Some 6.16 billion pounds were released that year, down from 7.1 billion pounds a year earlier, the Environmental Protection Agency reported.
Hard-rock mining companies and coal-burning power plants repeated their status as the biggest polluters. EPA's Toxics Release Inventory, created under 1986 law, includes information on more than 650 toxic chemicals.
Linda Fisher, EPA's acting administrator, said the inventory is one of the most important things EPA does. People can now see figures mapped by state and county on the Internet, she said.
By chemical, the most pollution came from copper and zinc compounds, hydrochloric acid, and lead, manganese, arsenic, nitrate and barium compounds. Sixty-nine percent of the chemicals went into the land, 27 percent into the air and 4 percent into the water.
EPA required facilities to provide data if they used or produced more than 100 pounds of lead; previously, they did so if they used more than 10,000 pounds or produced more than 25,000 pounds. Lead releases in 2001 increased to 443 million pounds, up from 374 million pounds in 2000.
Because of the change in how lead was tallied, EPA calculated that if lead is taken out of the picture the total amount of all other toxic chemicals released into the environment in 2001 was 15.5 percent less than in 2000.
Dioxin, a chemical that is worrisome in even small amounts, increased to 328 pounds, up from 220 pounds the year earlier.
"The good news is that overall pollution has declined," said Jeremiah Baumann, an environmental health specialist for U.S. Public Interest Research Group. "But the bad news is that for some of the most toxic chemicals, we're seeing more, not less pollution."
EPA said mining of hard-rock minerals such as gold, silver, copper and lead made up the biggest portion, 45 percent, of all chemical releases. The industry was responsible for nearly 2.8 billion pounds of toxic pollutants in 2001 — down from 3.4 billion pounds the year before.
Coal-burning electric generating plants were responsible for 17 percent of toxic pollutants in 2001. That was slightly more than 1 billion pounds, down from 1.2 billion pounds in 2000.
Industry spokesmen praised the latest figures.
"Once again the hard science backs up what we have been saying for years," said Jeffrey Marks of the National Association of Manufacturers. "America's environment is steadily improving. Our air and water are much cleaner today than they were 30 years ago."
Greg Lebedev, president of the American Chemistry Council, said some companies have taken it upon themselves to pollute less. "Because of the dialogue our companies have had with their communities, we've been performing better as an industry," he said.
Nevada, Utah, Arizona and Alaska were the top four polluters, each reporting more than 500 million pounds of toxic chemicals in 2001.
They were followed by Texas, with 271 million pounds; Ohio, with 255 million pounds; Pennsylvania, with 207 million pounds; Indiana, with 206 million pounds; Tennessee, with 149 million pounds; and North Carolina, with 148 million pounds.
By county, the largest number of chemical releases were in Utah's Salt Lake, with 732 million pounds; Alaska's Northwest Arctic, with 432 million pounds; and Nevada's Elko, with 328 million pounds.