The ADI is an estimate of the quantity of a chemical that may be consumed everyday for a lifetime without causing significant health problems. It is based on No-Observed-Adverse-Effect-Levels (NOAELs) found in a battery of animal toxicity studies and supplemented with human data when available. The NOAEL is the highest dose tested, so the ADI estimate will underestimate the true risk to humans who are exposed to higher doses over a longer period of time.
ADIs are used by regulatory agencies such as the U.S. Environmental Protection Agency (EPA) to set safety standards for chemicals. An agency may choose to regulate a chemical based on its actual adverse effects on humans, but often does so based on how it predicts those effects at lower doses over a longer period of time. Because animals usually are first given high doses of chemicals for several days or weeks before being given low doses over their entire lifespan, the high-dose data are more likely to cause cancer or other serious long-term effects. By using ADIs, regulators can ensure that even very small amounts of a carcinogen or other toxic substance won't cause cancer over a lifetime.
An ADI cannot be calculated for every chemical. Instead, it is determined by the regulator based on what they believe will protect the public from harmful effects of chemicals. Some regulators calculate individual ADIs for each compound they regulate while others use general guidelines or rules of thumb.
The ADI for humans is defined as an amount of chemical intake that may be consumed on a daily basis for the rest of one's life without posing a significant harm to one's health. It is computed by dividing the aggregate NOAEL from the animal studies by a factor of uncertainty (safety). This factor of uncertainty accounts for differences between animals and men in terms of sensitivity, metabolism, and other factors.
NOAEL means "no observed adverse effect level". It is the highest dose tested for a compound in animals without causing any adverse effects. The ADI value is then calculated by multiplying the mg/kg bw per day value by your body weight in kg. For example, if the NOAEL value is 1 mg/kg bw per day and you weigh 70 kg, then you can estimate that you can take 700 mg daily and still not experience any harmful effects.
There are two types of limits that regulators will use when determining an ADI: acute and chronic exposures. An acute reference dose (ARfD) is like an acute exposure limit; it is the maximum allowable concentration of a substance in air or water that would not cause problems over a short period of time. A chronic reference dose (CRFD) is like a chronic exposure limit; it is the maximum allowable concentration of a substance in air or water that would not cause problems over a long period of time.
The acceptable daily intake (ADI) is defined as the maximum quantity of a chemical that may be taken daily throughout a lifetime with no discernible health risk, and it is based on the greatest consumption that does not cause obvious harmful effects. For example, the ADI for mercury is 0.5 mg/kg of body weight per day; this means that if you weighed 180 pounds (82 kg), you could consume 90 ml (3 oz) of dried currant juice each day without risking toxicity from the mercury.
The ADI is determined by government agencies like the United States Food and Drug Administration (FDA). These agencies work with industry and other groups to come up with safe levels of chemicals in food, drugs, and other products that contact the skin or enter the body through ingestion. They do this by looking at the amount of a chemical that causes changes in animal studies or mutations in cell lines grown in the lab. If higher amounts have no effect, then the agency sets the level at which there should be no harm greater than any possible benefit.
For example, the FDA set the ADI for benzene at 5 ppm. This means that if you were exposed to 5 parts per million of air during work hours, there would be no apparent health risk. At home, when it's not being breathed in, it should be below 1 ppm.