Toxicity of Chemicals
Dose: How Much is too Much?
In general, the greater the amount of a substance that enters your body, the greater is the effect on your body. .
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Dose-Response Relationship: The dose-response relationship of a chemical refers to the relationship between the amount (dose) of a chemical that enters the body and the resulting biological effect (response). Open the link below to see an example.
Organic solvents such as toluene, acetone, and trichloroethylene all affect the brain in the same way, but to different degrees at different doses. The effects of these solvents are similar to those that result from drinking alcoholic beverages.
- At a low dose, you may feel nothing or a mild, sometimes pleasant ("high") sensation
- A larger dose may cause dizziness or headache
- With an even larger dose you may become drunk, pass out, or even stop breathing
When you inhale a toxic chemical, the dose you receive depends on four factors:
- the level (concentration) of chemical in the air;
- how hard (fast and deep) you are breathing, which depends on your degree of physical exertion;
- how much of the chemical that is inhaled stays in your lungs and is absorbed into your bloodstream; and
- how long the exposure lasts.
It is safest to keep exposure to any toxic substance as low as possible. Since some chemicals are much more toxic than others, it is necessary to keep exposure to some substances lower than others.
Threshold Level: The threshold level is the lowest concentration that might produce a harmful effect. It is different for every chemical. The threshold for one chemical may differ from person to person (see "Sensitivity").
If the concentration of a chemical in the air is kept well below the threshold level, harmful effects probably will not occur. Levels above the threshold are "too much." However, this means only that there is a possibility that health effects might occur, not that such effects definitely will occur.
Duration: How Long is too Long?
The longer you are exposed to a chemical, the more likely you are to be affected by it. The dose is still important-at very low levels you may not experience any effects no matter how long you are exposed. At higher concentrations you may not be affected following a short-term exposure, but repeated exposure over time may cause harm.
Chemical exposure which continues over a long period of time is often particularly hazardous because some chemicals can accumulate in the body or because the damage does not have a chance to be repaired. The combination of dose and duration is called the rate of exposure.
Accumulation: The body has several systems, most importantly the liver, kidneys and lungs, that change chemicals to a less toxic form (detoxify) and eliminate them. If your rate of exposure to a chemical exceeds the rate at which you can eliminate it, some of the chemical will accumulate in your body. Click on the link below to see an example.
Some chemicals, such as ammonia and formaldehyde, leave the body quickly and do not accumulate at all.
If you work with a chemical for eight hours each day, you have the rest of the day (16 hours) to eliminate it from your body before you are exposed again the next day. If your body can't eliminate all the chemical in 16 hours and you continue to be exposed, the amount in the body will accumulate each day you are exposed. Illness that affects the organs for detoxification and elimination, such as hepatitis (inflammation of the liver), can also decrease their ability to eliminate chemicals from the body.
Other chemicals are stored in the body for long periods. For instance, lead is stored in the bone, calcium is stored in the liver and kidneys, and polychlorinated biphenyls (PCBs) are stored in body fat.
There are a few substances, such as asbestos fibers, that, once deposited, remain in the body forever.
Knowledge Check Choose the best answer for the question.
3-4. Generally, what is the relationship between dose and response?
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