ENVH 8001ENVIRONMENTAL HEALTH RISK ASSESSMENT

Lecture 3:

Risk Assessment:

Exposure Assessment (EA)Winter 2011

Lecture 3: Objectives

1. List and describe six exposure pathways

2. List and describe three exposure routes

3. Define and calculate Estimated Daily Intake (EDI) and Estimated Dose (ED)

4. Define Tolerable Daily Intake (TDI)

5. Describe “Uncertainly Factor”

6. List and describe the steps used in EAReference: Investigating Human Exposure to Contaminants in the Environment: A Handbook for Exposure Calculations, DRAFT document, Health Canada

Units of Measurement for Contaminants in the Environment

In water or liquids: mg/L or μg/L In soil and other solids: mg/kg In air: mg/m3 or μg/m3

Occasionally units for chemical concentrations in water, soil and air are expressed in ppm, ppb, ppt or ppq

What is an Exposure Pathway?

Exposure refers to any contact between a substance and an individual or group. Can occur when an individual or group has touched, breathed fumes from, or swallowed, material or liquid from a contaminated source.

An exposure pathway describes how the contaminant travels through the environment to humans or other living organisms.

Exposure Pathways: WATER

Groundwater (aquifers, wells)

- Drinking water from wells bathing, showering

- Industrial, agricultural or recreational use

- Recreational and other use of natural springs, sink holes

Surface water (lakes, rivers)- Drinking, bathing, showering,

- Recreational use

- Industrial or agricultural use

Exposure Pathways: SOIL

SoilBare gound: (exposure of

workers to soil, swallowing soil, or contact of children’s skin to soil)

Contaminated soil blown as dust in air and particles deposited on other surfaces (e.g. Food)

Soil below the surface

Exposure Pathways: AIR

AirContaminated gases from

industrial or other processes (eg exhaust)

Evaporation of gases from contaminated soils or water bodies

Contaminants adsorbed onto dust particles in air

Contaminated soil which may be blown in the air to create contaminated dust

Exposure Pathways: FOOD

FoodConsumption of foods

produced with contaminated ground water, surface water, air and soil

Consumption of foods contaminated through the food chain (e.g. fish caught from contaminated rivers)

Exposure Pathways: SEDIMENTS

Sediments from

Contaminated river and lake bottoms.

Contaminated organisms living in river, lake and pond sediments.

Sediments stirred up and mixed back into the water by shipping and dredging activities.

Exposure Pathways: CONSUMER PRODUCTS

Cleaning products used in the home.

Pesticides and herbicides used in and around the home.

Exposure from sediments and consumer products will not be covered in detail

EXPOSURE ROUTES

1. Ingestion: Swallowing food, water, soil. The throat, stomach and intestines can absorb certain ingested materials rapidly.

2. Inhalation:Breathing in gases or vapour, or airborne particles. Lungs absorb gases and vapours quickly.

3. Skin Contact: some contaminants in water, air and soil can be absorbed through skin.

Pathways and Routes of Exposure

TOTAL HUMAN EXPOSURE = Σ (All exposure pathways and all exposure routes)

Exposure Routes

Inhalation Skin (dermal) Contact

Ingestion

Exposure Pathways

Air Water Soil

Soil Soil Water

Consumer Products

Air Food

Consumer Products

Consumer Products

Sediments Sediments

Dose-Response Relationship

The relationship between the amount of a contaminant that is absorbed (dose) and the potential or actual health effect (response).

Usually determined in laboratory animals; epidemiological data is used to a lesser extent.

Threshold concentration is where no adverse health effects can be observed at concentrations below a certain level (non-carcinogens).

Carcinogens have no threshold concentration.

Estimated Daily Intake (EDI)

We are all exposed to low levels of contamination via air, food, soil and water.

EDI = total exposure from all known or suspected pathways (air, water, soil, food) via all known or suspected routes of exposure (inhalation, ingestion, dermal absorption) for an average person.

