Evaluation of Mixture Exposures in Human Health Risk Assessments. Ruth Custance, MPH

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1 Evaluation of Mixture Exposures in Human Health Risk Assessments Ruth Custance, MPH March 2016

2 Objectives Objectives Describe each of the major steps of a HHRA Data Evaluation What chemicals and at what levels Where are they, what media? Exposure Assessment Determine potential for human contact with impacted media Toxicity Assessment Potential for health effects how much (dose)? Risk Characterization Combine exposure and toxicity assessments to estimate risk Examples of mixture HHRA

3 Overview What is a Human Health Risk Assessment (HHRA)? Used as a tool to identify potential hazards, determine who is at risk and estimate the probability of adverse health effects Identify individuals contacting chemicals and the potential for adverse health outcomes (e.g., cancer) Intended to be protective of individuals who are at greatest risk; those more sensitive to health effects (e.g., children, the elderly) Results tend to be overly protective for most individuals Not a clinical medical evaluation Used to evaluate the need for remediation/corrective action Use of generic cleanup goals Develop site-specific cleanup goals

4 Four Steps of Risk Assessment Hazard ID Exposure Assessment Toxicity Assessment Risk Characterization Your

5 Risk Characterization Adverse effect / risk depends on toxicity and exposure RISK Your

6 Data Evaluation Initial Step of an HHRA Develop a data set Identify media-specific Chemicals of Potential Concern (COPCs) Data Evaluation Duplicate/split samples Multiple analytical methods

7 Data Evaluation Selection of COPCs Comparison to Screening Levels Frequency of Detection (FOD; 5%) Other criteria Background Evaluation Metals Carcinogenic PAHs (cpahs)

8 Data Evaluation Background Evaluation of Metals Determine if the data demonstrates more than 1 population; the lower typically represents local background conditions and the other is considered impacted by site-related activities Use a weight of evidence approach where indicators of background consider: the degree to which the Site data are fit by a normal, lognormal, or other distribution (Cal-EPA 1997 states that ambient metals data follow a normal or lognormal distribution); 2) a graphical assessment (probability, or quantile-quantile plots, against the normal, lognormal, or other distribution) to identify breaks or nonlinearity indicative of more than a single population; and 3) the skewness of the data as indicated by the coefficient of variation (CV = standard deviation average)

9 Data Evaluation

10 Data Evaluation Evaluating Carcinogenic PAHs (cpahs) Current Scheme Benzo(a)pyrene equivalent concentration derived using toxicity equivalency factor (TEF) approach. TEFs based on shared characteristics of the cpahs Ranking by using BaP as the reference chemical TEFs were multiplied by the individual cpah concentrations. Adjusted concentrations were then summed to yield a total BaP-equivalent concentration. BaP-equivalent compared to southern CA background of 0.9 mg/kg

11 From EPA 2010 Proposed Scheme

12 Data Evaluation Evaluating Dioxin and Dioxin-like PCB Congeners Toxicity equivalency factor (TEF) approach. TEFs based on shared characteristics Ranking by using 2,3,7,8-TCDD as the reference chemical

13 Exposure Assessment Estimate the magnitude, frequency, duration, and routes of exposure Identify receptors potentially exposed to COPCs in environmental media, the exposure pathways and route of potential intake (conceptual site model; CSM); Estimate COPC concentrations to which the receptors are potentially exposed (exposure point concentrations, EPCs); Direct use of monitoring data Estimating EPCs using Fate and Transport models, which quantify relationship between COPC concentration in impacted medium (e.g., GW) and the concentration in the exposure medium (e.g., indoor or outdoor air); Estimate COPC intake

14 Exposure Assessment Conceptual Site Model (CSM) Identify potential chemical sources USTs; ASTs; chemical storage; offsite release; former agricultural area; transformers, former drycleaner; etc. Release mechanism accidental spills/leakage Impacted exposure media soil, groundwater Transport mechanism Volatilization; fugitive dust emissions; leaching; direct contact Exposure routes Incidental ingestion, dermal contact; indoor and outdoor inhalation Receptors of concern Depends on current/future land use: residential, commercial, recreational

15 Conceptual Site Model** Exposure Assessment

16 Exposure Assessment Exposure Point Concentrations EPCs are the concentrations of chemicals in environmental media to which receptors may be exposed through defined exposure pathways considered complete. Identify impacted media Shallow soil (0 to 10 ft bgs); soil gas; sub-slab; groundwater Use of the maximum versus the 95% Upper confidence limit of the average concentration (95UCL) Site-wide risk assessment (residential vs commercial) Point-by-point risk assessment Derivation of 95UCLs using ProUCL

17 Exposure Assessment Fate and Transport Modeling Quantitative analysis of how chemicals move through the environment and how they are transformed by processes such as chemical reaction and biological degradation Transport of particulate-phase COPCs (metals; SVOCs) from soil matrix to outdoor air; Transport of vapor-phase COPCs (VOCs) from soil matrix to outdoor air; Transport of vapor-phase COPCs (VOCs) from groundwater to outdoor air; and Transport of vapor-phase COPCs (VOCs) from the subsurface to indoor air (vapor intrusion pathway).

