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as sulfur dioxide gas. The most common TLV protects workers who experience exposure to low-level concentrations of a toxic chemical for 8 hours per day for five consecutive days. Sometimes regulations set a TLV for short-term exposure to protect workers who must briefly enter recently treated areas. In these cases, the allowable concentration of airborne chemical is higher than the long-term TLV.

Factors That Influence Pesticide Toxicity

Certain conditions increase or decrease the ability of an antimicrobial pesticide to control a microorganism. Some of these are temperature, humidity, and exposure to sunlight, wind, or rain. Even genetic varia- tions cause some microorganisms to respond differently. After application, some pesticides break down into different chemicals or chemi- cal compounds. These new chemicals may be less toxic or more toxic than the original pesticide. The time it takes for half of the chemical to break down in the environment or change from its original form is its half-life. This is a measure of the pesticide’s persistence in the environment. Factors such as the presence of other microbes, ultraviolet light, temperature, or impurities combined with the pesticide increase or decrease the half- life. Sometimes impurities contaminate pesticides during manufacture, formulation, storage, or while you are mixing or applying them.

Pesticide Toxicity Classification

Federal regulations group all pesticides into four categories according to their toxicity and potential to cause harm to people or the environment. One of three signal words on the pesticide label indicates the toxicity category for that pesticide. Different label and regulatory requirements apply to each category.

DANGER/POISON and DANGER pesticides are the most toxic or hazard- ous. Federal and state regulations may restrict their use and require that licensed or certified applicators handle or supervise the handling of them. In California, you need permits to buy, possess, and use most DANGER pesticides. Generally, to qualify for a permit, you must be a certified applicator. CAUTION pesticides are the least toxic to people and generally less hazardous. Different label and regulatory requirements apply to each category.

WHAT ARE PESTICIDES?

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