1. 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

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

7. RISK = HAZARD X EXPOSURE

8. 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

10. 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

11. 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

12. Overview: Dose Assessment of Contaminated Groundwater

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

14. Definitions
Exposure: physical contact
Dose: intake, absorbed

15. 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?

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

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

18. 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

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

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

21. 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

22. 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

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

24. 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)

25. 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.

26. 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!

27. 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)

28. 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

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

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

31. 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.

32. 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

33. 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)

34. 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)

35. 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

36. 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

37. 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: l/cm2-hr

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

39. 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

40. Example Bathroom Inhalation Dose
Cb= (240 ug/min)(10 min)[1-exp(( 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

41. Example Sum of Shower & Bathroom Inhalation
Typical Daily Inhalation Dose From Shower & Bathroom = = 78 ug
Average Daily Dose From Shower & Bathroom = = 67 ug
Average Yearly Dose = 17, = 24,500 ug
Total Cumulative Dose = 88, , 000= 123,000 ug

42. 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)

43. 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

44. 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

45. Example:
Summary
Inhalation Dermal Ingestion Inhalation Inhalation/ Dermal/
(ug) (ug) (ug) / Dermal Ingestion Ingestion
Daily
Avg.
Yearly
Total
24, , ,
123, , ,

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

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

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

49. 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.

50. 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