Approximately 500 chemicals and hazardous wastes are listed by their technical name in 40
CFR Part 261. These listed wastes are generated either as “process wastes” or “discarded
wastes”. Process wastes are industrial chemicals that are used for their intended purpose and
are under the F-List and K-List. Di scarded wastes are commercial chemical products that even
unused can cause a threat to human health and the environment. The P-List and U-List catalog
chemicals that when discarded are hazardous in their pure formulas. The following describes
the differences between the F, K, P and U Lists in greater detail.