A visitor's first impression of this town 20 miles southeast of Sao Paulo is smoke. It hovers in soup-thick clouds - of fluoride gas, sulfur dioxide, ammonia, and carbon monoxide - that often blot out the sun for days.
The next thing the visitor notices is the stench, a suffocating smell of sulfur and raw sewage.
The town, which lies at the foot of a steep escarpment, is Cubatao. It is known among its 85,000 residents as ''the inferno'' and ''the valley of death.'' Some say it may be the most polluted city on the planet.
Impresarios of the valley's 23 giant industries say such labels distort Cubatao's problems beyond reason. But Cubatao's petrochemical and other heavy industries pump some 750 tons of toxins - including sulfur dioxide, ammonia, carbon monoxide, and fluoride gas - into the air every day, according to figures released by a Sao Paulo state environmental agency. And this is after a reportedly rigorous cleanup campaign.
Last April, a team of scientists from the University of Sao Paulo recorded two days of ''emergency level'' air contamination by toxic trace elements in a 20-day period. And just last month, government pollution monitoring stations indicated there were several days in which air quality standards were ''inadequate.''
Fishermen long ago stopped working the rivers around the city, which are blackened from sewage and chemical effluents.
''In Cubatao,'' says Maria Alves, a single mother of six, ''people are the filters.''
Nature, indifference, and galloping industrialism - not necessarily in that order - have brought Cubatao to this state of affairs.
Situated on a river estuary 10 miles from the continent's largest seaport of Santos and a short drive from the metropolis of Sao Paulo, Cubatao has long been considered an ideal spot for industry. In less than 40 years, it grew to be South America's largest industrial park, today producing some 15 million tons of vital products and $480 million in exports annually.
But, says University of Sao Paulo physicist Celso Orsini, ''There was no thought given to environmental concerns, or to preservation of the Atlantic forest, or to human beings. All of a sudden, people have woken up to the fact that Cubatao has become one of the worst pollution problems in Brazil, possibly in the world.''
World attention focused on Cubatao several years ago when residents began documenting what appeared to be alarming numbers of infants being born with serious defects. Last month, Cubatao city councilor Romeu Magalhaes added to the worrying evidence, releasing a year-long study that documents an unusually high infant mortality rate in Cubatao last year.
Scientists are still studying the data. But Cubatao's birth defect rate is one of the highest in the Americas. In addition, the evidence suggests the problem is environmentally and not genetically induced.
Industrialists are quick to note that there is no hard proof that pollution is causing Cubatao's afflictions. They point instead to the high levels of malnutrition and extreme unsanitary conditions. Camal A. S. Rameh, director of the Sao Paulo Environmental Control Agency, also claims industries have cut significantly into air and water pollution, reducing the chief one, sulfur dioxide, by 50 percent. Yet Rameh concedes that other pollutants ''still surpass air quality standards.''
Rameh says it will be two years before Cubatao can be cleaned up. Others say five years is the minimum. But any timetable will depend on the goodwill of area industries. And residents of ''the inferno'' are not heartened by the fact that between 1979 and 1982 21 industries were fined or warned more than 180 times for violating pollution standards.
An active tenants group fights the spoiling of their environment. But in Cubatao a certain weariness has set in as residents face what looks like an uphill struggle to clean up their town.