Environmental Health
Integrated Pest Management (IPM)
  IPM - Pesticide Review Terminology  



A pesticide active ingredient is the chemical or chemicals in a product that is responsible for the killing action or controlling of a pest. Thurston County reviews pesticides by their active ingredients because there are thousands of pesticide products and only hundreds of active ingredients. Differences between products containing the same active ingredient typically include; the physical form (liquid, granular), concentration of the active ingredient, where they can be used, and the “other” ingredients added to each product. The reviews available to homeowners and land managers through this website are specific to pesticide active ingredients and not products.

Pesticide active ingredients are required to be listed on the each product label, but pesticides almost always contain other ingredients that are not listed on the label. These other ingredients used to be referred to as “inert” ingredients because they are not supposed to cause any pesticidal activity (not an active ingredient). These added chemicals may increase or decrease the toxicity (poison hazard) of the pesticide product; in some instances the final product is more toxic to certain organisms than the active ingredient alone. But, the other ingredients are trade secrets and manufacturers are not required to list them on the label. Also, the U.S. EPA requires a series of tests for pesticide active ingredients, and not for the pesticide products, therefore product specific toxicity and environmental fate data is often unavailable.



Thurston County’s IPM Pesticide Ranking System

Pesticide review ratings:
  • PASSED: The County’s first choice for product selection.
  • CONDITIONAL: The County’s second choice for product selection.
  • FAILED: The County’s last choice for product selection.

Elements for pesticide products to receive a “failed” review rating:

  • Active ingredient does not have a product registered by WSDA.
  • Contains an EPA designated List 1 or List 2 inert ingredient
  • Contains an ingredient that has a mammalian LD50 50 mg/kg
  • Contains a persistent ingredient that also has the potential to bioaccumulate
  • Contains ingredient with a cancer designation of:
    • EPA Group A – Human carcinogen
    • EPA Group B – Probable human carcinogen
    • EPA Group C – Possible human carcinogen
    • EPA – “Likely to be carcinogenic to humans” or “Known / Likely”
    • International Agency for Research on Cancer (IARC) Group 1, Group 2A, or Group 2B
    • National Institute of Environmental Health Sciences (NTP) designation - “Known to be human carcinogens” or “Reasonably anticipated to be human carcinogens”
  • Contains an ingredient with positive evidence of mutagenicity
    • Any mammalian cell mutation assay(s); or
    • Microbial assay(s) with mammalian enzyme activation.
    • Human risk assessment for active ingredient has less than a two-fold safety factor above the EPA’s level of concern for acute or chronic toxicity.

Elements for pesticide products to receive a “conditional” review rating:

  • Product is registered by the WSDA as a pesticide.
  • Contains an ingredient that is considered mobile and persistent, but low in acute and chronic toxicity hazards.
  • Human risk assessment for active ingredient has at least a two-fold, but less than a ten-fold, safety factor above the EPA’s level of concern for acute or chronic toxicity.

Elements for pesticide products to receive a “passed” review rating:

  • Product is registered by the WSDA as a pesticide.
  • Contains none of the criteria listed in the conditional or failed rating.
  • Risk assessment for active ingredient has at least ten-fold safety factor above the EPA’s level of concern for human acute or chronic toxicity.
  • Risk assessment for active ingredient does not exceed the EPA’s level of concern for non target organisms that have the potential to be at the application site.


Human toxicity is evaluated for each active ingredient by reviewing the chemical hazards and the risk of an adverse health effect from exposures to the chemical when used as a pesticide. The acute toxicity section includes a review of single exposures to a pesticide and exposures up to a week in duration (short-term). The chronic toxicity section includes intermediate-term exposures (longer than a week but less than a year) and long-term exposures that can represent occupational or lifetime exposures.

Toxicity hazard screening looks at a chemical’s potential to cause cancer, endocrine disruption, or mutagenicity. Chemicals that are known to cause mutagenicity and chemicals that are known or likely carcinogens are considered too high in hazard and fail the County’s review criteria. Since the evaluation of endocrine disruption is still an emerging science and the EPA has just finalized their testing methods, only known endocrine disruptors fail the review criteria. Because endocrine disruption may not be related to dose, chemicals that are potential endocrine disruptors will have to be re-evaluated when testing data is available. Also, if an active ingredient kills half of the test animals at a dose concentration less than 50 mg/kg, it is considered too acutely toxic (poisonous) and all pesticides with that active ingredient fail the review criteria.

