While it’s true that some herbicides, insecticides, and fungicides can break down during the composting process, there are many that cannot. It is important to know which types of pesticides DO NOT break down in compost so you can avoid ruining your product.

How does compost break down chemicals?

When chemicals from pesticides enter into the composting process, some begin to break down into simpler molecules by decaying. Some use the process known as adsorption to form bonds with other compounds. Other chemicals break down by way of volatilizing (evaporating into the atmosphere), leaching into the liquid ooze that compost forms, or mineralizing.

Mineralization is the ideal process that composters want for feedstock that has pesticides. This process happens when the organic compounds break down into their inorganic (or mineral) and organic parts. Any organic compounds that include carbon will break down even further into carbon dioxide and water, for example. The CO2 goes into the air while the water simply mixes into the compost. The non-toxic, inorganic compounds turn into minerals and find their place in the soil.

What happens to everything else?

The reason mineralization is ideal is because all the compounds break down into something non-toxic for the environment. For example, both leaching and volatilization don’t actually change a pesticide but move its components around. If an organic compound picks up the chemicals, it CAN make them bio-unavailable, but as soon as that status changes, the toxic identities of the pesticides go into the environment.

How pesticides get into the compost

The most common way that these products enter into a compost pile is when affected plants are used as feedstock. In areas where commercial pesticide use has been banned, it is less common for this to happen. But, municipal composting facilities can still run into the issue because individuals often use pesticides in their gardens. The fewer pesticides are in a compost mixture, the more likely the microbes are to break them down.

Types of toxins that may show up in the compost

There are many kinds of pesticides, herbicides, and fungicides that can show up in your compost. Some of the most troublesome toxins are from persistent pesticide residues.


This persistent herbicide is commonly used to destroy broadleaf weeds like clover and thistle. Clopyralid was once used in household gardens across the country and has also been found in the refuse of cattle. Today, it can no longer be used for residential purposes, but professional applicators must report using it on their land. The chemicals within this herbicide do not break down, even in the extreme environment of compost.


This is another herbicide that goes after broadleaf weeds with a post-emergence, broad-spectrum method. Although it is banned for residential use in some states, it can still be found in commercial-based compost feedstock.


This is an insecticide that is used to get rid of pests like ants and spiders. It has been found in large-scale compost facilities in some areas. Because it is persistent, it could end up hurting plants secondarily, just like the above herbicides.

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