Topic 2

Toxicology

Prof AA

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Toxicology & Industrial Hygiene

Toxicology

– A qualitative and quantitative study of the adverse

effects of toxicants on biological organism.

Industrial Hygiene

– Industrial hygiene is the science of anticipating, recognizing, evaluating, and controlling workplace conditions that may cause workers' injury or illness.

Definition

Toxicology

The way toxicants enter biological

organism

The way toxicants are eliminated from

biological organism

The effect of toxicants on biological

organism

Fundamental Principle of

Toxicology

There are no harmless substance,

only harmless ways of using

substances

Toxicants

A chemical agents

A physical (dusts, fibers, noise, and radiation) agents, e.g. asbestos

Toxicity is a property of toxicant that describe its effect on biological organism.

Toxic hazards is the likelihood of damage to biological organism based on exposure resulting from the use/transport/storage of the toxicants (property of hazardous material).

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Toxic Effect can be classified

according to:

Reversible Vs Irreviersible

Acute Vs Chronic (Duration of Exposure)

Local (Sk-dermal) Vs Systemic (Sk-systemic) (Location of the effect)

Reversible/Irreversible

Irreversible– Carcinogen-cause cancer

– Mutagen-cause chromosome (gene) damage

– Teratogen- cause birth defects

May or may not be irreversible– Dermatotoxic – affects skin

– Hemotoxic – affects blood

– Hepatotoxic- affects liver

– Nephrotoxic – affects kidneys

– Neutotoxic – affects nervous system

– Pulmonotoxic- affects lungs

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Acute / Chronic

Acute exposure

– High Dosage (e.g. due to accidental release)

– The effect is immediate

Chronic Exposure

– Normally lower dose

– The effect only noticed/detected following long exposure

– Sometimes, the worker could not recall the exposure.

Local/Systemic

Local

Damage to the part of the body that comes in contact with the substance.

Systemic

Chemical is absorbed by the body and attacks a target organ.

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Source of Toxicants

Toxic Release (emissions, rupture etc)

– Vapour/gas/liquid release from source

Fire and Explosion

– Fire and radiation

– Toxic release following fire/explosion (as products

of fire & explosion)

Route of Entry

Route of Entry

Injection: through cuts or hypodermic needles into the skin, usually cause highest blood level concentration.

Inhalation: through mouth/nose into the lungs (respiratory system), 2nd highest blood level concentration.

Ingestion: through mouth into stomach and gastrointestinal tract, 2nd lowest in blood level concentration.

Dermal (Skin) absorption: through skin membrane, lowest in blood level concentration, note: absorption of phenol could result in death

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Inhalation mouth, nose ventilation, hoods,

protection equipment

Injection cuts in skin protective clothing

Dermal Absorption skin protective clothing

Ingestion mouth, stomach rules on eating, drinking,

smoking

ROUTE ENTRY CONTROL

*

*

* industrially most significant

Route of Entry for Toxicants

RESPIRATORY SYSTEM

Upper respiratory

– Nose, sinuses, mouth, pharynx, larynx and tracea

– Filtering, heating, and humidifying the air

– Affected by toxicants that are soluble in water

– These toxicants will react or dissolve in the mucus to form acids or bases

– E.g. hydrogen halides, oxides, hydroxides, sodium dusts

Human Respiratory System

Respiratory System: Lower Respiratory

System

Lungs (bronchial tubes and alveoli for gas exchange with blood)

Toxicants affect the function of alveoli by blocking the transfer of gases or by reaction with alveoli wall to produce corrosive/toxic substances.

E.g. monomers (acrylonitrile), halides (Chlorine),hydrogen sulfide, methyl cynaide etc

Respiratory System

Effect of dust and insoluble materials

– The smaller the dust particles, the farther it

penetrate into respiratory system

– Particles >5 μ m are filtered in the upper respiratory

system.

– 5μm>Particles>2 μm can reach bronchial system

– Particles<1 μm can reach the alveoli

How toxicant are eliminated from

biological organism

Excretion- through kidneys (blood to urine), liver (selectively excrete certain chemicals indigestive tract to bile), lungs , skin (sweats), hair, nail or other organ

Detoxification-change the chemical into something less harmful by biotransformation through liver, can also occur in blood, intestinal wall, skin, kidney

Storage- in fatty tissue. Can create problem when fatty deposits are metabolized and released the toxic (e.g. during reduced food supply). Also store in bone, blood, liver, and kidney.

Massive exposure to hazardous chemical can damage majororgans (kidney, lung, liver), reduces their ability to excrete.

Kidney

Your kidneys receive the blood from the renal artery, process it, return the processed blood to the body through the renal vein and remove the wastes and other unwanted substances in the urine. Urine flows from the kidneys through the ureters to the bladder.