Estimated Daily Intake (EDI)

EDI = EDa + EDw + EDs + EDf + EDws + EDss

EDa = Amt of contaminant inhaled through air

EDw = Amt of contaminant taken in by drinking water

EDs = Amt of contaminant taken in by eating soil

EDf = Amt of contaminant taken in with food

EDws = Amt of contaminant absorbed through skin contact with water

EDss = Amt of contaminant absorbed through skin contact with the soil

Estimated DoseAn estimation of amt of contaminant taken in through exposure pathways, and routes:

ED = C x CR X EF

BW

ED = Estimated Dose (mg/kg/day)

C = [ ] of the contaminant in exposure pathway considered (e.g. air, soil, food, water)

CR = Contact Rate per day e.g. For food is in g/day

EF= Exposure Factor = how often exposure occurs/yr and for how many years. Important for occupational exposures, exposures associated with seasonal activities.

BW = Average body weight (kg)

Tolerable Daily Intake (TDI) TDI = Estimate of the quantity of a non-

cancer causing chemical that humans can consume every day for their whole life without threatening their health. Usually expressed as mg/kg/day. Aka ADI (acceptable daily intake).

TDIs are used by gov’t to establish guidelines to protect human health from potential health effects of exposure to environmental contaminants. Reviewed, revised periodically.

Tolerable Daily Intake (TDI), cont

TDIs for humans are based on animal studies, where NOAELs ([ ] of chemical that does not lead to any adverse health effect in animals) or LOAELs (lowest [ ] of contaminant at which adverse health effects are observed) are observed. These levels are divided by an uncertainty factor (UF) to calculate TDI.

TDI = NOAEL (LOAEL)

UF

Uncertainty Factor (UF)

UF reflects the uncertainty associated with the variety of scientific data used to estimate TDI.

UF of 10 is used for TDIs based on experimental

studies of prolonged exposure of healthy average humans (reflects sensitivity differences eg health status, age). If the TDI is not based on studies of prolonged human exposure, the basic UF of 10 is multiplied by another 10 for each of the following that applies:

Uncertainty Factor (UF), cont

For studies of long term animal exposure is used (accounts for uncertainty involved in applying animal data to human data)

When TDIs are based on LOAEL and not NOAEL (accounts for uncertainty in calculating NOAELS from LOAELS)

When TDIs are based on scientific studies which have not observed long term exposures of the animals to the contaminants (accounts for uncertainty associated in using less than chronic NOAELs to calculate chronic NOAELS)

Risk Specific Dose (RsD)

RsD ≈ TDI (but used for carcinogens). There may be no level of exposure to these contaminants that does not pose a risk to health. However, eliminating exposure may be impossible, especially for naturally occurring carcinogens, eg radon. Hence must reduce exposure to as low a level as possible, recognizing that zero exposure is impossible. Must decide how large a risk of cancer can be accepted to set acceptable intake levels, eg 1 in a million (1 x 10-6).

Risk Specific Dose (RsD), cont RsD = R

SF

Where R = acceptable level of risk, SF = Slope Factor (from IRIS database).Example: Calculate RsD for a contaminant known to cause cancer. The SF is 4.3 x 10-3 (mg/kg/day) and R is one extra cancer death per year per one million people exposed (10-6 )

RsD = 1 x 10-6

4.3 x 10-3 (mg/kg/day)

= 2.3 x 10-4 (mg/kg/day)

STEPS FOR ESTIMATING EXPOSURE TO ENVIRONMETNAL CONTAMINANTS

1. Identify Contaminant of Concern

2. Identify all pathways and routes of exposure for that contaminant

3. Obtain [ ] of the contaminant in each pathway

4. Estimate estimated dose (ED) of the contaminant for each pathway and sum to calculate EDI

5. Compare the calculated EDI to the available TDI (non-carcinogen) or RsD (carcinogen)

6. Decision: Is EDI for that contaminant a concern?

Exposure Factors (EF)Estimation of an average dose over the exposure period.

Calculated by multiplying the number of days in the year on which exposure occurs by the number of years that this pattern has been repeating itself. Then divide this number by the time period over which the dose is to be averaged.

