Can We Use a QSAR Model for Estimating the Fates of Contaminants in the Sub-Surface Environment?

Seung Joo Lim

doi:10.4172/2155-6199.1000103e

ISSN: 2155-6199

Journal of Bioremediation & Biodegradation

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Can We Use a QSAR Model for Estimating the Fates of Contaminants in the Sub-Surface Environment?

Seung Joo Lim^*
Radiation Research Division for Industry & Environment, Korea Atomic Energy Research Institute, 1266 Sinjeong, Jeongeup, Jeollabuk-do, 580-185 Republic of Korea
Corresponding Author :	Seung Joo Lim Radiation Research Division for Industry & Environment Korea Atomic Energy Research Institute, 1266 Sinjeong Jeongeup, Jeollabuk-do, 580-185 Republic of Korea Tel: 82-63-570-3357 Fax: 82-63-570-3348 E-mail: seungjoolim@gmail.com
Received: September 05, 2011; Accepted: September 07, 2011; Published: September 08, 2011
Citation: Lim SJ (2011) Can We Use a QSAR Model for Estimating the Fates of Contaminants in the Sub-Surface Environment? J Bioremed Biodegrad 2:103e. doi:10.4172/2155-6199.1000103e
Copyright: © 2011 Lim SJ. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Many natural and/or synthetic toxic chemicals have been detected and studied in the air, aquatic, soil, and sediment environments such as personal care products and pharmaceuticals (PPCPs) since steroid hormones were detected in a wastewater treatment plant (WWTP) in 1950s. Several investigators have focused on detecting micro pollutants and developing fate models to simulate them in the environment. As a matter of fact, a database for each contaminant in the air, aquatic, soil, and sediment environments is not sufficient because tones of new chemicals are synthesized annually and it is not possible to obtain a database for each contaminant in each localized environment.

However, the deficient of database can be solved when we use structure activity relationships (SARs). SARs can be defined as the property similarity between two molecules. If the structural property of a chemical is similar to that of another, most physicochemical or biochemical property of it can be inferred from that of the other as the property of each contaminant is closely related to the steric consequences of the structure. Since the concept of quantitative structure activity relationships (QSARs) was applied for environmental science, many investigators have estimated the fates of contaminants in the environment using QSAR. For years, researchers and organizations such as the Organization for Economic Cooperation management and Development (OECD), the United Nations Environment Programme (UNEP), the United States Environmental Protection Agency (US EPA), and the European Union (EU) have developed estimation tools for Persistence (P), Bioaccumulation (B), and Toxicity (T) of organic chemicals in the environment using QSAR.

Nonetheless, there is no QSAR model for the sub-surface environment yet because most models have focused on estimating of the persistence and long-range transport of contaminants in air, water, soil, and sediment environments. Also, it is not easy to estimate the fates of contaminants in the sub-surface environment. In the sub-surface, the environment conditions are very different from those in aqueous phase (i.e., river or lake). First, there exists a vadose zone between water resource and aquifer. The usual depth of a vadose zone is 20-60 m, and biochemical oxidation, sorption, and cometabolic oxidation of contaminants are expected. In the sub-surface, the biochemical oxidation of contaminants can be presented by a first-order reaction. A first-order reaction rate constant can be obtained using a regression analysis. However, this constant in a specific experiment cannot represent those in other soil aquifer conditions. Sorption plays a very important role in retaining the movement of contaminants and gives more chances for contaminants to be degraded by microorganisms. The capacity of sorption in a vadose zone is proportional to the specific surface area of media and the hydrophobic fraction in contaminants is significantly captured. The cometabolic oxidation often decreases the persistence of contaminants in the sub-surface environment. Unlike aqueous phase, the concentrations of contaminants in a vadose zone are commonly very low. It causes substrates not to support the growth of microorganisms directly in the sub-surface environment. In other words, it is necessary that the reaction rate constant for cometabolic oxidation be added in a QSAR model. Second, the quality of groundwater is extremely affected by surroundings. For example, a saturated aquifer is usually shown as an excellent buffer for groundwater and the quality of groundwater is not changed during the transport of groundwater. Meanwhile, the quality of groundwater can be significantly changed during the transport in the layers of calcite.

The sub-surface environment is not simple because we have to consider soil science, microbiology, oxidation-reduction, sorption, filtration, precipitation, etc. Thus, in order to estimate the fates of contaminants using QSAR in the sub-surface environment, it is essential to choose the key parameters influencing the prediction of persistence. The key parameters may be different for each sub-surface environment, but model developers have to consider developing a nonspecific model, representing sub-surface environment. If not, a QSAR model is requested to add other parameters since just QSARs are not enough to simulate the sub-surface environment.

Can we use a QSAR model for estimating the fates of contaminants in the sub-surface environment?