This presentation is about the Risk assessment in very effective way. I hope you all will like it,,, Don't forget to remember me in your precious Dua,,,

2. COURSE CONTENTS
ENVIRONMENTAL TOXICOLOGY ZOL 610 3(2-1)
Toxicology: History , Terms and definitions, principles of
Toxicology, Development and present scope of
environmental toxicology, Framework of environmental
toxicology, toxicological evaluation, Sources of
environmental toxicants, / Pollutants: Gaseous chemicals
and heavy metals, toxicity testing,
Characteristics of exposure, spectrum of Toxic effects,
Indices of toxicity, toxico- dynamics, toxico-kinetics
(absorption, distribution and elimination of toxic agents)
Biotransformation, Detoxification and biodegradation.
Pollution and remediation, ecological risk assessment

4.  Risk is defined as the possibility of loss or
injury
 Within the context of environmental
toxicology it is the possibility of an
undesirable biological response (toxicity) that
results from exposure to a toxicant.

5.  Risk may be expressed as a
 probability (e.g.,P=0.00001) or
 incidence (e.g., 1 in 100,000).
 Risk (probability or incidence) is based on
statistical estimates from sample populations
studied during toxicity testing and on other
observations

6.  Risk assessment is the process of examining
toxicological and epidemiological data
for a suspected toxicant and then, if
warranted, estimating permissible exposures

7.  Four steps characterize the process:
1 toxicant identification
2 toxicant evaluation
3 exposure evaluation
4 risk estimation.

8.  To identify a toxicant
 a review of existing literature,
include toxicity tests and
epidemiology
 descriptive toxicity testing
 Does the agent cause the adverse
effect?

9.  Different toxicity tests are performed. For
careful testing following points are important
 the applicability of those tests to humans
must be evaluated, carried out in non human
species
 Careful attention to variability in age, sex,
diet, circadian rhythms, hormonal status, and
biotransformation

10.  With good experimental design, exposure
to a suspected toxicant is precisely regulated
during toxicity testing.
 Descriptive toxicologists predetermine the
exposure parameters, including the
organisms exposed, route of entry, dose,
frequency (how often), and duration (how
long) of dosing.

11.  Under “field” conditions the regulation of
these parameters can present an illusive
element to the risk assessor
 the inability to control the test organisms
(young, old, male, female, or pregnant
female),
 route of entry (percutaneous, respiratory
or digestive system),
 dose (?mg/ kg),
 frequency of dose (?mg/kg/?min, day,
week, year, lifetime)
 duration of dose (seconds, minutes, hours,

12.  The assessment should examine exposures
currently experienced as well as those
anticipated under different conditions.

13.  Maximum daily dose (MDD)
Exposure for non carcinogenic toxicants
is expressed as maximum daily dose
(mg/kg/day)
 Lifetime average daily dose (LADD)
Exposure to carcinogens is stated as lifetime
average daily dose (LADD) (mg /kg /day
/lifetime).

14.  Risk
is the probability of an undesirable
biological response resulting from exposure
to a toxicant.
Estimating risk
requires an integration of the toxicity
conclusions
(toxicant identification and dose-response
evaluation) and exposure assessment (MDD
or LADD).

15.  Risk is approximated by the equation:
R = T x E
Where
risk=R
toxicity=T
exposure =E

16.  Dose-response relationships are not linear
(as in the characteristic sigmoidal graph
lines), exposure is more accurately expressed
as a function (f) as seen in the following
equation:
R = T x f (E)

17. R = T x f (E)
 This equation is the source of risk statements
such as 1 in 1,000 individuals will
develop toxicity (a specific disease) if
exposed
to a specific dose (MDD or LADD)
of a toxicant for a certain period of time.

18. Risk management is to examine risk
assessment data and, where needed, develop
regulatory options that address public health
and social and economic concerns.

19.  Federal agencies charged with overseeing risk
management often
 must overcome the influence of negative
public perceptions and
 legislative mandates to arrive at responsible
decisions.

20.  Safety is defined as the possibility that an
undesirable biological response (toxicity)
will not result from exposure to a toxicant—
it is the inverse of the probability of risk
(i.e., 1÷P).

21.  For example, when the risk of toxicity from a
given exposure is P=0.00001, safety equals 1
divided by 0.00001 (or
Safety = 1/0.00001
 It can be concluded that for every 100,000
exposures only 1 of those exposures will
result in an adverse response.

22.  Since toxicity studies depend on nonhuman
test organisms, some means of extrapolating
results to humans is required.
 One calculation that permits more realistic
extrapolations of toxicokinetic data from test
organisms to humans is the Safe Human Dose
(SHD) formula

23.  Safe Human Dose (SHD) formula:
 SHD = mg/ day
=ED0.0 x A1/h xT1/21/h x Wt x D1/h
SF
 The goal of the SHD is to establish doses at
which risk equals or approaches zero (P=0.0).

24.  where
 ED 0.0 = threshold dose of toxicant
 (NOEL)
 At/h = ratio of absorption of toxicant in test
organism and human
 T1/2t/h = ratio of half-life of toxicant in test
organism and human
 Wt = weight of exposed individual
 D t/h = ratio of toxicant test dosages in animals
to exposure dosages in humans
 SF = safety factor

25.  safety factor (SF)
 depends on the reliability of data used for
extrapolation—a subjective judgment based
on previous experience.
 may range from 10 to 1,000,
 with lower SFs being used when valid human
data is available and higher SFs indicative of a
lack of human data.

26.  Shaw, I. and J. Chadwick. 2002. Principles of
Environmental Toxicology. Taylor & Francis Ltd, 1
Gunpowder Square, London EC4A 3DF.
 Yu, Ming-Ho. 2005. Environmental toxicology:
biological and health effects of pollutants. 2nd
edition. CRC Press LLC, 2000 N.W. Corporate
Blvd., Boca Raton, Florida 33431
 Hughes, W. William. 2005. Essentials of
environmental toxicology: Risk Assessment.
Taylor & Francis, 325 Chestnut St., Suite 800,
Philadelphia, Pa 19106. pp. 143-147