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Preventing Chemical Accidents:  Understanding MSDS’s & Assessing Chemical Hazards

Factsheet #4

Dose and the Body’s Response

After ingestion, inhalation or skin contact, toxic chemicals as well as their by- products react in the body.  For most toxic substances to cause harm there needs to be a sufficient “dose” given.   

“Dose” refers to how much a substance reacts with the body.  Dose is measured by the concentration of the substance and the time period of the exposure.

The higher the concentration, the larger the dose.

The longer the exposure, the larger the dose.

There are basically two ways the body reacts to a dose of a toxic substance:

•  Linear/Non-Threshold For any dose, no matter how small, the body may have a reaction.  This type of response may be found with cancer-causing chemicals and cancer-causing physical agents, such as radiation.  Any dose carries a risk.

•  Threshold There needs to be a certain level of dose before there is a bodily response.  This type of response is found with most toxic chemicals (not for cancer-causing agents and chemicals).  For example, low-level exposure to methanol throughout the plant is not very harmful, but at higher concentrations it will cause irritation to the eyes, mucous membranes, and upper respiratory tract.  Nausea, dizziness and headaches may result.

Source: Moeller, Dade W., Environmental Health, Harvard University Press, Cambridge, Massachusetts and London, England, 1997.

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