Human Health Risk Assessment - Raytheon

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R = Ideal gas constant (cm 3 -atm/mole-K) T = Temperature (K) 4.2.7 Homegrown Produce 26 Human Health Risk Assessment DRAFT For residents who maintain a home garden and irrigate their crops or trees with groundwater, potential exposures to COPCs may occur via ingestion of homegrown produce and incidental ingestion of soil while gardening. As previously mentioned, most of the COPCs present in off- Site groundwater are volatile constituents, which will tend to be released to outdoor air during irrigation rather than accumulate in soil or taken up by plants. COPC concentrations in homegrown produce were estimated for root vegetables and aboveground fruits and vegetables using empirical correlations with octanol-water partition coefficient (Kow) established by Briggs et al. (1982, 1983) and later updated by Ryan et al. (1988). The root concentration factor (RCF) is defined in equation (4-15) RCF and estimated according to equation (4-16). ( mg / kg fresh weight) pore water ( mg / L) concentration in root = (4-15) concentration in soil 0. 77 log Kow −1. 52 RCF = 10 + 0. 82 (4-16) A stem concentration factor (SCF) derived by Briggs is used to estimate COPC concentrations in above-ground fruits and vegetables. The SCF is defined in equation (4-17) SCF and calculated according to equation (4-18). ( mg / kg fresh weight) pore water ( mg / L) concentration in stem = (4-17) concentration in soil 2 −0. 434( log Kow − 1. 78) − = ⋅ ⎜ 2. 44 SCF 0. 748 ⋅10 ⎟ (4-18) 0. 95 log Kow 2. 05 ( 0. 82 + 10 ) ⎛ ⎜ ⎝ ⎞ ⎟ ⎠
27 Human Health Risk Assessment DRAFT Because St Petersburg receives about 52 inches of rain per year 9 , we have assumed that the concentrations of COPCs in soil pore water are diluted by 50% compared to concentrations in irrigation water. This assumes that an equal amount of irrigation water (~50 inches per year) is applied to the home garden or trees. We have also assumed that some fraction volatilizes to outdoor air and is unavailable for plant uptake using equation (4-14). 4.2.8 Surface Soil Surface soil concentrations resulting from irrigation of lawns and gardens were calculated assuming equilibrium partitioning with irrigation water according to equation (4-19). where: C s C ( θ + ρ K f ) irr w b oc oc = (4-19) ρb Cs = Concentration in soil (mg/kg) θw = Volumetric water content (unitless) ρb = Dry soil bulk density (kg/L) Koc = Organic carbon-water partition coefficient (L/kg) foc = Fraction of organic carbon in soil (unitless) Soil parameters were chosen to be consistent with a loamy sand with a volumetric water content of 7.6% and soil bulk density of 1.62 kg/L (USEPA, 2004c). The fraction of organic carbon in the soil was assumed to be 1%. 4.3 Quantification of Exposure For the purpose of quantitative risk assessment, dose is the estimation of exposure to constituents in specific environmental media. This risk assessment considers two types of dose: administered dose and absorbed dose. An administered dose is the amount of constituent (concentration) in material that is ingested, inhaled, or applied to the skin and is available for absorption. Absorbed dose is the amount of constituent actually crossing the absorption barrier (i.e., the amount absorbed). The type of dose estimate used in a risk assessment is dependent on the route of exposure. Typically, ingestion and inhalation pathways are evaluated with the administered dose, and exposure is quantified by multiplying exposure concentrations by an intake rate (i.e., ingestion or inhalation rate, respectively). On the other hand, dermal exposure is evaluated not for intake but for absorption of the constituent. 9 Southeast Regional Climate Center http://www.sercc.com/cgi-bin/sercc/cliMAIN.pl?fl7886
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DRAFT Primary Primary Secondary Sec
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DRAFT Table A-1. Dose and Risk Calc
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DRAFT CSFd RfDd DA event C w DAD LA
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DRAFT CSFd RfDd DA event C w DAD LA
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DRAFT Table A-13. Dose and Risk Cal
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