When we consider chemical exposure, it’s important to think about frequency: how often will exposure occur? Imagine you are at the gas station. It’s a warm day, and as you fill you fill your tank with gas, you smell the faint scent of gasoline vapor in the air. As you wrap up and put the nozzle back on the pump, a few drops of gas fall from the nozzle, thus preparing the scene for the next person. You just experienced an acute inhalation exposure to gasoline vapor.
- Acute: exposure to a chemical for 24 hours or less
Thankfully for you, it is a low-level exposure; you will be fine. For the attendant who has been working at the gas station for the last few years, every time they tidy up the pumping area (take out the garbage, change out the soapy water for washing windshields, sweep up litter, and spread kitty litter to absorb larger gas spills) they are experiencing chronic exposure to inhaled gasoline vapors.
- Chronic: exposure to a chemical for more than 3 months
When it rains, those drops of gasoline are washed down into the sewers and are carried out into Puget Sound. Fish swimming in the area come into contact with the gasoline, absorbing it through their eyes and skin and inhaling it through their gills. The gasoline evaporates when the weather turns sunny again, so the fish are only exposed for a few days (sub-acute exposure).
- Sub-acute: exposure to a chemical for 1 month or less
Birds in the area feed on the gasoline-exposed fish. It takes a few months for the birds to fully metabolize the gasoline ingested with the fish (sub-chronic exposure).
- Sub-chronic: exposure to a chemical between 1 to 3 months