The Real Dirt on Sewage Sludge
by Wendy Priesnitz

Photo credit U.S. Fish and Wildlife Service

Hold your nose! Waste from households and industries treated at a sewage plant may be spread on a farmer's field near you. Unfortunately, it may contain heavy metals and other nasty surprises that could end up on your dinner plate.

The safe disposal of hazardous waste has been a challenge for both industry and governments for decades. Under increasing assault by environmental groups for dumping waste into landfills, oceans, rivers and lakes, or burning it in incinerators, corporations and governments seem to have agreed upon a new solution.

They rename the waste as fertilizer or dust suppressant and spread it on farmers’ fields and country roads. The code word for this practice is “beneficial use”. While it may be an environmentally sound example of recycling, in many cases it’s merely relocating pathogens rather than disposing of them.

Although many different industries are “recycling” their toxic waste in this manner, one of the most controversial substances is sewage sludge, which is widely used as a soil amendment by farmers in both the United States and Canada.

Sewage Sludge By Any Other Name

Sludge is the mud-like material that remains after treatment of the wastes that flow into local sewage treatment plants. In the U.S., it is estimated that approximately half of treated sewage sludge – about seven million dry tons per year – is applied to farm fields as fertilizer. In many cases, it is provided to farmers for free. If human wastes were the only thing entering the sewage treatment plants, then sewage sludge would be a relatively safe, nutrient-rich fertilizer that could be safely used in this manner. However, sewage treatment plants also inevitably receive industrial and household toxic wastes.

In a November, 1990 edition of the United States Federal Register, the Environmental Protection Agency (EPA) had this to say of sewage sludge: “Typically, these constituents may include volatiles, organic solids, nutrients, disease-causing pathogenic organisms (bacteria, viruses, etc.), heavy metals and inorganic ions, and toxic organic chemicals from industrial wastes, household chemicals and pesticides.”

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 dumped into a sewer – and that is removed from water by the treatment process – becomes sludge.

This sludge is being legally marketed to farmers who plough it into soil as fertilizer. Although the practice has been around for more than forty years, there has been a dramatic increase since 1990, according to Agriculture and Agri-Food Canada. This has prompted governments to put in place standards to regulate the levels of toxics in the final product.

Some Canadian provinces have their own regulations, as does the federal government. Agriculture and Agri-Food Canada’s Food Production and Inspection Branch has set maximum acceptable metal concentrations for processed sewage and sewage-based products which are sold as fertilizers or supplements.

Ontario’s guidelines require that each field on which sludge fertilizer is to be spread must be approved and monitored to ensure the mandated nitrogen to heavy metal ratio is not exceeded. The Ontario Ministry of the Environment and Energy maintains the practice is very safe and will not contaminate groundwater, since the fertilizer only penetrates the soil for four or five inches, just like liquid manure.

In the United States, the Clean Water Act contains specifications for metal concentrations, pathogen reduction, and disease-carrying animals such as rodents and vermin. These standards are permissive compared with those of other countries, including Canada.

Nevertheless, there is growing controversy about the safety of sludge-based fertilizer. As long ago as the late 1990s, in the U.S., the National Food Processors’ Association said it “does not endorse the use of sewage sludge on crop land.” And some of its members also shun the process. Heinz and Del Monte both said that none of their products are grown with sludge.

One of the reasons for the concern is confusion about the presence of heavy metals and the quantities in which they appear. Maximum allowable levels of metals vary widely around the world. Take cadmium, for instance. Denmark limits this metal to less than one part per million in sludge fertilizer. Germany allows ten parts per million, the state of New York allows twenty-five and the EPA allows thirty-nine parts per million. In Canada, the practice is to adopt metal concentration standards as a result of long-term (forty-year) effects of heavy metals in soils. The American standards were apparently set using different criteria.

After 1992, when a U.S. government ban on ocean dumping of sewage sludge went into effect, the one economical disposal option still available was land application. So with the blessing of the Environmental Protection Agency (EPA), the municipal waste industry hired the public relations firm Powell Tate, which rechristened sludge as “beneficial biosolids”. Then, with the sweep of a pen, the EPA reclassified sludge from “hazardous material” to “compost”.

PR Campaign

This amazing process of rebranding sludge into fertilizer is documented by authors John Stauber and Sheldon Rampton, in their book about the public relations industry, Toxic Sludge is Good for You. They write, “Our investigation into the PR campaign for ‘beneficial use’ of sewage sludge revealed a murky tangle of corporate and government bureaucracies, conflicts of interest, and a cover-up of massive hazards to the environment and human health.”