18 Exposure Assessment Fate and Transport Modeling Soil to Outdoor Air: Particulate emission factor (PEF) (Q/Cres CF) PEFres = 3 U M [0.036 (1- G) Fx ] U T Where: PEF res = particulate emission factor, cubic meters per kilogram (m 3 /kg); Q/C res = inverse of the ratio of the geometric mean air concentration to the emission flux at center of the source (g/m 2 -s per kg/m 3 ); CF = units conversion factor (3,600 s/hr); = empirical constant (g/m 2 -hr); G = fraction of vegetative or other cover (0.5 unitless; USEPA, 2002); U M = mean annual wind speed (m/sec; NCDC, 2010); U T = equivalent threshold value of wind speed at 7 meters above ground surface (11.32 m/sec; USEPA, 2002); and F x = function dependent on U M /U T (0.194 unitless; USEPA, 2002).

19 Exposure Assessment Fate and Transport Modeling Soil to Outdoor Air: Volatilization factors (VFs) VF soil = Q/C m cm 2 ( 2 Pb D ) ( 3.14 D T) A A 1/2 Where: VF soil = COPC-specific volatilization factor (m 3 /kg); Q/C = inverse of mean concentration at center of source (g/m 2 -s per kg/m 3 ); D A T = COPC-specific apparent diffusivity (cm 2 /s); = exposure interval (seconds; and Pb = soil bulk density (g/cm 3 ).

20 Exposure Assessment Indoor Air Garage Air Outdoor Air Indoor Sources Sub-Slab Soil Vapor AF attenuation factor

21 Exposure Assessment Fate and Transport Modeling Vapor Intrusion Pathway Soil Gas; Groundwater; Sub-slab Soil Gas Use of default (Cal-EPA VIG, 2011) versus site-specific attenuation factors

22 Exposure Assessment

23 Exposure Assessment

24 Exposure Assessment End product of the Exposure Assessment COPC Intake = An integration of the exposure parameters for the receptors of concern with the EPCs for the media of concern Average daily dose (ADD) for noncarcinogens Lifetime average daily dose (LADD) for carcinogens Generic Intake equation: EPC CR EF ED Intake or Dose = BW AT Where: EPC = exposure point concentration (e.g., mg of chemical per kilogram of soil); CR EF ED = contact rate with medium (e.g., mg of soil/day); = exposure frequency (days/year); = exposure duration (years); BW = body weight (kg); AT = averaging time (days): cancer effects: 70 yrs x 365 days; noncancer effects: ED x 365 days. Intake equations for specific exposure routes

25 Exposure Assessment Exposure Parameters HERO Note 1; Cal-EPA DTSC, September 2014 USEPA* Regional Screening Level (RSL); November 2015

26 Exposure Assessment Other Sources of Exposure Parameters Standard Default Exposure Factors; USEPA, 1991 Exposure Factors Handbook; USEPA, 2011 Child-Specific Exposure Factors Handbook; USEPA, 2008 Supplemental Guidance for Dermal Risk Assessment; USEPA, 2004 Risk Assessment Guidance for Superfund (RAGS). Volume I: Human Health Evaluation Manual, Part A. USEPA, 1989 Preliminary Endangerment Assessment (PEA) Guidance Manual. Cal-EPA, 2013

27 Toxicity Assessment Characterizes the relationship between the magnitude of exposure to a COPC and the nature and magnitude of adverse health effects that may result from exposure (dose-response). Cancer toxicity criteria: Carcinogens known to cause cancer Oral cancer slope factors (CSFs) Inhalation unit risk factors (URFs or IURs) Noncancer toxicity criteria: Noncarcinogens that may have adverse effects on reproductive, developmental, other target organs oral reference doses (RfDs) inhalation reference concentrations (RfCs) or reference exposure levels (RELs)

28 Toxicity Assessment Toxicity criteria are selected from the following sources, in order of preference and based on availability: Cal-EPA Office of Environmental Health Hazard Assessment (OEHHA) Toxicity Criteria Database, online (Cal-EPA, 2016); USEPA Integrated Risk Information System (IRIS) (USEPA, 2016); and USEPA Regional Screening Levels (RSL) for Chemical Contaminants at Superfund Sites (USEPA, 2015). For sites in California, final selection is based on recommendations presented in Cal-EPA DTSC s HHRA Note 3 (Cal-EPA, 2016).

