A few weeks ago, a client asked me if I had ever heard about a local company that makes garden compost. And for legal reasons, I'm not going to name the company, but several municipalities around the US use the same general model: recycle municipal waste biosolids into biosolid garden compost and sell at a very low price. To the average person, this sounds like a great idea. We've been conditioned to think that anything recycled is "good" for you and the environment. And recycling biosolids must be good too, as "bio" means life and solids are, well, solid--right? But you'd have to dig a little deeper to understand why this type of recycled product may not be the best for you and your garden beds and why I never recommend this recycled compost to my customers.
What are Municipal Waste Biosolids?
Ok, so what is a municipal waste biosolid? The US Environmental Protection Agency (EPA) defines a biosolid as a semisolid, nutrient-rich product originating from the separation of liquids and solids during the wastewater treatment process. Explained simply, biosolids are sewage sludge. Yup, you read that correctly; municipal waste biosolid compost found in stores is composted human sewage.
But let's back up for a few minutes and explain the basics of wastewater treatment. When you flush your toilet in the US, it usually goes one of two places: either your septic system or a municipal wastewater treatment plant. If you live in a city, chances are your wastewater goes to the wastewater treatment plant for treatment. At the wastewater treatment plant, there are several steps to making that wastewater safe again to release back into the watershed.
At the treatment plant, solids (poo and any other solid sent down the drain) are separated from liquids (water, pee, etc.) via screening, sedimentation, and filtering. Sludge is still pretty wet at this point, so it's aerated and bacteria break down organic matter into byproducts (aerobic decomposition). Byproducts are then sent to another sedimentation tank for the removal of excess bacteria (from the last step). Liquid effluent is then disinfected and discharged out of the treatment plant.
Now that the liquids are separated from the sludge, the sludge can undergo composting to further reduce water content, remove heavy metals, and eliminate pathogens and viruses. Pathogens and viruses make people sick, so biosolids are regulated to keep the general population safe from sickness and the spread of disease (this is good!).
Municipal waste biosolids packaged from home garden use are 'Class A' biosolids, which means there are more stringent regulations and are technically safer than 'Class B' biosolids. Biosolids are regulated by the federal regulation 40 CFR Part 503.
Biosolids are rich in organic matter and nutrients such as nitrogen and phosphorus, which are essential to plant growth. Plants composted with biosolids grow greener and taller than plants grown in other potting mediums--and this is why some people absolutely love using garden compost with biosolids. But what about all the other stuff flushed down the toilet that isn't removed during treatment and composting? Do those contaminants stay in the biosolids and get transferred to your garden?
As a personal antidote, anytime a customer asked me to spread biosolid compost, it smelled rather pungent, and anywhere the compost touched my skin I would get an itchy rash. That rash got me thinking and I took a deep dive to find out what's in municipal waste biosolid garden compost.
Potential Contaminants in Municipal Waste Biosolids
The US federal government regulates the wastewater treatment process for some but not all contaminants. And anything that isn't specifically regulated typically doesn't get much attention.
According to the US Geological Survey (USGS), "scientists found that biosolids contain relatively high concentrations (hundreds of milligrams per kilogram) of the active ingredients commonly found in a variety of household products and drugs" (USGS, 2008). Some of the chemicals found in a study of nine commercially or publicly available biosolids were an antimicrobial disinfectant (triclosan), a musk fragrance (tonalide), an antihistamine (diphenhydramine), and an anti-epileptic drug (carbamazepine) (USGS, 2008). Other studies have found biosolids containing heavy metals such as lead, cadmium, arsenic, mercury, and other chemicals like PCBs, PFAS (forever chemicals), dioxins, BPAs (plastic chemicals), flame retardants, hospital waste (Perkins, 2019) and microplastics from toothpaste and laundry wastewater (Popoola, 2023).
A scientist interviewed by The Guardian newspaper stated that "none of the thousands of chemicals known to be in biosolids, or tens of thousands of manmade chemicals for which the government doesn't test, are removed" (Perkins, 2019). They went on to note that "nothing that is done to the [municipal waste] sludge removes the chemicals. They just spend a little money on PR to convince us it's nice fertilizer and fail to mention all the other things that are in it" (Perkins, 2019).
