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Sewage Sludge as Fertilizer: Safe?

Using sewage sludge – one of two end products from any wastewater treatment plant (the other is effluent) – as fertilizer on food crops is a hotly debated food safety issue, but only among a very small group of people.  Most likely, the majority of Americans who are even aware of the issue actually work in the sewage industry.

Despite sludge’s relative obscurity, the newly formed Food Rights Network, founded by John Stauber, former Executive Director of the Center for Media and Democracy and author of the book “Toxic Sludge is Good For You,” is taking on sewage sludge as its flagship issue. Simply put, the group says that it is not safe to grow food in sewage sludge.

Why isn’t it safe?

Sewage sludge regularly tests positive for a host of heavy metals, flame retardants, polycyclic aromatic hydrocarbons, pharmaceuticals, phthalates, dioxins, and a host of other chemicals and organisms.  Of the thousands of contaminants that have been found in sludge, the U.S. government regulates exactly 10 of them (nine heavy metals and fecal coliform) if you want to spread the sludge on farm fields growing food crops.

When industry, hospitals, and households send their waste to wastewater treatment plants, the plants remove as many contaminants as possible from the water and then discharge the water as effluent.  The leftover solids are sludge.

Sewage sludge is typically treated to remove some–but not all–of the contaminants.  In recent decades, the sludge lobby (yes, there is one) has rebranded the treated sludge as “biosolids.”

Sludge that is applied to farmland–or even golf courses, home gardens, and, in the past, the White House lawn–comes in two flavors: Class A Biosolids and Class B Biosolids.  The only regulatory difference between the two is the level of fecal coliform, which is lower in Class A.

Class B Biosolids may be applied only to land where crops fed to animals are grown.  No restrictions apply to Class A Biosolids.   You as a home gardener can even buy these at your local gardening store and grow your own food in them.  Various cities get very creative at “branding” their sludge, so that gardeners can choose between “Milorganite” from Milwaukee, “Hou-Actinite” from Houston, or “GroCo” from Seattle.

Often, but not always, the various contaminants are found in sewage sludge at low levels. What happens to them once the sludge is applied to the soil is anyone’s guess.  Some chemicals bind to the soil; others do not.  Some chemicals leach into groundwater; others are insoluble in water.

Some chemicals are taken up by plants–perhaps into the roots only, or into leaves, or all the way into fruits.  Some chemicals break down into harmless components, others break down into dangerous components, and others don’t break down at all.

Understanding the path that low levels of thousands of chemicals take in the environment is a daunting task.

Once a contaminant makes its way from sewage sludge to soil, and into the human food supply, what happens?

Again, it depends.

Some chemicals are stored in the human body, and others pass through it.  Some break down in our digestive system and others don’t.  And each person is different, with a different body size, stage of development, and metabolism.  The same chemical may wreak devastating effects if a pregnant woman eats it but go unnoticed if eaten by a man.

Consider also the interaction between the many contaminants individuals may be exposed to if they regularly eat food grown in sludge.  While the effects of individual chemicals are often studied, less is known about the interactions between low levels of large numbers of chemicals.

To provide a more concrete example, take the chemical triclosan.  It has been used for several decades in antibacterial products like soaps, deodorants and cosmetics.  It is also nearly universally found in sewage sludge.  A recently published study found that soybeans planted in soil containing triclosan took the triclosan up into their beans.

Triclosan is a suspected endocrine disruptor and recent CDC reports show more than a 40 percent increase in triclosan levels in the urine of Americans over a recent two-year period.  The amount in our bodies isn’t entirely due to sewage sludge; humans can absorb triclosan through their skin and those who use triclosan-containing toothpastes put the chemical directly into their mouths.

Scientists are also finding that triclosan breaks down into dioxins in the environment.

A more extreme example of sewage sludge posing health risks

Andy McElmurray was a Georgia dairy farmer who accepted sewage sludge to fertilize his fields where he grew food for his cows over many years.  As the years went by, he noticed that his land was becoming more and more acidic.  McElmurray applied lime to raise the pH of his soil.  Soon after he did so, his cows became sick.

After many tests, he traced the cows’ illnesses back to the sludge.  The sludge he had applied contained high levels of molybdenum, cadmium, and thallium.  Molybdenum and cadmium are regulated in sewage sludge, whereas thallium is not.  

When McElmurray applied the lime, the contaminants became more bioavailable to the plants, and the cows ate the plants.  His cows suffered from telltale signs of molybdenum poisoning, and their milk was contaminated with thallium (a rat poison toxic to humans in small doses).

By the time the cows’ illnesses were traced to the sludge, it was too late to save McElmurray’s farm.  Worse, both McElmurray and his father became sick themselves from breathing sewage sludge dusts blowing from their fields.  