29 Toxicity Assessment Route-to-route extrapolation Toxicity criteria based only on oral and inhalation routes of exposure Oral toxicity criteria used to evaluate dermal exposures Sometime route-to-route between ingestion and inhalation Surrogate chemical Toxicity criteria for a structurally similar compound is assigned to a COPC lacking toxicity criteria

30 Toxicity Assessment Lead evaluated differently No reference dose available for lead (RfD assumes a threshold; no adverse effects if concentration below RfD) Evidence suggests that adverse health effects occur even at very low exposures to lead (e.g., neurological effects in children) Exposure/toxicity evaluated by comparison to blood lead (PbB) levels. Acceptable soil level based on 99% of a population having PbB levels <1 or 10 ug/dl For sites in California Residential soil CHHSL = 80 mg/kg; Commercial soil CHHSL = 320 mg/kg Cal-EPA LeadSpread Calculates cleanup levels for a 2-3 year old child Adult module being re-evaluated

31 Risk Characterization Integrates exposure and toxicity assessments to estimate potential cancer risks and noncancer hazards that are then compared to acceptable standards Risk Management Criteria (Target risk levels) Various demarcations of acceptable risk have been established. The National Oil and Hazardous Substances Pollution Contingency Plan (NCP; 40 CFR 300) = an acceptable risk range of to for carcinogens and a target noncancer hazard of 1 for noncarcinogens. DTSC considers the cancer risk level as the generally accepted point of departure for unrestricted land use (residential). A risk level (the mid-point of the risk management range) is commonly used for managing commercial/industrial land use sites in California.

32 Risk Characterization Site-Wide Risk Assessment Quantify Cancer Risks and Noncancer Hazards Individual COPC: Intake or Dose = Cancer Risk = LADD EPC CR EF ED BW AT ( CSF or URF) Hazard Quotient = ADD ( RfD or REL) Multiple COPCs and multiple pathways: Cancer Risk total n = i= 1 Noncancer Hazard Index ( CR + CR + CR ) total i,ingestion n = i= 1 i,dermal i,inhalation ( HQ + HQ + HQ ) i,ingestion i,dermal i,inhalation

33 Risk Characterization Point-by-Point Risk Assessment Derive Risk-Based Concentrations (RBCs): RBC Soil-C = [ CSF ( IF + IF )] + ( URF ECF CF ) oral oral dermal TR inh.s 1 RBC Soil-NC = IF RfD oral oral THQ IF + RfD dermal oral ECF + RfC inh,s Cumulative Risk at a given sample location: Cancer Risk Hazard Index n C = i= 1 RBC Si total Soil-C, i n C = i= 1 RBC TR Si total Soil-NC, i THI

34 Risk Characterization Point-by-Point Risk Assessment continued Results for each sample depth Risk Exceedance Figures Lead and Arsenic Identify Risk Drivers COPCs with Cancer Risk >1E-6 COPCs with Noncancer HQs >1

35 From EPA 2011 Risk Characterization

36 Risk Characterization of Mixtures - Component vs. Whole Mixture Approaches Component-based methods (Practical) simple models describe complex biological processesbased method Need good toxicity and exposure data on individual components Typically additivity is assumed Whole mixture based assessments (Preferred??) Need good toxicity and exposure data on the whole mixtures Need to evaluate sufficient similarity Can also assess fractions of the whole mixture Not many assessments done to date Adapted from EPA, 2011

37 Risk Characterization of Mixtures Which mixture to test? Actual environmental mixture Similar mixture Lab mixture Key chemicals Complex fractions of whole mixture Don t forget Fate & Transport Model needs

38 Risk Characterization of Mixtures - Component vs. Whole Mixture Examples Component Carcinogenic PAHS Dioxins Pesticides (Office of Pesticide Programs) Whole Mixture TPH (Fractions) Aroclors

39 TPH Risk Assessment TPH compounds include a wide range of chemicals that are found in crude oils, petroleum products, and other petroleum-related materials. Chemical properties and environmental behavior vary widely among the many hundreds of compounds present in these mixtures. TPH mixtures pose a challenge in risk assessment due to difficulty in predicting toxicity as well as environmental fate and transport

40 TPH Risk Assessment Traditional approaches to risk assessment evaluate: Indicator compounds (e.g., benzene) inadequate coverage Quantify the whole TPH mixture not relevant to many sites, as composition is highly variable Massachusetts Dept of Environmental Protection (2002, 2003) VPH/EPH approach VPH & EPH analytical methods differentiate & quantify aliphatic & aromatic fractions at a site Toxicity values assigned to each fraction, based on surrogate chemicals Assesses mixture risk, accounts for variations in mixture composition

