Global Pollution Gnaws Into Forest : Environment: Trace amounts of banned substances show up in New Hampshire.

On remote Mt. Moosilauke in New Hampshire’s White Mountains, scientists have found more signs that pollutants can be long-distance travelers.

Forest floor samples taken from Mt. Moosilauke and from the nearby Hubbard Brook Experimental Forest have yielded trace amounts of the insecticide DDT and industrial chemicals called PCBs, both banned in the United States since the 1970s.

Some of the toxic chemicals could have accumulated in the forest decades ago, when DDT was still used actively and PCBs were not so stringently regulated, the researchers said.

But the scientists think it’s likely that most of the chemicals originated outside the United States and were deposited in the forests relatively recently after being carried in the atmosphere, said William Smith, a Yale University forest biologist who led the study.

“It’s just another indicator of the smallness of our globe and the efficiency of the atmosphere in circulating persistent chemicals wherever they are released,” Smith said.

The study also underscores the need to combat pollution on an international basis and the important role forests play as air filters, said Smith, who serves on the science advisory board of the U.S. Environmental Protection Agency. The board is seeking broader cooperation on international environmental regulation.

The long-distance atmospheric transport of pollutants and their contamination of lakes and streams has been well documented in the United States. Less research has been done on their contamination of land, especially forests, Smith said.

Mt. Moosilauke, in north-central New Hampshire, is the westernmost peak of the White Mountains. Hubbard Brook is about five miles away. The sites are about 125 miles northwest of Boston.

The insecticide DDT, which can cause cancer in humans and is toxic to wildlife, has been banned in the United States since 1972 and is prohibited in most countries. But its use has increased in Mexico, Central America, India and eastern Europe, the scientists noted in their study, published in the November issue of Environmental Science Technology.

Production of PCBs, or polychlorinated biphenyls, was halted in the United States in 1977 because of their carcinogenic potential. The chemicals were widely used as lubricants and insulators and remain a significant source of pollution in urban and industrial areas.

Both DDT and PCBs are resistant to chemical breakdown and magnify in the food chain, meaning that concentrations of the toxic chemicals are highest in animals at the top of the food chain. Both can enter the atmosphere in the form of vapors or in combination with aerosols.

The test for the presence of DDT and PCBs came during a longstanding effort at Hubbard Brook to monitor the atmospheric transport and deposit of heavy metals generated by industry, motor vehicles and other sources. The scientists documented how lead deposits declined with the federal law banning lead in gasoline.

Because of continental air mass movement, storm tracks that have passed over centers of agricultural and industrial activity and large urban areas also frequently pass over northern New England.

Contaminants are trapped by trees and then washed to the ground or dropped there with leaves, needles and twigs. The thick organic layer in northern forests acts to absorb the chemical deposits.

“What is a bit disturbing about the PCBs and DDT is not that it is damaging the system . . . but that it is still accumulating in it,” Smith said.

In general, the Mt. Moosilauke samples had greater levels of the trace chemicals than the Hubbard Brook samples. At Moosilauke, the highest PCB reading was 252 per billion parts of soil; the highest DDT level was 192 per billion parts soil.

Samples were taken from various elevations on Moosilauke, starting about 2,700 feet and going up to the 4,810-foot summit. At Hubbard, samples were taken at elevations ranging from about 800 to 2,000 feet.

After clearing away freshly fallen leaves, twigs and other forest litter, the researchers dug no deeper than six inches to get their samples, a mix of decomposing and well-decomposed organic material.

Some samples were taken from forests 110 years old, others from areas clear-cut just five years ago. The age of the trees appeared to have no correlation to the amount of contaminants recovered.

Greater amounts of DDT and PCBs were found on slopes facing prevailing winds, which blow from the west, but the test was not large enough statistically to establish a pattern, Smith said.