The body of literature on sewage sludge is large, but much of it consists of articles seemingly intended to break down public resistance to the use of the product on farm land. There is, however, a core of serious scientific research aimed at discovering what the long-term consequences will be from using sewage sludge as fertilizer. Peter Montague in a late 1990s edition of Rachel's Environment & Health Weekly, summarized this literature at that time.

Negative Research

• Sewage sludge is mutagenic (it causes inheritable genetic changes in organisms), 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, neighbours 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 – are 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 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.

Substances like dioxins, furans and PCBs, which could be found in sewage sludge secondary uses, are not regulated by governments. Henri Dinel, a research scientist at Agriculture and Agri-Food Canada who specializes in this topic, says that our knowledge of the occurrence of these substances in sludge “may be limited by our technology”.

The study detected ten chemicals in the soil at depths between seven and fifty inches eighteen months after the sludge application. Other studies have found hormones, detergents, fragrances, drugs, disinfectants, and plasticizers in treated sludge used as fertilizer. But this is the first study to show how they can persist and move in soil. The antibacterial compound triclosan, which is used in soaps, toothpastes, and cosmetics, was found at the highest concentrations in the deep soil. The U.S Food and Drug Administration is concerned that triclosan and other antibacterials could be contributing to antibiotic resistance. It has also has been linked to altered thyroid hormones and estrogen-related reproductive effects.

Mixed Messages

According to Abby Rockefeller, a Boston philanthropist and advocate of waste treatment reform, the move to land application of toxic sludge in the United States was sanctioned by some of the country’s most respectable environmental organizations, like the Environmental Defense Fund and the National Resources Defense Council.

Nevertheless, Rockefeller states, “...the menace of toxic and otherwise non-life-compatible substances that can be found in sludge so greatly outweigh the potential nutrient benefit as to make that potential benefit an irrelevance...The sheer number of dangers associated with treating sludge as if it were a fertilizer is so great, so various, and so serious that it would be the life work of thousands of professionals to divide up and respond to the categories of problems that will arise from this practice.”

One of the reasons that many environmental organizations have either supported or not complained about the use of sewage sludge as fertilizer is that the alternatives of incineration or landfilling are just as bad, if not worse. And, according to some researchers, if the sludge is 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.

The Composting Council of Canada, an organization of companies, municipalities, and individuals involved in large-scale composting operations, provides extensive information to its members on composting organic wastes, including municipal sewage sludge.

Agriculture Canada’s Henri Dinel has recently published a paper which describes how composting may reduce the immediate availability of metals found in sludge. He reasons, “Metals are in our environment. Landfilling them is not a solution because they leach out eventually. So my philosophy is that we need to process them properly so they will release slowly enough to make them not toxic.”

Some organic certification agencies agree. The Organic Crop Producers and Processors (Ontario) Inc. allows the application of sludge fertilizer “on rotation on green manure crops if free of contamination”. According to CEO Larry Lenhard, “free” refers to the maximum allowable limits set by the Ontario Ministry of Environment and “contamination” refers to heavy metals. All other applications of sludge, he says, “should be avoided.”

However, most organic certifiers forbid its use outright. For instance, the Organic Crop Improvement Association (Ont.) prohibits sludge fertilizer as it’s “likely to be contaminated with heavy metals.”

Opposition Grows

Despite the high-powered lobbying efforts, opposition has been slowly growing, largely fuelled by problems that are surfacing. A 1997 series by the Seattle Times newspaper entitled “Fear in the Fields” documented a number of problems.

For instance, in Tifton, Georgia, more than 1,000 acres of peanut crops were killed by Lime Plus, a toxic brew of hazardous waste and limestone that had been sold legally to unsuspecting farmers. It is the worst confirmed case in the United States of heavy metals in fertilizer destroying crops aimed for human consumption.

There are other cases: Dairy farmers whose cows died apparently as a result of sludge contaminated with heavy metals and a man who ran a coffee truck near a sludge composting site who died from a variety of ailments apparently caused by inhaling Aspergillus fumigatus, a common by-product of sludge composting.

An environmental group in Santa Cruz, California called CURE has also found problems with composting sludge, pointing to a growing body of anecdotal evidence of a relationship between the recent increasing cases of human asthma and exposure to dried bioaerosol products in the sludge.

There is also a growing and vocal group of people who claim their health has been damaged while living near farms where sludge has been applied to fields. As research confirms the damage to soils, ground water, crops, and human health from these so-called "biosolids," we can only hope that their days are numbered. But, given that the original version of this article was written in 1997, I have to wonder how much longer it will take!

Wendy Priesnitz is Natural Life's editor and author of 13 books. This article won an Outstanding Media Contribution Award from the Recycling Council of Ontario when it was first published in 1997.

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