EDB's long-lasting legacy.

Ethylene dibromide (EDB), the toxic chemical banned last year from most agricultural uses (SN: 3/10/84, p. 151), has been turning up in groundwater throughout Florida's citrus regions, where it was widely employed for four decades to kill nematodes in soil. In hopes of gauging how long the carcinogen will continue to contaminate water and soil, Randy Weintraub at the University of Florida's pesticide research lab in Gainesville has been working to characterize EDB's chemical and microbial half-life--how long it takes for half of the chemical to degrade.

So far, he says, temperature seems to have the biggest effect on fostering chemical degradation -- the higher the temperature, the faster the breakdown. However, even at the 72[deg.]F typical of Florida's groundwater, Weintraub's research suggests the chemical half-life is very long--between 300 and 500 days. Additionally, he says, there is some concern that ethylene glycol, one breakdown product, might further degrade to formaldehyde.

Preliminary tests also indicate there might be some microbes capable of degrading contaminated water. However, Weintraub cautions that the brominated degradation products apparently generated by the microbes might themselves prove to be toxic. The tests mixed EDB-polluted water with sewage sludge--home to many chemical-degrading microbes. The Florida researcher has not yet identified which of the sludge's many indigenous microbes were active in degrading the pesticide.