Acute chemical toxicity is associated with the immediate health hazards caused by a single dose or multiple doses of a substance over a short period of time (hours to days). Acute toxicity is distinguished from chronic toxicity which typically describes an exposure to a harmful substance over the course of months or years.
Routes of exposure can include ingestion, skin contact, or breathing of the substance and are denoted as oral, dermal, and inhalation toxicities, respectively. Oral and dermal toxicities are typically communicated as LD50 values (lethal dosage to 50% of the affected population) with units of mg/kg (milligrams of substance administered per kilogram of body weight). Inhalation toxicities are typically communicated as LC50 values (lethal concentration to 50% of the affected population) with units of mg/L (milligrams of substance in 1 liter of air).
With all of the three toxicity measurements, a higher LD50 or LC50 measurement indicates a lower toxicity. As examples of this, consider three substances of varying toxicity: water, table salt (sodium chloride), and historical rat poison (arsenic (III) oxide) shown in the table below.
| Compound | Oral Toxicity (LD50) | Approximate lethal dosage to a 100 kg human |
| Water | 90,000 mg/kg | 9000 grams or 9 liters (~2.4 gallons) |
| Table salt | 3,000 mg/kg | 300 grams (~1/2 cup) |
| Historical rat poison | 15 mg/kg | 0.1 grams |
It is no surprise that arsenic, an element well known for its toxicity, has a low oral toxicity (LD50 = 15 mg/kg) and can be fatal in very small doses. What might be surprising to some is that common compounds such as table salt and water can also be fatal when taken in a large enough dose. This is reflected in their increasing oral toxicity values.
Products that are green certified by ITC labs must have measured or calculated LD50 and LC50 values above certain minimum levels making them less likely to contribute to accidental poisoning events.