WHEN ARE PESTICIDES CLASSIFIED AS POISONS?

Synopsis

The words "pesticide" and "poison" are not synonymous. Relatively few pesticides are poisonous to humans according to the standard meaning of the term.

“The dose makes the poison" is a saying all doctors understand. What it means, in essence, is that it’s not simply what you come in contact with or ingest that determines risk, it’s also how much you contact or ingest. This point is important because most pesticides are designed to control pests with amounts far smaller than the amount that would affect humans and pets.

In fact, many common substances that are beneficial—even necessary—to human health are also used as pesticides. Examples include vitamin D₃, chlorine, acetaminophen, iron and warfarin.

Poison paranoia impedes rational thinking about pesticides. Contrary to popular belief, pesticides are not a uniquely toxic class of substances. They range from practically non-toxic to highly toxic—as with other classes of natural and manmade substances.

Pesticides are similar in important ways to the medicines we use to preserve our own health. Whether it is an insecticide for controlling termites or fleas in your home, a herbicide for ridding your lawn of dandelions or a fungicide that protects plants during a disease outbreak, pesticides address pest problems much as medicines address health problems. In fact, antibiotics perform the same function in our bodies as many pesticides used in and around homes and on crops; they control unwanted organisms. Why, then, are some people categorically fearful of these problem solvers?

Partly, this fear is due to terminology that leaves many people confused. Many individuals equate the word "pesticide" with “manmade poison.” However, the words "pesticide" and "poison" are not synonymous. While it’s true that some pesticides are poisonous to humans, most are not. Nor are all pesticides manmade.

By definition, poisons are substances that are toxic or lethal in tiny quantities. Among pesticides, poisons are a small group of materials that vary widely in structure, origin, use, etc., but which have in common the ability to be toxic or lethal in very small amounts. Any pesticide may be toxic under some set of conditions; the same is true of nearly every substance. However, relatively few are poisonous to humans according to the standard meaning of the term. Understanding how pesticide toxicity is defined and what makes something a "poison" can help lessen an unreasoned fear of pesticides that too often propels us into hasty reactions. Poison paranoia impedes rational thinking about pesticides.

The dose makes the poison

Pesticides are developed to be toxic to the intended pest(s). They may also be harmful to humans, pets or other organisms if they are mishandled. However, it is a well-established medical principle that it is the amount of a substance that determines if it is harmful. A saying with which nearly all doctors are familiar is “The dose makes the poison." In other words, it’s not simply what you come in contact with that poses a risk, it’s also how much you contact. A lot may hurt you, but a little may not (or it may even save you).

This point is important because most pesticides are designed to control pests with amounts far smaller than the amount that would affect humans and pets.

"What is there that is not a poison? All things are poison and nothing is without poison. It is only the dose that makes a thing not a poison."—Paracelsus, the father of modern toxicology (1493-1541) (More properly known as Theophrastus Phillippus Aureolus Bombastus von Hohenheim.).

This principle comes into play with many everyday products, including the very food and medicine we consume. For example, you can receive a lethal dose of caffeine in approximately 100 cups of strong coffee; a lethal dose of aspirin in a bottle of 100 tablets; a lethal dose of solanine in 100 to 400 pounds of potatoes; a lethal dose of oxalic acid in 10 to 20 pounds of spinach or rhubarb; and a lethal dose of ethanol in a fifth of Scotch, bourbon, vodka or gin.

In fact, many common substances that are beneficial—even necessary—to human health are also used as pesticides, though most people are unaware of it. For example, vitamin D3, which is intentionally added to milk for improved human nutrition, also is sold as a rodenticide. Here are some other examples:

� We require an atmosphere of 21% oxygen for human and animal life; yet breathing 100% oxygen for several days will lead to fatal lung damage.

� Chlorine is a poisonous gas, but it often is purposefully added to drinking water for disinfectant purposes. Without disinfection, water supplies may contain microbial contaminants that can cause disease outbreaks of epidemic proportion.

� Pesticide active ingredients that are also used as human pharmaceuticals include acetaminophen and iron. Warfarin is used as a rodenticide, yet also as a pharmaceutical blood thinner.

� BHA, which is classified as a carcinogen when found in pesticides, is an approved preservative used in bread.

Pesticide labeling

When the U.S. Environmental Protection Agency reviews a pesticide product, it assigns a signal word to it that must appear on the label. The signal word is determined by the results of the product's acute-toxicity studies (taking into account various routes of exposure) or by the presence of other ingredients that, by regulation, require specific labeling. EPA-assigned signal words are:

� Danger. Toxicity Category I

� Warning. Toxicity Category II

� Caution. Toxicity Categories III and IV

It is important to note that all products are assigned no less than Category IV, regardless of toxicity. Therefore, even if a hypothetical pesticide contained only water, it's label would prominently display the word "Caution".

