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
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.
Municipal sewage sludge is being marketed to farmers as
fertilizer. It may contain
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.
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
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
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”.
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.
- 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
- 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
- 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
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”.
A U.S. government study reported in May, 2014 in
Environmental Health News found traces of prescription drugs and household
chemicals deep in the soil as a result of a couple of decades of use of
biosolids as fertilizer. Researchers, including hydrologists for the U.S.
Geological Survey, tested an eastern Colorado wheat field that used treated
sludge from a Denver sewage treatment plant. Chemicals in antibacterial
soaps, cleaners, cosmetics, fragrances and prescription drugs such as Prozac
and Warfarin not only persisted in the topsoil, but migrated downwards.
"With the blessing of the Environmental Protection Agency
(EPA), the municipal waste industry hired a public relations firm to
rechristen sludge as 'beneficial biosolids.' Then, with the sweep of
a pen, the EPA reclassified sludge from 'hazardous material' to
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
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
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
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.”
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
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.