Here are a few contaminants that have been found in municipal waste biosolid fertilizers.
Heavy Metals
Heavy metals such as arsenic, cadmium, copper, lead, mercury, molybdenum, nickel, selenium, and zinc are federally regulated and cannot exceed maximum amounts in municipal waste biosolids. Other metals such as antimony and chromium are also found in biosolids. While plants do need trace amounts of metals for growth and reproduction (molybdenum, zinc, and copper), other heavy metals such as lead, cadmium, mercury, and arsenic can be fatal (Popoola, 2023). It's important to note that while many heavy metals are federally regulated and cannot exceed certain concentrations in individual batches of biosolids, repeated application can lead to the accumulation of heavy metals in the soil and plants (Popoola, 2023). Once heavy metals are in the soil, there is no method of remediation.
For plants, heavy metal exposure in the soil may result in stunted growth, reduced crop yields, and altered metabolism (Uchimiya et al., 2020). While bioaccumulation of heavy metals in the human body may result in nervous system disorders, gastrointestinal and kidney dysfunction, immune system dysfunction, skin lesions, birth defects, vascular damage, and cancer (Balali-mood et al., 2021).
Pharmaceuticals and Personal Care Products
A research paper published in the International Journal of Environmental Research and Public Health by Bolesta et al (2022), noted that the concentration of pharmaceuticals in sludge is not controlled and research needs to be undertaken to "clearly show that there is no risk from pharmaceuticals or vice versa."
Some of the pharmaceuticals and personal care products (P&PCPs) found in municipal waste biosolids include anti-inflammatory agents, steroidal hormones, antibiotics, detergents (soap), perfumes, and active ingredients in soaps (Kumar et al., 2022).
Additionally, prescription drugs taken by people for the treatment of various ailments, are not completely absorbed by the body; excess drugs leave people during excretion and travel to wastewater treatment plants. Some drugs break down quickly and do not pose a threat to humans and animals alike; however, other pharmaceuticals take a long time to break down and remain in wastewater biosolids long after treatment and composting. Some of these drugs include Carbamazepine, Sulfamethazine, Triclocarban, Triclosan, and Triclocarban (Popoola, 2023).
P&PCPs have been found to have harmful effects on plants such as leaf chlorosis, tissue necrosis, inability to produce fruit, root and stem elongation, root decay, and death (Popoola, 2023). In humans, P&PCPs have equally toxic side effects including life-threatening allergic reactions, a decrease in red blood cells (which can lead to gum bleeding, nosebleeds, heavy menstruation, shortness of breath, and mouth sores), anaphylaxis, angioedema, and urticaria hypersensitive reactions (skin rash, fever, etc.) (Popoola, 2023). Clearly, pharmaceuticals and personal care products found in biosolids can have extremely detrimental effects on humans and plants.
Industrial Chemicals
Per- and poly-fluoroalkyl substances (PFAs) are synthetic, organic compounds commonly used in fabrics for water and heat resistance, cleaning products, shampoo, cosmetics, non-stick cookware, and even dental floss have been found in municipal waste biosolids (Popoola, 2023). At present, there are more than 5,000 PFA compounds, and due to their chemical makeup, can easily bond to soil and bioaccumulate (Popoola, 2023). These synthetic, organic compounds pose extreme health risks to people and animals, as exposure to high levels of PFAs includes "reproductive defects, neurological developmental delays, low birth weight, bone variation, accelerated puberty, changes in liver and kidney functions, thyroid disease, testicular cancer, etc." (Popoola, 2023).
Microplastics
If you haven't been living under a rock the last couple of years, you've heard about microplastics (MPs) and how they've infiltrated the ocean, drinking water supplies, and even starting to bioaccumulate in human bodies. Microplastics are plastic particles with diameters less than 5 mm. Think about those every-day cleaners that advertise "microbeads" for easy cleaning; those microbeads are actually microplastics masquerading under a different name. Microplastics can also originate from synthetic fibers (that favorite microfleece pullover), personal care products, and consumer plastics.
When sewage with microplastics arrives at a wastewater treatment plant, most MPs accumulate in sludge and are not removed when converted into biosolids (Tang et al., 2021). When biosolids are applied to agricultural soils, microplastics can persist in the environment for several years and can also fragment into smaller nanoplastics, which are even more problematic than microplastics. Nanoplastics have been shown to be carriers of pollutants, pathogens, and heavy metals and can cause adverse health effects in humans and animals (Campanale et al., 2020).