Liver

Entry & Removal of Toxicants

Dose-Response

Relationships

"Dosis facit venenum" - The Dose

Makes the Poison

All substances are poisons; there is none which is not a poison. The right dose differentiates a poison…." Paracelsus (1493-1541)

10 Grams Caffeine – Usually Fatal– 150 mg – Stimulate Entire Spinal Cord

– 65 to 350 mg in 8 oz. of Coffee

– 55 mg in 12 oz Can of Mountain Dew®

– 45 mg in 12 oz Can of Coke® or Diet Coke®

Key Factors Related to Dose

Response

The dose-response curve may differ for different populations.

Individuals vary with regard to response to drugs or toxins.

Dose-Response Curve

Dose-response curve graphically represents the relationship between the dose of a stimulant (e.g. chemicals, drugs) the response elicited

Responses - Toxicology

Toxicology:– Only toxic effects are of

concern.

– Low doses NOEL

(no observable effect

level)

– Greater than NOEL toxicity

Toxicity is the ability of a chemical to damage an organ system, to disrupt a biochemical process, or to disturb an enzyme system.

Responses (Pharmacology

Perspectives)

Low dose no observable response

(subtherapeutic)

Increase dose leads to increase in therapeutic response-desirable (and side effects usually undesirable)

Greater than therapeutic dose toxicity (overdose)

Factor Influencing a Dose-Response

Curve?

Species

Gender

Genetic strain

Age

Route of administration

Environmental conditions

Nutritional status

Effects of More Than One

Chemical

Additive Effect: the combined effect of the two chemicals is equal to the sum of the effects of each agent given alone. This is the most commonly observed effect when two chemicals are given together. (2 + 2 = 4)

Effects of More Than One

Chemical – Continued

Synergistic Effect: occurs when the combined effects of two chemicals are much greater than the sum of the effects of each agent given alone.

– CCl4 and ethanol are hepatotoxic alone but when given together produce much more liver injury than the mathematical sum of their individual effects. (2 + 2 = 20).

– Smoking and asbestos exposure is another example.

– Cocaine use with alcohol is the third example.

Effects of More Than One

Chemical – Continued

Potentiation: occurs when one compound does not have a toxic effect on a certain organ or system but when added to another chemical makes that chemical much more toxic.

– CCl4 is hepatotoxic, isopropanol is not hepatotoxic, when given together the effect of CCl4 is more than expected. (0 + 2 = 10)

Effects of More Than One

Chemical – Continued

Antagonism: occurs when two chemicals administered together interfere with each other’s action. Antagonistic interactions are very often desirable in toxicology and are the basis of many antidotes. (2 + (-2) = 0).

Types of Antagonism

Functional antagonism occurs when two chemicals counterbalance each other by producing opposite effects on the same physiological function.

Chemical antagonism is a chemical reaction between two compounds that produces a less toxic product. Example = a chelator and a metal.

Determination

of Exposure Limits

Toxicology study

To quantify the effects of toxicant on target organism

Usually done on animals (lung, kidney, liver) and the results are extrapolated to human. For genetic effect, the study is on single-cell organism.

Different routes requires different toxicological study

Toxicological study

Involve identifying,

– The toxicant

– The target or test organism

– The effect or response to be monitored

– The dose range

– Ingestion or injection , mg toxicant/kg of body weight

– Gaseous Inhalation, ppm or mg/m3 air

– Particle inhalation, millions of particle per cubic foot (mppcf) or mg/m3 air

– The period of the test (mostly acute tocixity study)

– Acute toxicity, single exposure or series of exposure in a short time

– Chronic toxicity, multiple exposure over a long period of time, also difficult to perform

Acute Exposure - Continued

Mouse and rat are the species most commonly used for testing

Both sexes are used

Food is withheld the night before testing

The number of animals that reach a prescribed endpoint at each dose are tabulated

10 animals per dose

5 dose levels

Acute Exposure - Continued

If larger animals are used the dose is increased in the same animal until the prescribed endpoint is reached

Endpoints could be

– Lethal dose (death)

– Toxic dose (ex. Liver injury)

– Effective dose (ex. Relief from itching)

Subchronic Testing

90 days is the most common test duration but 30 days to 90 days can be used

Usually oral administration of the chemical via food; also implant

Used to further characterize the specific organs affected by test compound after repeated administration of the chemical

Subchronic Exposure

At least 3 doses

– A high dose that produces toxicity but death in less than 10% of the animals

– A low dose that does not produce apparent toxic effects during an acute exposure

– An intermediate dose

For Drugs Under Development

Acute and Subchronic studies must be completed before company can file an IND (Investigate New Drug) application with the FDA (Food and Drug Administration).

If the application is approved then Clinical Trials can begin. Chronic tests can begin at the same time.

Chronic Exposure

Exposure to a chemical for a period longer than 3 months, usually 6 months to 2 years in rodents

Drug Testing – 6 months

Food Additives with potential lifetime human exposure – 2 years required

Chronic Exposure - Continued

Designed to assess cumulative toxicity of chemicals including consideration of carcinogenic potential

Mice – 18 months to 2 years

Rats – 2 to 2.5 years

Start with 60 animals/sex/dose to end up with 30 animals to survive study (LD50/LC50)

What Can Be Learned From A Dose-

Response Curve?