The risk assessment section of the review compares the chemical dose that causes a known adverse toxicological effect to the application rate and routes of likely exposure.  In the EPA’s required toxicity testing the manufacturer is supposed to identify the highest dose that does not cause an adverse effect to the test animals and the lowest dose that causes an adverse effect. Typically, what Thurston County calls the “dose of concern” is the highest dose that DID NOT produce an adverse effect. The active ingredients that have a small margin of safety (less than two-fold), from the calculated dose of concern, are rated as high in hazard. Active ingredients that have a margin of safety at least ten times greater than the calculated dose of concern are rated as low in hazard. The pesticides that create exposures that are calculated to have margins of safety between two and ten times the dose of concern are rated as moderate in hazard.



The following table rates lethal dose concentrations to 50% of the tested rats (LD50) and is used to score mammalian toxicity. When both oral and dermal toxicity values are found, the chemical is rated by the worst-case of the two toxicity hazard values. According to the county IPM policy, an acute toxicity LD50 of less than 50 mg/kg to mammals fails the review.

Oral LD50
Dermal LD50(mg/kg) EPA Class County Rating
>2,000 >20,000 Practically non-toxic Low
51-2,000 200-20,000 Slightly or Moderately toxic Moderate
<50 <200 Highly toxic FAIL


Avian studies also use lethal dose concentrations (LD50) to indicate the acute toxicity of the chemical in a bird’s diet. Toxicity studies of aquatic organisms generally use lethal chemical concentration (LC50) to indicate acute toxicity (because the chemical is not put into their diet, instead it is added to the water they live in). The rating table below depicts EPA toxicity classifications. Unlike mammalian toxicity, there is no value that results in a product failing based solely on its LD50 or LC50 to these organisms.

Avian LD50 mg/kg Avian LD50(ppm) Aquatic Organisms
EPA Class County Rating
>2,000 >20,000 >100 >11 >1,000 Practically non-toxic Low
51-2,000 200-20,000 1-100 2-11 10-1,000 Slightly or Moderately toxic Moderate
<50 <200 <1 <2 <10 Highly toxic FAIL


Pesticide mobility is rated on the potential of a pesticide’s active ingredient to move with water away from the point of application. The other ingredients (surfactants, wetting agents, etc.) that are added to a pesticide’s active ingredient will influence the mobility, but these ingredients cannot be reviewed because they are different for each product and manufacturers are not required to list these ingredients (so they are unknown).

Components of the mobility rating assessment include water solubility and soil adsorption for both inorganic soil (sands and gravel) and organic soil (clay, sediment, etc.). Because the overall mobility of an active ingredient is primarily dictated by the chemical’s ability to attach to soil, the rating should be most reflective of the value for chemical sorption to organic soil (Koc). However, some chemicals (like diquat dibromide) bind well to sand and so the Kd value can show that mobility is even less than the Koc value may suggest. Solubility should only change a rating when chemical sorption to soil is on the low end of the moderate scale and solubility is very high. In these instances, the overall mobility rating should be high because the chemical will want to move with water and will not likely attach to the soil.


Since pesticide mobility is related to its ability to travel with water, solubility is an important factor to determine. The greater the solubility of a pesticide in water the higher the risk of mobility. Typical solubility units are milligrams per liter (mg/L) but sometimes is expressed in parts per million (ppm).

Solubility (mg/l or ppm) County Rating
<10 Low
10 - 1,000 Moderate
>1,000 High


To help evaluate a chemicals potential to bind to soil, a chemical sorption test is performed. A pesticide solution is added to a known amount of soil and the soil organic partition coefficient (Koc) relates the ratio of adsorbed chemical in the soil to the pesticide concentration in the liquid solution. The more chemical that is in the soil (the higher the Koc value), the less likely the chemical is to move through the soil. Actual chemical adsorption can vary tremendously with soil type and its organic matter content. This rating can be made specific to a location if the type of soil is known (for Thurston County reviews the location is unknown).

