Download Assessing Dose and Potency of Chemicals

Assessing Dose and
Potency of Chemicals
Robert Blaisdell, Ph.D, Chief
Exposure Modeling Section
Office of Environmental Health Hazard
Assessment
Air Programs Using Risk Assessment
Information in California

Toxic Air Contaminant Program. Chemical
specific risk assessments (developed by
OEHHA) and emission data, exposure
assessment (ARB) are to used to inform Air
Toxics Control Measures (ATCMs) (180
chemicals).
 ATCMs are industry-wide requirements for air
pollution control (ARB).
 Chemical specific risk assessment (doseresponse assessment) allows prioritization so
that high risk industries are addressed (e.g
diesel emitters, dry cleaners and metal platers).
Air Programs Using Risk
Assessment Information in California
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The Hot Spots Program uses both chemicalspecific risk assessment and exposure assessment
to address air pollution from stationary sources
(~400 chemicals).
Facilities must report emissions every four years.
Facilities that may pose a threat to public health are
required to do a risk assessment.
Facilities are required to notify the exposed public if
the risks are above a certain level.
Info is used in the Risk Reduction and Audits
program to require additional pollution control
devices on high risk facilities.
How is Chemical Risk Assessment
Done?
 Hazard
Identification—Do the chemicals in
question pose a potential risk?
 Exposure assessment—How much of the
chemical are people exposed to?
 Dose-Response Evaluation—What is the
relationship between the dose of the
chemical and the health effect?
 Risk Characterization—What is the risk
from the facility?
Noncancer Health Effects DoseResponse

It is generally accepted that there is a threshold
or level of exposure at or below which
noncancer health effects will not occur.
 Noncancer health values are designed to be
“safe” levels where health impacts are not
expected even in sensitive members of the
general population.
 Limited number of chemicals have been
considered due to lack of resources and data.
Non Cancer Health Effects DoseResponse

Multiple noncancer health effects on different
organ systems can occur with one chemical at
different doses.
 Human and animal toxicology studies are
reviewed and the health effect occurring at the
lowest dose is selected as the basis for the REL.
 A No Observed Adverse Effect Level (NOAEL)
or Lowest Observed Adverse Effect Level
(LOAEL) is determined from the study.
 Benchmark dose applies a statistical approach
to estimate REL.
Reference Exposure Level
inhalation REL—a “safe” air
concentration (µg/m3) for continuous
inhalation exposure (80 chemicals).
 Acute inhalation REL—a “safe” air
concentration (µg/m3) for 1 hour infrequent
exposures (52 chemicals).
 Oral Chronic REL—a “safe” level of
exposure through the oral route (mg/kg
body weight/day) [7 chemicals].
 Chronic
Reference Exposure Level
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Uncertainty factors are used to ensure that the
noncancer health value will be below the
threshold. Typical uncertainty factors include:
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10 X for animal to human.
10X if short term study is used for a chronic REL.
10X currently for variability in the human population.
10 X if a LOAEL is used instead of a NOAEL.U
Uncertainty factors are multiplied together and
are not usually higher than 3000.
 Exceeding the REL means the likelihood of
health effects is increased but does not
necessarily mean that they will occur.
Cancer Potency Factors

Cancer-causing Chemicals (carcinogens) are
not considered to have a threshold below which
there is no risk.
 Animal studies or human epidemiological
studies (usually workers) are used to estimate
the relationship between dose and excess
cancer risk.
 The cancer potency factor is the slope of that
dose-response relationship (121 chemcals).
 The dose (mg/kg-day) is multiplied X the cancer
potency factor [1/(mg/kg-day)] to give cancer
risk.
Cancer Risk Estimation

Cancer risk can be defined as the excess risk of
getting cancer with a 24 hour/day exposure to a
given daily dose of a chemical for 70 years.
 1 X 10-6 (1 in a million) cancer risk means that if
a million people are exposed, one additional
cancer case would be expected.
 The level of cancer risk considered acceptable
or de minimus is politically determined. It varies
in different programs from 1 X 10-6 to 1 X 10-4 (1
per million to 100 per million).
Cancer Risk
 The
background lifetime risk of getting all
types of cancer is around 1 in 3 to 1 in 4.
 The inhalation cancer risk from breathing
the general air pollution in the South Coast
is somewhere around 700 in a million.
 The acceptable cancer risk from stationary
facilities, as determined by the local Air
Pollution Control District is generally 10 in
a million for lifetime exposures.
Exposure Assessment of Airborne
Chemicals
 The
amount of chemical emitted from a
stationary facility, freeway or rail yard can
be estimated.
 The dispersion of the chemical can be
estimated using local meteorological data
and a computer air model.
Exposure Assessment of Airborne
Chemicals
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Air modeling techniques have been validated
with air monitoring and are generally considered
to be accurate within about a factor of 2.
 Accuracy in a given situation is dependent on
terrain, applicability of the meteorological data to
the site and other factors.
 Modeling of multiple facilities, complex facilities,
freeways, etc within a small region is currently
feasible with high end desktop computers.
Exposure Assessment of Airborne
Chemicals
 Many
airborne chemicals are gases and
exposure only occurs by inhalation.
 The ground level air concentrations as well
as the deposition of metals and
semivolatile organic chemicals onto to soil
or plants can be modeled.
Exposure Assessment of Airborne
Chemicals

