1. Toxicology in 50 Minutes Instructor’s Notes Phone: (304) 253-8674
Vincent J. Giblin, General President
Phone: (304)
Fax: (304)
1293 Airport Road
Beaver, WV
Operating Engineers National Hazmat Program

2. This material was produced under grant number 46C5-HT16 from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

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What is toxicology?
The study of the negative effects of chemicals on living things
A chemical is considered toxic depending on
How much of it is necessary to cause harm
How easily it can enter the body
Almost anything - even water - can cause illness if taken in large enough quantity. On the other hand, all hazardous chemicals are safe if the quantity taken into the body is small enough.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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Routes of exposure
In order for a chemical to cause injury, it must enter the body
Inhalation
Ingestion
Absorption through the skin
Injection
Inhalation is a very effective way for chemicals to enter the body, because of the way the lungs work. Inhaled air is carried through the breathing passages to smallest division of the lungs - the alveoli. There are three million alveoli, each having a wall only one cell thick. Oxygen - and chemicals - can cross that one cell easily, and go directly into the bloodstream to be carried throughout the body.
Ingestion occurs when chemicals are swallowed. We may carry the chemical to our mouths on our hands when smoking, eating, drinking, or applying cosmetics. Ingestion can also occur when we inhale chemical particles which become trapped in mucus in the respiratory passages, and then reflexively swallowed.
Absorption through the skin is a surprisingly common route of entry. Chemicals can be absorbed most easily where skin is very thin: eyelids, arm pits, and scrotum.
Injection occurs when the skin is physically penetrated - for example, by a wound, or by a thin stream of fluid under high pressure, needle stick, or insect bite.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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Chemicals in the body
Distribution - spread throughout the body
Metabolism - broken into smaller chemical compounds
Storage - kept in the body for a long time
Excretion - passed out through urine, feces, exhaled air, or sweat
Once a chemical has entered the body, it tends to be distributed - to be spread throughout the body. The body can then do several things with the chemical:
Metabolize it - break it down into simpler compounds. Sometimes this renders the chemical harmless, but sometimes the simpler compounds are more harmful than the original.
Store it - lead, for example, is placed in the bone marrow. It can stay there for years, to be released and cause problems later.
Excrete it - this is the least harmful alternative.
Often the body does a combination of these: stores part of the chemical, metabolizes part of it, and excretes part of it.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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Toxic effects
Toxic chemicals disrupt the normal functions of the body. Effects can be
Local - at the site of exposure
Systemic - affecting the entire body
target organs - organs or systems where symptoms of exposure appear
An example of a local effect would be a rash on the hand where contact was made with the chemical.
When the chemical is carried throughout the body, it can cause multiple problems that seem unrelated to the site of exposure. For example, getting the chemical on your hand might not cause a rash, but headaches, blurred vision, and unconsciousness.
Headache, blurred vision, and unconsciousness are all symptoms that show that the functions of the central nervous system are being disrupted. In this case, the central nervous system is the target organ. Often the liver, which attempts to detoxify the blood, is a target organ. Many chemicals have multiple target organs.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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Dose and response
The reaction is dependent on the amount of the chemical received, but...
Some doses are so small they produce no response
Once the maximum reaction has occurred, increasing the dose doesn’t change the reaction
These assumptions, which are basic to toxicology, are just common sense. We are all familiar with the concept of dosage in medication, and the same principle applies to toxicology. In general, the more of something that you take into your body, the more it will affect you.
When we talk about extremely small and extremely large doses, the usual relationship between dose and response doesn’t hold true. Some doses are so small they they produce no noticeable reaction. At the other extreme, once the greatest possible reaction has occurred, adding more of the chemical produces no change.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