LD50 – Median Lethal Dose, quantity of the chemical that is estimated to be fatal to 50% of the organisms

– LD50 values are the standard for comparison of acute toxicity between chemical compounds and between species

TD50 – Median Toxic Dose

ED50 – Median Effective Dose

LC50 – Median Lethal Concentration

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LD50 is commonly used for assessment of toxicity

%

affected

population

100

50

0

LD50

Dose

LD50 = 50% fatality

LD-50

Examples of LD50 Values

Mathematical Expression

for dose related event

E = magnitude of exposure

t2-t1 = exposure duration

a = availability factor

C(t) = exposure as a function of time

IR = ingestion or inhalation rate

f(t) = nonlinear absorption function

Probit Analysis

Probit Analysis

The dose level of the various hazard events

against fatality can be conveniently determined

using Probit Analysis.

It is a graphical and Look-up Table approach to

determine probability of fatality

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Probit Analysis

The probit variable Y is computed from:

Y = k1 + k2 ln V

Values of constants k1, k2 and causative

variable V (representing the dose) are

given in table

Once the probit is obtained, it can be

converted into % fatality

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Probit: Toxic Release

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Causative variable, V = Probit Parameters

Type of Injury a K1 K2

Ammonia Death 2.0 -35.9 1.85

Carbon Monoxide Death 1.0 -37.98 3.7

Chlorine Death 2.0 -8.29 0.92

Ethylene Oxide Death 1.0 -6.19 1.0

Hydrogen Chloride Death 1.0 -16.85 2.0

Nitrogen Dioxide Death 2.0 -13.79 1.4

Phosgene Death 1.0 -19.27 3.69

Propylene Oxide Death 2.0 -7.42 0.51

Sulfur Dioxide Death 1.0 -15.67 1.0

Toluene 2.5 -6.79 0.41

Probit: Fire and Explosion

Type of injury or damage Causative

Variable (V)

Probit parameters

k1 k2

Fire

Burn deaths from flash fire

Burn deaths from pool burning

Explosion

Deaths from lung hemorrhage

Eardrum ruptures

Deaths from impact

Injuries from impact

Injuries from flying fragments

Structural damages

Glass breakage

p0

p0

J

J

J

p0

p0

-14.9

-14.9

-77.1

-15.6

-46.1

-39.1

-27.1

-23.8

-18.1

2.56

2.56

6.91

1.93

4.82

4.45

4.26

2.92

2.79

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Here, te is the effective time duration (s), t is the time duration of pool burning (sec), Ie is the effective radiation intensity (W/m2), I is the radiation intensity from pool burning (W/m2), te is the effective time duration (s), p0 is peak overpressure (N/m2), J is impulse (Ns/m2), C is concentration (ppm) and T is time interval (min).

Conversion of Probit to Fatality data

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% 0 1 2 3 4 5 6 7 8 9

0 - 2.67 2.95 3.12 3.25 3.36 3.45 3.52 3.59 3.66

10 3.72 3.77 3.82 3.87 3.92 3.96 4.01 4.05 4.08 4.12

20 4.16 4.19 4.23 4.26 4.29 4.33 4.36 4.39 4.42 4.45

30 4.48 4.50 4.53 4.56 4.59 4.61 4.64 4.67 4.69 4.72

40 4.75 4.77 4.80 4.82 4.85 4.87 4.90 4.92 4.95 4.97

50 5.00 5.03 5.05 5.08 5.10 5.13 5.15 5.18 5.20 5.23

60 5.25 5.28 5.31 5.33 5.36 5.39 5.41 5.44 5.47 5.50

70 5.52 5.55 5.58 5.61 5.64 5.67 5.71 5.74 5.77 5.81

80 5.84 5.88 5.92 5.95 5.99 6.04 6.08 6.13 6.18 6.23

90 6.28 6.34 6.41 6.48 6.55 6.64 6.75 6.88 7.05 7.33

% 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

99 7.33 7.37 7.41 7.46 7.51 7.58 7.65 7.75 7.88 8.09

Monty Herr

Types of Antagonism-Continued

Dispositional antagonism occurs when the disposition of a chemical is altered so that the concentration and/or duration of the chemical at the target organ are diminished. Ex. Metabolism is increased –Excretion is increased, therefore half-life is decreased

Receptor antagonism occurs when two chemicals that bind to the same receptor produce less of an effect when given together than the addition of their separate parts. Receptor antagonists are often termed blockers.

Chronic Exposure - Continued

Highest administered dose = “Estimated Maximum Tolerable Dose (MTD) derived from subchronic study

The National Toxicology Program defines the MTD as “a dose that suppresses body weight slightly (i.e. 10%) in a 90 day study

Also use ½ MTD, ¼ MTD, and a control group