Risk-based Screening Levels Research Articles

Characterization of EPA’s 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in tank bottom solids and associated contaminated soils at oil exploration and production sites in Texas

The purpose of this study was to determine the concentration and types of polycyclic aromatic hydrocarbons (PAHs), a group of environmentally toxic and persistent chemicals, at contaminated oil exploration and production (E&P) sites located in environmentally sensitive and geographically distinct areas throughout Texas. Samples of tank bottom solids, the oily sediment that collects at the bottom of the tanks, were collected from inactive crude oil storage tanks at E&P sites and hydrocarbon contaminated soil samples were collected from the area surrounding each tank that was sampled. All samples were analyzed for the 16 PAH priority pollutant listed by US EPA and for total petroleum hydrocarbons (TPH). The results demonstrate that overall average PAH concentrations were significantly higher in tank bottom solids than in contaminated soils. Total PAH concentrations decreased predictably with diminishing hydrocarbon concentrations; but the percent fraction of carcinogenic PAHs per total measured PAH content increased from approximately 12% in tank bottom solids to about 46% in the contaminated soils. These results suggest that the PAH content found in tank bottom solids cannot reliably be used to predict the PAH content in associated contaminated soil. Comparison of PAHs to conservative risk-based screening levels for direct exposure to soil and leaching from soil to groundwater indicate that PAHs are not likely to exceed default risk-based thresholds in soils containing TPH of 1% (10,000 mg/kg) or less. These results show that the magnitude of TPH concentration may be a useful indicator of potential risk from PAHs in crude oil-contaminated soils. The results also provide credibility to the 1% (10,000 mg/kg) TPH cleanup level, used in Texas as a default management level at E&P sites located in non-sensitive areas, with respect to PAH toxicity.

Site-specific natural background concentrations of metals in topsoil from the Trail region, British Columbia, Canada

The natural background level of elements in the surface soil of a given area is largely dependent on the geological setting of the region and the underlying soil parent material. Due to the heterogeneity of soil in various environments, it is essential to determine the site-specific natural background levels of elements to quantify the degree of influence of the anthropogenic source(s) within a given study area. This paper discusses the process involved in establishing the natural background level of trace metals and other elements in topsoil for the area surrounding the Teck Cominco zinc–lead smelter in Trail, British Columbia, Canada. The environmental assessment of soil in the Trail region is difficult due to the natural enrichment of metals in surficial material and topsoil as a result of the influence of mineralized bedrock in the region. Detailed examination of the study area based on the deposition data and previously collected soil data led to the selection of presumably the least anthropogenically influenced background sites in the study area, which also reflect the geological diversity of the region. The range of background was defined using the median plus or minus two median absolute deviations [median±(2 × MAD)], after the outliers were excluded. The outliers were identified using the Tukey boxplot concept and the cause of high metal concentrations in the outlier samples is attributed to their proximity to the historical mining sites in the region. The upper limit of the background range was estimated to be (in mg/kg): As, 11.0; Cd, 0.81; Cu, 38.1; Hg, 0.07; Pb, 27.7; Zn, 152. The resulting values are significantly more conservative estimates than would be obtained by other widely used methods (e.g. the mean plus or minus two standard deviations) due to the robust procedure, which prevents any interference by the extreme values in the collected soil background dataset. The upper background thresholds of metals estimated by the 95th percentile resulted in significantly different estimates, especially for As, Hg, Pb and Zn, from the previously reported values. This highlights the need for revision of the risk-based screening levels by environmental regulations in the study area.

Approaches to Ecological Risk Characterization and Management: Selecting the Right Tools for the Job

ABSTRACT Chemical-specific hazard quotient (HQ) risk characterization in ecological risk assessment (ERA) can be a value-added tool for risk management decision-making at chemical release sites, when applied appropriately. However, there is little consensus regarding how HQ results can be used for risk management decision-making at the population, community, and ecosystem levels. Furthermore, stakeholders are reluctant to consider alternatives to HQ results for risk management decisions. Chemical-specific HQs risk characterization should be viewed as only one of several approaches (i.e., tools) for addressing ecological issues; and in many situations, other quantitative and qualitative approaches will likely result in superior risk management decisions. The purpose of this paper is to address fundamental issues and limitations associated with chemical-specific HQ risk characterization in ERA, to identify when it may be appropriate, to explore alternatives that are currently available, and to identify areas that could be developed for the future. Several alternatives (i.e., compensatory restoration, performance-based ecological monitoring, ecological significance criteria, net environmental benefit analysis), including their limitations, that can supplement, augment, or substitute for HQs in ERA are presented. In addition, areas of research (i.e., wildlife habitat assessment/landscape ecology/population biology, and field validated risk-based screening levels) that could yield new tools are discussed.

An Evaluation of Tertiary‐Butyl Alcohol for the Development of a Drinking Water Action Level in Delaware

AbstractFor regulators to develop risk‐based screening levels (RBSLs) for a petroleum constituent, a maximum allowable concentration at an exposure point, such as a drinking water action level, must be established. Of particular interest to regulators of leaking underground storage tank (LUST) sites in Delaware is the development of RBSLs for the oxygenated compounds that are added to gasoline to increase octane rating and promote cleaner burning fuel. Whereas methyl‐tertiary butyl ether (MTBE) became the first of the oxygenated compounds to gain regulatory attention in Delaware, tertiary‐butyl alcohol (TBA) is not far behind. TBA has been detected at LUST sites throughout Delaware and in some cases has been detected in private water supplies. However, Delaware does not currently have a drinking water action level, or maximum allowable exposure concentration, on which to base regulatory decisions regarding TBA.Toxicological data is inconclusive in classifying TBA as a carcinogen. However, carcinogenic responses are reported in rat and mice studies at extremely high doses. To address TBA in Delaware's Risk‐Based Corrective Action Program, the Delaware Division of Public Health must calculate drinking water action levels based on the results of the toxicological data. However, the establishment of TBA action levels could have a tremendous impact on the costs associated with investigating and remediating a LUST site. TBA may add $2000 to $5000 per year in analytical costs alone for an average LUST site in Delaware.

Calculation of Human Health Risk-Based Screening Levels (Rbsls) for Petroleum

ABSTRACTHazardous waste site managers and regulators can decide easily whether site contamination requires remediation to protect human health, but defining the extent of cleanup is often an enormous challenge. When is the site clean enough for human access and use? Risk assessment tools can be used to help answer this question. One can calculate chemical-specific risk-based screening levels (RBSLs) in environmental media (e.g. soil, water, and food) that correspond to “acceptable” levels of risk. RBSLs can be calculated for individual chemicals and chemical mixtures, specific to various exposure pathways. In calculating RBSLs, one must account for the fact that people may be exposed to more than one chemical by more than one exposure pathway. Fate and transport models may be needed to predict how people might become exposed to site contamination in the future. Example RBSLs for non-cancer effects are calculated to illustrate the utility and limitations of RBSLs for making risk-based decisions at petroleum release sites.