Ecological Exposure Model Inputs

The inputs to the ecological exposure model are soil concentrations and ecological exposure factors. Estimation of soil concentrations is discussed in Section 5.3.4. The key ecological exposure factors used as inputs to the analysis include the following factors.

Plant Toxicity

Manganese and nickel were retained for further study in Phase II due to the potential for phyto-toxicity. Because the toxicity of metals is dependent on the soluble soil fraction, the risk posed to terrestrial plants will be directly related to the amount of metal that can desorb from

SFS particles and become available in the soluble fraction. In her review of plant responses to metal toxicity, Reichman (2002) noted that:

The total metal concentration of a soil includes all fractions of a metal, from the readily available to the highly unavailable. Other soil factors, such as pH, organic matter, clay and redox conditions, determine the proportion of total metal which is in the soil solution. Hence, while total metal provides the maximum pool of metal in the soil, other factors have a greater importance in determining how much of this soil pool will be available to plants (Wolt, 1994). In addition, researchers have found that while total metal correlates with bioavailable soil pools of metal, it is inadequate by itself to reflect bioavailability (Lexmond, 1980; Sauve et al., 1996; McBride et al., 1997; Sauve et al., 1997; Peijnenburg et al., 2000).

Lacking empirical data on the soluble fraction of metals in SFS-amended soil, this evaluation used SFS sample-specific pore water concentrations as a surrogate to develop estimates of the soluble (and therefore bioavailable) fraction in soil. This approach defines the constituent-specific bioavailable fractions as the ratio of SFS sample-specific pore water concentrations to corresponding total concentrations (see Appendix B Tables B-26 and B-19). The empirical distributions of the “pore water/total” ratios establishes a reasonable range for the bioavailable fraction. The 95th percentile of the ratio range (i.e., an estimate of the bioavailable fraction that is higher than 95 percent of other estimates) was used as a reasonably conservative estimate of the bioavailable fraction. Therefore, the maximum soil concentrations for manganese and nickel would be adjusted by a fraction of 0.10 and 0.07, respectively. In effect, this

adjustment estimates that the majority of manganese and nickel is in a solid form unavailable for plant uptake. That is, only a fraction of the metals found in SFS-amended soil behaves similarly to the metals added in spiked soil studies (e.g., soluble metal salts).

Dietary Exposure to Mammals

Antimony, chromium, and copper were retained for further study in Phase II due to the potential for toxicity to small insectivorous mammals (based on studies for the short tailed shrew). The area of the home garden (i.e. 405 m2) may be substantially less than the home range for the shrew. In developing the ecological risk assessment methodology for 3MRA, EPA determined that it was reasonable to prorate exposures based on a comparison between the “habitat” (i.e., the area in which the material is managed – the home garden in the SFS

evaluation), and the median home range for the animal so that dietary exposure was not grossly overestimated. This methodology was reviewed and approved by EPA’s Science Advisory Board in 2003, as a reasonable method to account for the spatial heterogeneity in animals’ use of

feeding and foraging areas.44 The same method is used in this risk assessment to avoid the

unrealistic and overly conservative assumption that 100% of the shrew diet comes from the home garden.

Information on home ranges of species was reviewed for northern, southern, Adirondack, Sherman’s, and Elliot’s short-tailed shrews (ADCNR, 2008; FFWCC, 2013; Getz and McGuire, 2008; KBS, 2014; MNHP, 2014; Saunders, 1988; U.S. EPA, 1993 and 2002; VDGIF, 2014). The short-tailed shrew diet consists primarily of insects, earthworms, slugs, and snails, while plants,

44 _{The SAB review report is available at}

http://yosemite.epa.gov/sab/sabproduct.nsf/95eac6037dbee075852573a00075f732/99390efbfc255ae885256ffe005 79745/$FILE/SAB-05-003_unsigned.pdf

Risk Assessment of Spent Foundry Sands in Soil-Related Applications 5-32 fungi, millipedes, centipedes, arachnids, and small mammals also are consumed (U.S. EPA, 1993b). The literature on short-tailed shrews noted that these animals can be found in a wide variety of habitats, although areas with litter/grass cover (e.g., forest, wetlands) and high moisture levels are clearly preferred (Miller and Getz, 1977; van Zyll de Jong, 1983). A variety of factors that influence the home range and habitat preference for short-tailed shrews were identified; for example, the availability of prey, season, and reproductive status were shown to influence movement and home ranges for short-tailed shrews in east-central Illinois (Getz and McGuire, 2008). Figure 5-7 presents the median home range values identified in that review, ranging from 0.06 to 6.2 acres with a median (of the medians) of 2.4 acres (9700 m2), and a 10th percentile value of 0.7 acres (2800 m2). The variability in results shown in Figure 5-7 suggests that the species, as well as the geographical location, has a significant influence on the home range and movement (a surrogate for foraging behavior) for the short-tailed shrew.

Figure 5-7. Analysis of Home Range Sizes for the Short Tailed Shrew.

Comparing the home garden area of 0.1 acres (405 m2_{) to the 10}th _{percentile value for}

home ranges shown in Figure 5-7, 0.7 acres (2800 m2) attributes roughly 15% of the short-tailed shrew diet to the home garden. As a consequence, a fraction of 0.15 was assumed for all three COCs to reflect the percentage of diet likely to come from the home garden.