Thematic Articles

Remediation with engineered nanomaterials (ENMs) promises more effective and cheaper approaches than conventional methods due to the increased reactivity of nanoparticles and the possibility of in situ treatment. Three examples of the use of ENMs in soil remediation are nanoscale zero-valent iron for the degradation of halogenated organic compounds, nanoscale calcium peroxide for the destruction of organics (e.g. gasoline) and nanoscale metal oxides for the adsorption of metals. However, these methods are very new, and more research is needed on the mobility of ENMs in the soil and their impact on the environment.

Soil bioremediation is a complex and costly process that aims to restore contaminated sites to environmentally sustainable conditions using microorganisms. The process relies upon the ability of microorganisms to degrade organic molecules, but it also depends on the microorganisms coming into contact with the contaminants, and the environment in the contaminated soil being conducive to the survival of the bacteria. A wide variety of techniques have been developed to ensure that these latter two constraints are overcome and to enhance contaminant biodegradation. Future developments in bioremediation are likely to lead to a reduction in both the energy used and the resulting pollutant and greenhouse gas emissions.

Phytoextraction is a process in which plants are used to remove trace metal contaminants from soils. This approach for cleaning soils appears very attractive, but essentially it is still at the development stage. Assisted phytoextraction, also called enhanced phytoextraction, seeks to improve metal extraction rates by manipulating the growing conditions of the plants. However, major technical challenges remain to be resolved.

Amending soils with mineral-based materials to immobilize contaminants is both old and new. Although mineral amendments have been used for decades in agriculture, new applications with a variety of natural and reprocessed materials are emerging. By sequestering contaminants in or on solid phases and reducing their ability to partition into water or air, amendments can reduce the risk of exposure to humans or biota. A variety of mineral types are commonly used to amend contaminated soils, with different modes of molecular-scale sequestration. Regulatory, social, and economic factors also influence decisions to employ mineral amendments as a treatment technology.

The incorporation of common organic wastes (e.g. compost, biosolids, recycled paper waste) into soil promotes contaminant removal and stabilization, and diverts waste from landfill or incineration. However, implementation is constrained by public perception, timescale, cost and the pollutant burden of the organic waste itself. In addition, the high nutrient content of most organic wastes can lead to low biodiversity value at restoration sites. These potential negative aspects are now being countered by the mixing of waste streams, thus providing a multifunctional solution to land remediation where pollutant removal is not the only long-term goal.

Humanity requires healthy soil in order to flourish. Soil is central to food production, the regulation of greenhouse gases, recreational areas such as parks and sports fields and the creation of an environment pleasing to the eye. But soil is fragile and easily damaged by uninformed management or accidents. One type of damage is contamination by chemicals that provide the lifestyles to which the developed world has become accustomed. Traditional soil “clean-up” has entailed either simple disposal or isolation of contaminated soil. Clearly this is not sustainable. Modern remedial techniques apply mineralogical and geochemical knowledge to clean up contaminated soil and make it good for reuse, rather than simply discarding this precious and finite resource.