Environmental Impact of Municipal Waste Biosolids
On an individual level, any singular contaminant found within a municipal waste biosolid could have a serious environmental impact. However, current wastewater treatment and composting practices of biosolids do not remove hundreds--if not thousands--of different contaminants in sewage or biosolids. The most egregious contaminants discussed previously include heavy metals, pharmaceuticals and personal care products, industrial chemicals, and microplastics. With repeated application of biosolids in home gardens or agricultural fields, the accumulation of these contaminants could have serious adverse effects whereby soil health is compromised, drinking water and oceans become contaminated (from runoff), and biota (including humans!) may develop serious health issues--if not death (when in contact with or ingesting contaminated food).
People rely on healthy soils and water for life--contaminating the gardens and fields where we grow fruits, flowers, vegetables, and livestock will adversely affect our ability to live.
Alternatives to Municipal Waste Biosolids
Ok, so now that I've thoroughly turned you off to using municipal waste biosolids compost, what are some garden compost alternatives?
Compost and Composting
Build yourself a backyard compost bin and close the energy loop within your property. If you have the space (and patience), composting your food waste and garden green waste is the best and cheapest method for amending your home garden. At my home, we utilize a two-bin system, where one side of the compost is where I'm actively adding more food scraps, leaves, grass clippings, etc. While the other side is undergoing the secondary stage of composting and not growing (it should actually shrink a bit!). After about 6 months of the secondary stage, I sieve out all the rocks and larger chunks of organic matter and have a beautiful home-grown compost ready for the garden (worms included!).
Sadly, I don't always have enough from my home compost to cover the entire garden, so I supplement with some non-biosolid composts. My favorite is G&B Organics Soil Building Conditioner, which is made from recycled forest products, arbor fines, composted chicken manure, gypsum, oyster shell, dolomite limes (as pH adjuster), vermicompost, bat guano, kelp meal, and mycorrhizae. This compost is advertised to improve drainage, promote root development (due to the mycorrhizae), and can be used as mulching and top dressing. I really love the texture of this product, have never found plastic trash in it (like in other bagged composts), and I've noticed a positive difference in the beds amended with G&B Organics Soil Building Conditioner.
Organic Fertilizers
Adding organic matter in the form of compost is a great way to grow your soil and create a healthy soil microbial environment (no microbes means no decomposition, nutrient cycling, or plants), but sometimes plants need a little more available nutrients. I like to add organic fertilizers in the form of liquid fertilizers or powders. Fertilizers have come a long way since I first started gardening. Now, you can even buy fertilizers specifically formulated for whatever plant needs fertilizing. I like using Down to Earth Fertilizers, which are derived from natural and organic plant, animal, and mineral sources.
Green Manure and Cover Crops
Green manure, also known as cover crops, are nitrogen-fixing plants specifically grown to be tilled back into the soil. Some cover crops include fava beans, peas, and ryegrass. In theory, if a nitrogen-fixing plant is tilled back into the soil before it blooms and reproduces, then all the nitrogen within the plant will be fed back to the soil. I love growing cover crops in the winter here in the PNW. It's always fun watching plants slowly grow throughout the winter and seeing a little green during the dark months. Cover crops typically start growing faster in the spring when temperatures warm and there's more sunlight.
Conclusion
A biosolid is a semisolid, nutrient-rich product originating from the separation of liquids and solids during the sewage wastewater treatment process. Biosolids are marketed to homeowners and farmers as an eco-friendly, nutrient-rich method of fertilizing gardens and agricultural fields. While biosolids are regulated by the federal government, many of the contaminants found in sewage are not regulated or removed during the treatment process. Contaminants include heavy metals, pharmaceuticals and personal care products, industrial chemicals, and microplastics--all of which can cause severe environmental and human health risks, especially when accumulated. It's important to be informed and aware of the products you add to your garden and make choices that won't harm the environment or your health. Alternatives to municipal waste biosolid fertilizers include home composts, purchased composts (that do not contain biosolids), organic fertilizers, and cover crops.
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