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ERT 312
Lecture 3
Toxicology
What is toxicology?
•
•
•
•
Qualitative and quantitative study of adverse effects of
toxicants on biological organisms
Toxicant - A chemical or physical agent, including dusts,
fibers, noise and radiation
Toxicity – property of the toxicants describing its effect
on biological organisms
Toxic hazard – a likelihood of damage to biological
organisms based on exposure resulting from transport
and other physical factors of usage
Trivia
Which
one can be reduced?
Toxicity
Toxic Hazard
Things that should be clarified
Getting
the toxic into your body
Ways to eliminate
Harmful effects of toxicants
4 entry modes
Ingestion
- mouth
Inhalation – Respiratory
system
Injection – skin cut
Dermal absorption - skin
3 exit modes
Excretion
– kidneys, liver,
lungs, skin
Detoxification – downgrade
the toxicants into
something less harmful
Storage – fatty tissue
Table 1: Various Responses to Toxicants
(Crowl & Louvar, 2002)
Irreversible
Effects
Reversible/Irreversible
Effects
Carcinogen
Mutagen
Reproductive hazard
Dermatoxic
Hemotoxic
Hepatoxic
Teratogen
Nephrotoxic
Neurotoxic
Pulmonotoxic
Individuals affected
Dose vs. Response
Low response
Average response
High response
Gaussian/Normal Distribution Curve
(Equa.1)
1 x 2
(
)
1
2
f ( x)
e
2
f(x)
x
σ
µ
the probability (or fraction) of individuals
experiencing a specific response
the response
the standard deviation
the mean
n
MEAN,
x f (x )
i 1
n
i
i
f (x )
i
i 1
n
VARIANCE,
Equa.3
2
Equa.2
(x ) f (x )
i 1
2
i
i
n
f (x )
i 1
i
Example 1
A safety engineer of one leading fertilizer brand is very
concern on the irritancy effect of ammonia, a main raw
material used to produce the fertilizer. A toxicology study
has been conducted on 75 employees. The responses are
recorded on scale from 0 to 10, with 0 indicating no
response and 10 indicating a high response. Details of the
findings are presented in the table 2
Table 2
Response
Number of individuals affected
0
1
0
5
2
3
4
10
13
13
5
6
7
11
9
6
8
9
10
3
3
2
a.
b.
c.
Plot a histogram of the number of individuals affected
vs. the response
Determine the mean and the standard deviation
Plot the normal distribution on the histogram of the
original data
Answers
f ( x) 13.3e
0.100( x 4.51) 2
Mean, µ = 338/75 = 4.51
Variance, σ2 = 374.75/75 = 5
SD, σ = 2.24
Therefore; the normal distribution is,
f ( x) 0.178e
0.100( x 4.51)
2
To plot a normal distribution curve, you need to convert
a distribution equation to a function representing the
number of individuals affected.
In this case, total individuals affected = 75
Refer to table 2.3
(Crowl & Louvar, 2002)
x
f(x)
75f(x)
0
0.0232
1.74
1
0.0519
3.89
2
0.0948
7.11
3
10.6
4
13.0
4.51
13.3
5
13.0
6
10.7
7
7.18
8
3.95
9
1.78
10
0.655
Response – Log Dose Curve
For convenience, the response is plotted versus
the logarithm of the dose
If the response of the interest is death or lethality
= lethal dose curve, LD
LC = lethal concentration (gas)
If the response to the chemical or agent is minor
or irreversible = effective dose, ED
If the response to the agent is toxic (not lethal
but irreversible) = toxic dose, TD
Models for Dose and Response
Curves
The probit (probability unit) method is very common for
single exposure computational.
The probit variable Y is related to the probability P by
(Equa.4)
1
Y 5
2
u
P
)du
1 exp(
2
2
(2 )
Fig X: The probit transformation converts the sigmoidal response vs. log
dose curve into a straight line when plotted on a linear probit scale
Question 2.2 (Crowl & Louvar, 2002)
The effect of rotenone on macrosiphoniella sanborni sp. was investigated. Rotenone
was applied in a medium of 0.5% saponin, containing 5% alcohol. The insects were
examined and classified one day after spraying.The obtained date were:
Dose (mg/l)
Number of insects
Number affected
10.2
50
44
7.7
49
42
5.1
46
24
3.8
48
16
2.6
50
6
0
49
0
From the given data, plot the percentage of insects affected versus the natural
logarithm of dose
Convert the data to a probit variable, and plot the probit versus the natural
logarithm of the dose. If the results is linear, determine a straight line that fits the
data. Compare the probit and number of insects affected predicted by the straight
line fit to the actual data
Probit Variable Y
Equa.5
Y k1 k2 lnV
k1, k2
V
Probit parameters
Causative factor represents the dose
OTOH, conversion from probits to percentage is given by
(Equa.6)
Y 5
Y 5
P 501
erf
2
Y 5
erf
the error function of Y