Oral occupational poisonings might occur by contamination of food or cigarettes from unwashed hands, and by accidental swallowing. In general, the smaller the LD50 value, the more toxic the chemical is. The LD50 gives a measure of the immediate or acute toxicity of a chemical in the strain, sex, and age group of a particular animal species being tested. The LD50 test was neither designed nor intended to give information on long-term exposure effects of a chemical. Once you have an LD50 value, it can be compared to other values by using a toxicity scale.
Confusion sometimes occurs because several different toxicity scales are in use.
These tables differ in both the numerical rating given to each class and the terms used to describe each class. It is important to reference the scale you used when classifying a compound. The toxicity rating can be different for different animals. The data above show that dichlorvos is much less toxic by ingestion in pigs or dogs than in rats. In general, if the immediate toxicity is similar in all of the different animals tested, the degree of immediate toxicity will probably be similar for humans.