Washington (CNN) -- The U.S. government is not fully guarding against the contamination of meat by traces of antibiotics, pesticides or heavy metals, a new report warns.

The U.S. Department of Agriculture's inspector general said federal agencies have failed to set limits on many potentially harmful chemical residues, which "has resulted in meat with these substances being distributed in commerce."

When it comes to pesticide traces, only one type is tested for, according to the report. There are also no set limits for some heavy metals, like copper.

In 2008, Mexican authorities turned away an American shipment of beef, because it did not meet Mexico's limits when tested for copper traces. But the very same rejected meat could be sold in the United States, since no limit has been set, the analysis says.

That example shows "the government has fallen down on the job here," said Tony Corbo of the consumer advocacy group Food and Water Watch.

"Some of the residues that the inspector general cited could be carcinogenic, as they accumulate over a period of time in the body," he said.

The study focused on contamination by chemical residues, rather than bacteria. While bacteria like E. coli and Salmonella can cause an illness that is acute but brief, chemical residues are more like to build up over time, and no amount of cooking will destroy them.

The USDA pledged to "swiftly implement the corrective actions" recommended by the inspector, which including testing for more kinds of residue and setting limits on how much of each substance is allowable. A department spokesman pointed out that this kind of fix, which is expected to require coordination with the FDA and the EPA, was one of the main reasons President Obama created a Food Safety Working Group last year.

The National Cattlemen's Beef Association said in a statement, "We fully support the critical role of the federal government in ensuring beef safety."

"While the U.S. beef supply is extraordinarily safe by any nation's standards," it added, "the beef industry is constantly looking for ways to improve the systems that ensure the safest product possible for our consumers."

The study, first reported by USA Today, also says that when cattle test positive for residue, it is difficult to track back where it came from because it often passes through several buyers and sellers.

The American Meat Institute said that problem "underscores the need to implement comprehensive livestock traceback procedures," with a national animal identification system.

CNN's Brian Todd contributed to this report.