Are CFLs in the trash a bad idea? Yes.
Compact fluorescent light (CFL) bulbs should not be thrown in the trash but should be recycled so that the mercury, metal, and glass can be reclaimed and it doesn’t get into our water system. CFLs do contain a small amount of mercury, so used CFLs are considered in the category of household hazardous waste.
A CFL contains about 4 milligrams of mercury, much less than the approximate 500 milligrams of mercury found in old thermometers. The mercury content allows the bulb to work efficiently and does not present a risk as long as it remains sealed in the glass tubes. However, if the glass is broken, either in the home or in the landfill, the mercury can be dangerous to human and animal health.
Some people do throw CFLs in the trash, but the best way to recycle CFLs is to save them in a box and then drop them off at a household hazardous waste collection facility. Some cities and counties have set up special facilities for this, and some retailers accept CFLs to be recycled in large lots. There are also scheduled collection events where the organization accepts used CFLs and other hazardous materials like paint, pesticides, and household chemicals.
For a specific location, you can call the contractor who picks up your trash or contact your local government. As for retailers, both Home Depot and IKEA accept CFLs from customers and will recycle them free of charge.