41 From EPA, 2009 TPH Risk Assessment

42 TPH Risk Assessment Often assume 50:50 mix if no sitespecific fraction data TPH-G = TPH-D = TPH-Mo = 50% of TPH Aliphatic: C5-C8 50% of TPH Aliphatic: C9-C18 50% of TPH Aliphatic: C18+ 50% of TPH Aromatic: C9-C16 50% of TPH Aromatic: C9-C16 50% of TPH Aromatic: C17+

43 Comparison of Site-Specific TPH Risks Compared indicator chemical risks/hazards to TPH hazards Did the Risk Management Decision Change? Decision Criteria assuming residential land-use Cancer Risk of 1 x 10-6 Hazard Index of 1

44 Comparison of Site-Specific TPH Risks in Soil Case #1 Constituent of Concern Units EPC EPC Basis SSCGnc Onsite Resident SSCGc Noncancer Hazard Cancer Risk Benzene µg/kg UCL 6.7E E+02 5E-03 2E-06 Benzo (a) Pyrene mg/kg UCL E E-07 Naphthalene mg/kg UCL 1.5E E+00 4E-02 2E-06 TPH as Diesel mg/kg UCL 1.3E E Case #2 Constituent of Concern Units EPC EPC Basis SSCGnc Onsite Resident SSCGc Noncancer Hazard Cancer Risk Benzene µg/kg UCL 6.7E E+02 5E-03 2E-06 Benzo (a) Pyrene mg/kg UCL E E-06 Naphthalene mg/kg UCL 1.5E E+00 6E-02 2E-06 TPH as Diesel mg/kg UCL 1.3E E+00 --

45 Comparison of Site-Specific TPH Risks in Soil Case #3 Constituent of Concern Units EPC EPC Basis SSCGnc Onsite Resident SSCGc Noncancer Hazard Cancer Risk Benzene µg/kg UCL 6.7E E+02 4E-03 1E-06 Benzo (a) Pyrene mg/kg UCL E E-06 Naphthalene mg/kg UCL 1.5E E+00 6E-02 2E-06 TPH as Diesel mg/kg UCL 1.3E E Case #4 Constituent of Concern Units EPC EPC Basis SSCGnc Onsite Resident SSCGc Noncancer Hazard Cancer Risk Benzene µg/kg UCL 6.7E E+02 2E-04 5E-08 Benzo (a) Pyrene mg/kg UCL E E-07 Naphthalene mg/kg UCL 1.5E E+00 2E-02 6E-07 TPH as Diesel mg/kg UCL 1.3E E+00 --

46 Comparison of Site-Specific TPH Risks in Sub-Slab Soil Gas TPH - aliphatic: C5-C8 5.2E-03 TPH - aliphatic: C9-C18 1.3E-01 TPH - aromatic: C9-C16 2.9E+00 1,2,4-Trimethylbenzene 1.4E-01 1,3,5-Trimethylbenzene 1.1E-02 2-Butanone (MEK) 4.1E-05 2-Hexanone 6.3E-04 4-Ethyltoluene 3.1E-03 4-Methyl-2-pentanone (MIBK) 8.1E-06 Acetone 3.1E-05 Benzene 1.2E-02 Carbon disulfide 1.4E-05 Chloroform 2.8E-04 Chloromethane 1.1E-04 Ethylbenzene 1.0E-04 Napthalene 2.6E-02 Toluene 7.6E-04 Trichloroethene 2.6E-02 Xylene, o- 1.8E-03 Xylenes, m,p- 4.3E-03 Cum ulative Risk and Hazard 3E+00

47 Comparison of Site-Specific TPH Risks For soil, conclusions are the same in 3 out of 4 cases In one case where the indicator chemicals did not indicate risk/hazard the TPH hazard was marginally elevated (2 versus Target HI of 1) This site was dominated by Diesel TPH other sites may differ For soil gas VOCs under predicted estimated hazard

48 Uncertainties in Assessing Chemical Mixtures Few Mixtures/Chemical Classes Currently Represented Lack of Chemical/Physical Properties for EF&T Modeling Site-specific conditions can change mixtures, e.g. TPH weathering is the toxicity data really representative of your mixture?

49 Questions?

Risk Assessment Report for AGSS-ICS

Risk Assessment Report for AGSS-ICS 1. INTRODUCTION This Risk Assessment evaluated the human health risks from exposure during and after application of AGSS-ICS. This information will determine whether AGSS-ICS used to treat soil will present