Where Our Materials Come From and Where They Go: A USGS Look at Material Flows

The materials-flow cycle. U.S. Geological Survey.

More people using more goods and services have a growing effect on the environment. Studies once focused on the obvious harms, polluted rivers, smog and acid rain, and then widened to subtler ones: ozone depletion, greenhouse gases, lost biodiversity and toxic substances building up in living things. A U.S. Geological Survey circular looked at the part materials play: how the economy uses them, how they flow from mine or forest to the dump or back into use, and whether they will run short.

An economy made of stuff

Between 1950 and 2000 the U.S. economy grew nearly fivefold, from $2.0 trillion to $9.9 trillion (in 2000 dollars), while the population rose from 152 million to 281 million; by 2000 the world held more than 6 billion people, nearly half of them in cities. Meeting their material hopes means extracting, processing and moving ever more renewable and nonrenewable resources.

World population passed 6 billion by 2000. U.S. Geological Survey.

"Consumption" in these statistics means using up the service a product gives, not destroying its material. A car is counted as consumed the year it leaves the showroom, but it carries its owner for years and then goes to be recycled. The cement, sand and stone "consumed" by the Hoover Dam (built from 1931 to 1936) are still at work, like those in the Golden Gate Bridge, the Statue of Liberty and the Empire State Building; infrastructure can last 35, 50 or 100 years, so today's materials are an investment in tomorrow. Other uses dissipate their materials: the part of a brake lining that wears away as dust along the road can never be recycled.

Renewable and nonrenewable materials used in the United States. U.S. Geological Survey.

What America uses. By weight, crushed stone, sand and gravel make up as much as three-quarters of the new raw materials used each year, a share that jumped with the building of the Interstate highways after the Second World War and now goes mostly into rebuilding roads, bridges and buildings. Other industrial minerals come next: cement, potash and phosphate for fertilizer, gypsum for drywall, soda ash for glass, sulfur and more. Nonrenewable organic materials, plastics, synthetic fibers and the like, grew from about 2 million tons in 1900 to 148 million tons in 2000, replacing wood, natural fibers and metals where they were cheaper or better.

U.S. flow of raw materials by weight over the twentieth century. U.S. Geological Survey.

A global trade

Resources are extracted where they occur, processed wherever it pays and consumed somewhere else again, so materials are heavily traded. In 2000 the United States relied entirely on imports for a list of nonfuel minerals, among them bauxite and alumina, manganese, fluorspar, graphite, niobium, quartz crystal, sheet mica, strontium and asbestos, bought from countries such as China, Brazil, Canada, Mexico and South Africa.

Recycling

Better technology, lower costs and consumer demand have driven recycling of metals, paper, concrete and wood. In 2000, an estimated 62.1% of aluminum beverage cans and 45% of paper were recovered for recycling, and the recycling rates for steel were 95.0% for cars, 84.1% for appliances and 58.4% for steel cans.

Following one substance

Material-flow studies track a material from extraction through processing and use to disposal or recycling, and find where it leaks into the environment along the way. Two examples:

• Mercury. Mercury, its vapor and most of its compounds are poisonous, and the amount released into the living world has grown since the Industrial Revolution. All the mines producing primary mercury were abroad, most of the world's mercury-cell chlor-alkali plants were outside the U.S., and international trade in mercury ran to about 1,400 tons in 1996, under rules that differ from country to country.
• Sulfur. Through sulfuric acid, the chemical the United States produces in the greatest quantity, sulfur is one of the most important industrial raw materials; sulfuric acid use has long been an index of a country's industrial development. Unusually, the sulfur industry's problem is too much supply: most sulfur now comes not from mines but from pollution controls, recovered at oil refineries and metal smelters to cut sulfur dioxide emissions and removed from natural gas as poisonous hydrogen sulfide.

The domestic flow of mercury in 1996, in metric tons. U.S. Geological Survey.

The many contributors of sulfur to the environment. U.S. Geological Survey.

Such studies need consistent, reliable data, including "hidden flows" such as mine waste and the earth moved to build roads, which never appear in ordinary statistics.

Balancing needs and impacts

As population grows and people everywhere seek a richer material life, the world is being changed, and waste generated, on an unprecedented scale. Nothing can be supplied without some harm somewhere: a road displaces animals, a dam changes fish habitat, a house takes trees. Some resources will always be needed. The challenge, the report concludes, is to use them wisely, weighing material needs against their effects on the planet's life-support systems and on the environmental values people hold.

Sources

• U.S. Geological Survey, "Materials in the economy; material flows, scarcity, and the environment," Circular. Pictures in the report from commercial clip-art collections are not reproduced.