Photo courtesy Shutterstock Images

Chlorine bleach has long been a home care staple, used for disinfecting and restoring bright luster to dingy clothes. But be warned: that over-the-counter bleach bottle can contain a caustic poison, which can profoundly irritate eyes, noses, throats and lungs. Like an evil genie, it can be potently harmful when it leaves its bottle.

Some very damaging substances—dioxins and furans, for example, and also trihalomethanes—can arise when chlorine products come in contact with organic matter such as wood, soil, waste, etc. Dioxins and furans can form when chlorine atoms react with wood pulp, as is the case in the paper bleaching process, or when municipal waste or backyard garbage is burned but not thoroughly. Dioxins and furans are extremely toxic chemicals, known carcinogens and hormone distruptors, and are among the "dirty dozen" chemicals targeted for elimination in the 2001 Convention on Persistent Organic Pollutants. Trihalomethanes—including the carcinogen chloroform—are formed when chlorine reacts with carbon-containing organic matter. Some studies suggest that trihalomethanes may cause miscarriages, birth defects, and bladder and rectal cancers.

The news about household bleach isn't all bad: it is a relatively weak solution of sodium hypochlorite or sodium hydroxide, a chlorine compound. Household chlorine bleach breaks down quickly in the environment to release salt, oxygen, water and chlorine. Chlorine is an abundant element (it is a major constituent of salt, for example) and does not bioaccumulate, so there isn't a risk of gradual buildup in one's body over years to a toxic dose.

Unfortunately, household bleach usually contains trace amounts of hazardous organochlorine compounds, particularly in scented varieties, according to Philip Dickey, Ph.D., staff scientist with Washington Toxics Coalition, and tiny amounts are further produced as it breaks down. Martin Wolf, Director of Product Quality and Technology at Seventh Generation, says that chlorine from bleach could produce dioxins, dioxin-precursors, and bioaccumulating chlorophenols from contact with humus in the waterways. Also, both he and Dickey note that small amounts of trihalomethanes can be produced as well, since they can form whenever chlorine encounters common sources of carbon such as dirt, sewage, or leaves in the water stream.