443011.13 Toxicity and Hazards of Pesticides
The relative toxicity and hazards of pesticides should be considered when there is a choice of recommended spray materials. Toxicity is the degree to which a pesticide is poisonous; hazard is the risk of being exposed to poisoning. Proper precautions and safe use of pesticides require a thorough understanding of the hazards.
In addition to the direct exposure hazard for humans, there are hazards to the environment. Some pesticides persist for a long time in soil and water. Through the soil and water, some pesticides may be eaten or absorbed and even concentrated by certain animals and plants and stored in their tissues with no observable ill effects. These organisms, as part of the food chain, may eventually concentrate pesticides to the point where the larger organisms in the food chain are affected if they eat the animal or plant that stores (concentrates) the pesticide.
Pesticide fate in soil and water is now of public concern, and some pesticides are restricted in geographical regions containing sandy soils. In urban/suburban environments where thatch and quantities of organic mulch exist on the soil surface, pesticides may be chemically bound to the organic matter, which greatly inhibits movement of the pesticide through the soil.
443021.13.1 Toxicity Ratings and Signal Words on Pesticide Labels
Toxicity ratings are a guide to the potential effect of a chemical on humans and animals. Toxicity is not the only factor associated with human exposure to pesticides. A compound may be extremely toxic but present very little hazard because of dilution, low volatility, or safe use. On the other hand, a chemical with low toxicity can be hazardous because of concentration, high volatility, or careless use.
There are three types of toxicity based on how a person comes in contact with a pesticide: oral, dermal, and inhalation. Pesticides are generally categorized according to acute oral toxicity. Users do not ingest pesticides during application, although they may inadvertently do so while eating or smoking on the job.
Dermal toxicity is of equal or greater practical importance to the applicator since users may absorb measurable quantities of certain pesticides through the skin. Applicators may also be exposed by breathing in pesticide spray or dust (inhalation toxicity).
The LD50 and LC50 are reference standards indicating the relative toxicity from exposure to the technical grade of chemical or active ingredient, based on the Lethal Dose (or Concentration in air) to 50% of a test population. The values are determined on rats or rabbits in support of the pesticide registration. The concentrations are usually expressed in milligrams of test material per kilogram of animal body weight for oral and dermal exposure or per liter of air (in the case of inhalation toxicity). Toxicity ratings are also based on the potential for eye and skin effects. While they cannot be directly extrapolated to humans, the figures do show relative toxicities among active ingredients.
The range in acute oral, dermal, or inhalation values for a particular material is usually related to the sex or strain of the test animal used. Pesticides are classified in four toxicity categories (I, II, III, IV) based on LD50 and LC50 values (Table 1.13.1). The lower the LD50 value, the more hazardous the material. Categories III and IV are generally considered to be low hazard. Required protective gear for these materials will generally be minimal compared with products in categories I and II. Since other factors can be important in determining hazard, LD50 values should not be used as ultimate indices of toxicity and hazard in practical fieldwork.
Note that restricted use status in New York may bear no relationship to toxicity. The NYSDEC designates products as restricted use for a variety of reasons such as where labeling limits use to commercial use only.
Pesticide Label Signal Words:
Caution: Category III or IV pesticide labels will bear a Caution signal word (Table 1.13.1).
Warning: Pesticides classed in Category II will have a Warning signal word on labels.
Danger: The signal word Danger will be found on Category I pesticides. Products assigned to this category based on oral, inhalation or dermal toxicity (as distinct from skin and eye effects) will also add the word "Poison'' and the skull and crossbones to labels. These materials should be applied only by experienced persons thoroughly familiar with the hazards.
Child hazard warning - "Keep out of reach of children'' will also appear on pesticide product labels, except possibly in cases where the likelihood of contact with children is extremely remote or if the pesticide is approved for use on infants or small children.