Toxins in San Francisco Sludge

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WARNING! Sewage sludge is toxic. Food should not be grown in "biosolids." Join the Food Rights Network.

Toxins in San Francisco Sludge include a number of chemicals found in either San Francisco's sewage sludge itself or the compost given to gardeners that was made from the sewage sludge of nine counties. Four different tests exposed these toxins, two performed by the San Francisco Public Utilities Commission itself, one commissioned by the Center for Food Safety, and a fourth commissioned by the Food Rights Network. Although the results of the Center for Food Safety tests are not public, the results of the other three tests are. The results, shown below, revealed a number of toxins in the sludge, including many chemicals that are not regulated by the U.S. EPA in sludge applied to land as fertilizer.

Toxins Found in San Francisco's 2009 Sludge Testing

San Francisco's Pretreatment Program Semi-Annual Report, covering the third and fourth quarters of 2009, tested San Francisco's sewage sludge from its Southeast and Oceanside plants. San Francisco's sludge is disposed of in a variety of ways, including application to cropland as fertilizer. At the time of the report, a small amount of San Francisco's sludge was mixed with sludge of eight other counties, composted, and given away free to San Francisco gardeners. (For more information, see the article on Disposal of San Francisco's Sewage Sludge.) Below, the toxins found in San Francisco sludge from the Pretreatment Program Semi-Annual Report are listed.


1,2-Dibromo-3-Chloropropane (DBCP) is a nematicide (nematode killer) that is sold under the trade names Nemagon and Fumazone. It was used in the United States prior to 1979. In 1979, DBCP was banned in the U.S. for all uses except for Hawaiian pineapples, which was permitted until 1985. DBCP can cause kidney and liver damage, infertility, atrophy of the testes, and cancer. In the 2009 tests, it was present in the sludge from San Francisco's Oceanside facility at 89 ppb.


Bis(2-ethylhexyl) phthalate (DEHP) is an endocrine disrupting chemical commonly used in plastics for a wide range of products. In the U.S., it was banned in all children's toys and child care articles beginning February 10, 2009. DEHP was present in San Francisco's sludge from Southeast Facility in a sample from July 2009 at the concentration 0.37ppm.

Dioxins and Furans

Dioxins and furans are potent carcinogens. Because dioxins and furans vary in toxicity, they are collectively measured and compared using a TEQ - Toxic Equivalent. A sample of sludge from San Francisco's Southeast facility in August 2009 had a TEQ of 23.5. A sample from the Oceanside facility from the same time had a TEQ of 28.4.


4-Isopropyltoluene was found in San Francisco's sludge from its Southeast facility at 540ppb and in sludge from the Oceanside facility at 420ppb.

Toxins Found in San Francisco's 2010 Sludge Compost Testing

After challenges by Organic Consumers Association and the Center for Food Safety questioning the safety of San Francisco's sludge compost, a product made by Synagro using the sewage sludge of nine counties, San Francisco tested a sample of the sludge compost for 127 chemicals in 2010. The test looked for pesticides, dioxins, polycyclic aromatic hydrocarbons, volatile and semivolatile organic compounds, and heavy metals. They did not test for pharmaceuticals, flame retardants, or pathogens. Their positive findings are listed below.


San Francisco found cyanide at a concentration of 2.90 parts per million.

DDT Breakdown Products

San Francisco found two DDT breakdown products, DDE and DDD, in their sludge compost. These were present at concentrations of 14 and 37 parts per billion, respectively.


Like the prior 2009 testing of San Francisco's sludge, DEHP, an endocrine disruptor used in plastics, was found. In the 2010 tests of the sludge compost, it was present at 11 parts per million.

Dioxins and Furans

San Francisco found dioxins and furans with a TEQ (Toxic Equivalent) of 3.75 in their sludge compost.

Heavy Metals

San Francisco found a nice collection of heavy metals in its sludge compost, although none were over the legal limits for sewage sludge applied to land as fertilizer. For example, they found chromium at 39.1 parts per million, lead at 19.2 parts per million, and zinc at 495 parts per million. Interestingly, they also tested their “class B biosolids” (a.k.a. sludge) that are sent to neighboring counties for fertilizer on land growing animal feed crops and, while the class B biosolids tested under the legal limits for each of the metals, they also tested much higher than the compost itself. This is likely because the sewage sludge in the compost is diluted with yard waste and wood chips. Also, while metals are nearly the only contaminant regulated at all (aside from fecal coliform) in sludge applied to land, chromium is not regulated.

2010 Tests of San Francisco Sewage Sludge Find PBDEs, Triclosan

On August 10, 2010, the Food Rights Network announced in a news release that "Independent tests of sewage sludge-derived compost from the Synagro CVC plant -- distributed free to gardeners since 2007 by the San Francisco Public Utilities Commission in their "organic biosolids compost" giveaway program -- have found appreciable concentrations of contaminants with endocrine-disruptive properties. The independent tests were conducted for the Food Rights Networkby Dr. Robert C. Hale of the Virginia Institute of Marine Sciences."

In an August 6, 2010, letter reporting on his findings to the Food Rights Network Robert Hale wrote: "A sewage sludge-derived compost from the Synagro CVC plant, distributed by the San Francisco Public Utilities Commission in their "compost give away" program, was analyzed for synthetic pollutants. Several classes of emerging contaminants with endocrine disruptive properties were detected in appreciable concentrations, including polybrominated diphenyl ether (PBDE) flame retardants, nonylphenols (NPs) detergent breakdown products and the antibacterial agent triclosan." PDFs are attached here of the letter and the data: [1] [2] [3] [4]

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