Acute Toxicity
Acute toxicity refers to the immediate effects (0-7 days) of exposure to a pesticide. Highly acutely toxic pesticides can be lethal at very low doses.
There are several organizations that evaluate and rank chemicals for their acute toxicity. Active ingredients of pesticides are ranked by the World Health Organization (WHO). Formulated pesticide products (which often include inert ingredients) are given a toxicity rating by the U.S. EPA which is shown as a warning label on the pesticide product.
Because toxicity designations from different sources sometimes conflict with each other, PAN created a summary acute toxicity designation that reflects the most toxic ranking assigned by any referenced organization. PAN’s summary listing is derived from the WHO and U.S. EPA hazard ratings. For more detail, see the Acute Toxicity page in the Resource Library.
Bee Toxins
The U.S. EPA Office of Pesticide Programs, after reviewing individual toxicity or ecological effect studies for a pesticide, summarizes the toxicity of each chemical to certain species groups. In developing its ecological effect characterizations for bees, the agency uses a three-step scale of toxicity categories to classify pesticides based on bee toxicity data. Based on this analysis, EPA defines a pesticide as highly toxic to bees if the LD50 (exposure level at which half the bees die) is lower than two micrograms per bee (μg/bee).
All pesticides classified as ‘highly toxic to bees’ are listed in the PAN HHP list. The Pesticide Properties Database (maintained by the University of Hertfordshire) has been used by PAN International experts to identify pesticides with the characteristics of being toxic to bees (LD50 <2 µg/bee).
Carcinogens
Because carcinogenicity designations from different sources sometimes conflict with each other, PAN created a summary carcinogen designation that reflects the most toxic ranking assigned by any organization. In addition, the different terms used by different organizations to describe carcinogen status were translated into a consistent set of terms.
For a chemical to be classified as a PAN Bad Actor, it must be in either the Known or Probable summary category. For more detail, see the Carcinogens page in the Resource Library.
Cholinesterase inhibitors
Many pesticides, particularly insecticides, are neurotoxic to humans and other animals because their mechanism of action targets the insect nervous system. The most common mechanism of action is inhibition of the enzyme cholinesterase, which is essential for transmission of nerve impulses.
Cholinesterase-inhibiting pesticides disable this enzyme, resulting in symptoms of neurotoxicity — tremors, nausea, and weakness at low doses; paralysis and death at higher doses. Exposure has also been linked to impaired neurological development in the fetus and in infants, chronic fatigue syndrome, and Parkinson’s disease.
Most of these pesticides are insecticides with a similar mechanism of action in both insects and humans, and most cholinesterase-inhibiting pesticides are organophosphorus or carbamate compounds. For more detail, see the Acute Toxicity page in the Resource Library.
Drift-prone pesticides
Vapor pressure (VP) is the physical property of a pesticide that most affects its ability to move through the air or “drift” — it is a measure of the tendency of a material to change into a gaseous or vapor state. VP increases with temperature, and the higher the vapor pressure, the more volatile the chemical.
In the PesticideInfo database, we report vapor pressures measured between 20-25 degrees C. The vapor pressure is a good predictor of the volatility of the chemical and allows determination of which pesticides might be prone to evaporate from leaf and soil surfaces and drift off-site after application. For more details, see the Pesticide Drift page in the Resource Library.
Endocrine disruptors
Many pesticides and industrial chemicals are capable of interfering with the proper functioning of estrogen, androgen and thyroid hormones in humans and animals. These “endocrine disruptors” can cause sterility or decreased fertility, impaired development, birth defects of the reproductive tract, and metabolic disorders.
PAN’s summary listing is derived from the EU, the Danish government and U.S.-based Our Stolen Future. For more detail, see the Endocrine Disruptors page in the Resource Library.
EPA Warning Labels
In the U.S., formulated pesticide products are required to carry an acute toxicity rating by the U.S. EPA which is reflected in the warning label on the pesticide container. EPA gives a warning label of Category 1 to the most acutely toxic pesticide products and Category 4 to the least acutely toxic pesticide products.
The different toxicity categories are based on the LD50, the dose (in milligrams of substance per kilogram of body weight) that kills 50% of the test animals in a standard assay. For inhalation exposures, the LC50 is used—the concentration in air in milligrams per liter that kills 50% of the test animals.
| U.S. EPA Warning Label | ||
| Category | PAN Narrative Rating | Warning Label |
| 1 | Highly Toxic | Danger-Poison* |
| 1 | Highly Toxic | Danger |
| 2 | Moderately Toxic | Warning |
| 3 | Slightly Toxic | Caution |
| 4 | Not Acutely Toxic | None |
For more detail, see the Acute Toxicity page in the Resource Library.
Highly Hazardous Pesticides
The PAN International List of Highly Hazardous Pesticides (HHPs) was initially developed by PAN Germany in 2009, in response to a need identified through participation in the FAO/WHO Joint Meeting on Pesticide Management. Listing criteria include acute toxicity, long term health effects, environmental hazards and status under global pesticide-related conventions.
Long term health effects evaluated include endocrine disruption, carcinogenicity and reproductive/developmental toxicity. Environmental criteria include toxicity to bees and aquatic organisms, persistence in the environment and ability to bioaccumulate.
The PAN HHP list is currently based only on classifications by recognized authorities, including the World Health Organization (WHO), U.S. EPA, the EU Commission and the Pesticide Property Database maintained by the University of Hertfordshire. The HHP list is updated annually by PAN International experts, and hazard criteria are updated periodically, most recently in 2018. For more details see the Highly Hazardous Pesticides page in the Resource Library.
