Principles of Occupational Principles of Occupational Toxicology 2 Toxicology 2

– Types of toxicity– Types of toxicity

Tiina Santonen

Paide 3.11.03

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Types of ToxicityTypes of Toxicity

Acute toxicityIrritation and corrosivitySensitizationRepeated dose toxicityGenotoxicityCarcinogenicityReproductive toxicity

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Types of toxicity Types of toxicity continuescontinues

Mechanisms of toxicity:– Direct local toxicity to tissues first in contact

with the substance– Systemic effects due to the absorption of the

substance– Mechanism may be relevant to all species or it

may be species-specific– Quite often with industrial chemicals the

mechanism is unknown– Does the mechanism of toxicity possess a

threshold? (What is the shape of the dose-response curve like?)

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ExamplesExamples Sulphuric acid:

– strong acid, miscible in water– corrosive, exposure to fumes may cause

damage to the respiratory tract, and in repeated exposure in the respiratory tract cancers (laryngeal cancer)

– type and mechanism of toxicity: locally toxic at the first site of contactmechanism of cancer related to its destructive effect

on respiratory tract epithelium threshold

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Examples, con’tExamples, con’t

Cyanides– toxic when absorbed into the body,

mechanism well-known and apply to all species

Phthalates (e.g. Di(2-ethylhexyl) phthalate)

– causes liver effects and liver tumours in rodents, however the mechanism of action (peroxisome proliferation) is known not to be relevant to humans

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Dose-responseDose-response

DOSE

EFFECT

linear,no threshold

non-linear,threshold

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Dose-response relationship: lead decreased erythrocyte delta-ALAD activityincreased zinc protoporphyrin

anemia

CNS effectsdecreased peripheral nerve conductivityNervous paralysis, lead colics

Adapted from Elinder C-G et al., Biologisk monitoring av metallerhos människa. Arbetsmiljöfonden, Uppsala, 1991

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Information of the potential health hazards of chemicals is derived from...

1) Toxicological studies (in vivo, in vitro)

2) Case reports

3) Epidemiological studies

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Toxicity testingToxicity testing

Systematic toxicity testing started in 1960’s

testing guidelines: OECD guidelines, EU guidelines for industrial chemicals

GLP guidelines

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Acute toxicity testingAcute toxicity testing acute oral, dermal or inhalation toxicity provides information on acute health

hazards likely to arise from acute exposure to the substance by the given route, and on the magnitude of acute toxicity of the substance

usually these tests are made with rodents, dermal test quite often with rabbits

LD50/LC50 values (dose level which is caused death to 50% of animals)

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Acute toxicity testing, con’tAcute toxicity testing, con’t principle of the acute LD50/LC50 tests:

– At least 3 groups of animals are exposed to different concentrations of the chemical, observations of effects and deaths are made, LD50/LC50 value is statistically derived value determined from the dose-response curve by using certain accepted extrapolation methods

oral LD50 test is not used anymore, new substitutive tests are fixed dose test and acute oral class method which give an idea of the magnitude of the toxicity, but do not define the LD50 value

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Irritation and corrosionIrritation and corrosion Acute skin irritation/corrosion test (Draize test)

– usually albino rabbits are used, the test substance is applied to the skin of the rabbits and held under the semi-occlusive dressing usually for four hours. The degree of irritation is scored at specified intervals.

– NOT if the substance is a strong acid or a strong base (pH<2 or >11.5), or it has not caused skin irritation at maximal dosage in acute dermal toxicity test.

– Note: albino rabbits are usually more sensitive to the skin irritation/corrosion than humans

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Irritation and corrosion con’tIrritation and corrosion con’t

Alternative methods:– Two in vitro skin corrosion –test

included in EU test guidelines (rat skin TER assay and human skin model assay)

– Several promising in vitro skin irritation tests have been developed but have not yet been ready for systematic use in skin irritation testing

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Irritation and corrosion con’tIrritation and corrosion con’t Acute eye irritation/corrosion test (Draize test)

– principle: the test substance is applied to the conjuctival sac of albino rabbit, the effects are observed and scored according to the severity of the effects. Repeated examinations at specified intervals

– NOT if the substance is a strong acid or a strong base (pH<2 or >11.5), or it is corrosive to the skin

– Note: albino rabbits are usually more sensitive to the eye irritation/corrosion than humans

– In vitro –methods for eye irritation testing has been developed, but have not yet been good enough to replace in vivo eye irritation test

