I believe the "oz" is "os" in this case which stands for "oral administration". Anyway, see below for the definition of LD50, along with some of the references found on Internet.


What does LD50 mean?
LD stands for "Lethal Dose". LD50 is the amount of a material, given all at once, which causes the death of 50% (one half) of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.

Toxicologists can use many kinds of animals but most often testing is done with rats and mice. It is usually expressed as the amount of chemical administered (e.g., milligrams) per 100 grams (or kilogram) of the body weight of the test animal. The LD50 can be found for any route of entry or administration but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.
http://www.ccohs.ca/oshanswers/chemicals/ld50.html

Other references are:

http://www.sepro.com/horticulture/decree/DcreMSDS.PDF (see page 3 of this document which is a data sheet for a fungicide)

http://www.rxlist.com/cgi/generic/trisulf_od.htm



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Note added at 2002-08-30 13:32:56 (GMT)
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There are close to 6,000 results that refer to the LD50 toxicological evaluation as being \"os\" (orally administered). This is the reason why I think the \"oz\" is a mispelling, along with the fact that the two weight measurements have nothing to do with each other.