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Toxicology. What is toxicology ? The study of the effects of poisons. Poisonous substances are produced by plants, animals, or bacteria. Phytotoxins Zootoxins Bacteriotoxins Toxicant - the specific poisonous chemical.

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What is toxicology? The study of the effects of poisons.

Poisonous substances are produced by plants, animals, or bacteria.




Toxicant - the specific poisonous chemical.

Xenobiotic - man-made substance and/or produced by but not normally found in the body.



  • Toxicology is arguably the oldest scientific discipline, as the earliest humans had to recognize which plants were safe to eat.

  • Most exposure of humans to chemicals is via naturally occurring compounds consumed from food plants.

  • Humans are exposed to chemicals both inadvertently and deliberately.


Did You Know ?

  • 92% of all poisonings happen at home.

  • The household products implicated in most poisonings are: cleaning solutions, fuels, medicines, and other materials such as glue and cosmetics.

  • Certain animals secrete a xenobiotic poison called venom, usually injected with a bite or a sting, and others animals harbor infectious bacteria.

  • Some household plants are poisonous to humans and animals.


Swiss physician Paracelsus (1493-1541) credited with being

“the father of modern toxicology.”

“All substances are poisons: there is none which is not a poison. The right dose differentiates a poison from a remedy.”


Dose/Response Relationships

“Everything is poisonous, yet

nothing is poisonous”

Most substances in too great amounts

can be dangerous, but in small

amounts are harmless.

Ex: table salt, vitamins


Dose response curves illustrate the

relationship between concentration

and toxicity.

Trace concentrations may be very

useful, then a certain concentration

is reached where the substance

becomes toxic.


LD-50,ED-50,and TD-50

Individuals differ in their response

to an environmental toxin, so a way

to measure the overall toxicity is


LD-50 represents the concentration

that is lethal to 50% of the

population exposed to the toxin.


The lower the LD-50, the more

toxic the substance.

Some LD-50’s:

Sodium Chloride- 4000 mg/kg

2,4-D (weed killer) 368 mg/kg

DDT 135 mg/kg

Caffeine 127 mg/kg

Nicotine 24 mg/kg

Strychnine sulfate (rat poison) 3 mg/kg

Botulinum toxin 0.00001 mg/kg


In toxicology testing, the most

common route of exposure is tested,

and is the basis for setting rules for

exposure to the toxins

Ex: inhalation, skin and eye exposure,



Acute vs. Chronic Toxicity Tests

Can broadly classify toxicity tests based on length of exposure

  • Acute Toxicity test

    • Drop dead testing

    • Time = 2 days (invertebrates) to 4 d. (fish and mice)

      • LD50

      • LC50

      • TLm (median tolerance dose)

      • EC50 (effective concentration)

        • Lose equilibrium, sit on bottom  “ecologically” dead

    • Not very ecologically relevant but quick, relatively cheap (but still ~$700-1,200 per test)


Acute vs chronic toxicity testing (con’t)

  • Chronic toxicity testing

    • Growth, reproduction

    • More ecologically relevant data but takes longer, more expensive

    • Shows effect at much lower dose

    • Test requires much more “baby-sitting”


Acute Testing - theory

  • Population of organisms has normally distributed resistance to toxicants  acute toxicity test designed to identify mean response

  • Regulations allow 5% of species to be impacted

  • Most tests only use 2-3 species (up to 6)  not really enough to protect 95% of all species!


Acute Toxicity Test Organisms

  • Use of test species based on

    • Lab hardiness

    • Common

    • Known life cycle

    • Cheap

    • Short-lived


Normal distribution of resistance/sensitivity

Mean response


5% allowable impact



Chronic toxicity testing

  • Sublethal

  • Time = 7d. to 18 months

  • Endpoints are

    • growth

    • Reproduction

      • brood size (Ceriodaphnia dubia can have 2-3 broods in seven days)

      • Reproductive success

      • Teratogenicity studies (birth defects)


The ED-50 represents the amount

that is effective in 50% of the


Ex: concentration of aspirin needed

to be effective in 50% of the



The TD-50 is defined as the dose

that is toxic to 50% of the population.