List of International Bans
PAN International maintains a Consolidated List of Banned Pesticides to identify which pesticides have been banned by particular countries. The list is updated annually, based on information available for 150 countries. There appears to be no other comprehensive compilation of such information.
The most recent List was published in March 2019, and shows that one or more countries have banned a total of 366 pesticide active ingredients or groups of actives regarded as still ‘currently in use’ in the global market. The List also shows whether these pesticides are regarded as highly hazardous. It does not include severe restrictions; entries are for complete bans only. For more detail, see the Banned Pesticides page in the Resource Library or visit our interactive Global Bans map.
PAN Bad Actor Pesticides
To identify a “most toxic” set of pesticides, Pesticide Action Network (PAN) created the term PAN Bad Actor. These pesticides are at least one of the following:
- Known or probable carcinogens, as designated by the International Agency for Research on Cancer (IARC), Globally Harmonized System of Classification and Labelling of Chemicals (GHS), U.S. National Toxicology Program, US EPA Toxic Release Inventory (TRI) cancer list or the state of California’s Proposition 65 list.
- Reproductive or developmental toxicants, as designated by Globally Harmonized System of Classification and Labelling of Chemicals (GHS), US EPA Toxic Release Inventory (TRI) reproductive and developmental toxicant lists, and the state of California’s Proposition 65 list.
- Neurotoxic cholinesterase inhibitors, as designated by California Office of Environmental Health Hazard Assessment, U.S. EPA, and/or PAN staff evaluation of chemical structure (for organophosphorus compounds).
- Known groundwater contaminants, as designated by the state of California (for actively registered pesticides) or from historic groundwater monitoring records (for banned pesticides).
- Pesticides with high acute toxicity, as designated by the World Health Organization (WHO), the Globally Harmonized System of Classification and Labelling of Chemicals (GHS), or U.S. EPA.
See the Resource Library for more detailed information on the individual categories above.
PAN Groundwater Contaminants
The PAN groundwater contaminant rating can be either Known, Potential, or Insufficient data.
A number of pesticides, primarily herbicides and soil fumigants, have been found repeatedly in California groundwater. These compounds are labeled as Known groundwater contaminants. Most of these chemicals are on a list maintained by the California Department of Pesticide Regulation (DPR); however, pesticides that were banned from use in California before they were evaluated for their potential to contaminate groundwater are not included in DPR’s lists. PAN staff has added these chemicals from California groundwater monitoring reports.
Potential groundwater contaminants are those that meet DPR’s criteria for water solubility, ability to bind to soil, and half life. If the rating is Insufficient data, we do not yet have the data to make an assessment of whether a pesticide is likely to contaminate groundwater.
For more detail, see the Water Pollution page in the Resource Library.
POPs Pesticides
Persistent organic pollutants, or “POPs,” are chemicals that persist in the environment for years – sometimes decades. POPs travel long distances in the environment, and “bioaccumulate” in most or all living creatures, including humans. They become more concentrated as they move up the food chain, and are linked to a range of serious health effects, including birth defects, infertility and cancer.
Throughout the 1990s, PAN worked with partner groups around the world to win the Stockholm Convention on Persistent Organic Pollutants (POPs Treaty), which targets this entire class of chemicals for global elimination. The POPs Treaty sets timetables for phaseout of target chemicals, provides assistance to help countries eliminate POPs, and works with scientists to expand the list of target chemicals. To date, fourteen pesticides have been targeted for global elimination. For more details, see the POPs Pesticides page in the Resource Library.
Prior Informed Consent
Millions of barrels of pesticides travel the global marketplace. In the 1980s, PAN experts proposed that importing nations should be informed when pesticides were banned in other countries, and be given the right to refuse the import of such chemicals.
The UN Food and Agriculture Organization took up the idea, and began implementing a voluntary notification procedure for banned chemicals. The process eventually became international law with the signing of the Rotterdam Convention on Prior Informed Consent (PIC) in 1998. The PIC Treaty has now been adopted by more than 130 countries.
Like the Stockholm Convention on Persistent Organic Pollutants ( POPs Treaty), the Rotterdam Convention has a scientific process for adding new chemicals to the list. For more detail, see the Pesticide Trade page in the Resource Library.
Related Chemicals
PAN groups chemicals in our pesticide database based on their relationship to a parent compound, which is labeled with a “P” in the Related Chemicals table. The parent is chosen on the basis of available toxicity information, where chemicals with sufficient toxicity information are assigned to parent status. For some groups with no obvious parent, assignment of parent status is arbitrary.
While you cannot be absolutely sure of the toxicological properties of a particular compound unless it has been through the full battery of toxicological tests, you can make reasonable estimates of toxicity by knowing what happens to the related parent compound after it enters the environment or the human body.
All chemicals in a group are related to the parent in one or more ways. The 17 “Reasons” for combining chemicals into rollup groups are defined in detail on the Related Chemicals section on the Sources & Methodology page.
Reproductive and Developmental Toxicants
Some pesticides are known to cause reproductive and developmental harm, including birth defects, infertility, sterility and impairment of normal growth and development. Many pesticides that disrupt endocrine hormone functions also cause reproductive and developmental harm, as well as other adverse effects.
Evaluations of this type of toxicity have been conducted by the state of California, US EPA, and the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) which maintain lists of reproductive and developmental toxicants. The absence of a chemical on any of these lists does not necessarily mean it is not a reproductive or developmental toxicant. It may mean that it has not yet been evaluated.
PAN’s summary listing is derived from the State of California, U.S. EPA and GHS determinations. For more detail, see the Reproductive and Developmental Harms page in the Resource Library.