E.g. If a child comes into contact with contaminated soil 3 days/week over a four year period, the EF is:

EF = (3 days/week) x (52 weeks/year) x (4 years) (4 years) x (365 days/year)

EF = 0.43 (unitless)

In this example, the dose resulting from one day on which the child was exposed would be multiplied by 0.43 to give the average daily dose over the 4 year period

Estimated Dose: Water Ingestion

EDw = C x IR x EF where,

BW

EDw = Estimated Dose from drinking water (mg/kg/day)

C = [ ] of contaminant in water (mg/L )

IR = Ingestion rate: amt of H2O a person drinks/day (L/ day)

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.

Estimating Water Ingestion Exposures

Calculate human exposure to contaminants in the drinking water at work. The water is contaminated with 367 mg/L methyl chloride. To calculate an adult exposure dose over a lifetime, assume BW = 70 kg (table 2) and a 30 year career, with 5 working days per week, and 50 work weeks per year. Assume IR = 1.5 L/day (table 1)

EF = 30 work years x 50 work weeks/yr x 5 work days/wk

70 years x 365 days/yr

= 0.29

Hence

EDw = C x IR x EF,

BW

= 367 mg/L x 1.5 L/day x 0.29

70 kg

= 2.28 mg/kg/day = lifetime exposure to methyl chloride

Estimated Dose: Inhalation

EDa = C x IR x EF where,

BW

EDa = Estimated dose through inhalation (mg/kg/day)

C = [ ] of contaminant in air (mg/m3 )

IR = Inhalation rate: Amt a person breathes/day (m3/ day )

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.

Estimating Exposures from Air Pollution

Estimate the exposure for an 11, almost 12, yr old child who has been exposed for 2 hrs per day every day since birth to lead in outdoor air at a [ ] of 8 x10-6 mg/m3. Exposure ended at age 12 when the family moved to another area. Calculate exposure periods 0 - < 0.5 yrs. 0.5 - < 5years and 5 - <12 years. In this case, the inhalation rate is a fraction of the total amount of air breathed in a day.

It is: 2 hrs/day x total daily amt of air inhaled

24 hrs in a day

ED Calculation for Air, cont

The total amount of air inhaled changes as a child grows (See Table for values at each stage of life). Multiplying each of these values by 2/24 = 0.0833 gives an IR of 0.166 m3/day, 0.415 m3/day and 0.996 m3/day for each of the 3 age periods.

Exposure Factor 0 - < 0.5 yrs = 183 days of exposure in first 6 months/4380 days in

lifetime (12 years) = 0.042 0.5 - < 5years = 1642 days days of exposure second period/4380

days in lifetime (12 years) = 0.375 5 - <12 years= 2555 days days of exposure third period/4380 days

in lifetime (12 years) = 0.583

ED Calculation for Air, cont

Daily Inhalation Dose

Age (yrs)

Concentration IR EF BW mg/kg/day

0 - < 0.5 8 x10-3 0.166 0.042 7 7.97 x 10-5

0.5 - < 5 years

8 x10-3 0.415 0.375 13 9.58 x 10-5

5 - <12 years

8 x10-3 0.996 0.583 27 17.21x 10-5

EDa 3.48 x 10-4

ED Calculation for Soil Ingestion

EDs = C x IR x EF x10-6

BW

EDs = Estimated dose through eating soil (mg/kg/day)

C = [ ] of contaminant in soil(mg/kg)

IR = Ingestion rate: Amt of soil a person eats/day (mg/day )

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.

Estimating Soil Ingestion Exposures

Calculate the exposure of an adult to soil at the workplace. The soil is contaminated with 0.9 mg/kg of cadmium. Assume BW = 70 kg (table 2) and a 30 year career, with 5 working days per week, and 50 work weeks per year. Assume a soil IR = 20 mg/day (table 1)

EF = 30 work years x 50 work weeks/yr x 5 work days/wk

70 years x 365 days/yr

= 0.29

Hence

EDw = C x IR x EF x 10-6,

BW

= 0.9 mg/kg x 20 mg/day x 0.29 x 10-6,

70 kg

= 7.46 x 10-8 mg/kg/day cadmium = lifetime exposure to cadmium

ED Calculation for exposure thru skin from contaminated water

EDws = C x P x SA x ET x EF x10-3

BW x AT

EDws = Estimated dose through water on the skin (mg/kg/day)

C = [ ] of contaminant in water (mg/L)

P = permeability constant (number of cm teh chemical will travel thru skin in 1 hour (cm/h) (table 4)

SA = Surface area: cm2 (Table 2)

ET = Exposure time: hr/day contaminated water is in contact with skin

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.

