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The "Other" Ingredients in Pesticide Formulations

Look at the label of any modern commercial pesticide or herbicide, and you'll see an ingredient list of active and inactive (also known as "inert" or simply "other") ingredients. For the purposes of pesticide labeling, "active" ingredients are those chemicals that directly attack the targeted pest, while inert ingredients are added to help improve the formulation in effectiveness, storage and lifespan. For most pesticides, the inert ingredients can compose over 90% of the total volume or weight of the pesticide. It does not, however, mean they are completely safe and non-toxic to the environment.


Inert does not Mean Safe

Inert ingredients are included in pesticides to perform a variety of functions, such as promoting better coverage, stickiness to the target, the prevention of foaming, and increasing shelf life. Many are included to actually allow the active ingredients to work properly. For instance, many pesticides would be useless without the combination of a particular substance that strips away the protective waxy coat on the skin of a plant, or the tough exoskeleton of an insect.

The word "inert" and its implication that the ingredients do nothing implies that they are safe to humans and to the environment. This is not necessarily true. Some inactive ingredients are harmless. Others are considered active ingredients in other pesticides. Some can be highly toxic and dangerous independent of the active ingredient. The problem is that you will never know this by reading a pesticide label.

Inert Ingredient Labeling

Current pesticide regulation in North America requires that all pesticides for sale be labeled with specified information, either by the EPA (United States) or the PMRA (Canada). Pesticides must be labeled with the total percentage of active ingredients, and provide an itemized list of the active ingredients.

Pesticide manufacturers and retailers, however, are not required to provide an itemized list of inactive ingredients, but are only required to list them as a bulk percentage. This makes it difficult or impossible to determine what ingredients are actually included in different pesticide formulations.

So What are Some Actual Inert Ingredients?

The EPA list of permitted inert ingredients is over 300 pages long. The ingredients are categorized by their toxicity level - demonstrating that the pesticide regulatory agency is aware that inactive ingredients can, in fact, cause problems. Inactive ingredients on the permitted list are wide ranging. Here is a select list, from safe household ingredients to harmful chemicals:

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From the Organic Authority Files

  • benzoic acid
  • castor oil
  • nitrous oxide
  • sulfuric acid
  • boric acid
  • ethanol
  • canola oil
  • diesel fuel
  • fuel oil
  • aromatic petroleum hydrocarbon
  • formaldehyde

The loose requirements for including inactive ingredients on pesticide labels also allows advertisers to make false claims about their products, not fully disclosing the harmful effects the product, as a whole, can cause.

Okay, so some inactive ingredients can be toxic. What happens when an active and inert chemical is combined?

POEA and Glyphosate - A Deadly Combination

The active ingredient in the branded product Roundup® is glyphosate. Glyphosate is a generally safe chemical, but it does cause mild irritation to the eyes, skin and lungs. It causes no known damage to aquatic life. However, combining the inactive ingredient POEA (polyethoxylated tallowamine, a chemical derived from animal fat) with glyphosate makes it extremly toxic to fish and amphibians. POEA is used in herbicide formulas as a surfactant, helping the active ingredient of the herbicide penetrate the plant. Because POEA is considered an inactive ingredient, its exact percentage in different formulas of glyphosate-based herbicides are unknown. Additionally, as an inactive ingredient, it is normally not even included on the label.

Another factor to consider is that most pesticide tests 1) test for active ingredients only and 2) are done in very controlled environments. This means that the public's overall perception of a pesticide is that it is relatively "safe," and very few realize what could happen when it is misapplied. In the case of Roundup®, it could be sprayed on the banks of rivers, lakes or ponds to kill weeds along the edge, but an application near water will also do great harm to the aquatic wildlife - either by drift into the water, or by runoff of contaminated soil. (Glyphosate formulas bind tightly to soil, so erosion of contaminated soil can also cause problems.)

A 2006 report by Caroline Cox and Michael Surgan delves into the details about the effects of active and inert ingredients combining with each other, and the environmental damage and persistence they cause.

Changing Labeling Practices

Because current labeling regulations do not require companies to list inactive ingredients, there is little data about individual ingredients and their specific effects on the environment. Taken as a whole, the studies that do exist suggests that inactive ingredients play a much more damaging role in pesticide activity than previously determined. Complete pesticide formulas need to be tested for toxicity, and regulations must be changed so labels include the entire formula, not just the active ingredients.

Written by Chris Molnar of, a site promoting healthy organic gardening and composting tips. Read articles and information on organic herbicides and safe home-made pesticide recipes.

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