CUBATAO, Brazil -- After school let out one recent afternoon here, Cleiton Celio Silva Araujo grabbed hooks, a line and a bamboo pole and scrambled down a bank of the Cubatao River. Within an hour, the gangly 13-year-old was filling a plastic bag with fish.
Out of place in this tableau was the background: the metal chimneys and ducts of a riverside styrene plant. Even more out of place was a label that Brazilian environmentalists long ago gave to this industrial spot: the Valley of Death.
After a striking reduction in industrial pollution in Latin America, Cubatao's residents are now enjoying the benefits of a frontal attack on the poisons that once flowed freely from Brazil's largest industrial park.
Today, verdanttrees and bushes cover the mountainsides that surround the steel, fertilizer and petrochemical plants of Cubatao Valley.
Less than a decade ago, clouds of ammonia and fluoride had rendered the mountain ridges a lifeless skyline, covered with dead tree trunks.
Today, in health clinics here, the infant mortality rate has dropped in half, and oxygen masks have fallen out of fashion as the number of life-threatening smog alerts has dropped from 16 in 1984 to one last year.
And in a city that once prided itself on growth at any cost, the mayor, a former business leader, now takes pride in his campaign: "Cubatao City -- Symbol of Ecology."
This campaign includes planting 130,000 trees, establishing four municipal "ecological parks," requiring environmental education in city schools, building bicycle pathways and a sewer system, and getting Brazil's renowned landscape artist, Burle Marx, to design a parkway entrance for the city.
"Cubatao was always described as one of the most polluted places in the world," the mayor, Nei Eduardo Serra, said. "Today, Cubatao has become an example of a solution to the problem of Third World pollution."
Convinced that others should learn from Cubatao's experience, Mr. Serra plans to charter buses to bring delegates here from the United Nations Conference on Development and the Environment, which will be held next year in Rio de Janeiro.
Riding buses to this city of 130,000 people, 35 miles south of Sao Paulo, will undoubtedly be American and Mexican environmentalists interested in cutting pollution in Mexico, as part of a North American free trade pact.
"The mayor has managed to make lemonade from the lemon," said an admirer, Werner E. Zulauf, an engineer who in the mid-1980s was president of Cetesb, Sao Paulo state's environmental protection agency.
Cubatao appeared to have hit bottom in 1981, the year Mr. Serra and a group of fellow thinkers formed a group called Valley of Life.
Because Cubatao is blocked by a 2,800-foot mountain range, thermal inversions routinely occurred, fueled by the 114,416 tons of particulate matter that its smokestacks belched into the air annually.
Deadening the rivers, the valley's 23 major industries poured out a liquid filth that added up to 22,678 tons of organic matter and 1,467 tons of heavy metals annually, according to Cetesb.
The plants here were built during Brazil's industrialization of the 1960s and 1970s, and few had pollution controls.
Mr. Zulauf recalled businessmen's reactions in December 1983, when he ordered companies to comply with existing anti-pollution regulations.
"The industrialists immediately started telephoning the governor," he recalled, referring to Franco Montoro. "But the governor refused to take their calls. He told them to see me."
Political backing turned out not to be enough. In the next year, Cubatao hit bottom.
One evening in February 1984, gas leaking from a pipeline collected below a slum of wooden shanties. A spark set off an inferno that claimed 99 lives, by official count.
In January 1985, summer downpours touched off a series of landslides from denuded mountain slopes. Mud first blocked a highway to the Atlantic coast and then a rail link to the interior.
Finally, the shifting earth hit a factory, sending a cloud of 15 tons of ammonia heading toward Vila Parisi, a slum built in the industrial zone. Civil defense authorities had to evacuate 5,000 people temporarily.
Soon, industrialists started to negotiate timetables and technologies for cutting pollution.
Today, the results are "impressive," said Rolando Roebbelen, owner of a natural food restaurant here and founder of a private group, the Ecological Association of Cubatao.
By installing filters, scrubbers and precipitators, the companies cut overall emissions of particulates in the valley by 72 percent, to 31,545 tons a year.
The slum threatened by toxic clouds has been razed, and its inhabitants have been relocated outside the industrial zone.
With ammonia and fluoride emissions cut to 4 percent of previous levels, leafy vegetation began to spread across the mountain ridges.