p-value A measure of statistical signi cance. A small value (e.g., ≤ 0.05) is strong evidence for statistical signi cance (speci cally, strong evidence against the ‘null’ hypothesis [that is, a counterclaim]). Statistical signi cance does not necessarily mean a ‘practical’ signi cance.

r [Correlation coef cient] ‘r’ indicates the degree of relationship between two variables, that is, r indicates the level of statistical association between two things. A value close to +1 indicates a strong positive relationship (i.e., as one variable goes up, so does the other). A value close to -1 indicates a strong inverse relationship (i.e., as one variable goes up, the other goes down). A value of 0 indicates no relationship. It is important to note that even a strong statistical relationship does not necessarily mean one variable causes another, there may be some other factor not being considered.

Absorption [Absorbed] Absorption can mean the transport (active or passive) of a substance into an organism. More narrowly, absorption is the process by which a substance reaches a human or animal’s bloodstream.

Adverse effect [Adverse effects] Harmful or abnormal changes in an organism (including humans, plants and animals) as a result of exposure to a chemical, physical or biological agent. This may include a reduction in life-span or ill-health.

Analogy Using a well-understood chemical (or other agent) to explain a similar chemical (or other agent).

Antagonism [Antagonistic] When the effect of two substances together is less than one on its own. Contrast with synergism.

Association [Associated; Associations] A statistical relationship between two variables. The variables may or may not have a causal relationship. See also “r”.

Biological gradient [Biological gradients] Larger exposure leads to a larger effect and smaller exposure to a smaller effect.

Biological plausibility Given what we know about biology, physiology, biochemistry, etc., does it seem feasible that a given substance or agent can cause a given effect? Is there a plausible mechanism?

Carcinogen A chemical, physical agent or biological agent that can cause cancer.

Causation [Cause and effect; Causal relationship; Causal] The concept that one event (‘cause’) results in another event (‘effect’) occurring. For example, if you heat ice with a flame (cause) it will melt (effect).

Coherence Do the observations fit within current knowledge? If so, they are coherent.

Confounding factor [Confounding variable; Confounding factors] When considering two variables in a study, a confounding factor is a third (or more) variable affecting these two variables, leading to distorted associations.

Dependent variable [Dependent variables] Usually the y-axis (vertical axis) on a graph, it is the variable dependent on another variable being analysed; it is the variable that demonstrates ‘effect.’ In a graph of ingested drug versus blood levels of that drug, the ‘blood levels of that drug’ would be the dependent variable. Contrast with independent variable.

Dose [Doses] In narrow toxicological terms, dose is the concentration of a poison at a site of action (e.g., in a specific tissue). In broader terms, dose is the quantity of a substance taken/administered or absorbed by an organism following exposure. Dose-response As a dose changes, so too does the response (e.g., the severity of an effect or the number of individuals experiencing that effect).

Elimination [Eliminated] The removal of waste and foreign substances from the body, including through exhaled breath, perspiration, urination and bowel movement.

Epidemiology [Epidemiological; Epidemiologic; Epidemiologist] The study of the distribution and rates of disease (or good health). One of the aims of epidemiology is to and causes of disease in populations.

Exposure [Exposed; Exposures] The amount or intensity of a chemical or other agent (like radiation) that reaches a population, organism (including a human, plant or animal), or specific part of an organism (like an organ or cell).

Hazard [Hazards] Something (e.g., a drug) that can cause harm. Contrast with ‘risk’. Herbicide A substance toxic to plants (e.g., glyphosate or ‘Roundup’ used to reduce weeds).

Hormesis A potentially toxic substance which stimulates at a low dose but inhibits at a large dose. Characterised by a U or J shaped dose-response curve.

Independent variable [Independent variables] Usually the x-axis (horizontal axis) on a graph, it is the variable that is not dependent on the second variable being analysed; it is the variable controlled by an experimenter or a proposed ‘cause.’ In a graph of ingested drug versus blood levels of that drug, the ‘ingested drug’ would be the independent variable. Contrast with dependent variable.

keratinocyte A common type of cell found in the skin.

