By the time the bright, velvety flowers reach your Valentine, they will have been sprayed, rinsed and dipped in a battery of potentially lethal chemicals.

Most of the toxic assault takes place in the waterlogged savannah surrounding the capital of Colombia, the world's second-largest cut-flower producer after the Netherlands. It produces 62 percent of the flowers sold in the United States.

With 110,000 employees -- many of them single mothers -- and annual exports of $1 billion, the industry provides an important alternative to growing coca, source crop of the Andean nation's better-known illegal export, cocaine. But these economic gains come at a cost to workers' health and Colombia's environment, according to consumer advocates.

The U.S. requires imported flowers to be bug-free, but unlike edible fruits and vegetables, they are not tested for chemical residues.

The tropical climate that drew U.S. flower growers to Colombia and neighboring Ecuador is a haven for the flowers' natural enemies. So growers facing stiff competition from emerging flower industries in Africa and China apply pesticides and fungicides, some of which have been linked to elevated rates of cancer and neurological disorders and other problems.

Colombia's flower exporters association responded by creating Florverde, which has certified 86 of its 200 members for taking steps to improve worker safety and welfare. Florverde says its members have reduced pesticide use by 38 percent since 1998.

Still, 36 percent of the toxic chemicals applied by Florverde farms in 2005 were listed as extremely or highly toxic by the World Health Organization.

A survey of 84 farms between 2000 and 2002, partly financed by Asocolflores, the exporters' association, found that only 16.7 percent respected pesticide manufacturers' recommendations to prevent workers for 24 hours from re-entering greenhouses that were sprayed with the most toxic of pesticides.

Carmen Orjuela said she began having dizzy spells and repeated falls in 1997 while working at a flower farm outside Bogota. During the peak season before Valentine's Day, she said her employer forced workers to enter greenhouses a half-hour after they had been fumigated.

"Those who refused were told they could leave -- that 20 people were outside waiting to take their job," said Orjuela, who quit in 2004. Orjuela's employer, Flores de la Sabana, denied ever disregarding manufacturer-recommended re-entry times. But a 2005 toxicology study from Colombia's National University confirmed that Orjuela's illness was "directly related to an important exposure to potentially toxic chemical substances." A government arbiter ordered the company to pay her a pension equal to the $200 monthly minimum wage earned by most workers.

Government oversight is relatively strict in the United States. In California, each flower farm's pesticide use is available for review on the Internet.

But there are no reliable statistics on chemicals used by Colombia's 600-plus flower farms, in part because only a third belong to Asocolflores, which keeps records.

Although the industry has made huge strides because of Florverde, accidents continue to happen.

On Nov. 25, 2003, about 200 workers at Flores Aposentos, near Bogota, were hospitalized after fainting and developing mouth sores. Authorities said the mass poisoning could have been caused by pesticide-handling violations, but fined the company only $5,770.

Causal links between chemicals and illnesses are hard to prove, because chronic pesticide exposure has not been studied in enough detail. But the Harvard School of Public Health examined 72 of the 7- and 8-year-olds in a flower-growing region of Ecuador whose mothers were exposed to pesticides during pregnancy. It found they had developmental delays of up to four years on aptitude tests.

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