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Risks & Rewards of Nanoremediation

Michael Crichton’s 2002 novel Prey features a terrifying interpretation of nanotechnology, when swarms of “nanobots” become self-aware and predatory. His book is entirely fictional, but even outside the realm of popular culture, mentions of nanotechnology can stoke our fears about what might happen if science advances beyond our control.

What is nanotechnology? Any technology that works with and manipulates particles between 1 and 100 nanometers in length or width can fall under the nanotech umbrella. Particles of this size are too small to see with the naked eye – they are about the size of a virus or of your DNA. In the real world, predatory nano-swarms don’t top the list of scientists’ concerns. Instead, they are engaged with determining the environmental and health impacts of our increasing use of nanotechnology in medicine, energy generation, communication technology, and even environmental remediation.

In the environmental field, nanotechnology is used to remediate or clean up polluted groundwater, wastewater, soil and sediment. Nanoremediation methods use materials at the nanoscale to reduce pollutant levels at contaminated sites. Nanomaterials have several properties that make them well-suited to this task. They are tiny in size, enabling them to enter very small spaces and travel further and more widely than larger particles. They also have a high surface area relative to their mass, making it easier for them to react with compounds. (Karn et al., 2009).

When nanoparticles interact with toxic compounds, they operate in one of two ways – breaking down the compounds, or immobilizing them. Nanoparticles can cause reactions that transform toxic compounds to less harmful products. They also can bind to the compounds, immobilizing them and preventing them from exerting further harm on the environment. Iron nanoparticles are one of the most commonly used compounds, used to break down or bind and immobilize harmful contaminants (Karn et al., 2009).



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Site remediation with iron nanoparticles. Credit: Lehigh University


According to the EPA, federal, state and local governments, as well as private industry, are expected to spend billions of dollars each year cleaning up hundreds of thousands of contaminated sites over the next three decades. Researchers have concluded that by using nanotechnology in environmental remediation, we have the potential to reduce the cost, time and effort involved with cleaning up contaminated sites (Karn et al, 2009). One major advantage of nanoremediation is its ability to be used as an on-site, or in situ, treatment method. Removing and transporting toxic sediment or soil can involve excessive time and effort, and in situ methods like nanoremediation eliminate this cost.

However, concerns naturally emerge any time we introduce new compounds to the environment. While nanoparticles are designed and used to reduce contaminant toxicity, they may have the potential to generate harmful byproducts, or products that are even more mobile in the environment. While nanomaterials typically stay in or near the site where they are applied, several studies have shown their ability to travel larger distances, carrying with them absorbed contaminants (Karn et al, 2009). Recent research has also investigated the potential for nanoparticles to enter the food chain and bioaccumulate.

Nanoremediation has the potential to revolutionize contaminated site cleanup, but it also carries unknown risks. Balancing these risks and benefits will be critical to the future of environmental management. The good news? We are (probably) safe from predatory nanobots.

Image: National Science Foundation

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Helping can hurt: Complications and consequences of remediation strategies

Environmental remediation often involves a) moving large amounts of contaminated material from one place to another, b) treating the polluted material with chemical compounds, or c) both. The Interstate Technology and Regulatory Council says it best in their guideline document on managing risks during remediation: “Investigation and remediation activities have their own set of risks, apart from the risks associated with chemical contamination.” These risks range from spending time and resources on an ineffective remedy, to the chance of causing adverse ecosystem and health impacts through the cleanup process.

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Project risks - from ITRC document

I recently read a report from a site where engineers were pumping methanol into the groundwater to aid in breaking down the compound of interest, TCE. They soon found that their shipment of methanol was contaminated by PCE – another toxic compound with which they were effectively re-polluting their treatment area. Introducing further contamination through remediation may be less common, but dealing with large amounts of polluted material can potentially cause existing contaminants to become more mobile. Especially when remediation projects deal with contaminated sediments, a question of critical importance is whether to remove the offending substance or to leave it in place. Dredging of contaminated sediment underwater must be done very carefully so as to avoid remobilizing contaminants into the water column.  There are surprises, too; sometimes, the EPA says,  “dredging uncovers unexpectedly high concentrations of contaminants beneath surface sediments.”

When contaminated materials are left in place, or before they are removed, the remediation process often involves introducing new chemical compounds to the polluted material. These “additives” help cause reactions that break down toxic chemicals into less toxic forms. However, Lisa Alexander of the Massachusetts Department of the Environment writes that these additives can cause contaminants to migrate into water, or release potentially harmful gases.

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Gulf Coast cleanup worker - from CNN

The complexities of remediation have been especially apparent in the aftermath of the Deepwater Horizon spill. Dispersants were released to break down oil in the Gulf, but years later the substances are still being found in tar balls washing up on the beach. The combination of oil and the dispersant Corexit has also proven to be more toxic to marine organisms than oil alone. Corexit, encountered primarily by cleanup workers after the tragedy, is also potentially toxic to humans, and its longterm health effects are unknown.

Cleaning up contaminated sites involves taking calculated risks of disrupting or polluting an already-damaged ecosystem. When even our most practiced remediation methods carry with them uncertain outcomes, how can we strike a balance between trying innovative treatment methods for contamination and avoiding unreasonable risk? I’ll explore one case in particular in my next entry: nanomaterials.

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Fracking for Environmental Remediation

Most of us are familiar with hydraulic fracturing as a technique used for oil and natural gas drilling. The process uses a slurry of chemicals and sand to prop open rock fissures, allowing the release of fossil fuels. However, natural gas and oil are not the only constituents trapped in rock layers; these layers can also serve as a reservoir for contaminants. At Superfund sites and other polluted areas, the process of remediation, or cleanup, can be extended and expensive. Hydraulic fracturing has been utilized as an environmental cleanup method, where the same process is used to release trapped contaminants in rock layers. The EPA provides information on the process at

http://cluin.org/techfocus/default.focus/sec/Environmental_Fracturing/cat/Overview/

In fracking for environmental remediation just as in fracking for oil and gas drilling, a slurry of chemicals is pumped into the ground, typically containing a combination of water, sand to prop open fissures, detergent, and nutrients/amendments which stimulate the process of chemical breakdown. According to the EPA, “Environmental fracturing can be used to make primary treatment technologies…more efficient.” By enhancing the access of chemicals for pollution treatment to the rock layers where the pollutants are trapped, fracking has the possibility to decrease treatment times at polluted sites.

Fracking for fossil fuel extraction – specifically, horizontal drilling which uses a very large volume of chemicals- has been faulted for a number of high-profile instances of water contamination. When the process fails, the stakes are high for communities whose water supplies are in proximity to fracking wells. Through environmental hydraulic fracturing is intended to clean up already-polluted sites, the parallels between this process and fracking for natural gas are difficult to ignore. Is it possible for the process to further spread contamination in instances that pipelines or wells fail? The research is slim on this topic so far, but we do know that even with the best of intentions, remediation processes do not always go as planned. In my next post, I’ll explore the potential for unintended consequences from remediation.