Inhalation exposure can be estimated by using a
daily breathing rate and the air concentration.
 Estimation of noninhalation routes of exposure
to metals and semivolatile organic chemicals
deposited into soil is more complex (and less
certain).
 Exposure to these chemicals may occur by
inadvertent soil ingestion, consumption of home
grown produce, meat, contaminated surface
water (as a drinking water source), mother’s
milk, or from skin contact with contaminated soil
or surfaces.
Site-Specific Exposure Assessment
 Estimates
of the dose that an individual is
exposed from all the pathways that occur
at particular site can be made.
 The procedures in the Hot Spots risk
assessment guidelines will tend to
overestimate rather than underestimate
exposure (and thus dose) in order to
protect public health.
Risk Characterization for the Hot
Spots program--Cancer Risk

The dose of the emitted carcinogens are
estimated using standardized exposure
parameters.
 The estimated doses are multiplied times the
cancer potency factors to give cancer risk for
each chemical.
 Cancer risks from all emitted carcinogens are
summed.
 Carcinogens without sufficient data for cancer
potency slopes cannot be evaluated.
Risk Characterization for Hot Spots
Program-Noncancer Health Effects
 A noncancer
hazard quotient is
determined by dividing the modeled air
concentration by the REL.
 The hazard index is the sum of all hazard
quotients for all chemicals emitted that
impact a particular organ system.
Risk Characterization-Hot Spots

A chemical may be a carcinogen and/or cause
noncancer health effects.
 The cancer and noncancer risks are determined
for the following receptors:
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The Residential Maximally Exposed Individual—the
existing residence with the highest noncancer and
cancer risk (could be different locations for noncancer
and cancer risk).
The Maximally Exposed Individual Worker—this is for
offsite workers.
The Maximally Exposed Individual—the point with
highest risk offsite.
Public Comment and Peer Review
OEHHA’s chemical specific risk assessment and
exposure assessment documents are released
for public comment.
 There is a formal response to public comment
and revision of the document.
 The State’s Scientific Review Panel on Toxic Air
Contaminants then reviews and endorses the
documents.
 This process, although lengthy, helps ensure the
scientific validity of risk assessment procedures.
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Concerns about Risk Assessment
 The
first administrator of USEPA
compared risk assessment to a captured
spy. If you torture it long enough it would
tell you anything.
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Comment: “Gaming” can be minimized with
standardized procedures for emissions
estimation, air modeling, dose response and
exposure assessment, and oversight, such as
we have in California’s Hot Spots program.
Concerns About Risk Assessment

Communities often do not have the expertise to
use the tools or verify the results, or the
resources to hire experts to evaluate the results.
 Risk assessment has been used to look at one
facility at a time and does not consider the entire
burden of multiple facilities. This can a particular
problem in environmental justice communities
with mixed residential-industrial zoning and bad
historical land use decisions.
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Comment: Risk assessment now has the capability of
modeling multiple sources, unlike a few years ago.
Concerns About Risk Assessment
 The
current toxicological scientific body of
literature is inadequate. Basic
toxicological Information is lacking on
many chemicals in current use.
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Comment: Yes a serious problem for those
chemicals lacking data.
Concerns About Risk Assessment
 Asthma
induction and asthma
exacerbation are not well characterized in
terms of dose-response.
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Comment: Work in progress--may be
possible in the future for some chemicals.
Advantages of Risk Assessment
 Risk
assessment provides a useful tool
that incorporates scientific information and
serves as a yardstick for comparison.
 Risk assessment can be used to compare
the risks between chemicals as well as
between different facilities and to inform
risk management decisions.
Advantages of Risk Assessment
 Risk
assessment incorporates health
conservative assumptions.
 It is much more defensible than not
considering issues of chemical toxicity and
exposure in decision-making.
For More Information
Air Toxics "Hot Spots" Program
Risk Assessment Guidelines
 Parts
I, II, III & IV Technical Support
Documents
 And the overview: Air Toxics Hot Spots
Program Guidance Manual for Preparation
of Health Risk Assessments.
 All at:
http://www.oehha.ca.gov/air/hot_spots/ind
ex.html