ENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 1 CONCENTRATION ASSESSMENT Generic exposure equation:Where:C = Concentration of substance in MEDIUM CR = Contact Rate with mediumED = Exposure DurationIntake of MEDIUMBW = Body WeightAT = Averaging Time AT BWED CR Dose C ---ENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 2 CONCENTRATION ASSESSMENT PLANSpecify Data Quality Objectives Decide what to test for Contaminants know to be present  Target Analyte List – Routine Analytical Services24 inorganic chemicals51 volatile organic compounds (plus 10 highest peaks)66 semivolatile organic compounds (plus 20 highest peaks)28 pesticides/arochlors 17 chlorinated dibenzo-p-dioxins/chlorinated dibenzofurans (CDDs/CDFs) Other information needed for modeling Decide where to test Media Locations Decide when to test Season WeatherENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 3 CONCENTRATION MODELINGTypes of fate and transport models Surface water Ground water Air BioaccumulationExample – dust from unpaved roads:whereC(X) = air concentration of dust at distance X from siteM = vehicle miles traveled per yeark = particle size multipliers = silt content of road surfaceSp = mean vehicle speedW = mean vehicle weightw = mean number of wheelsDp = number of days with 0.01 inch precipitation per yeary= dispersion coefficient in the lateral (crosswind) directionz= dispersion coefficient in the vertical direction= mean wind speed-----zy365Dp - 3654w3W30Sp12skM5.9 C(X)5.07.0ENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 4 DATA NEEDED FOR MODELING – CHEMICAL SPECIFIC Inherent chemical characteristics:Property EffectSolubility in water Dissolving vs. floating or sinkingRelative solubility octanol:water (Kow) Partitioning – fat:water, soil:waterHenry’s Law constant Transfer between water and airEnvironmental fate Chemical changes photolysis oxidation reduction hydration hydrolysis Biological changes biotransformation bioaccumulationENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 5 DATA EVALUATION – QUALITATIVEStep 1: Qualitative data analysisA. Is the chemical detected?1. What are detection limits? IDL – Instrument Detection Limit MDL – Method Detection Limit CRQL – Contract Required Quantitation Limit SQL – Sample Quantitation Limit2. If the chemical is detected in any sample, keep it in analysisB. Is the chemical site-related?1. Not if “background” Natural or anthropogenic Must do statistical analysis2. Not if in blanks Types of blanks laboratory – calibration, reagent trip field Chemical is “detected” If concentration is > 5 times blank concentration If concentration is > 10 times blank concentration for methylene chloride, acetone, toluene, 2-butanone, and phthalate estersENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 6 DATA EVALUATION – QUANTITATIVEStep 2: Quantitative Data AnalysisA. Chemicals not detected in all samplesUse substitution for “below QL”ZeroQL/2QL/QLB. Calculate mean and upper bound values1. mean = average2. upper bound = mean + 1.96 × SEMa. SEM = Standard Error of the Meanb. Confidence in mean, not in range of data3. Example: mean = 0.10, 3 samples vs. 15 samples20.00 0.04 0.08 0.12 0.16 0.20 0.240.00 0.04 0.08 0.12 0.16 0.20 0.24mean UL UL mean datamean UL UL mean dataENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 7 C. Data gaps – options collect new data narrow scope of assessment use conservative assumptions use models use surrogate data use professional judgmentENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 8 INTAKE ASSESSMENTExposure  DoseChemical location Process DoseOuter boundary Contact Applied doseCrossing boundary Absorption Absorbed doseInternal organs Distribution Internal doseExposure requires:1. A complete exposure pathway source transport medium point of contact route of intake2. A receptor – WHO? Actual person or population Hypothetical person or population Susceptible subpopulationUncertainty: o Calculate two values: central tendency and high endo Use entire distribution for later Monte Carlo analysisENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 9 INTAKE CALCULATIONSGeneric exposure equation:Where:C = Concentration in mediumCR = Contact Rate with medium BW = Body Weight (kg) ED = Exposure Duration (years)AT = Averaging Time (years)) waterofliter chemical mg (e.g.)day waterof liters (e.g. ATED BWCR C Dose --ENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 10 Body weight (BW) valuesCentral Tendency(traditional) NewAdult 70 kg 71.8 kg (mean)Child 1 to 6 years 15 kg Yearly valueChild 6 to 11 years 30 kg Yearly valueExposure duration (ED) valuesResidential Exposure Duration: Adults 9 years – central tendency 30 years – high end 70 years – maximum Children 6 years (ages 1 to 6: highest soil exposure; ages 7 to 12 highest trespassing)Occupational Exposure Duration Work activities  6.6 years at a single job – central tendency 21.9 years for working lifetime – central tendencyRecreational Exposure Duration same as residential OR site specificENV U6220 THURSDAY, 7/28/05 – EXPOSURE ASSESSMENT PAGE 11 Averaging time (AT) values Noncarcinogenic effects – same as exposure duration Carcinogenic effects – 70 years (25,550 days)Recent EPA discussion: “For less-than-lifetime human exposure scenarios, too, the lifetime average daily exposure or dose has often been used. The use of these lifetime average exposure metrics was adopted with low-dose linear cancer assessments in mind. The lifetime averaging implies that less-than lifetime exposure is associated with a linearly proportional reduction of the lifetime risk, regardless of when exposures occur. Such averaging may be problematic in some situations. This can be illustrated using both the multistage model and the two-stage clonal expansion model that predict thatshort-duration risks are not necessarily proportional to exposure duration andcan depend on the nature of the carcinogen and the timing of exposure (Goddard et al., 1995; Murdoch et al., 1992). These examples indicate some circumstances in which use of a lifetime average daily dose