SAN FRANCISCO — Wal-Mart Stores Inc. admitted to improperly handling and disposing of hazardous materials at its stores nationwide, pleading guilty Tuesday to several federal criminal and civil counts and agreeing to pay more than $81 million.

The accusations against the retail behemoth spanned three criminal cases from the Justice Department and a related civil case brought by the U.S. Environmental Protection Agency.

Wal-Mart said its failings — not training workers to properly deal with and discard hazardous waste, including pesticides, detergents, paints and aerosols, some of which ended up in municipal trash bins or in local sewers — were remedied years ago.

Prosecutors also said waste taken back to stores by customers was delivered by the company to product return centers without required safety documentation.

“The incidents on which the charges are based occurred years ago and involved the transportation and disposal of common consumer products,” the company said in a statement. “No specific environmental impact has been alleged and since then, Walmart designed and implemented comprehensive environmental programs that remain in place today.”

The U.S. attorney’s offices in Los Angeles and San Francisco consolidated six misdemeanor counts in the Northern District of California accusing Wal-Mart of violating the Clean Water Act. Starting in 2003, employees were seen pouring “corrosive and hazardous liquid wastes” down drains linked to public sanitation works in Southern California, according to court filings.

The Bentonville, Ark., retailer struck a plea agreement to pay a $40 million criminal fine while also shelling out $20 million for community service projects.

In a separate criminal case in Kansas City, Mo., Wal-Mart admitted that it violated the Federal Insecticide, Fungicide and Rodenticide Act when it sent some 2 million pounds of pesticides and other hazardous products in damaged containers to an overwhelmed and under-registered third party recycling business from 2006 to 2008.

The company agreed to pay $11 million in fines and an additional $3 million to the state’s Department of Natural Resources to fund future inspections and education efforts.

“Today’s criminal fine should send a message to companies of all sizes that they will be held accountable to follow federal environmental laws,” said Tammy Dickinson, U.S. attorney for the Western District of Missouri.

Wal-Mart will also pay a $7.6 million civil penalty.

In 2010, facing related accusations in California, Wal-Mart agreed in a settlement to pay the state $27.6 million. It also addressed similar complaints in Missouri last year. In total, the company faces $110 million in fines and settlements at the state and federal levels.

Wal-Mart said it began implementing an environmental compliance program in 2006 that includes nearly 50 dedicated staff members, hazardous waste identification via workers’ handheld consoles and shelf labels, and more training efforts.

“We are pleased that this resolves all of these issues raised by the government,” Phyllis Harris, chief compliance officer for Wal-Mart U.S., said in a statement.