Acute toxicity studies and the pesticide's composition determine the product's signal word designation. Acute oral, acute dermal and acute inhalation studies measure the lethality of a product through its respective route of exposure. Eye irritation and skin irritation studies measure the severity of irritation or corrosivity caused by a product

Caution indicates that the pesticide is no more than slightly toxic if eaten, absorbed through the skin, inhaled or if it causes slight eye or skin irritation.

Warning indicates that the pesticide is moderately toxic if eaten, absorbed through the skin, inhaled, or if it causes moderate eye or skin irritation.

Danger indicates that the pesticide is highly toxic. It is corrosive or causes severe burning to the eyes or skin that may result in irreversible damage.

Danger-Poison also indicates the pesticide is highly toxic, but only if it is eaten, absorbed through the skin or inhaled.

Contrary to popular belief, pesticides are not a uniquely toxic class of substances. They range from practically non-toxic to highly toxic—as with other classes of natural and manmade substances. Despite media portrayal of most pesticides being chemical cousins of nerve gas, the largest volume of pesticides are herbicides targeted at selected weeds and that have generally low toxicity to mammals.

Although most pesticides are developed to be toxic to the intended pest, others serve as repellents, plant growth regulators, pheromones or have other non-toxic uses. In any case, only a few pesticides are considered poisons. To label all pesticides as "poisons" is a misleading use of the term and may create an inappropriate sense of danger. If pesticides are handled and applied with care according to label directions, they do not represent a risk of poisoning to the health of those who apply them or to the public. When used properly, pesticides offer many benefits to our environment, health and society.

RISE (Responsible Industry for a Sound Environment)^® is an association that was created in 1991 to address the critical needs of the specialty pest management industry. RISE can provide current and accurate information on issues and research affecting the specialty pesticide and fertilizer industry. RISE is able to provide viewpoints from its members—as well as legislative viewpoints, as it monitors legislative and regulatory issues in Washington and in the states.

To contact RISE, call (202) 872-3860, fax (202) 463-0474 or write 1156 15th Street, NW; suite 400; Washington, DC 20005.

How pesticide toxicity categories are determined
Pesticides are assigned a toxicity category based on the results of several types of toxicity studies. Acute toxicity values of pesticides are determined based on animal studies. A group of uniform animals (rats, rabbits, guinea pigs, etc.) is divided into groups and each group is exposed (orally, dermally, etc.) to a different dose level of the pesticide. The dose is commonly expressed in milligrams (a milligram is 1/1,000 of a gram, or 0.0000353 ounces) of pesticide per kilogram (a kilogram is 1,000 grams, or 2.2 pounds) of body weight. After a given time, the mortality (percentages of deaths) in each group is measured. From these values, the LD50 is determined. LD50 is the dose of the pesticide required to be lethal to 50% of the test animals under the experimental conditions, and is a standard method of characterizing toxicity The 50% response level is chosen to represent the toxicity tested because this number represents the best single value to characterize the sensitivity of the experimental animals (i.e., it is the "typical" response) and also because it is statistically the most certain value compared to other possible LD values. The lower the LD50 value, the higher the toxicity. For example, the toxicity of a pesticide with an LD50 of 100 mg/kg is higher than that of a pesticide with an LD50 of 1,000 mg/kg. The results of other toxicity testing are represented in a similar manner. LC50 is the concentration of a pesticide required to be lethal to 50% of the experimental animals (used in systems where the exact dose is unknown, such as an aquatic toxicity or inhalation study). When EPA makes the "POISON" classification, the pesticide label must bear the word "POISON" on the label in red on a contrasting background with the skull and crossbones symbol (below) in close proximity.
Hazard indicators	Toxicity categories
	I	II	III	IV
Oral LD50	< 50 mg/kg	50-500 mg/kg	500-5,000 mg/kg	>5,000 mg/kg
Dermal LD50	<200 mg/kg	200-2,000 mg/kg	2,000-5,000 mg/kg	>5,000 mg/kg
Inhalation LC50	<0.05 mg/liter	0.05-0.5 mg/liter	0.5-2.0 mg/liter	>2.0 mg/liter
Eye effects	Corrosive (irreversible destruction of ocular tissue) or corneal involvement or irritation persisting for more than 21 days.	Corneal involvement or irritation clearing in 8 to 21 days	Corneal involvement or irritation clearing in 7 days or less.	Minimal effects clearing in less than 24 hours.
Skin effects	Corrosive (tissue destruction into the dermis and/or scarring).	Severe irritation at 72 hours (severe erythema or edema).	Moderate irritation at 72 hours (moderate erythema).	Mild or slight irritation (no irritation or erythema).