Soil screening level

Conservative (i.e., stringent and precautionary) in nature and with no regulatory enforceability, such as the Canadian Water Quality Standards and Eco-Soil Screening Levels.1... 

Provisional RfDs and RfCs for 25 degradation products, impurities and stabilizers (Bausum, 1998) are listed in Table 5. These values can be compared with the estimated oral RfD for VX of 0.0006 qg/kg/day (Opresko et al., 1998). Where data were unavailable for a degradation product, but the mechanism of action for the chemical was the same or predicted to be the same as that of VX, the value for VX was assigned. Thus, although both EA 2192 and bis(,S, S-(diisopropylaminoethyl) methylphosphonodithi-olate are less toxic than VX, the conservative value of 0.0006 qg/kg/day value was proposed. Health-based soil screening levels for the parent compound range from 0.042 to 0.047 mg/kg of soil (US Army CHPPM, 1999). 

Compliance tests that are used to determine whether the material complies with specific reference values such as soil screening levels for remediation purposes, or waste acceptance criteria for landfill disposal. These tests focus on key variables and aspects of leaching behaviour identified by basic characterisation tests. 

USA. There are a number of federal and state sets of guideline values. The US EPA federal soil screening levels were developed to help standardise and accelerate the evaluation and clean-up of contaminated soils at sites on the National Priorities List (NPL).21 The US EPA are clear that the soil screening levels (SSLs) are not national clean-up targets and exceeding them does not necessarily trigger the need for remedial action. Rather they were developed to screen out areas of a site on the NPL that do not require further action or study under the Comprehensive Environmental Response, Compensation and Liability Act (CERCLA)—better known as the Superfund. The SSLs anticipate a future residential land use. 

EPA Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites, Interim Guidance. (2001a). OSWER 9355.4—24. 

U. S. EPA. 2007. SO EPA R4 Soil Screening Benchmark Ecological Soil Screening Levels for Polycyclic Aromatic Hydrocarbons (PAHs). Interim Final. OSW ER Directive 9285.7-78. [on line]. [2009-01-20]. URL http9/www.epa.gov/ecotox/ecossl/pdf7eco-ssl pah.pdf>... 

The U.S. Environmental Protection Agency has proposed that "The annual alpha radiation dose rate to members of the critical segment of the exposed population as the result of exposure to transuranium elements in the general environment should not exceed either 1 millirad per year to the plumonary lung, or 3 millirad per year to the bone" (54). The USEPA also derived a soil contamination level of 0.2 pCi/m2 Tl cm depth, soil particles less than 2 mm) as a reasonable "screening" level for which the resultant dose rates to the critical segment of the exposed population could be reasonably predicted to be less than the guidance recommendations. 

A minimal risk level (MRL) is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse noncancer health effects over a specified duration and route of exposure. These substance-specific estimates, which are intended to serve as screening levels, are used by ATSDR health assessors and others to identify contaminants and potential health effects thai may be of concern at hazardous waste sites. The chronic-duration oral MRL of 1 picogram/kilogram/day or pg/kg/day for TCDD, or total TEQs, (ATSDR 1999) was based on neurobehavioral effects in monkeys. Based on this value, an EMEG of 50 ppt (0.05 ppb) TCDD, which is equivalent to 50 ppt (0.05 ppb) TEQs, was derived for exposure from contaminated soil. Uncertainty factors of 90 (total) were used in the calculations of the MRL (for further details, see ATSDR 1999). Based on a review of more recent literature, ATSDR scientists conclude that the MRL of 1 pg/kg/day is approximately two orders of magnitude below the noncancer health effect levels observed in recent studies. This is also true for cancer effect levels. 

For ecological receptors, a similar approach may be employed for secondary receptors that could be influenced by a change in the soil environment. For instance, it is possible to model the potential for soil to influence an adjacent surface water body and therefore to screen the soil criteria for impacts on an aquatic receptor. When applied, this leads to intercompartment harmonization of standards, by which soil or sediment standards pose no problems for water bodies and vice versa. In addition, it may be possible to use screening-level models to assess the potential for a bioaccumulable substance to influence a tertiary ecological receptor, usually a top predator or a protected species. In this approach, the reference dose can be borrowed from other sources (e.g., use of an aquatic criterion to determine a critical water concentration). The model is then used only to assess how the soil may influence transfer to the critical receptor. However, it should be noted that this type of procedure cannot be used for guideline development related to primary terrestrial receptors since there are no reliable models to estimate dose-response relationships for these receptors. Therefore, other techniques described in this chapter are recommended for screening against primary receptors. 

Health Based Environmental Screening Levels (HBESLs). These HBESLs are endorsed by military policy as criteria to assess potentially contaminated soils (Table 6.6) (USACHPPM, 1999 OASA, 1999 Watson and Dohslager, 2007). 

For practical considerations, one can use a conservative value of 7.4 kBq of plutonium proposed by the U.S. Environmental Protection Agency in 1985 as a recommended screening level , below which land can be considered suitable for unrestricted use (US EPA, 1985). This corresponds to a concentration of approximately 0.5 Bq g" for the soils in the region, where the observed penetration of plutonium into the soil is about 1 cm, or to a surface density of approximately 1 kBq m of Am in the north-west plume for which the measured ratio of plutonium to americium is seven (Bums et al., 1989). 

In this section, the screening-level assessment of ecological risk to aquatic, sediment- and soil-dwelling organisms are conducted. Human health risk assessment is also conducted. CPs are usually mixtures of different carbon chain length and different degrees of chlorination therefore, this assessment is concerned with the short-chain length (Cio-i3) CPs as mixtures. 

In the screening-level assessment of SCCPs to aquatic, sediment-, and soil-dwelling organisms, risk characterization is conducted to find whether SCCP concentrations are larger than the HC5 estimated fi om SSD. The data obtained from the SCCP... 

As there is no monitoring data for soils, the screening-level assessment is conducted using the regional SCCP concentration in soil estimated at 0.150 mg kg ww, which is two orders lower than the HC5. When the distribution of SCCP concentrations in soil is estimated, the possibility is extremely low that the estimated value will exceed the HC5. This result indicates that there is a low potential risk to soil-dwelling organisms in the regions. 

The approach is very commonly used in transport models because mathematically it is relatively easy to incorporate. Goyette and Lewis [28] highlighted the utihty of values in screening level ground water contaminant transport models of inorganic ions with the caution that experimental conditions such as pH, electrolyte composition and soil type are similar to those being modeled. Viotti et al. [29] used values to model phenol transport in an unsaturated soil. Schroeder and Aziz [30] used this approach to account for PCBs sorption into dredged materials. Buczko et al. [31] used the Freundlich approach to model chromium transport in unsaturated zone. 

---