In this case, the Augusta, GA wastewater treatment plant that provided the sludge fudged its numbers and broke the law, providing McElmurray with sludge that contained higher levels of heavy metals than allowed.  In the end, however, scientists also found that if the wastewater treatment plant had followed the law and limited molybdenum to the legal levels, McElmurray’s cows still would have gotten sick.

Sludge Regulation

Given the complexity of the many chemicals found in sewage sludge–and consider that each wastewater treatment plant’s sludge is different over time and different from another plant’s sludge–how could sewage sludge be regulated in such a way that it is safe to use?

Regulators must consider that humans will be exposed to any contaminant in sludge in several ways.  McElmurray and his father became ill after inhaling sewage sludge dusts.  Gardeners who use sewage sludge as fertilizer touch the soil directly, and small children may even eat soil.  If it could be done, regulating sewage sludge to guarantee safety and then following through with those regulations would be infinitely difficult and expensive.

Currently, sewage sludge is disposed of via landfills and incineration as well as land application. According to the EPA, about half of all sewage sludge is applied to land, but it is only applied to about one percent of the nation’s farmland.  The likely result is that, if dangers do lurk in the sludge applied to land, we rarely find out about them.

Most people’s chances of eating enough tainted food from farms that apply sewage sludge as fertilizer to cause an acute reaction are pretty slim.  The chance that anyone who got sick would be able to correctly trace his or her illness back to the farm and to sewage sludge is even smaller.  However, a lack of easily traceable acute illnesses does not prove that sewage sludge is safe.  Health harm due to exposure to low levels of toxins over a long period of time is no more acceptable than acute problems, even if they are less obvious.

As a consumer, the only sure way to avoid food grown in sewage sludge is to buy organic food (or grow your own).  If you are a gardener and you wish to avoid sewage sludge fertilizers or composts, avoid any product that says it contains “biosolids.”  Last, if you wish to keep sewage sludge from being spread on farm fields near where you live, you can take action locally to make it illegal in your city or county.

Editor’s Note:  Jill Richardson has written about sewage sludge for the Center for Media & Democracy.

© Food Safety News
  • http://www.schwingbioset.com Gregg Johnson

    Our company uses a patented lime stablization process to create Class A biosolids. We are using The Bioset Process in FL, LA, WI, TX, NC and will soon build a facility in MN. It is completely safe. Class B biosolids are NOT safe. Safe Class A land application is a much better alternative to sending the biosolids to a landfill. Please check out our webiste.

    • J Ray

      Gregg, Can heavy metals like molybdenum, cadmium, thallium and chemicals like triclosan be removed, like they are at soft drink plants before the water is used for production. The Class B biosolids could then be used safely as fertilizer and the resulting solids burned or recycled for extraction of the metals’ use in manufacturing.

  • Nancy Holt

    The EPA regulations allow human food to be grown on sludge applied farmlands (See 40 CFR Part 503). Almost every permit I have examined over the last 10 years has shown the farm to be permitted to grow forage for cattle. However, it is amazing to drive by the grass permitted fields and find sweet potatoes, corn, carrots, green leafy vegetables and soybeans growing on the sludge applied fields. There are waiting periods (up to 38 months)–depending upon the type of human food crop and whether the sewage sludge was plowed into the ground immediately and whether the crop would be grown underground (potatoes, peanuts, carrots, etc. or would lie on top of the soil.
    When I talked to farmers about the delays (14-38 months), they were astounded–because no farmer can allow his land to lie fallow for that period of time and not generate income.
    Nobody (EPA, state or local governments) are paying attention to this program that brings the risk of toxic foods into the grocery store and into our homes. None of the chain grocery stores had even heard of sewage sludge used as fertilizer and they could not tell us if the produce they sold had been grown in sewage sludge applied land. Everyone should be careful and ask questions of every grocery chain in the USA–that is–if they want to eat foods without the addition of heavy toxic metals, chemicals and even drugs in the plants or in the milk or beef.

  • Doc Mudd

    Seems like the underlying problem is sewage sludge exists as a toxic by-product of trendy, extravagant modern urban and suburban culture. Sorta like nuclear waste, but hazardous over a much shorter half-life.
    Why is no one raising hell over our production of toxic sewage sludge and mountains of municipal waste in the first place? Why, instead, only fretting over how to dispose of it all? Granted, it’s much easier simply to dump it on agriculture and lash out at farmers than to curb our own excessive cultural habits. Disingenuous as hell, though.
    Millions upon tens of millions of trendy urban and suburban Americans eating & flushing, consuming & rinsing toxic chemicals down the drain. Tons and tons of toxic municipal human waste clogging our landfills & flowing into our rivers, unfit for application to farmland. Unfit for natural recycling! That is the real scandal, is it not?

