The border between the United States and Mexico is fortified with walls and fences and patrolled by aircraft, remote-sensing technology, and an increasing number of border patrol agents.

But just putting up barriers doesn’t break the deep-rooted economic and cultural ties between the two countries. And it doesn’t stop the environmental and public health concerns that straddle the border and demand solutions from both nations.

At the recent American Association for the Advancement of Science meeting in San Diego, scientists described how the Los Laureles Canyon, which stretches from Tijuana to the San Diego wetlands, is ravaged by pollution. This causes public health problems for impoverished Tijuana residents and environmental problems that affect migratory birds and people on both sides of the border.

Hiram Sarabia of the UCSD NIEHS Superfund Research Program describes the canyon as an “urban observatory” that mirrors thousands like it along the 2,000-mile length of the border. Debris, wastewater, and contaminated dust and soil from a large swath of Tijuana funnel into the canyon streams, which ultimately empty into the Tijuana estuary and then the Pacific Ocean on the U.S. side of the border.

The debris-filled, dusty hillsides of the canyon, home to 65,000 Mexicans, are within several miles of the opulent hotels and popular beaches of downtown San Diego, though most Americans have never been there.

As Kim Larsen documented in a Fall 2009 cover story for OnEarth, impoverished Mexican residents typically have little access to quality health care, and public health issues that arise in Mexico also impact U.S. residents. The United States spends about a million dollars a year dredging the estuary, and the pathogens and toxicants streaming through the canyon into the estuary and local beaches have other financial and health costs.

Tijuana’s population increased quickly and exponentially in recent decades, largely to fuel the maquiladora sector, which are factories owned by U.S. and foreign companies that line the Mexican side of the border. Shantytowns sprung up with little infrastructure or planning, meaning roads are unpaved and there are no sewage systems. Soapy water and raw sewage run in streams of “agua negra” running through the canyon, where kids play and stray animals drink.

Pathogens from raw sewage, dead animals, and other sources accumulate in the water and in the dust that permeates Tijuana and washes into the estuary. Canyon residents are at high risk for Valley Fever, a bacterial disease spread through dust. Residents in the “colonias” (or villages) hugging the canyon hillsides report high incidences of skin and respiratory disease and eye irritation.

Meanwhile, toxicants including PCBs, PAHs, heavy metals, and dioxins are rampant. Water and air emissions and solid waste from maquiladoras make their way into soil and streams. Illegal dumping of hazardous chemical and industrial waste is widespread. And heavy metals and chemicals slough off from the tires, trashed appliances, and other discards used to build retaining walls and shacks throughout the canyon.

These old tires and washing machines symbolize the interlocked fortunes of the United States and Mexico in this region: they are likely to be manufactured by American companies in Mexican maquiladoras, then sold to U.S. consumers, then returned to Mexico on the second-hand market, then reused to bolster crumbling shantytown cliffs. Ultimately, toxics from these products flow through the canyon back into the United States.

Scientists and advocates say environmental and planning policy at the border is a messy realm, with a serious dearth of agencies, policies, or legal frameworks to facilitate infrastructure and environmental improvements. The North American Free Trade Agreement, which took effect in 1994, was supposed to create mechanisms for environmental protection and bi-national cooperation, but that has not been the case in any meaningful way.

San Diego State University professor and author Lawrence Herzog said the maquiladora industry bears much responsibility for addressing the environmental and health problems in Los Laureles canyon and beyond.

“The U.S. and multinational corporations who use the border to profit have not stepped up to the plate to pay for the advantages they are gaining from the region,” Herzog said. “Why aren’t the multinational companies that are making billions from cheap labor paying for infrastructure and the problems they’re creating?”

Some solutions are relatively simple and inexpensive. Scientists and advocates are involving U.S. volunteers and Tijuana residents to pave roads with hexagonal concrete tiles, which cuts down on dust and erosion. Oscar Romo, with NOAA’s coastal training program, has worked with locals to build strategically engineered retaining walls out of tires.

Romo said this doesn’t create contamination like the haphazard tire retaining walls, and it diverts tires from ending up in the estuary. He said his project reused 10,000 tires in a month, while the government of Baja state has only removed 2,000 tires in a year.

Scientists are also mapping and analyzing contamination and sedimentation patterns to better understand the challenges and possible solutions. Keith Pezzoli of the UCSD NIEHS Superfund Research Program said that while U.S. agencies spend about a million dollars a year dredging the Tijuana estuary, “with a fraction of that amount of money you could do a proactive intervention in the (Tijuana) hillsides to stabilize the land.”

Sarabia said that scientists gathering information and working with community groups in Tijuana can help build the political will and grassroots process needed to address the canyon’s problems on a number of levels.

“Our role builds capacity of the community to identify, prioritize and address contamination and public health problems,” said Sarabia. “You can’t make decisions in a vacuum. We need to work closely with the community, to provide incentives for them to work with us, and our projects have the potential to create jobs in the community.”

By Kari Lydersen, OnEarth Magazine