoremediation must be considered at each step of the remediation process including the handling of the NPs on site, the injection of the reactive media, to the operation of the process, any post remediation monitoring (if required) and ultimate fate of the NPs.
Nanoremediation Handling and InjectionUse of nanoparticles is subject to the same regulatory requirements as other products. These include REACH. Material Safety Data Sheets for a nanomaterial to be used in nanoremediation have to be developed according to these standards and requirements. New nanomaterials will be expected to have been subject to appropriate toxicological and hazard assessment and potential hazards associated with the use of NP shall be clearly identified and indicated.
For example, the higher surface reactivity and surface-area-to-volume ratio of some types of nano-iron powder potentially increases the risk of dust explosion and the ease of ignition; so that careful handling os these materials is required. Again, this is a fairly routine hazard assessment, handling concerns of such particles are not unique to NPs and the remediation sector has long recognised the need for good handling, storage and transportation procedures for other hazardous substances, such as those used for in situ chemical oxidation. Typically the majority of NPs are delivered to site (or produced on site) in the form of a slurry, which eliminates this risk of dust explosion and minimize the risk of inhalation of powder.
Nanoremediation operation and post-remediation monitoringConcern has been raised that following nanoremediation there may be a mixture of spent and unreacted nanomaterials which will pose risks to the environment. Following their introduction and residence in the sub-surface, NPs will undergo transformations (e.g. passivation, agglomeration, sedimentation) which will change their physical properties and toxicity. In addition, of course, NPs will react with the contaminants to be degraded. The available published evidence suggests that spent particles represent less of risk then the unreacted NPs. However, outcomes are site specific and NanoRem is carrying out very site-specific and NP specific alterations. Further R & D is needed to clarify these aspects. Further information can be found in our Thematic Page on: Factors affecting potential deployment risks from nanoparticle release into the environment.
NanoRem’s current view is that the use of NPs in remediation should be accompanied by a “deployment risks assessment” specific to the NPs and site being used to provide suitable level of reassurance to the site stakeholders. See our Thematic Page: Summary of the renegade nanoparticle risk assessment protocol for NanoRem field deployments
The key role of Conceptual Site ModelsThe starting point of the implementation of all remediation technologies (including nanoremediation) is the development of a conceptual site model (CSM) which incorporates the potential risks associated with any source-pathway-receptor linkages on site.
In the case of nanoremediation, the risks from the NP reactive agent used should also be decribed using a conceptual site model. This would include mapping NP source(s), including quantity and number of injections, potential pathways of migration of NPs and exposure routes and receptors to NPs. The pathway term will strongly depend on the injection method, the hydrogeological context and the fate and transport of NPs.
In the absence of a current robust fate and transport model for NPs, currently published information suggests a travel distance of iron NPs ranging from less than 1m to theoretically 100m, with most reports indicating a few metres at most. (See Issues Paper). A major part of NanoRem’s programme is concerned with providing further field measurements and model validation.
The receptors and exposure routes of concern are limited as the treatment is in situ and underground. Firstly, groundwater is considered as a receptor in itself with respect to requirements of the Daughter Framework Directive and the associated objectives to preserve or achieve good ecological status. Man or terrestrial fauna can be exposed to NP by three means of exposure:
- Indirect ingestion of NP through drinking surface or groundwater containing NPs
- Direct dermal exposure through bathing in water containing NPs or direct contact with soil containing NPs
- Direct ingestion of NPs is a possibility if NPs have reached the surface as a result of “daylighting” during injection processes
Plants can be exposed to NPs through uptake via soil or watering with water containing NPs. Subsurface microbiological life can be directly exposed to injected media. Note some in situ bioremediation processes may be enhanced in the presence of nZVI.
The use of nanotechnology for environmental remediation has been described as a classic case of failure to transfer knowledge from the research laboratory to markets. An absence of well validated field scale application case studies is recognised to be part of this failure. NanoRem seeks to fill this gap. However, a case study taking place in one EU-Member State is not necessarily transferable or usable in other countries. NanoRem needs case studies that are seen as relevant on a European rather than a solely national basis. The following information is seen as important in achieving this:
Proposals for regulatory information requirements for deployment of nanoparticles is currently being developed in Nanorem (What affects regulatory acceptance for nanoremediation?) and may assist to appreciate and manage the risks from nanoremediation.
- Describing the site related context (e.g. geology, hydrogeology, contamination type, extent and occurrence).
- Transparent consideration of any additional risks from deploying nanoparticles in the project design and implementation, encompassing reactive and spent NPs, and associated coatings, modifiers or catalysts.
- Conceptual site models will be used to convey this information. NanoRem includes a number of case study nanoremediation deployments (see WP10 description), which will be encouraged to provide this information.
This information is drawn from
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.