ENDANGERED MEXICO: An Environment on the Edge.<i> By Joel Simon</i> .<i> Sierra Club Books: 276 pp., $27</i>

Last July, Pati Ortiz, a 34-year-old mother of three, was sitting at an outdoor food stand in the poor Mexico City neighborhood of Iztapalapa when she disappeared into the ground. There was a loud noise, witnesses said, and seconds later, she was gone, sucked into a 20-foot sinkhole. In a doomed rescue attempt, several bystanders jumped into the hole and were immediately met by poisonous underground fumes. When an ambulance arrived 90 minutes later, four people, including Ortiz, were dead.

This is one of the many terrifying images in Joel Simon’s “Endangered Mexico,” a powerful corrective to the glossy travel magazines and tourist guidebooks whose pages are filled with seductive photographs and appealing descriptions of Mexico’s natural landscape. But for every natural wonder like Zihauatenejo, Tulum and the Copper Canyon, countless areas have been soiled by industrialization gone awry.

“Endangered Mexico” is a portrait of a nation reeling from five centuries of environmental degradation. The consequences are apparent to anyone who has experienced Mexico City (or “Makesicko City,” in Carlos Fuentes’ formulation): a place where birds fall dead from the smog-choked sky, where the nitrogen dioxide levels are equal to levels in New York’s Lincoln Tunnel and where one can get intestinal parasites simply by breathing the air.

Yet Simon, an associate editor at Pacific News Service, comes to realize in the course of his investigation that Mexico City’s air pollution is symptomatic of a much deeper crisis. Armed with camping equipment and a notebook, he embarks on a journey that takes him from the shantytowns of the capital to the impoverished Mixteco villages of Oaxaca; from the Lacandon jungle, home of the Zapatista rebels, to the lakes and rivers of Tabasco, ruined by decades of brazen abuse by Pemex, the state oil monopoly. Wherever he goes, he finds environmental destruction and plunder and, among the local population, a strong undercurrent of sadness and resignation. But he also finds activists determined to protect their land, resources and dignity, even if it means confronting hired thugs and violent drug traffickers.

Simon’s story begins five centuries ago, when a small group of Spaniards led by Hernando Cortes arrived in Mexico and discovered the Aztec city of Tenochtitlan, which consisted of thousands of small islands divided by canals--the “Venice of the New World.” Aztec engineers had constructed a dazzling urban infrastructure: A giant stone aqueduct delivered fresh water to the city, while other ingenious methods were employed to dispose of human waste. In contrast to filth-ridden 16th century European cities, Tenochtitlan’s streets were lined with flowers and rooftop gardens.

But most of the city’s hydraulic infrastructure was deliberately destroyed by Cortes during his two-year campaign, and in subsequent years, Tenochtitlan--renamed Mexico City--degenerated into squalor. Ignorant of the complex ecosystem they had inherited, the Spaniards dumped the corpses of Indians, dogs and horses (not to mention garbage and other refuse) into the canals. Frustrated by continuous flooding, the Spaniards eventually made a fateful decision, one that would forever influence the future of Mexico City: Hundreds of square kilometers of lakes and rivers were drained in a massive undertaking that effectively destroyed the ecological makeup of the entire region.

These are the roots of Mexico City’s late 20th century woes, which include a severe water shortage in addition to air pollution. Today, 70% of the water supply for a city of more than 20 million people is provided by an underground aquifer that is rapidly drying up, resulting in a contraction of the soil. Consequently, Mexico City is literally sinking: The downtown portion of the capital is 34 feet lower than it was at the time of the conquest. The sinkhole in Iztapalapa--which like many poor barrios was built on a dried lake bed--is a direct result of this subsidence.

While the harrowing chapter on Mexico City is essential reading for any visitor to the sprawling metropolis, the rest of the book contains equally fine reportage and analysis. In a chapter on the crisis in the countryside, where many villages have been abandoned by people looking elsewhere for work, Simon argues that the exodus can be traced, paradoxically, to the popular agrarian reform policies undertaken in the 1930s by Lazaro Cardenas, Mexico’s most revered president. Much of the redistributed land was barren, barely suitable for growing corn and beans, and in a relatively short time became useless. Later, the government urged peasants to make use of chemical fertilizers, but few villages could afford them.