Toxic responses can be things such

as reduced enzyme activity, lowered

reproduction, or onset of specific

symptoms (known to be associated

with the toxin. )


All toxicity tests try to determine level of toxicant which will or will not cause an effect

  • NOEC – No Observable Effect Concentration

    • Highest conc not signficantly different from control

  • LOEC – Lowest Observable Effect Concentration

    • Lowest test concentration that is significantly different from control

  • MATC – Maximum Allowable Toxicant Concentration

    • Geometric mean of NOEC and LOEC

    • Often called the “chronic value”


MATC will or will not cause an effect



Sources of Pollution will or will not cause an effect

Point Source vs. Non-Point Sources:

-Point source polluters are single

sources of pollution, such as pipes,

smokestacks, or spills

Non-Point sources (also Area Sources)

are spread over the land, and do not

have a single outflow of pollution.

Ex: runoff from polluted land areas,

automobile exhaust


Categories of Pollutants will or will not cause an effect

  • Infectious agents: diseases, spread

  • through interactions of environment and

  • man.

EX: Salmonella, a food poisoning bacteria spread

via water or food.

Giardiasis, a protozoan infection spread via water,

or person-to-person contact.


2) Toxic Heavy Metals: will or will not cause an effect

-metals with high atomic weight

-Pose health hazards to humans and ecosystems


chromium, vanadium, thallium

-most of these metals are by-products

of a modern industrialized society


Body Burden of Heavy Metals will or will not cause an effect

-Body Burden is defined as the amount

of heavy metals contained within an

organisms tissue.

-heavy metals are accumulated over

an organisms lifetime, and biomagnify

in the food chain.

Human averages: 13 mg mercury, 150mg lead

30mg cadmium.


Biomagnification will or will not cause an effect is the accumulation of

a substance up the food chain by transfer

of residues of the substance in smaller

organisms that are food for larger

organisms in the chain.

Biomagnification can result in higher

concentrations of the substance than

would be expected if water were the only

exposure mechanism.


One small fish needs 10 insects to live, if each insect has 25 microscopic drops

of methylmercury in its body, then one fish would have __________

microscopic drops of methylmercury.

One big fish eats 5 small fish to live. Each small fish has __________

microscopic drops of methylmercury in its body, therefore, one big fish would

collect a total of __________ microscopic drops of methylmercury in its body.

What about you and me? Lets say we eat 1 big fish a day for 3 days. If each

big fish has __________ drops of methylmercury in its body then we would

collect a total of __________ drops of methylmercury in our body over the 3



3) Organic Compounds: 25 microscopic drops

-produced naturally, or synthetically

by humans.

-compounds containing carbon as an


-many synthetic organic compounds

are used in industrial processes, food

additives, pesticides, and drugs.


-Some synthetic organics are called 25 microscopic drops

“persistent organic pollutants” or


POP’s have several characteristics that

make them particularly bad for the


  • They are carbon-based, and often contain

  • chlorine,which is highly reactive (and toxic) in the

  • environment.


2) They are synthetic 25 microscopic drops

3) They are long-lived in the environment

4) They are very toxic to a variety of organisms

5) They are soluble in fat, so they accumulate

within the fatty tissue of organisms

6) They occur in forms which allow them to be

transported in a large variety of ways (wind,

water, sediment)


Some Organic Pollutants 25 microscopic drops

-Aldrin (1949) :Insecticide

-Dieldrin (1948) :Insecticide

-DDT (1942): Insecticide

-PCB’s (1929) : Electrical Insulators

-Dioxins (1920’s) :by-product of

herbicide production


4)Particulate pollution 25 microscopic drops

-small particles of dust, released

into the atmosphere by many

human activities.

Ex: construction, exhaust

-Particulates are also released

Into the atmosphere by natural

processes as well.

Ex: volcanoes, wind erosion


Particulates can cause many 25 microscopic drops

respiratory problems, from asthma

to cancer.

Particulate pollution has been

declining in the U.S., mostly due

to pollution limits on coal fired

power plants.