II.) General Toxicology Flashcards
Toxicology
All pesticides , are toxic at some level, though some are more than others and therfore present a higher risk.
Toxicology: Is the science that deals with poisons and their effect on living organisms.
-Deals with the premise that a relationship exists between the dose and the response. Once this relationship is understood, the risk of using a particular pesticide can be properly evaluated.
Toxicity
Is the general term used to describe the potential for a chemical to cause harm.
Measured by the LD50 or LC50, though often time toxicity measuremnts are only guidelens.
Lethal Dose 50 (L.D.50)
LD50: Toxicity is generally expressed by the LD50; that is the dose that kills 50% of the animal tested on.
LD50 is commonly expressed as milligrams (mg) of active ingredient (a.i.) of pesticide per kilogram (kg) of body weight of the test animal (mg/kg).
- A pesticide with a low LD50 such as 5mg/Kg is very toxic.
- whereas a pesticide with a high LD50 is considered to have a low toxicity such as 1000mg/Kg.
Lethal Concentration 50 (L.C. 50)
LC50: Is another measurement of toxicity in the air or water that will kill 50%of a test animal population and commonly expressed in micrograms (1 gram= 1,000,000
) per liter or air or water (microg/l).
Half-life
Half-life: Represents the time it takes for a given quantity of pesticide to break down to half of its original quantity, and is a measurement of pesticide. persistence
Threshold limit value (TLV):
TLV: Gives indication of the air-borne concentration of the chemical that produces no adverse effects over a period of time and is measured in parts per million (ppm).
- Are commonly established for worker exposed for 8 hours for 5 consecutive days to low-level concentrations of a toxic chemical.
- The TLV is set at a level to prevent minor adverse reactions such as skin or eye irritation.
No Observable Effect Level (NOEL):
NOEL: Is the largest or highest dose or exposure level tested that produces no noticeable toxic effect on test animals.
-Maximum exposure levels for human are commonly set from 100 to 1,000 times less than the NOEL to provide a wide margin of safety.
Hazard vs Risk
Hazard: The inherent ability of a pesticide to produce an adverse affect, is a constant for a particular pesticide product.
Risk: Risk is a function of hazard and dose , where the probability that a chemical will cause harm can depend on concentration, handling practices, and exposure. Factor that impact pesticide risk:
-Formulation
Environmental Conditions
-Proximity of Sensitive Organisms
Formulation
May affect the percentage of active ingredient, propensity to drift, phytotoxicity, or persistence in the environment. It may also affect a pesticide’s potential for dermal uptake, inhalation, or ability to pass through the skin.
Environmental Conditions
Conditions such as heat, light, and precipitation can speed up or slow the breakdown the toxic residues. Other factor include wind drift/inversion layers, type of soil, and watershed features.
Proximity of Sensitive Organisms
The risk of exposure to people and other sensitive organisms depends on their proximity to the application site during and after the application.
- Risk is highest during mixing, loading, and application of the material.
- Risk also increases due to residues on the crop.
Ways to Reduce Risk
Many steps can be taken to reduce the potential of pesticide.
- Using closed mixing systems allow for the safe handling of toxic liquid pesticides because applicators do no have to handle opened pesticide containers, thereby eliminating accidental contact. The same can be said for water-soluble packaging.
- Wearing PPE reduce the risk when handling pesticide or when entering application sites. (Include: Water proof aprons, chemical resistant boots, gloves hats, clean coveralls, goggles/face shield, respirators/disposable masks.
- Observing the REI is an important requirement to reduce exposure shortly after applications.
- Choosing proper formulation in the form of a the least toxic material to prevent injury against people, non-target organisms, that environment.
Single vs. Multiple Exposures
One good source of information to assess the potential health hazard from a pesticide is by consulting the Material Safety and Data Sheet (MSDS)
In some situations, a single exposure to a sufficient dose of certain pesticides will produce illness. This is acute illness.
-Signal Words on the label, indicate the degree of acute risk to the user and is usually measured in oral or dermal toxicity. They are
~Danger (Highly toxic)
~Warning (Moderate toxicity)
~Caution (Slightly Toxic)
In other cases, one exposure will not cause illness, but the effects of repeated, low-level exposures may accumulate in the body so that person may not develop experience symptoms until several day, months, or even years (delayed onset) later. This is chronic illness.
Many times exposure to a pesticide can produce a combination of immediate and delayed affects.
Residues and Persistence
Residues are important and necessary in some types of pest control because they provide continuous exposure to the pest, improving the chances of control. However
They are undesirable when they expose people and other non-target organisms to unsafe levels of pesticides.
To protect the public from harmful residues on harvest produce, feral law establish pesticide residue tolerances for all materials registered for use on agricultural products. These tolerances are based on laboratory and animal testing with a margin of safety to allow for differences in humans. The tolerances are established for each commodity the pesticide is used on.