Estimating Exposure Thru the Skin from Contaminated Water

Calculate the exposure through the skin of a contaminant in the water for a woman who lives in an area where [benzene] is 0.002 mg/L. She has been living in her house for 25 yrs and has bathed every day. Ignore other skin contact with the water. Assume that the whole body (SA = 18,175 cm2 ) is exposed for ¼ hr (ET = 0.25) during bathing. Benzene moves through the skin at a rate of 0.11 cm/hr (P). Calculate daily skin exposure of this woman, averaged over a lifetime which is 70 yrs.

EF = 25 years x 365 days/yr

70 years x 365 days/yr

= 0.36

ED Calculation for Skin, cont

EDsw = C x P x SA x ETx EF x 10-3,

BW= 0.002 mg/L x 0.11 cm/hr x 18,175 cm2 x 0.25 hr/day x 0.36 x 10-3,

70 kg

= 5 x 10-6 mg/kg/day

The skin exposure of this woman to benzene from bathing water, averaged over her lifetime is 5 x 10-6 mg/kg/day.

ED Calculation for exposure thru skin from contaminated soil

EDss = C x A x BF x EF x 10-6

BW

EDss = Estimated dose through skin contact with soil (mg/kg/day)

C = [ ] of contaminant in soil(mg/kg)

A = Total soil adhered. Amt of soil that will stick to a person (mg/day)

BF= Bioavailability factor = 1.0 (Table 5 for certain chemicals)

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.

Estimating Exposure Thru the Skin from Contaminated Soil

Estimate the exposure for an 11, almost 12, yr old child who has had skin contact with contaminated soil every day since birth. The [ ] of contaminant in soil is 100 mg/kg. BF= 1.0 (100% available). Calculate exposure periods 0 - < 0.5 yrs. 0.5 - < 5years and 5 - <12 years. In this case, the total soil adhered (A) to the child is 2200 mg/day, 3460 mg/day, and 5800 mg/day (table 1).

Exposure Factor (see previous example on childhood exposure to contaminated air)

0 - < 0.5 yrs = 0.042 0.5 - < 5years = 0.375 5 - <12 years= 0.583

ED Calculation for dermal exposure to soil

Age (yrs)

C A BF EF Conversion factor

BW Daily skin exposure

0 - < 0.5 100 2200 1.0 0.042 10-6 7 0.001

0.5 - < 5 100 3460 1.0 0.375 10-6 13 0.010

5 - <12 100 5800 1.0 0.583 10-6 27 0.013

ED ss 0.024mg/kg/d

Estimating Food Ingestion Exposures

Food grp 1 Food grp 2 last Food grp

EDf = CF x CR x EF x PH + CF x CR x EF x PH ... CF x CR x EF x PH

BW BW BW

EDf = Estimated dose from food (mg/kg/day)

CF = [ ] in food groups (mg/g)

CR = Consumption rate: mg/day (table 3)

EF = Exposure Factor (unitless)

BW = Body weight (kg) based on age group.PH = percentage of food that is home grown

ED Calculation for food consumption

Estimate the exposure of a child, between the ages of 5 and 11 years, to lead from food that is produced on the farm where she lives. Since she lives on a farm (agricultural land), assume 50% (ie PH = 0.5) of the meat, dairy products, fruit and vegetables eaten by this child are produced on the farm. To calculate exposure dose thru food, assume a BW of 27 kg (table 2) and CR = 120 g/day, 609 g/day and 198 g/day respectively (table 3). EF = 1.0 since the child eats every day. This estimate is only for lead from the locally grown food. It does not consider other sources of lead such as purchased food.

