Chronic exposure can lead to resistant strains of the pests that were to be eliminated. Some materials are exempt from this if they are essential in small doses for life and health. The dose is normally listed as the amount of substance in milligrams and is compared to the body weight of the organism in kilograms. The last column extrapolates the LD50 for a 150 pound human. Higher numbers indicate the material is less toxic.
Some natural toxins are far more toxic than manmade synthetic pesticides.
The toxin botulinum is produced by the bacterium Clostridium botulun that causes food poisoning, which is fatal for most of its victims. The amount of hydrogen cyanide in 4 pounds of lima beans These amounts are relative to the size of the person and a small child could more easily be poisoned by smaller amounts. Farmers normally apply pesticides at a rate of one pound per acre or some fraction of a pound per acre. An application rate of one pound per acre is the equivalent of a single teaspoon of sugar spread evenly over 5,000 5-inch cereal bowls. Pesticides, like all chemicals can be toxic whether they are manmade or occur naturally, but it is the amount of the substance that determines its effect.