  • http://urbanfoodproducer.blogspot.com/ Kate Kurtz

    We slather these toxic chemicals all over our bodies, scrub our homes in them, put them in our furniture, clothing, food containers, and then complain about them showing up at the wastewater treatment plant. Something is wrong with this argument — it doesn’t make sense. Most of the scary toxic chemicals that we are talking about here: flame retardants, estrogen mimicking compounds, pharmaceuticals, etc… are found in higher concentrations in household dust than in biosolids. What we should be focusing on is not using these toxic compounds in the first place, rather than complaining about them ending up in a specific product like biosolids… these compounds are EVERYWHERE and that is the real problem.
    I believe we can all agree that plumbing and sanitation is very good thing. Wastewater treatment as a technology has done wonders for both human and environmental health. I don’t hear anyone suggesting that we get rid of wastewater treatment. Given this, if we don’t use biosolids as fertilizer, what do we do with it? Also, what is a better source of nutrients and organic matter for our farmland? manure? compost from green waste? synthetic fertilizer? These products are also full of toxic compounds…
    The conversation needs to be shifted away from villainizing biosolids, and towards the removal of toxic compounds from our homes and businesses for a wholistically cleaner world.

    • http://www.facebook.com/victor.lamont.gallagher Victor Gallagher

      A voice of reason, Thank you !!!

    • Gary Dohanish

      Good argument and I agree but that is for the long term. For now we should stop spreading our existing wastes all over creation. I live in PA and looking for Organic Fertilizer for my garden I came across a facility that made it. Beside the local manure and other balancing additives I saw a huge mountain of sludge used in the mix. As you point out, we are all guilty of polluting ourselves but we should be able to depend on a simple bag of fertilizer when it says Organic on the bag. This small example is just symptomatic of the big problem, and the big problem, as you point out is that the compounds are everywhere, but I would add, their regulation is not.

  • http://www.whiteravendata.com Darrel Fleischman

    I agree with Kate and Doc, above. I’d take it one step further. Let’s all go back to the 19th century and dig pit privies in our back yards…if we have one. Because once the global warming fanatics find out that wastewater treatment plants produce lots of carbon dioxide in their biological processes, we’ll be forced to shut them all down.
    As a 38-year veteran of public health and public utilities (mostly wastewater treatment), I can tell you it has been a constant war–everybody wants you to “pick it up”, but “don’t you put it down anywhere”.
    USEPA and the state departments of environmental quality have done the best jobs within reason and available technology to assess the risks and regulate accordingly. I have no fear of biosolids, having treated, land applied, breathed, eaten the fruits of, and been splashed with it for 34 years. What I’m scared of is…dirt! OMG, grains and veggies are grown in dirt! It might have Nagasaki radioactive fallout in it. Better get the aluminum foil hat on.
    Over…

  • jim bond

    i have been in wastewater treatment field for years and have seen some scary things as per putting biosludges on the ground for food supply and monitoring plant discharge for downstream water supplies. As in anything today, lies will become the truth when the proper data and paperwork are produced. The proper thing to do is “burn or bury” the stuff. Chickens should not even be allowed to eat their own #hit! Maybe the government is allowing us to kill ourselves. nwo

  • d l nichols

    I do not think that burning the stuff (as the previous comment recommends) would be good either given the fact that there are a lot of significant chemicals in the sludge that would pollute the atmosphere terribly. Burying the stuff may be the only answer along with stopping ourselves from using the chemicals that are sold to us every day may prevent the toxic sludge to begin with. Let’s go back to the basics and start using biodegradable products such as hemp.
    Given the pollutants in the sludge differ from the sludge of our ancestors, this is a different time from the 19th Century as there were not all the thousands of chemicals that exist today. And the diseases and illnesses that are environmentally related greatly differ from those of yesteryear. All those pharmaceuticals and antibiotics around today that are going into farmlands could be the reason why there are so many new illnesses. Perhaps you all should start thinking about it. I have because I have one of those autoimmune diseases so in vogue today.

  • Steve Reinke

    Is it legal to dump untreated human waste on a field and at the same time plant a soybean crop over it. I was a installer at one time and now have a pumper or maintainer spreading on land near my home without liming or incorperating. Now as I watched him spread on one part of the field they were planting soybeans right behind him. I thought the land needed to set for a while before human crops are planted.

  • carla

    Of course its not effing safe! what the hell is wrong with people. Does anyone not notice that everyday there is another outbreak of food born bacteria illness from fresh produce. Everyone of the bacteria’s are from fecal matter.. Hello 1 + 1 makes 2 people

    • Will

      youre confusing fecal with salmonella. most of the stuff is from salmonella.