RISK ASSESSMENT FOR PETROLEUM CONTAMINATED SITES BASED ON NOVEL HYDROCARBON FRACTIONATION AND MODIFIED KOREAN STANDARD TEST METHOD

Abstract

Contaminated site management paradigms continue to change from ‘concentration-based’ approaches to ‘risk-based’ approaches in Korea, as well as in other countries. Human health risk assessment was partially introduced into the Korean regulatory framework through the amendment of the Soil Environment Conservation Act (SECA) in 2005 and through the establishment of the Soil Contamination Risk Assessment Guideline that provides legal justifiability for a risk-based management process. Despite these initiatives, thoroughly evaluating risks posed by petroleum, oil, and lubricant (POL)-contaminated sites remains difficult because the current risk assessment process only focuses on a few risk indicator compounds, such as benzene, toluene, some heavy metals and so on. There has been little concern about non-carcinogenic risks from total petroleum hydrocarbon (TPH), although these compounds are toxic to human and environmental receptors. Therefore, the objective of this study is to propose the reliable and feasible human health risk assessment strategy for POL-contaminated site in domestic regulatory framework. Human health risk assessments for POL-contaminated sites are more complicated than for sites contaminated by single compounds due to the complex composition and various analytical methods associated with TPH. Although several TPH fractionation methods are commonly used, including that of the TPH Criteria Working Group (TPHCWG), an efficient and economical human health risk assessment method is not yet available. To address this concern, a new modified fractionation strategy is recommended in this study, which resolves the problems of the current TPH fractionation methods while retaining reliability in the results. For the purpose of this study, the distribution characteristics of the 13 TPHCWG fractions were examined, and human health risk assessments for the POL-contaminated sites were performed. The results show that aliphatic EC8~16 and aromatic EC10~21 among the 13 TPH fractions are major contributors to human health risks along all exposure routes, making up approximately 96 % of the hazard index (HI) of the TPH fractions, on average. Therefore, it is reasonable to concentrate on aliphatic EC8~16 and aromatic EC10~21 fractions, rather than to study all of the TPH fractions, in evaluating human health risk for TPH-contaminated sites. Since risk assessment is a technique of policy analysis, risk assessment process should address the specific policy issues of relevant countries including social, economical and institutional needs as well as scientific knowledge. In order to satisfy these requirements, this study recommends a new human health risk assessment strategy for POL-contaminated sites. The strategy is based on a newly-modified TPH fractionation method and includes an improved analytical protocol. The proposed TPH fractionation method is composed of ten fractions (e.g., aliphatic and aromatic EC8~10, EC10~12, EC12~16, EC16~22 and EC22~40). Although it is found that aliphatic and aromatic EC22~40 fractions are less important in evaluating human health risks in previous study, the proposed TPH fractionation method includes these fractions due to the compatibility with a domestic management framework. Physicochemical properties and toxicity values of each fraction were newly defined in this study. In devising a risk-based framework for POL in soil matrix, it is critical to establish robust analytical protocols that are capable of reliably and reproducibly estimating the concentrations of risk-critical compounds and TPH fractions. For the efficient analysis of TPH fractions, the stepwise ultrasonication-based analytical process was established based on Korean Standard Test Method (KSTM). Analytical results were compared with those from the TPHCWG Direct Method. Better analytical efficiencies in TPH, aliphatic, and aromatic fractions were achieved when contaminated soil samples were analyzed with the modified KSTM analytical protocol. The risk assessment process is a more labor, cost and time-intensive work compared to the ‘concentration-based’ management process. In order to balance scientific defensibility with reasonable cost and time, 3-tiered approach was incorporated with the domestic POL-contaminated site management process. A human health risk assessment was performed based on the developed tiered risk assessment framework. Results showed that the tier II process can be applied to make an effective decision on whether there are potential adverse health effects at a POL-contaminated site and if further remedial actions are necessary. Also, to determine scientifically and economically appropriate cleanup target levels for remediation of POL-contaminated sites, a detailed quantitative risk assessment should be conducted, although the tier II process is useful for determining the potency of human health risks posed by POL-contamination. The proposed risk assessment strategy is reasonable, practicable and well-organized process and this process is compatible to domestic management framework and analytical protocol. Thus, this strategy can not only effectively manage POL-contaminated sites in terms of human health protection but also reduce excessive remedial cost and time.