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How much is a part per million?
The health effects of any toxic substance are related to the amount of exposure, often referred to as the dose. Typically, the greater the dose, the more severe the effects.
Part per million (ppm), part per billion (ppb), and part per trillion (ppt) are the most commonly used terms to describe very small amounts of contaminants that are in the environment that can have a toxic effect. They are also the measures of the concentration of one material in a larger amount of another material. For example, it is recommended that sanitizing solution be at 50 ppm. This simply represents the amount of chlorine that must be in water.
To help illustrate how small the ppm and ppb are, one dollar in a pile of 1,000,000 dollar bills is a ppm. One pinch of salt in 10 tons of potato chips is a ppb. These amounts reflect very small amounts. If a contaminant is shown to exist in water at a level of 1 ppb, this is the equivalent of one drop of impurity in 500 barrels of water.
SOURCE: Angela M. Fraser, Ph.D., Associate Professor/Food Safety Education Specialist, NC State University