Was Your Food Grown in Sewage Sludge?

With all the poo-pooing of organic food in the media lately, here are some reasons to eat organic that might convince even the most die-hard skeptic.

With all the poo-pooing of organic food in the mainstream media lately, I thought I’d post this week on one little-known reason to eat organic that might convince even the most die-hard organic skeptic:


Ironically, while industrial agriculture methods leave vast quantities of extremely useful animal manure to languish in toxic lagoons that destroy quality of life all around them, it is common practice for industrial farmers to use human waste-water treatment by-products, also known as sewage sludge (or, in industry PR-speak, “biosolids”), as fertilizer.

But, not all poop is created equal.

Theoretically human urine and feces (“humanure”) could make an effective fertilizer source for crops, and in a true closed-loop agricultural system, we would return all of our organic waste to the land.

However, human waste isn’t the only thing we flush down the drain.

This means that whatever the stew of sewage contains—things like drain cleaner, industrial chemicals, heavy metals, radioactive medical fluids, heart medications, antibiotics, birth control pills, statin drugs, etc.—will get into the soil, the food supply, and the ecosystem.

In fact, there are thousands of substances that can be found in typical sewage sludge, including any of the 100,000 or so chemicals produced and used in industrialized nations, many of which illegally end up in the sewers.

Anything that is washed down the sink, flushed down the toilet, or dumped into a sewer—and that is removed from water by the treatment process—becomes sludge.

Cultivating Super Bugs

According to research published in the European medical journal Acta Veterinaria Scandinavica, scientists have recently found antibiotic resistant “super bugs” in sewage sludge—and they are sounding the alarm about the danger of antibiotic resistant genes passing into the human food-chain.

Leena Sahlstrom, from the Finnish Food safety Authority, with a team of scientists from the Swedish National Veterinary Institute, investigated sewage sludge from a waste-water treatment plant in Uppsala, Sweden. The researchers gathered sludge from the plant each week for four months.

Out of the of 77 samples collected, 79 percent of these tested positive for the drug-resistant super bugs known as vancomycin-resistant enterococci (VRE).

Enterococci are bacteria that are normally present in the human intestines and the female genital tract. They can also sometimes be found in the environment. However, if the immune system doesn’t keep these germs in balance, enterococci can gain an upper hand and cause infections in skin wounds, the urinary tract, and the bloodstream—and the resulting illnesses can range from mild to life-threatening, especially for those with compromised immune systems.

But the risk VRE strains pose by getting into the food supply isn’t only related to the possibility people and animals may get infections from them. The Finnish research points out this disturbing possibility: VRE in the fertilizer-used sewage sludge may pass on their resistance genes to other bacteria, creating a host of new super bugs.

Dr. Sahlstrom concluded that:

“Antimicrobial resistance is a serious threat in veterinary medicine and human healthcare. Resistance genes can spread from animals, through the food-chain, and back to humans. Sewage sludge may act as one link in this chain.”

If you needed any more reasons to eat only organic food, here’s a great one!

Just Say NO to “Biosolids”

Antibiotic resistant bacteria is a significant problem, but it is definitely not the only problem with using sewage sludge as fertilizer:

  • Sewage sludge can cause inheritable, genetic mutations in DNA, but no one seems sure what this means for human or animal health. Regulations for the use of sewage sludge ignore this information.
  • Two-thirds of sewage sludge contains asbestos. Because sludge is often applied to the land dry, asbestos may be a real health danger to farmers, neighbors and their children. Again, regulations don’t mention asbestos.
  • Governments issue numeric standards for metals. However, the movement of metals from soils into groundwater, surface water, plants and wildlife—and of the hundreds of other toxins in sludge—is poorly understood.
  • Soil acidity seems to be the key factor in promoting or retarding the movement of toxic metals into groundwater, wildlife and crops. The National Research Council (NRC) of the National Academy of Sciences gives sewage sludge treatment of soils a clean bill of health in the short term, “as long as…acidic soils are agronomically managed.” However the NRC acknowledges that toxic heavy metals and persistent organic pollutants can build up in treated soils.
  • Research clearly shows that, under some conditions (which are not fully understood), toxic heavy metals and organic industrial poisons can be transferred from sludge-treated soils into crops. Lettuce, spinach, cabbage, Swiss chard, and carrots have all been shown to accumulate toxic metals and/or toxic chlorinated hydrocarbons when grown on soils treated with sewage sludge. In some instances, toxic organics contaminate the leafy parts of plants by simply volatilizing out of the sludge.
  • There is good reason to believe that livestock grazing on plants treated with sewage sludge will ingest the pollutants—either through the grazed plants, or by eating sewage sludge along with the plants. Sheep eating cabbage grown on sludge developed lesions of the liver and thyroid gland. Pigs grown on corn treated with sludge had elevated levels of cadmium in their tissues.
  • Small mammals have been shown to accumulate heavy metals after sewage sludge was applied to forest lands.
  • Insects in the soil absorb toxins, which then accumulate in birds.
  • It has been shown that sewage sludge applied to soils can increase the dioxin intake of humans eating beef (or cow’s milk) produced from those soils.
  • Lethal substances like dioxins, furans and PCBs, which can be found in sewage sludge, are not regulated by governments.

Fortunately, sludge-based fertilizers, or biosolids, are not allowed in certified organic agriculture.

Related: Can Organic Farming Feed the World?


One of the reasons that environmental organizations have either supported or not complained about the use of sewage sludge as fertilizer is that the alternatives of incineration or landfilling our waste are just as bad, if not worse.

But, according to some researchers, if the sludge is properly composted, it may be relatively benign. In fact, composting sewage sludge is being promoted within the organic movement by Compost Science, a sister publication to Rodale’s respected Organic Gardening magazine.

Others suggest that sludge can be recycled in a variety of ways that are both environmentally beneficial and sustainable, and don’t involve application of potentially toxic materials to croplands.

These include using anaerobic digestion to produce biogas, pyrolysis of the sludge to create syngas and potentially biochar, or incineration in a waste-to-energy facility for direct production of electricity and steam for district heating or industrial uses.

If methane from sewage sludge is captured rather than allowed to outgas, it can be used for fuel, closing the carbon cycle.

Until we can figure out how to properly compost or recycle all sewage sludge, we shouldn’t be using it on arable land at all! In the meantime, add the fact that you don’t want to consume antibiotic resistant super-bugs, heavy metals, pharmaceuticals or toxic pollutants to your long list of reasons to eat organic.




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