7.7 Toxicity7.7 Toxicity
Toxicity refers to the ability of a chemical to cause harmful effects to the body. As was described by Paracelsus (1493-1541):
There are a number of factors that influence the toxic effects of chemicals on the body. These include, but are not limited to:
- The quantity and concentration of the chemical.
- The length of time and the frequency of the exposure.
- The route of the exposure.
- If mixtures of chemicals are involved.
7.7.1 Toxic Effects7.7.1 Toxic Effects
Toxic effects are generally classified as acute toxicity or chronic toxicity.
- Acute toxicity is generally thought of as a single, short-term exposure where effects appear immediately and are often reversible. An example of acute toxicity relates to the over consumption of alcohol and “hangovers”.
- Chronic toxicity is generally thought of as frequent exposures where effects may be delayed (even for years) and are generally irreversible. Chronic toxicity can also result in acute exposures, with long term chronic effects. An example of chronic toxicity relates to cigarette smoking and lung cancer.
7.7.2 Evaluating Toxicity Data7.7.2 Evaluating Toxicity Data
SDSs and other chemical resources generally refer to the toxicity of a chemical numerically using the term Lethal Dose 50 (LD50). The LD50 describes the amount of chemical ingested or absorbed by the skin in test animals that causes death in 50% of test animals used during a toxicity test study. Another common term is Lethal Concentration 50 (LC50), which describes the amount of chemical inhaled by test animals that causes death in 50% of test animals used during a toxicity test study. The LD50 and LC50 values are then used to infer what dose is required to show a toxic effect on humans.
As a general rule of thumb, the lower the LD50 or LC50 number, the more toxic the chemical. Note there are other factors (concentration of the chemical, frequency of exposure, etc.) that contribute to the toxicity of a chemical, including other hazards the chemical may possess.
While exact toxic effects of a chemical on test animals cannot necessarily be directly correlated with toxic effects on humans, the LD50 and LC50 can give a good indication of the toxicity of a chemical, particularly in comparison to another chemical. For example, when making a decision on what chemical to use in an experiment based on safety for the lab worker, a chemical with a high LD50 or LC50 would be safer to work with, assuming the chemical did not possess multiple hazards and everything else being equal.
In general terms, the resource Prudent Practices in the Laboratory lists the following table for evaluating the relevant toxicity of a chemical:
|Probable Lethal Dose for 70 kg Person (150 lbs.)
|Less than 5 mg/kg
|A taste (7 drops or less)
|5 - 50 mg/kg
|< 1 teaspoonful
|Arsenic trioxide, Strychnine
|50 - 500 mg/kg
|< 1 ounce
|0.5 - 5 g/kg
|< 1 pint
|Aspirin, Sodium chloride
|5 - 15 g/kg
|< 1 quart
|Ethyl alcohol, Acetone
In addition to having a toxic effect on the body, some chemicals can be carcinogenic, mutagenic, teratogenic, and acutely toxic. These specific chemical hazards are covered in more detail under the Particularly Hazardous Substances section in this manual.