A national environmental group is focusing attention on a San Francisco program that transforms human waste into backyard compost, calling the program little more than a scheme to sling toxic toilet sludge back at the people who produced it.

The hullabaloo is over a program by the San Francisco Public Utilities Commission, which once a year distributes biosolid compost to gardeners, school groups and homeowners for free. The commission claims the compost is heat-treated fertilizer that is as good as the stuff sold in gardening stores.

But the Organic Consumers Association insists that the sacks given out to San Franciscans contain a stew of excrement and toxic chemicals from the sewer.

“The problem with sewage sludge or the euphemistic term ‘biosolids’ that they use is that all of this is hazardous material that potentially contains thousands and thousands of contaminants,” said John Stauber, a member of the group’s advisory board and the author of several articles and a book on sewage sludge. “Everything that goes in the sewer potentially ends up in it.”

The San Francisco PUC has largely dismissed the criticisms, saying the levels of toxins found in the compost are well below federal and state standards.

“We are giving away highly treated, heat-pasteurized biosolids,” said Tyrone Jue, spokesman for the Public Utilities Commission. “It has been tested for metals and pathogens and is basically sterile.” High-profile protests

The consumers association and another nonprofit environmental group, the Center for Food Safety, staged a protest on March 4 in San Francisco, where demonstrators dumped the compost on the steps of City Hall. The organizations sent a letter to Mayor Gavin Newsom demanding a halt to the distribution of the soil-like material, which they believe contains heavy metals, pharmaceuticals, flame retardants and other hazardous material.

The leaders of the group are concerned children and others who touch the compost might swallow or absorb chemicals into their bloodstreams. They are also afraid that food grown in the stuff could be contaminated.

The dustup has since spread to Berkeley where the group last week picketed Chez Panisse and criticized the restaurant’s famous chef, Alice Waters, for allegedly turning a blind eye to the PUC’s antics. The demonstrators accused Francesca Vietor, the executive director of the Chez Panisse Foundation, of “actively promoting sewage sludge,” because she is also a PUC commissioner.

Stauber has claimed that tests conducted by his organization found dioxins, flame retardants and other chemicals in the compost, but he has declined to release comprehensive results.

“They have chosen not to release those tests to the public or us,” Jue said. “Yet they are willing to stand in front of a camera and say our biosolids are toxic. How can we even respond to this if they aren’t releasing their information to be analyzed?”

Waters, too, hit back, accusing the group of engaging in a smear campaign that “shamelessly misrepresented her position.” The Chez Panisse Foundation accused Stauber of knowingly repeating “false accusations” against Vietor.

“Mr. Stauber and the OCA have attempted to taint the reputations of Alice Waters and Francesca Vietor, both of whom have long and outstanding records as environmental advocates,” the foundation said in a statement. “Alice Waters believes deeply in organic farming and gardening. Her 40 years of advocacy on this issue speak for themselves.”

The issue is a complicated one. Composting has for decades been considered an ecologically sound way to recycle eggshells, lettuce and other food waste. Soil naturally breaks down such material, almost as if it was the Earth’s microbial liver.

The San Francisco PUC began the composting program in 2007 in an effort to help the environment and reduce the city’s carbon footprinw by eliminating dump truck trips. Compost chemistry

The program uses about 20 tons of the 82,000 tons of solid material removed from the city’s sewage every year. The treated waste is taken to a regional composting facility in Merced County, where it is mixed with green yard waste and heated to 130 degrees for 30 days, Jue said.

The end product is touted by the PUC as a valuable source of nutrients that can be used to improve soil fertility, plant growth and lessen the need for synthetic sprays.

Yet critics insist that the process does not neutralize heavy metals, pesticides or drug residue. Exacerbating the problem is the fact that the U.S. Environmental Protection Agency requires the compost be tested for only nine pollutants, about 1 percent of the hazardous materials that can be found in sewage. Dioxins, flame retardants and PCBs are not among the chemicals tested.