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Skin sensitizationSkin sensitization Traditional Guinea Pig models for skin

sensitization– guinea pig maximization test (GPMT)– Buehler test

New alternative: Local lymph node assay (LLNA)– measures cellular proliferation in the lymph

nodes draining the site of topical application of the substance

– more specific, objective and reproducible, gives more quantitative information

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Repeated dose toxicityRepeated dose toxicity 28- or 90–day toxicity tests (usually oral or

inhalation studies) provide information on health hazards

likely to arise from repeated exposure by the given route of exposure

throughout evaluation of every organ system

interpretation of the results demands careful consideration

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Special tests...Special tests...

e.g. neurotoxicity test– evaluates potential neurotoxic effects of

chemicals– should be performed if there is a reason

to believe that the substance may have effects on nervous system

– e.g. organophosphate pesticides

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GenotoxicityGenotoxicity

the ability of the substance to induce genetic damage in cells

In vitro tests:– bacterial tests (e.g. Ames test); gene

mutations– mammalian cell gene mutation assays– in vitro chromosomal aberration test

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Genotoxicity con’tGenotoxicity con’t

In vivo tests:– e.g. bone marrow micronucleus test or

chromosomal aberration test– germ cell mutagenicity tests

ability to cause genetic damage in germ cells

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CarcinogenicityCarcinogenicity

2-year cancer bioassay usually rat or mouse are used, can be

performed by any relevant route of exposure (usually oral or inhalation)

should be performed if some indication that the substance could be carcinogenic

laborous and costly, high number of animals needed

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Reproductive toxicityReproductive toxicity

2-generation reproductive toxicity test– evaluates the reproductive system as a

whole over 2-generation, both male and female

– laborous and costly, high number of animals needed

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TREATMENT

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Reproductive toxicity, con’tReproductive toxicity, con’t Developmental toxicity study (teratogenicity)

– treatment during the organogenesis, careful evaluation of fetal losses and malformations

– In interpretation attention is given to the severity of the effects and to the effects seen in fetuses without signs of maternal toxicity

(Developmental neurotoxicity)

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EU Classification and EU Classification and Labelling principlesLabelling principles

EU classification and labelling is very much based on the data obtained from toxicity tests

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T+ Very toxic

T Toxic

Xn Harmful

C Corrosive

Xi Irritating

F+ Extremely flammable

F Flammable

O Oxidizing

E Explosive

N Environmentally dangerous

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Very toxic (T+)Very toxic (T+)

acutely very toxic chemicals – e.g. oral LD50 is < 25 mg/kg or dermal LD50 <50 mg/kg– LC50 is <0,25 mg/l for aerosols or <0,5 mg/l for gases or

fumes labelling:

R 26 (very toxic by inhalation)R 27 (very toxic in contact with skin)R 28 (very toxic if swallowed)

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Toxic (T)Toxic (T) Acutely toxic chemicals

– e.g. oral LD50 is bw 25 – 200 mg/kg,or dermal LD50 is bw 50 – 400 mg/kg

– LC50 is bw 0,25-1 mg/l for aerosols and 0,5-2 mg/l for gases or fumes

labelling R23/24/25 (toxic by inhalation, in contact with skin or if swallowed)

Cat 1 and 2 carcinogens (R45 or R49), mutagens (R46) and reproductive toxicants (R60, R61)

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Harmful (Xn)Harmful (Xn) e.g. acute toxicity:

– Oral LD50 between 200 –2000 mg/kg,or dermal LD50 bw 400 – 2000 mg/kg

– LC50 between 1-5 mg/l for aerosols and 2-20 mg/l for gases or fumes labelling R20/21/22 (harmful by inhalation, in contact with

skin or if swallowed) if there is data showing that prolonged exposure can cause

serious damage to health at the dose levels significantly lower than the dose levels used for acute toxicity classification (R48) ......continues in next slide....

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Harmful (Xn), con’tHarmful (Xn), con’t

Respiratory tract sensitizers (R42)Cat. 3 carcinogens (R 40, Limited evidence

of a carcinogenic effect), cat. 3 mutagens (R 68, Possible risks of irreversible effects), and cat. 3 reproductive toxicants (R 62, Possible risk of impaired fertility or R 63, Possible risk of harm to the unborn child)

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Irritants (Xi)Irritants (Xi)andand

Corrosives (C)Corrosives (C)Irritants:

– R-phrases: R36/R37/R38 and R41(risk of irreversible eye damage)

– skin sensitizers R43

Corrosive: – R-phrases R34 or R 35 (causes burns or

causes severe burns)

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Classification and labellingClassification and labelling

Note: based on hazard, not on riskIf there is a risk caused by these

inherent characteristics of the chemical depends on the use and exposure potential

In future: Global harmonization of Classification and Labelling