Eohs: Environmental Toxicology

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Basic assumption of toxicology

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"all substances are poisons; there is none that is not a poison. The right dose differentiates a poison from a remedy"

Hint 1

physiology, pharmacology, pathology, epidemiology, chemistry and statistics

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Definition of toxicology

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Toxicology is defined as "the study of the adverse effects of chemicals on living organisms."

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History of Toxicology

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Paracelsus was one of the founders of modern toxicology

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Active during the time of Da Vinci and Copernicus (early 16th century).
Contributions:
-the concept of the dose-response relationship
-the notion of target organ specificity of chemicals

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History of Toxicology

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Mathieu Orfila- another important figure in the field of toxicology

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in the 1800's he authored a number of significant works, among them "Trait des Poisons (1813)
Contributions:
-types of poisons and their bodily effects
-contribution to the foundations of forensic toxicology

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What is a toxicologist?

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A toxicologist is a scientist who has received extensive training in order to investigate in living organism "the adverse effects of chemicals...(including their cellular, biochemical, and molecular mechanisms of action) and assess the probability of their occurrence."

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Fields within toxicology

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1. regulatory
2. forensic
3. clinical
4. Environmental
5. reproductive
6. developmental

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Environmental Toxicology

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Environmental Toxicology is concerned with the study of chemicals that contaminate the food, water, soil, or the atmosphere and their effects on biological organisms.

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Poison:

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"any agent capable of producing a deleterious response in a biological system"

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Toxicity:

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"The degree to which something is poisonous"

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-related to a material's physical and chemical properties

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toxicants

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Toxic substances that are MAN-MADE or result from human (anthropogenic) activity

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Toxin

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a toxin usually refers to a toxic substance made by living organisms including reptiles, insects, plants, and microorganisms.

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Examples of Toxic Plants:

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-Some mushrooms (e.g. Amanita phalloides, "death cap")
-poison hemlock
-foxglove
-poison oak/poison ivy
-rhubarb, especially the leave, which have high levels of oxalates
-some houseplants, such as dieffenbachia

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Dose:

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A dose is "the amount of a substance that enters the body"

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-acute exposure: over a very short period of time, usually 24 hours
-chronic exposure: over long periods of time such as weeks, months or years

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Several ways of describing a dose:

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1. exposure dose
2. absorbed dose
3. total dose
4. external dose
5. internal dose
6. biologically effective dose

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Table 3-1: Ways to describe a dose:

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1. Exposure dose
2. External dose
3. Absorbed dose
4. Internal Dose
5. Administered dose
6. Biologically effective dose
7. Total dose

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Exposure dose

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Exposure dose is: The amount of a substance encountered in the environment

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External dose

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An external dose is a dose acquired by contact with contaminated environmental sources.

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Absorbed dose

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An absorbed dose is the amount of a substance that is available to the internal organs of the body

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Internal dose

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An internal dose is the portion of a substnace that becomes internalized in the body through ingestion, absorption and other means

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administered dose

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the quantity of a substance that is administered

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Toxin

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a toxin usually refers to a toxic substance made by living organisms including reptiles, insects, plants, and microorganisms.

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Examples of Toxic Plants:

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-Some mushrooms (e.g. Amanita phalloides, "death cap")
-poison hemlock
-foxglove
-poison oak/poison ivy
-rhubarb, especially the leave, which have high levels of oxalates
-some houseplants, such as dieffenbachia

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Dose:

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A dose is "the amount of a substance that enters the body"

Hint 23

-acute exposure: over a very short period of time, usually 24 hours
-chronic exposure: over long periods of time such as weeks, months or years

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Several ways of describing a dose:

Back 24

1. exposure dose
2. absorbed dose
3. total dose
4. external dose
5. internal dose
6. biologically effective dose

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Table 3-1: Ways to describe a dose:

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1. Exposure dose
2. External dose
3. Absorbed dose
4. Internal Dose
5. Administered dose
6. Biologically effective dose
7. Total dose

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Exposure dose

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Exposure dose is: The amount of a substance encountered in the environment

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External dose

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An external dose is a dose acquired by contact with contaminated environmental sources.

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Absorbed dose

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An absorbed dose is the amount of a substance that is available to the internal organs of the body

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Internal dose

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An internal dose is the portion of a substnace that becomes internalized in the body through ingestion, absorption and other means

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administered dose

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the quantity of a substance that is administered

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Dose Response

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-threshold dose
-no observed adverse effect level (NOAEL)
-no effect level (NEL)

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Threshold dose of carcinogens?
we don't know the threshold dose of carcinogens because cancer takes longer to develop

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Factors that affect the concentration and toxicity of a chemical:

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-route ot entry into the body
-received dose of the chemical
-duration of exposure
-interactions that transpire among multiple chemicals
-individual sensitivity

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Most frequent site of exposure to environmental chemicals:

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1. gastrointestinal tract
2. respiratory system
3. skin

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Routes of exposure:
1. ingestion (e.g. consumption of contaminated food or drink)
2. injections into the bloodstream
3. contact with the surface of the skin (topical mode)
4. inhalation

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definition of carcinogen:

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A chemical (or substance) that causes or is suspected of causing cancer, a disease associated with unregulated proliferation of cells in the body.

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define latency:

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latency is the time period between initial exposure and a measurable response.
The latency period can range from a few seconds (in the case of acutely toxic agents) to several decades for agents that may be carcinogenic.

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Direct adverse effects of exposure to chemicals:
local, systemic, and target organ

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local effects: damage at the site where a chemical first comes into contact with the body
systemic effects-generalized distribution of the chemical throughout the body by the bloodstream to internal organs.
-target organ effects: some chemicals may confine their effects to specific organs.

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Table 3-3: Direct and Indirect Adverse effects of Xenobiotics

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Direct adverse cell effects:
Cell replacement, such as fibrosis, build up of scar tissue
-damage to an enzyme system
-disruption of protein synthesis
-production of reactive chemicals in cells
-DNA damage

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Indirect Adverse effects:
-modification of an essential biochemical function
-interference with nutrition
-alteration of a physiological mechanism

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Testing for toxicity

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The subjects used for testing the toxicity of chemicals used include the following:
-volunteers who have had normal or accidental exposures
-animals exposed purposively (in vivo experiments)
-cells derived from human, animal, or plant sources (in vitro experiments)