PESTICIDE ACTIVE INGREDIENT
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
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 RATING
Thurston County’s IPM Pesticide Ranking System
Pesticide review ratings:
- PASSED: The County’s first choice for product
- CONDITIONAL: The County’s second choice for product
- FAILED: The County’s last choice for product
Elements for pesticide products to receive a “failed” review
- Active ingredient does not have a product registered by
- 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
- 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 /
- 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
- 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”
- 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
- 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.
||Slightly or Moderately toxic
TOXICITY, BEE TOXICITY, AQUATIC TOXICITY
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
||Slightly or Moderately toxic
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)
|10 - 1,000
SORPTION TO ORGANIC SOIL
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).
|5,000 - 500
CHEMICAL SORPTION TO INORGANIC SOIL
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.
|100 - 5
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
|1 - 7
|8 - 60
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
BIOACCUMULATION FACTOR OR
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.
|100 - 999
|| > 100 - 4,999
PARTITION COEFFICIENT (Kow)