Linear Data which provides a straight line when plotted. Put another way, it is when a change in one variable will result in a corresponding change in the other variable of interest with this relationship forming a straight line.

Mechanism of Action (MOA) [Mechanism of Action; Mechanism(s); Mechanism(s) of Action] The specific cellular, biochemical and molecular interactions through which a toxic substance produces a harmful effect in a living organism. For example, glyphosate binds to and inhibits the plant enzyme 5- enolpyruvylshikimate-3-phosphate synthase. Contrast with ‘mode of action.’ Sometimes used synonymously with ‘mode of action.’ Metabolism Chemical and physical changes to a substance that occur within a living organism.

Mode of Action (MoA) [Mode of Action; Mode(s) of action] The functional or anatomical changes at the animal, system, organ and/or cellular level, resulting from the exposure of a living organism to a substance. For example, glyphosate (herbicide) interferes with the production of certain amino acids in plants. Contrast with ‘mechanism of action.’ Sometimes used synonymously with ‘mechanism of action.’

Monotonic When there are only increases or only decreases on a graph (but not both in the same graph).

Multifactorial Multiple factors are involved.

Observational studies A study where the researcher observes individuals and simply measures outcomes without manipulating the independent variable. For example, in the case of lead it would be unethical to intentionally expose children and then watch the effect on blood lead levels. Instead the researcher might compare blood lead levels of children against environmental exposures to lead (which is out of the direct control of the researcher).

Olfactory Epithelia Tissue involved in smell.

Pathophysiology [Pathophysiological] The study of functional changes in the body associated with or due to disease (including the harms from toxic chemical exposure).

Pharmacology [Pharmacological] The study of the uses, effects, properties and actions of medicines and other drugs on organisms.

Poison [Poisonous] A substance with harmful effects on a living organism if a sufficient quantity is absorbed.

Presystemic elimination The process by which an active substance (e.g., a poison or drug) is metabolised between the site of exposure and the systemic circulation, reducing the amount of active substance that reaches the bloodstream.

Risk The probability that a harm will occur following exposure to a chemical, physical agent or biological agent. It combines considerations of hazard and exposure. Contrast with ‘hazard’.

Specificity [Specfic] An exposure produces a single effect.

Statistical significance A measure of if a result is simply due to chance or ‘real’. See also p-value.

Synergism [Synergistic] When the effect of two substances together is greater than the sum of each substance working alone. Contrast with antagonism.

Systemic circulation The part of the cardiovascular system carrying oxygenated blood from the heart to the rest of the body, and deoxygenated blood back to the heart.

Temporality A cause must occur before its effect (e.g., an exposure to poison must occur before its harm is seen; if a harm is seen before the exposure to poison then the poison cannot be the cause of the harm).

Toxic [Toxicity] The ability of a chemical, physical agent or biological agent to cause harm to living systems or ecosystems.

Toxicant [Toxicants] Often used interchangeably with ‘poison’. It can more specifically mean a poison made by humans or which is found in the environment due to human activity.

Toxication The process by which a substance is converted in a living organism or environment (e.g., through metabolism), making it more toxic.

Toxicology The study of the harmful effects of chemicals (like lead), physical agents (like radiation) or biological agents (like snake venom) on living organisms and the ecosystem. Toxicology looks at how (and how much) exposure causes harm, evaluations of safety, prevention, diagnosis of exposures, and treatment. Known as the ‘science of poisons’ and the ‘science of safety.’

Toxin [Toxins] A poison made by a living organism, including bacteria (e.g., botulinum toxin or ‘botox’), plants (e.g., ricin) or animals (e.g., spider venom).

Venom [Venoms] A toxin injected by an animal bite or sting that is usually used in defense or to attack prey.

Xenobiotic [Xenobiotics] A substance foreign to an organism or ecosystem. μg/dL Micrograms (1/1,000,000 of a gram) per decilitre (1/10th of a litre).