ED Calculation for food consumption

Food group

CF CR PH EF BW Daily intake of contaminant

Meat 0.01 120 0.5 1.0 27 0.022

Dairy 0.005 609 0.5 1.0 27 0.056

Vegetables 0.002 198 0.5 1.0 27 0.007

ED f 0.085mg/kg/d

Calculating Estimated Daily Intake: Σ Estimated DosesCalculate the EDI of pentachlorophenol of a person living near a suspected contaminated site. Assume you are averaging exposure over a lifetime of 70 years. The estimated dose or each possible combination of exposure pathway and exposure route are given below. Note that each ED has been calculated separately for each of the 5 life stages. This can increase the accuracy of the total estimate. Each ED was calculated using the equations described on earlier slides. All values are expressed in nanograms of pentachlorophenol per kg body weight (ng/kg/day).

EDI = Sum of Estimated Dose for all pathways

AGE (yrs)

Pathway 0 - <0.5 0.5- <5 5 - <12 12 - <20 20+ ED (ng/kg/day)

Air 0.079 0.823 1.430 1.634 6.786 10.752

Water 0.001 0.007 0.005 0.006 0.029 0.048

Soil 0.007 0.012 0.014 0.016 0.064 0.113

Food 0.705 6.711 4.990 5.703 19.786 37.955

Water skin

0.003 0.003 0.002 0.002 0.014 0.024

Soil skin 0.004 0.071 0.009 0.010 0.036 0.013

EDI 0.799 7.687 6.450 7.371 26.715 49.022

Comparing EDI with TDI (tolerable daily intake) or RsD (risk specific dose)

Carcinogen: The EDI for pentachlorophenol, calculated in the example is found to be 49.022 ng/kg/day (4.9 x 10-5 mg/kg/day). Assume a Slope Factor (SF) or 1.2 x 10-1(mg/kg/day) for pentachorophenol and that the level of risk for cancer that was considered acceptable was one excess cancer death per year per 100,000 people exposed (ie 1 x 10-5).

How does the EDI compare with the RsD?

Comparing EDI to RsD

1. Calculate RsD:RsD = R/SF

= 1 x 10-5

1.2 x 10-1 (mg/kg/day)

= 8.3 x 10-5 mg/kg/day

2. Compare EDI (4.9 x 10-5 mg/kg/day ) to RsD (8.3 x 10-5

mg/kg/day ). EDI is about ½ the RsD, therefore this indicates that the exposure is within the level of risk of cancer considered acceptable.

Comparing EDI to TDI

Consider the exposure of a commercial fisherman to methyl mercury, whose EDI has been estimated at 0.61μg/kg/day. How does this compare with the known TDI?

The TDI for methyl mercury from Table 6 is 0.47 μg/kg/day. The EDI of 0.61μg/kg/day is about 1.3 times above the TDI. This indicates that the exposure exceeds the level considered a risk to health. Steps should be taken to reduce exposure to methyl mercury in this situation.

What to Do Next? Think Salt

If EDI is below TDI or RsD, the risk to people’s health may be considered small because the potential exposure to the contaminant is low. No further actions are necessary.

If TDI or RsD are exceeded, the following risk management options should be considered: Providing info to the public on how to minimize exposure. Recommending measures to reduce the release of the contaminants into the environment. Recommending voluntary standards for manufacturers. Setting standards and guidelines at levels that protect human health.

In Class Question

Calculate ED for children aged 5 – 12 years for (i) inhalation, (ii) water ingestion, (iii) soil ingestion and (iv) dermal exposure through soil to chlorobenzene found at the landfill site. Assume children play at the site 2 days per week for 12 weeks of the year (summer) from the ages of 5 yrs – 12 yrs only (8 yrs). Assume that the bioavailability factor (BF) is 1.0 (= 100% availability) children absorb 100% of chemical that is in sand. 100% of the soil is adhered. Use table below plus the tables 1 and 2.

Example based on concentrations of chemicals found at the landfill site

Air Ground water

Soil

Chemical Mean mg/m3

Max mg/m3

Mean mg/L

Max mg/L

mean mg/kg

Max mg/kg

Chlorobenzene 4.09E-08 8.09E-08 2.50E-04 1.10E-02 1.39E+0 6.40E+00

Choroform 1.12E -12 3.12E-12 4.30E-04 7.60E-03 1.12E+0 4.10E+0

1,2 DCE 1.40E-08 2.40E-08 2.10E-04 2.00E-03 ND ND

BEHP 3.29 E-07 8.29E-07 ND ND 1.03E+02 2.30E+02