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.
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.
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.