TOXICOLOGY AND RISK ASSESSMENT ENVIRONMENTAL RISK ASSESSMENT Session 2B TOXICOLOGY AND RISK ASSESSMENT Mark G. Robson, Ph.D., M.P.H. UMDNJ - School of Public Health

RISK ASSESSMENT Hazard ID Dose Assessment Health Status Exposure Assessment Exposure Measurement Control Measures Risk Characterization Health Surveillance Medical Survey Bio Monitoring Records

RISK = HAZARD X EXPOSURE

Risk Assessment Process Hazard Identification Toxicity Assessment – Dose/Response Exposure Assessment Risk Characterization Some people add a 5th and 6TH step Risk Management Risk Communication

Absorption & Distribution External Exposure to Xenobiotic Internal Exposure Free (X) or Bound (X-P) Xenobiotic in Blood Absorption across Membranes into Blood Storage Sites Target Sites Biotransformation Excretion

Lifetime Risk Average lifetime risk of work-related death in the private sector assuming 45 years employment in a particular occupation. Employment Risk Mining 19/1000 Construction 10/1000 Transportation 8/1000 Agriculture 7/1000 Average 2.9/1000 Manufacturing 2/1000 Services Wholesale/Retail 1/1000 Finance/Insurance

Overview: Dose Assessment of Contaminated Groundwater

Exposure Assessment/ Dose Calculation Procedure Identify Hazard - Chemical - Metal Determine likely exposure pathway Calculate concentration Calculate dose Determine applicable time average

Definitions Exposure: physical contact Dose: intake, absorbed

Hazard Identification What is the chemical of concern? What’s been spilled, leaked, emitted, etc. Does the chemical undergo transformation? 1) Biotic – Microorganisms 2) Abiotic – Chemistry If transformed, which product is of most concern? If mixture, which chemical is the most toxic?

Exposure Media Air: Gas/Vapor, Liquid Aerosol, Particulates Water Soil Food

Routes of Exposure Ingestion Inhalation Dermal Water Food Volatilization of chemical from water Water aerosols (<5um) Dermal Water: Shower/Bath

Factors Affecting Ingestion Quantity of Water Ingested Climate Physiological Factors: age, weight, gender Level of Physical Exertion: resting, exercising, working Ability of the body to absorb contaminant Chemical Target organ Concentration of chemical in water

Factors Affecting Inhalation Concentration in Air Physiological Factors Breathing rate Age, weight, gender Exposure Duration (hours/day) Exposure Frequency (day/week)

Factors Affecting Indoor Inhalation Ventilation Rate Shower Bathroom House – Geographic Location Time per Day Spent in House Number of People in House – Water Use

Factors Affecting Dermal Absorption Permeability of Skin to Chemical in Question Unique Property of Chemical Lipophilicity Usually Based on Animal Measurements Concentration of Chemical Air/Water Duration of Contact

Factors Affecting Dermal Absorption Exposure Media Air/Water/Soil Exposed Skin Surface Area Physiological: Age, weight, gender Activity during contact Water – Shower/Bath/Washing Hands Soil – Gardening/Playing

Time Averaging Daily Yearly Days during which had exposure “typical, daily” Average daily during the year Yearly typically 350 days per year

Time Averaging Lifetime: 70 - 75 years standard U.S. EPA Cumulative total dose over entire exposure period Other based upon exposure scenario (e.g. weekly)

General Modeling Principles A model is only a mathematical representation of a real world phenomena A model cannot be more accurate than our understanding of this phenomena All models are WRONG. Some are useful We can never understand physical processes to a sufficient level of detail to model with 100% accuracy. Sometimes an order of magnitude may be the best we can do.

General Modeling Principles Garbage IN. Garbage OUT. Model output cannot be more precise or accurate than the input data. Variability vs. Uncertainty A model is a Black Box Most people will never understand your model equations Make people understand and agree to your assumptions and input data. They will then have to believe your results!

Generic Chemical Dose Equation Intake = C x CR x (EF x ED) Where: Intake – quantity entering the body (ug) C – chemical concentration (ug/m3) CR – contact rate (m3/day) EF – exposure frequency (days/year) ED – Exposure duration (years) Dose = (Intake)(Fraction Absorbed)

Household Exposure to VOC Contaminated Water Inhalation – transfer chemical to air Showering Post Shower Bathroom Time Remainder of House – Misc. Water Use Dermal Shower/Bath/ Washing Cleaning House Ingestion Tap Water

Household Exposure to VOC Contaminated Water QUESTION?? WHAT’S TOTAL DOSE AND WHICH PATHWAY IS MOST IMPORTANT?

VOLATILIZATION OF VOC IN SHOWER Bathroom Remainder of House Conceptualized House Compartments

Equations to Calculate Shower/Bath Air Concentration Assumptions: Contribution from remainder of house small. At time zero shower/bathroom concentration zero. After shower, all VOC in bathroom originated from shower water use.