8. Dose-response curve - alcohol
Death
Labored breathing
Coma
Response
Sleep
Slurred speech
Dose-response curves are frequently used to draw a picture of the relationship between dose and response. The curve above is a typical shape. We can see that the curve indicates that there is no effect at a very small dose of ethanol - the type of alcohol normally consumed. The curve levels off at the far right, because death is the greatest possible reaction to an over-dosage of alcohol.
Relaxed
No effect
Dose
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9. Acute and chronic exposures
Acute - sudden, brief
A bee sting
Chronic - repeated small doses over time
Smoking cigarettes for years
The words “acute” and “chronic” are used to describe kinds of exposures and kinds of reactions, which can lead to some confusion.
In general, chronic exposures are more common than acute exposures, because small, habitual exposures tend not to attract our attention.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

10. Acute and chronic effects
Acute - lasting hours
Chronic - lasting a long time - possibly years
The redness and swelling that occur after a bee sting are acute effects. Morning coughing is a chronic effect of smoking.
Acute effects are not necessarily mild - sudden death is an acute effect.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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LD50 and LC50
These terms derive from laboratory tests on animals
LD50 is the dose which when swallowed, injected, or applied directly, kills half the test subjects
LC50 is the concentration of a chemical in a test atmosphere that kills half the test subjects within one hour when inhaled
This information appears frequently on Material Safety Data Sheets. For example, the MSDS for vanadium pentoxide indicates that the LD50 is 11 mg/kg given by mouth to rats, while that for chlorobenzene states an LD50 of 1110 mg/kg. In other words, it takes one hundred times more chlorobenzene to kill rats.
The implication is that even a very small amount of vanadium pentoxide is dangerous to humans. If you work with vanadium pentoxide, this is information that you should know.
LC50 is similar to LD50, except that it measures inhaled concentrations rather than ingested amounts. LC50 is a useful measurement for airborne substances. Often you see LC50 mentioned in regard to respiratory protection.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

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Exposure Limits
PEL - permissible exposure limit - airborne concentration enforced by OSHA
STEL - short-term exposure limit -15 minutes four times a day, with l hour free of exposure between each 15 minute exposure
IDLH - immediately dangerous to life and health - maximum airborne concentration which would not interfere with ability to escape
PEL - Permissible Exposure Limit - Represents conditions under which it is believed that nearly all workers may be repeatedly exposed for eight hours, day after day, without adverse effect. PELs are set by OSHA, are are legally enforceable.
STEL - Short-term Exposure Limit - The concentration to which workers can be exposed continuously for a short period of time without suffering from: 1) irritation, 2) chronic or irreversible tissue damage, or 3) loss of consciousness sufficient to increase the likelihood of accidental injury, impair self-rescue, or materially reduce work efficiency; and provided that the daily PEL is not exceeded. STELs are expressed in terms of number of exposures per day and times between exposures. STELs are recommended limits set by the American College of Industrial Hygienists. Although they are not legally binding, they are generally followed.
IDLH - Immediately Dangerous to Life or Health (OSHA) A maximum concentration from which one could escape within 30 minutes without any escape-impairing symptoms or any irreversible health effects. IDLH limits are set by OSHA, and are legally binding.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

13. Operating Engineers National Hazmat Program
Good work practices
Read the MSDSs
Use PPE when required
Practice good hygiene
Don’t eat, drink, smoke, or apply cosmetics around hazardous chemicals
Wash your hands
If showering and changing clothes after your shift is recommended, do so
Knowledge is power, and understanding the health hazards of chemicals alerts us to take the actions needed to protect ourselves. Many workers have had their health permanently damaged on the job because they did not understand the risks to which they were being exposed.
Often, we become complacent about hazardous chemicals we work with daily, because they seem so familiar. Instead, we need to make good work practices a habit - starting with reading labels and MSDSs.
Operating Engineers National Hazmat Program
Operating Engineers National Hazmat Program

14. This material was produced under grant number 46C5-HT16 from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U.S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government.

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END
This publication was made possible by grant numbers 5 U45 ES AND 5 U45 ES from the National Institute of Environmental Health Sciences (NIEHS), NIH. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS, NIH.
Operating Engineers National Hazmat Program