Pollution knows no borders - and that creates problems for the US and Mexico

The border lands of the United States and Mexico are a strange territory when it comes to controlling the natural environment. Pollution problems get top-level attention from far-away Washington and Mexico City because they are matters of international relations. But doing something about them is an awkward and difficult exercise.

What encourages environmental scientists on both sides of the border is that the governments of the two countries view this dilemma roughly the same way.

A common example of how the border foils environmentalists is the case of DDT. Banned in this country, the pesticide is still produced by American companies for export to Mexico.

There, Mexican growers use 10 to 20 times the normal dosage of the toxin to make their fruits and vegetables ''look good,'' according to environmental engineer Fernando Ortiz de Monasterio of El Colegio de Mexico.

Much of this produce, of course, comes right back across the border into the United States, where border inspectors often judge it best - most pest-free - when ''dripping with pesticides,'' according to Paul Ganster of the Latin American Center at the University of California, Los Angeles.

Although American problems get more attention, Mexico has border pollution problems, too.

One is that Americans sometimes cross the border to do what Americans have disallowed on their own turf. Americans have recently been caught hauling toxic industrial chemicals south of the border to dump them.

More significant to Mexicans, says Dr. Ortiz, are plans for a permanent radioactive-waste dump at Carlsbad, N.M. The plans call for storing 57,000 cubic meters of waste in cannisters there over a period of 10 years. If those cannisters were to leak, says Ortiz, the only underground flow would be due south into Mexico.

Environmental concern in Mexico is on the rise, according to Dr. Ganster, especially because of the ''catastrophic situation'' in the Mexico City area, where the smog is legendary and industrial waste dumping has been virtually unrestricted for 50 years.

''A very unique thing about the border,'' says Ganster, ''is that domestically a lot of these things would be ignored, but when people across the border start screaming, then it gets attention.''

An August agreement signed by the presidents of both countries launched what could amount to a major binational effort to improve the border environment.

This environmental diplomacy has moved very slowly in the past, but now negotiations appear to have been taken more seriously, says Ortiz.