Shower Source Term Sw = (Fs x C x TE) Sw – shower source term (ug/min) Fs – shower water flow rate (l/min) C – VOC concentration in water (ug/l) TE – transfer efficiency (water-to-air) determined experimentally, or related to experimentally determined values

Shower Air Concentration Cs = (Sw/(Vs*Es)) * [1 + (1/(Es*ts))e-Es*ts – (1/(Es*ts))] CS – average shower air concentration (ug/l) VS – shower volume (l) Es – shower air exchange rate (min-1) Sw – shower source term (ug/min) ts – shower time (min)

Bath Air Concentration Cb = [(Sw*ts)/ (tb*Vb*Eb)] * (1-e-Eb*tb) Cb – average bathroom air concentration (ug/l) Vb – bathroom volume (l) Eb – bathroom air exchange rate (min-1) Sw – shower source term (ug/min) ts – shower time (min) tb – bathroom time (min)

Inhalation Absorbed Dose Inhalation Dose: BR[(Cs)(ts) + (Cb)(tb)]Frac BR – breathing rate (m3/min) Cs – shower air concentration (ug/m3) Ts – shower time (min) Cb – bath air concentration (ug/m3) Tb – bath time (min) Frac – inhalation fraction absorbed

Example: Scenario Parameters Scenario – Shower/Bathroom Inhalation, Dermal, and Ingestion Only • TCE in Water • 50 ug/l • 40 year old male exposed for 5 years

Example: Physiological Parameters Breathing Rate 15.8 l/min Inhalation absorption fraction: 0.7 Ingestion absorption fraction: 0.1 Skin Area 18,000 cm2 – 40% exposed Skin permeability constant: 0.002 l/cm2-hr

Example Input Data Shower time 10 mins Shower frequency 6 days/week Bathroom time 10 mins Water flow rate 8 l/min Daily tap water ingestion 2 liters Shower volume 2000 liters Bathroom volume 10,000 liters Shower air exchange rate 0.05 min-1 Bathroom air exchange rate 0.033 min-1 Transfer efficiency 0.6

Example Shower Inhalation Dose Sw = (8 l/min) x (50 ug/l) x (0.6) = 240 ug/min Cs = (240 ug/min) x [1 + 1/(0.05 min-1 x 10 mins)exp(-(0.05 min-1 x 10 mins)) – 1/(0.05 min-1 x 10 mins)]/ [(2000 l) x (0.05 min-1)] = 0.51 ug/l Typical Daily Inhalation Dose from Showering =(0.51 ug/l)(10 mins)(15.8 l/min)(0.7) = 56 ug Average Daily Dose From Showering =56 ug (6/7) = 48 ug Average Yearly Dose = 48 ug (365) = 17,600 ug Total Cumulative Dose = 17,600 ug (5) = 88,000 ug

Example Bathroom Inhalation Dose Cb= (240 ug/min)(10 min)[1-exp((-0.033 min-1)(10 mins))] (10 mins)(10,000 l)(0.033 min –1) = 0.20 ug/l Typical Daily Inhalation Dose from Bathroom =(0.2 ug/l)(10 mins)(15.8 l/min)(0.7) = 22 ug Average Daily Bathroom Dose = 22 ug (6/7)= 19 ug Average Yearly Dose = 19 ug (365)= 6900 ug Total Cumulative Dose = 6900 ug (5)= 35,000 ug

Example Sum of Shower & Bathroom Inhalation Typical Daily Inhalation Dose From Shower & Bathroom =56 + 22= 78 ug Average Daily Dose From Shower & Bathroom =48 + 19= 67 ug Average Yearly Dose = 17,600 + 6900= 24,500 ug Total Cumulative Dose = 88,000 + 35, 000= 123,000 ug

Example Shower Dermal Dose Equation Shower Dermal Dose: (C)(kp)(Sf)(Sa)(ts)(1-TE) kp – skin permeability constant (1/cm2-hr) Sf – skin fraction exposed Sa – skin surface area (cm2) Ts – shower time (hr)

Example Shower Dermal Dose Typical Daily Dermal Absorption from Shower = (50 ug/l)(0.002 l/cm2-hr)* (0.4)(0.167 hrs)(1-0.6)(18,000 cm2)= 48 ug Average Daily Dose from Shower = 48 ug (6/7)= 41 ug Average Yearly Dose = 41 ug (365)= 14,965 ug Total Cumulative Dose = 14,965 ug (5)= 74,825 ug

Example Ingestion Dose Typical Daily Ingestion = (2 l)(50 ug/l)(0.1) = 10 ug/day Average Daily Ingested Dose (assume drink water 7 days/week) = 10 ug/day Average Yearly Dose = 10 ug (365)= 3650 ug Total Cumulative Dose = 3650 ug (5)= 18,250 ug

Example: Summary Inhalation Dermal Ingestion Inhalation Inhalation/ Dermal/ (ug) (ug) (ug) / Dermal Ingestion Ingestion Daily Avg. Yearly Total 78 48 10 1.6 7.8 4.8 67 48 10 1.6 6.7 4.1 24,500 14,365 3,650 1.6 6.7 4.1 123,000 74,825 18,250 1.6 6.7 4.1

Dose Pathway Inhalation Dermal Ingestion Dose (ug) 100000 Daily 10000 Avg. Daily Yearly Total Dose (ug)

Time Average Daily Avg. Daily Yearly Total 100000 10000 1000 Inhalation Dermal Ingestion

Summary Inhalation dose is almost an order of magnitude greater than ingested dose! Dermal dose and inhalation dose are of almost equal value

Summary Intake/Absorbed dose due to contaminants in ground water more than just inhalation. Inhalation and dermal dose pathways are more important (for cited example) than ingestion.

Summary Distribution of bottled water to exposed population may or may not substantially reduce intake/absorbed dose of contaminants of groundwater Remediation or a new source of water may be required