Ch. 3: Environmental Toxicology

Toxic Substances

A material that has toxic properties; can be a single toxic chemical (ex: arsenic, lead) or a mixture of toxic chemicals (ex: gasoline). Can be categorized as organic toxins and inorganic toxins.

Toxicologist

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

Hazard

As the inherent capability of an agent or a situation to have an adverse effect. A factor or exposure that may adversely affect health.

Exposure Assessment

As the procedure that identifies populations exposed to the toxicant, describes their composition and size, and examines the roots, magnitudes, frequencies, and durations of such exposures.

Poison

Defined as any agent capable of producing a deleterious response in a biological system.

Toxicants

Denote toxic substances that are man-made or result from human (anthropogenic) activity. The toxic effect may occur directly or indirectly.

Chemical Idiosyncrasy

Meaning that they have either extreme sensitivity to low doses of a chemical or insensitivity to high doses.

Exposure

Proximity and/or contact with a source of a disease agent in such a manner that effective transmission of the agent or harmful effects of the agent may occur.

Target Organ Effects

Some chemicals may confine their effects to specific organs; the most common organs affected by such chemicals are the liver, lungs, heart, kidneys, brain and nervous system, and the reproductive system.

Antagonism

That two chemicals administered together interfere with each other's action or one interferes with the action of the other.

LD50 (Lethal Dose 50)

which is the dosage (mg/kg body weight) causing death in 50 percent of exposed animals.

Additive

The combination of two chemicals produces an effect that is equal to their individual effects added together.

Factors That Affect Responses to a Toxic Chemical

The concentration and toxicity of the chemical are affected by the following: Route of entry into the body, Received dose of the chemical, Duration of exposure, Interactions that transpire among multiple chemicals, Individual sensitivity.

Toxicology

A cornerstone of environmental health, overlaps other disciplines, including physiology, pharmacology, and pathology, and to some extent epidemiology, chemistry and statistics. Assumption: "all substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy."

Reproductive Toxicology

Examines the association between chemicals and adverse effects upon the reproductive system.

Hazard Identification

Examines the evidence that associates exposure to an agent with its toxicity and produces a qualitative judgment about the strength of that evidence, whether it is derived from human epidemiology or extrapolated from laboratory animal data.

Dose-Response Assessment

The measurement of the relationship between the amount of exposure and the occurrence of the unwanted health effects.

Systemic Effects

Adverse effects associated with generalized distribution of the chemical throughout the body by the bloodstream to internal organs.

Xenobiotics

Chemical substances that are foreign to the biological system; they include naturally occurring compounds, drugs, environmental agents, carcinogens, and insecticides.

Risk Management

Consists of actions taken to control exposures to toxic chemicals in the environment. Exposure standards, requirements for premarket testing, recalls of toxic products, and outright banning of very hazardous materials are among the actions that are used by governmental agencies to manage risk.

Local Effects

Damage at the site where a chemical first comes into contact with the body. Ex: redness, burning, and irritation of the skin.

Carcinogen

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

Spectrum of Toxic Dose

Describes the toxicity or hazards that are related to exposure to a particular chemical.

Risk Characterization

Develops estimates of the number of excess unwarranted health events expected at different time intervals at each level of exposure.

Synergism

Greek word synergos means working together; indicates that the combined effect of exposures to two or more chemicals is greater than the sum of their individual effects.

Potentiation

Happens when one chemical that is not toxic causes another chemical to become more toxic.

Risk Assessment

Refers to a process for identifying adverse consequences and their associated probability. Steps: (1) hazard identification, (2) dose-response assessment, (3) exposure assessment, and (4) risk characterization.

Toxin

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

Chemical Allergy

Refers to an immunologically mediated adverse reaction to a chemical resulting from previous sensitization to that chemical or to a structurally similar one.

Sister Chromatid Exchange

Refers to reciprocal exchanges of DNA between pairs of DNA molecules.

Dose

Refers to the amount of a substance administered at one time.

Threshold

Refers to the lowest dose at which a particular response may occur.

Toxic Agent

Refers very generally to a material or factor that can be harmful to biological systems.

Developmental Toxicology

Researches the effects of natural and man-made chemicals (some classified as teratogens-substances that cause birth defects) on prenatal development.

Coalitive Interaction

Several agents that have no known toxic effects interact to produce a toxic effect.

Toxicity

The degree to which something is poisonous; related to a material's physical and chemical properties.

Modern Toxicology

The science of poisons or the study of the adverse effects of chemicals on living organisms; is not confined to the study of humans, but can be applied to other species organisms as well.

Environmental Toxicology

The study of how ecological systems--their structures, dynamics, functions, etc.--are affected by pollutants.