Natural Attenuation: How Is Mother Nature Aiding Us to Cleanse Our Environmental Sins?

Abstract

For a long time, mankind has ~purposely or negligibly! forgotten that we are not alone on this planet, and the ecosystem and its plentiful ~but not unlimited! resources do not exclusively belong to us ~either as a species or as a generation!. Although we may have the ‘‘divine’’ entitlement ~and obligation! to utilize, develop and indeed enjoy these resources for our well-being and prosperity, we have no right whatsoever to alter, abuse, damage, and/or over-exploit such wealth at the expense of the rest of earth’s fellow residents or future human generations. Even if we try, with all of our technological advancement and economic affluence, to remedy our old/new environmental mistakes, we will not be successful without the sustainable aid of nature itself. Nature has the strength to rectify assaults, assimilate alien substances and phenomena, attenuate toxins, mitigate injuries, and purify itself. This compassionate and intrinsic healing power of nature however is not infinite. Natural attenuation ~occasionally designated as intrinsic remediation! is an inherent natural cleanup process achieved when integrated assimilation mechanisms of self-purification are instinctively triggered ~or activated! at a contaminated site. The merits of natural attenuation are often recognized not only by bringing about diminishing ~or neutralization! of contaminants, but also by the nonintrusive nature of its processes. Natural attenuation mechanisms contain a variety of physical, chemical, and/or biological processes that, under favorable conditions, act without human intervention to reduce the mass, toxicity, mobility, bioavailability, volume, or concentration of contaminants in soil and groundwater ~and other media!. Such mechanisms nevertheless can be classified as either destructive or nondestructive. The destructive mechanisms ~mainly biological and chemical! include biodegradation, abiotic oxidation, transformation, hydrolysis, UV destruction ~in surface media!, stabilization and mineralization. The nondestructive mechanisms ~mostly physical! include sorption, dilution, dispersion, and volatilization. The term ‘‘monitored natural attenuation’’ was denoted by the United States Environmental Protection Agency ~USEPA! to indicate: ‘‘the reliance on natural processes to achieve site-specific objectives within a time frame that is reasonable compared to that offered by other more active methods.’’ The USEPA ‘‘does not view Monitored Natural Attenuation to be a no-action or walkaway approach, but rather considers it to be an alternative means of achieving remediation objectives.’’ Accordingly, the successful implementation of natural attenuation entails the need for systematic characterization, monitoring, analyses, risk assessment, and demonstration protocol, to illustrate that degradation and cleanup of contaminants ~and therefore restoration of the site! are occurring at a satisfactory rate to protect human health and the environment. The most important among natural attenuation processes is