Three years after the unrest in Chiapas burst into the news, media coverage of the conflict has waned. But Simon reminds us that the region remains volatile.

He depicts the Lacandon jungle, on the border of Chiapas and Guatemala, not as merely a battleground between the Mexican army and the Zapatista rebels but as an arena of competition for scarce resources among groups of poor farmers--some of whom are indigenous to the region and many others of whom are land-hungry migrants drawn from neighboring states. The most impoverished among them have little choice but to practice slash-and-burn farming and small-scale cattle raising, both of which are contributing to the swift destruction of the jungle.

This helps explain why Mexico has the highest rate of deforestation in the world, and it is difficult to calculate the loss. Standing in a remote corner of the rain forest, Simon is reminded of the innumerable ecological tragedies that occur every day because of deforestation; a biologist tells him that in a single cecropia tree there are more species of ants than you’ll find in all the rest of North America.

By any measurement these are tragic, even heartbreaking developments. But given the domestic problems in the United States, should Americans concern themselves with the amount of fecal dust in Mexico City’s air, the poisoning of Sinaloa’s farm workers or the details of the Mexican government’s agricultural policies? Yes, because the destinies of the United States and Mexico are linked in countless ways other than stock transactions and debt payments.

The decline of Mexico’s subsistence agriculture matters because many of those forced off their land will eventually find their way to Chicago or New York or Los Angeles. Indeed, the most astonishing statistic in “Endangered Mexico” is the fact that by the first decade of the next century, somewhere between 5 million and 15 million farmers are expected to leave the countryside; there is no evidence that the Mexican economy in the largest cities can absorb even 20% of them. Meanwhile, peasants who choose to stay on their land are increasingly switching from corn to opium and marijuana production (just like their counterparts in Peru and Colombia). Meanwhile, deteriorating ecological conditions in Mexico City, home to a third of the population, will only spur additional migration.

Though pollution on the border is a topic of increasing public concern in the United States, it is nevertheless essential that we acknowledge the risk of a major environmental catastrophe. For example, a Pemex oil spill sent 3 million barrels into the Bay of Campeche in 1979, and some of it landed on the Texas shore. And in 1992, the Environmental Protection Agency learned about the release of a cloud of hydrochloric acid in Mexicali (an accident that resulted in the evacuation of 10,000 residents) two days after the incident, despite an accord promising immediate notification. This incident ought to remind us that the Institutional Revolutionary Party, Mexico’s ruling party, is first and foremost interested in its own political health. (Recall that during the recent debate over the United States’ certification of Mexico as a cooperative ally in the worldwide narcotics battle, the Zedillo administration withheld information about narcotics-related corruption until the day after the president’s decision.)

As long as Mexico is governed by an astoundingly corrupt authoritarian regime--a regime that did not acknowledge Mexico City’s air pollution until 1979, 20 years after it was initially documented--Simon reminds us that in spite of NAFTA, Mexico is an incompetent and wholly unreliable ally in the fight against pollution and environmental devastation.

This admirable book, written with the proper combination of controlled passion and detachment, contains a few omissions. Today, the most dynamic political force in Mexico is the conservative National Action Party, which governs four key states and 38% of the overall population. PAN stands to do very well in the July 6 midterm congressional elections, and many analysts expect a PAN candidate to win the presidency in three years.

In this context, a careful assessment of the environmental situation in PAN-controlled regions such as Guanajuato and Jalisco would have been useful. Moreover, Simon has little to say about Mexico’s Green Party, which garnered less than 1% of the vote in the 1994 presidential election: In one of the most polluted countries on Earth, what explains the weakness of the Green movement?

The book ends in the Chincua Reserve in the mountains of Michoacan, home to a large number of monarch butterflies that take refuge there each winter. When a freak snowstorm jeopardizes their survival, Simon joins environmentalists in the United States and Mexico who are concerned about the butterflies’ possible imminent extinction. He decides to investigate and drives to Michoacan.

He surveys the landscape with a mixture of “awe and horror”: millions of butterflies cover every inch of each tree, but the snow-covered ground is littered with many that have died. Suddenly, to his amazement, the ground moves--the butterflies are fluttering their wings. “They’re not dead,” declares his scientist companion. “They’re only stunned. They’re moving their wings in order to raise their body temperature so they can fly again.”

Whether Mexico’s environment will, like the butterflies, get a second chance remains to be seen.