Toxicology Notes
- PPM-Parts per million (1 in 1,000,000)
- PPB-Parts per billion (1 in 1,000,000,000)
- PPT- Parts per trillion (1 in 1,000,000,000,000)
- These are dimensionless quantities (they are pure numbers with no units of measurement) because they are parts-per notations and are quantity-per-quantity measures
- On the left side of the decimal point:
- 1 trillion > 1 billion
- 1 billion > 1 million
- 1 million > 1 thousand
- On the right side of the decimal point
- 1 part per trillion < 1 part per billion
- 1 part per billion < 1 part per million
- 1 part per million < 1 part per thousand
- 1 cubic centimeter (cc) = 1ml = 1g
- 1000ml (1 liter of water) = 1kg (1000g)
- 1mg (1/1000g) / kg (1000g) = 1ppm
- 1mm^3 (1/1000cm^3) / liter (1000cm^3)= 1ppm
- 1mg (1/1000g) / liter (1000g)= 1 ppm
- Toxicity of chemicals is determined in a lab
- The normal procedure is to test animals: ingestion, application to skin, inhalation, forced feeding, other methods that introduce the material to the body, or by placing the test material in the water or air of the test animal environment
- Toxicity is measured as clinical "endpoints"
- death
- Teratogenicity (ability to cause birth defects)
- Carcinogenicity (ability to cause cancer)
- Mutagenicity (Ability to cause heritable change in DNA)
- When you are using morality as the "endpoint", there are 2 measures of mortality
- LD50- The dose of a chemical which produces death in 50% of a population which it is administered by any variety of methods
- LC50- The concentration of a chemical in an environment (air or water) which produces death in 50% of an exposed population in a specified time frame
- There are three routs by which organisms are exposed to pesticides: oral, dermal, inhalation
- Oral- Exposure to pesticides when the chemical is taken through the mouth and passes through gastrointestinal tract. During oral exposure, the pesticide is still outside of the body until is passes through epithelial cellular membranes
- Dermal-Exposure of the skin to a pesticide. It is the most common rout of human exposure. This exposure is not serious with proper hygiene, unless there is a specific rapid toxicological effect.
- Inhalation- When a pesticide is breathed into the lungs through nose or mouth. It is significant for aquatic organisms. It is not a concern until it crosses from the lung into the body (unless the chemical is corrosive)
- There are three terms used to describe duration of doses
- Acute- single exposure of short time (toxic symptoms referred to as symptoms of "acute toxicity")
- Chronic- repeated long term contact (toxic symptoms referred to as symptoms of "chronic toxicity")
- Subchronic- repeated exposure (toxic symptoms referred to as symptoms of "subchronic toxicity)
- For pesticides, less is more when dealing with toxicity
- The less you need to cause a toxic effect, the more toxic the substance is.
- LD50 of 25mg/kg is more toxic than is one of 7,000mg/kg
- The toxicity of a pesticide is reflection on the label in the form of a signal word
- Caution-lowest degree of relative toxicity. All pesticides w/ LD50 of greater than 500mg/kg must have this on their label.
- Relatively nontoxic- >5,000mg/kg
- Slightly toxic-500-5,000 mg/kg
- Warning- intermediate degree of relative toxicity. All pesticides w/ LD50 of greater than 50 and less than 500mg/kg must have this on their label.
- Moderately toxic- >50 but <500 mg/kg
- Danger-highest degree of relative toxicity. All pesticides with an LD50 of less than 50mg/kg must display this word on the label.
- Poison is a legally defined term- not just anything a person doesn't like. It is any pesticide with an LD50 of 50mg/kg or less. Labels must reflect this classification and must have the signal word danger plus poison. It must also display the skull and crossbones label.
- Chemicals must be evaluated in their biological context of behavior in organisms
- The mode of action, not the source is the concern of toxicologists and informed users of pesticides.
- Herbicides act on biological pathways not present in humans
- Herbicides approved for use in the region have LD50s of 50mg/kg or greater have intermediate are relatively low toxicity
- Some insecticides used are highly toxic
- Examples of pesticides and other chemicals are given to show relative risk of pesticides in the environment
- Nicotine- 50mg/kg
- Carbaryl-270mg/kg
- Malathion 370kg/mg
- Always treat pesticides with caution and respect, but have a realistic recognition of their risk in a world of risks.
- Highly toxic chemicals 0-50mg/kg range
- Strychnine 30.0
- Nicotine 50.0
- Moderately toxic chemicals 50-500mg/kg range
- Caffeine 200
- Carbaryl 270
- Slightly toxic chemicals 500-5000mg/kg range
- Tebuthiuron 644
- Dicamba 757
- Pesticides are chemicals introduced into the environment to perform a function
- The source of a chemical is irrelevant when considering toxicity
- Pesticides should be treated with care and proper respect, so should household cleaners, gasoline, kerosene, bleaches paints and other chemicals.