Transcript Risk

RISK DUE TO AIR
POLLUTANTS
What is Risk Assessment?
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The characterization of the potential adverse health
effects of human exposures to environmental hazards
In a risk assessment, the extent to which a group of
people has been or may be exposed to a certain chemical
is determined
The extent of exposure is then considered in relation to
the kind and degree of hazard posed by the chemical,
thereby permitting an estimate to be made of the present
or potential health risk to the group of people involved
Risk assessment provides information on the health risk,
and risk management is the action taken based on that
information
Purpose of Risk Assessment
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To provide a characterization of the types of health
effects expected
To provide an estimate of the probability (risk) of
occurrence of these health effects
To provide an estimate of the number of cases with these
health effects
To provide a suitable acceptable concentration of a
toxicant in air, water, or food
To cover cancerous as well as non cancerous chemicals
Process of Risk Assessment
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Hazard identification : A determination is made as to
whether human exposure to the agent in question has the
potential to increase the incidence of cancer
Dose-response assessment: A quantitative relationship is
derived between the dose, or more generally the human
exposure, and the probability of induction of a
carcinogenic effect
Exposure assessment: An evaluation is made of the
human exposure to the agent. Exposure assessments
identify the exposed population, describe its composition
and size, and present the type, magnitude, frequency, and
duration of exposure
Risk characterization: The exposure and dose-response
assessments are combined to produce a quantitative risk
estimate and in which the strengths and weaknesses,
major assumptions, judgments, and estimates of
uncertainties are discussed
CHARACTERIZATION OF RISK
ASSESSMENT
Hazard
Assessment
Technical
Hazard
Characterization
Data
Response
Assessment
Technical Dose
Response
Characterization
Exposure
Assessment
Technical
Exposure
Characterization
Population
Integrative
Analysis
Risk
Characterization
Summary
EPA IRIS Database
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http://www.epa.gov/iris/index.html
What is Risk?
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Hazard is the potential of an entity (or activity) to cause harm to
nature, property, or people
Risk from an hazard :risk (harm/unit time) = frequency (event [exposure]/ unit time)
* Consequence (harm/event [exposure])
What is Total Risk?
Total risk :n
R = i = 1∑ R i= 1,2,3,…,n
where,
i is hazard
 For low value of C , R = f x Ch
n
 For high value of C, R = f x Ch where n is some
known number that reflects the roles of disruptions by
severe accidents, as well as the public perception
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How to calculate frequency (f)?
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Frequency (f) = Exposure / Unit time
= Daily amount of air pollutant inhaled
over a life time / person’s weight
= (Breathing rate ( m3 / day) x indoor
concentration ( µg/ m3) )
( Weight of an individual in kg)
= (B x C) / W
where,
B is breathing rate
C is concentration
W is weight of an individual
Units of frequency is ( µg / kg-day)
How to calculate
Consequence (C) ?
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Consequence (c) = Life time excess cancer risk / Daily
exposure to 1 µg of the pollutant / weight of an individual
= βa x K ah x I
where,
βa = “potency” of the pollutant for inhalation in (µg/kg-day) -1
K ah = a conversion factor expressing the ratio of the risk to a
human to the corresponding risk to an animal based on
inhalation toxicity data (potency)
I = a factor relating inhalation data to risk if other pathways were
also available
What is lifetime excess cancer
risk ?
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It is expressed as follows:
R = (B x d). (βa x K ah x I )
W
Calculation of Cancer Risk
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Cancer Risk is a function of the lifetime average daily dose and the chemical specific
potency slope.
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For inhalation:
cancer risk is calculated using unit risk factor and ground level concentration.
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Risk (non-inhalation pathways ) = Dose * Potency slope
Risk (inhalation) = Cg * Unit Risk
Where:
Dose = Dose or the sum of doses from all routes of exposure ( mg/kg/day )
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Potency Slope = Pollutant specific potency (1/mg/kg/day )
Cg = Ground level concentration ( 10-6 g/m3 )
Unit Risk = Pollutant specific unit risk
Assumptions :
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Exposure is for 70 years
Range of Air Unit Risk Factor for
Benzene
2.2x10-6 per ug/m3
(Low-dose linearity utilizing maximum
likelihood estimates)
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7.8x10-6 per ug/m3
(Low-dose linearity utilizing maximum
likelihood estimates)
Source: IRIS (USEPA)
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EVALUATION OF NON CANCER
HEALTH EFFECTS
The chronic hazard index for each
substance is calculated by dividing the
estimated annual average exposure level
by the REL (reference exposure limit).
This ratio is called the hazard index.
 The potential for acute health effects
should be evaluated by comparing the
estimated one- hour maximum
concentrations with the acute RELs.
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Example of lifetime excess
cancer risk
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Risk to an adult from the exposure to tetrachloroethylene
is calculated as follows by using the given information
B = 20 , W = 70 , d = 3.5 , βa = 9.2 x 10-6 , K ah = 1 , I = 1
By using the above formula and substituting the above
given values in the formula we get the lifetime excess
cancer risk to an individual is R = 9.2 x 10 -6.
The above value of risk implies that an individual has a
9.2 chance in a million of getting cancer over his or her
lifetime because of the daily exposure to
tetracholoroethylene at a concentration level of 3.5 µg/m3
of air. If an individual has a life span of 70 years, then
chance of getting cancer in any one year is 9.2/70 = 0.13
in a million
Why are risk studies conducted
on Animals?
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While carrying out experiments there are risks from a spectral of
real, suspected or conjured hazards related to chemical and
biological substances.
The effect from a single substance on humans under controlled
conditions cannot be studied .
Therefore, studies are conducted on test animals that are subjected
to massive doses of a substance on a relatively short time scale.
These test conditions carried out on animals like rats and monkeys
are atypical of human exposures.
The results of these animal studies are extrapolated for
applications to human conditions by the use of mathematical
models.
The mathematical models are actually equations which are
formulated and solved for applications to animal test conditions