Koc Value County Rating
>5,000 Low
5,000 - 500 Moderate
<500 High


The soil partition coefficient (Kd) is the experimental ratio of adsorbed chemical in inorganic soil to that of the pesticide solution. The Kd reflects a chemical’s ability to attach to inorganic soil or leach through it.  Typically, Kd values will be considerably lower than Koc values and usually represent the worst-case scenario for soil mobility.

Kd Value County Rating
>100 Low
100 - 5 Moderate
<5 High


Persistence is defined as the amount of time it takes for a pesticide to break down (degrade) or be removed from the environment.  The overall score for persistence includes all potential routes of degradation, but is rated more heavily on the most likely route (e.g. abiotic degradation is used to rate pesticides used in wall voids while microbial degradation is used for pesticides sprayed on soil).  The overall persistence rating of “low” to “high” will consider the following criteria:


To better understand the likely persistence of a pesticide, several types of degradation routes are evaluated. The degradation routes are then compared to the environment the pesticide is expected to be used in to best predict what is most likely to occur. The following chemical half-life time scale is used to rate all forms of degradation. If a pesticide takes sixty days for it to degrade 50% (a first order half-life), 1.5% of the applied pesticide will remain after one year. Pesticides that have a half-life longer than 60 days will start to build up if used at the same site in consecutive years.

Half-life (Days) County Rating
1 - 7 Low
8 - 60 Moderate
> 60 High


Biotic degradation is scored on the amount of time it takes for a chemical to be broken down by microbial activity.  Studies that include degradation by sunlight, volatilization, hydrolysis (breakdown by water) or any other type of outside influence are excluded because field dissipation studies should reflect those interactions.


Abiotic degradation is the process of organic chemicals broken down by chemical (hydrolysis) or physical (photolysis, volatilization) reactions. Abiotic soil tests use sterilized soil to ensure that there is no microbial breakdown of the chemical. If abiotic studies are not found, then chemical half-life studies may be used as a substitute.

DISSIPATION RATE - Terrestrial and aquatic (field tests)

Field dissipation studies are used to rate the expected half-life of the product in similar environmental conditions as the proposed application area (terrestrial or aquatic).  As much as possible, the score is based on chemical breakdown and not off-site migration or dilution.


Anaerobic degradation half-life is the amount of time it takes for a chemical to break down to half of its original concentration in an oxygen deficient environment. If a pesticide is introduced in an aquatic environment, anaerobic degradation reflects chemicals degrading in sediment. Pesticides that leach into soils will have more opportunity for anaerobic degradation than aerobic.


Hydrolysis is scored on the amount of time it takes for a chemical to be broken down by its interaction with water. This parameter is important for degradation in aquatic environments.


Bioaccumulation is defined as the ability of a chemical to accumulate in living organisms as they take in contaminated air, water, soil, sediment, or food. Chemicals that bind to fats, and are very slowly metabolized or excreted, tend to bioaccumulate. Bioaccumulation factor values (BAF) are not always found, so they can be substituted by using bioconcentration factor values (BCF) or the octanol-water partition coefficient (Kow).But, because BCF and Kow values do not take into account metabolism, depuration, or excretion, the overall bioaccumulation hazard is rated more heavily on BAF values for their increased accuracy.


Bioconcentration factors are determined by measuring the difference in chemical concentration between an organism’s tissue and the amount of chemical issolved in the medium, generally water.

To be considered likely to bioaccumulate through the food chain a substance must be characterized by either a BAF value greater than 1,000 or a BCF value greater than 5,000. BCF and Kow values are rated less conservatively because they are a less accurate measure of bioaccumulation potential.

BAF BCF County Rating
<100 <100 Low
100 - 999  > 100 - 4,999 Moderate
>999 >4,999 FAIL



The octanol-water partition coefficient (Kow) can be used to estimate a chemical’s likelihood to bind to organic substances like fat. The Kow value (which is documented in the log scale) is measured by adding a chemical to water and octanol (an organic solvent), and determining the ratio of chemical in water and solvent. The rating of Kow for bioaccumulation implies that the greater the attraction to organic matter (high Kow value) the greater the potential for the chemical to bioaccumulate.

log (Kow value) County Rating
<2 Low
2 - 4.9 Moderate
>4.9 High

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This page last updated: 08/05/13