The term "dirty dozen" in the context of the environment refers to the twelve persistent organic pollutants (POPs) that have been identified as the most hazardous to human health and the environment. These pollutants are known for their long-lasting presence in the environment, bioaccumulation in living organisms, and their ability to travel long distances through air and water.

Persistent organic pollutants are a group of highly toxic chemical substances that are resistant to degradation and can persist in the environment for long periods of time. They are primarily generated through human activities such as industrial processes, agricultural practices, and waste disposal. These pollutants can have severe impacts on ecosystems, wildlife, and human health.

The twelve substances identified as the "dirty dozen" are:

1. Aldrin: A pesticide used to control termites, ants, and grasshoppers.
2. Chlordane: A pesticide used to control termites and as a wood preservative.
3. DDT: A widely used insecticide that was banned in many countries due to its persistence and harmful effects on wildlife.
4. Dieldrin: A pesticide used to control termites, locusts, and soil insects.
5. Endrin: A highly toxic pesticide used to control insects, rodents, and birds.
6. Heptachlor: A pesticide used to control termites, ants, and grasshoppers.
7. Hexachlorobenzene: A fungicide used on crops and as a wood preservative.
8. Mirex: A pesticide used to control fire ants and as a flame retardant.
9. Polychlorinated biphenyls (PCBs): Industrial chemicals used in electrical equipment, hydraulic fluids, and plasticizers.
10. Toxaphene: A pesticide used to control insects on cotton, cattle, and other crops.
11. Dioxins: Highly toxic byproducts of industrial processes, such as waste incineration and chemical manufacturing.
12. Furans: Chemical compounds that are often produced alongside dioxins.

These pollutants have been recognized as significant threats to human health and the environment due to their persistence, ability to accumulate in the food chain, and their harmful effects on reproductive, immune, and hormonal systems. Efforts have been made at the global level to reduce and eliminate the production and use of these pollutants through international agreements such as the Stockholm Convention on Persistent Organic Pollutants.

In conclusion, the term "dirty dozen" refers to the twelve persistent organic pollutants that pose significant risks to human health and the environment. These substances have been identified as highly toxic, persistent, and capable of bioaccumulating in living organisms. Measures are being taken to reduce and eliminate their production and use in order to protect the environment and human well-being.