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Pure Appl. Chem., Vol. 65, No. 9, pp. 2003-2122, 1993.



Glossary for chemists of terms used in toxicology
(IUPAC Recommmendations 1993)


Alphabetical entries

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haematemesis: Vomiting of blood.
haematoma: Localised accumulation of blood, usually clotted, in an organ, space, or tissue, due to a failure of the wall of a blood vessel.
haematuria: Presence of blood in the urine.
haemodialysis: Use of an artificial kidney to remove toxic compounds from the blood by passing it through a tube of semipermeable membrane. The tube is bathed in a dialysing solution to restore the normal chemical composition of the blood while permitting diffusion of toxic substances from the blood.
haemoglobinuria: Presence of free haemoglobin in the urine.
haemolysin: Substance that damages the membrane of erythrocytes causing the release of haemoglobin.
haemolysis: Release of haemoglobin from erythrocytes, and its appearance in the plasma.
haemoperfusion: Passing blood through a column of charcoal or adsorbent resin for the removal of drugs or toxins.
haemosiderin: Iron-containing pigment that is formed from haemoglobin released during the disintegration of red blood cells and that accumulates in individuals who have ingested excess iron.
half-life (half-time) (t1/2): Time in which the concentration of a substance will be reduced by half, assuming a first order elimination process or radioactive decay.
haploid (monoploid): State in which a cell contains only one set of chromosomes.
RT diploid, gamete, meiosis.
hapten: Low-molecular-weight molecule that contains an antigenic determinant (epitope) that may bind to a specific antibody but which is not itself antigenic unless complexed with an antigenic carrier such as a protein or cell; once bound it can cause the sensitization of lymphocytes, possibly leading to allergy or cell-mediated hypersensitivity.
After Nagel et al. (eds), 1991
RT allergy, antigen, antibody, cell-mediated hypersensitivity, epitope.
harm: Damage or adverse effect to a population, species, individual organism, organ, tissue or cell.
SN adverse effect.
harmful occupational factor: Component of the work environment the effect of which on a worker under certain conditions leads to ill health or reduction of working ability.
harmful substance: Substance that, following contact with an organism can cause ill health or adverse effects either at the time of exposure or later in the life of the present and future generations.
SN noxious substance.
hazard: Set of inherent properties of a substance, mixture of substances or a process involving substances that, under production, usage or disposal conditions, make it capable of causing adverse effects to organisms or the environment, depending on the degree of exposure; in other words, it is a source of danger.
RT risk.
hazard assessment: Determination of factors controlling the likely effects of a hazard such as the dose-effect and dose-response relationships, variations in target susceptibility, and mechanism of toxicity.
RT exposure assessment, hazard evaluation, hazard identification, risk assessment, risk characterization, risk estimation, risk evaluation, risk identification, risk perception.
hazard communication standard: US OSHA standard requiring all employers to inform employees of the hazard of substances in the workplace and the steps necessary to avoid harm.
hazard evaluation: Establishment of a qualitative or quantitative relationship between hazard and benefit, involving the complex process of determining the significance of the identified hazard and balancing this against identifiable benefit: this may subsequently be developed into a risk evaluation.
RT exposure evaluation, hazard assessment, hazard identification, risk assessment, risk characterization, risk estimation, risk evaluation, risk identification, risk perception.
hazard identification: Determination of substances of concern, their adverse effects, target populations, and conditions of exposure, taking into account toxicity data and knowledge of effects on human health, other organisms and their environment.
WHO, 1988
hazard quotient (HQ): Ratio of toxicant exposure (estimated or measured) to a reference value regarded as corresponding to a threshold of toxicity: if the total hazard quotient from all toxicants to a target exceeds unity, the combination of toxicants may produce (will produce under assumptions of additivity) an adverse effect.
RT hazard, pollutant, toxic substance.
hazardous production factor: Production factor the effect of which on a worker under certain conditions results in injury or some impairment of health.
SN hazard at work, hazardous occupational factor.
IRPTC, 1982
1. State of complete physical, mental and social well-being, and not merely the absence of disease or infirmity.
   WHO, 1978b
2. State of dynamic balance in which an individual's or a group's capacity to cope with the circumstances of living is at
   an optimal level.
3. State characterized by anatomical, physiological and psychological integrity, ability to perform personally valued
   family, work and community roles; ability to deal with physical, biological, psychological and social stress; a feeling
   of wellbeing; and freedom from the risk of disease and untimely death.
   Last, 1988
health-based exposure limit: Maximum concentration or intensity of exposure that can be tolerated without significant effect (based on only scientific and not economic evidence concerning exposure levels and associated health effects).
de Koning, 1987, ACGIH 1975
health hazard: Any factor or exposure that may adversely affect health.
Last, 1988
health surveillance: Periodic medico-physiological examinations of exposed workers with the objective of protecting health and preventing occupationally related disease.
Berlin, Yodaiken, and Henman, 1984
RT biological monitoring, biomarker, monitoring.
healthy worker effect: Epidemiological phenomenon observed initially in studies of occupational diseases: workers usually exhibit lower overall disease and death rates than the general population, due to the fact that the old, severely ill and disabled are ordinarily excluded from employment. Death rates in the general population may be inappropriate for comparison, if this effect is not taken into account.
WHO, 1989a
hepatic: Pertaining to the liver.
hepatotoxic: Poisonous to liver cells.
Henry's law constant: At constant temperature and pressure, the ratio of the partial pressure of a gas above a liquid to its molal solubility in the liquid and therefore a measure of its partition between the gas phase and the solute phase.
herbicide: Substance intended to kill plants.
histogenic origin: Germ cell layer of the embryo from which a given adult tissue develops.
histology: Study (usually microscopic) of the anatomy of tissues and their cellular and subcellular structure.
histopathology: Microscopic pathological study of the anatomy and cell structure of tissues in disease to reveal abnormal or adverse structural changes.
homeostasis: Normal, internal stability in an organism maintained by co-ordinated responses of the organ systems that automatically compensate for environmental changes.
homology: Degree of identity existing between the nucleotide sequences of two related but not complementary DNA or RNA molecules; 70 % homology means that on the average 70 out of every 100 nucleotides are identical in a given sequence. The same term is used in comparing the amino acid sequences of related proteins.
hormesis: Stimulatory effect of small doses of a potentially toxic substance that is inhibitory in larger doses.
hormone: Substance formed in one organ or part of the body and carried in the blood to another organ or part where it selectively alters functional activity.
human ecology: Interrelationship between humans and the entire environment - physical, biological, socio-economic, and cultural, including the interrelationships between individual humans or groups of humans and other human groups or groups of other species.
human equivalent dose: Human dose of an agent that is believed to induce the same magnitude of a toxic effect that the known animal dose has induced.
IRIS, 1986
hydrophilic/ adj., -ity n.: Describing the character of a molecule or atomic group which has an affinity for water.
hydrophobic/ adj., -ity n.: Describing the character of a molecule or atomic group which is insoluble in water, or resistant to wetting or hydration.
hygiene: Science of health and its preservation.
hyper-: Prefix meaning above or excessive: when used with the suffix "-aemia" refers to blood and with the suffix "-uria" refers to urine, for example "hyperbilirubinaemia".
hyperaemia: Excessive amount of blood in any part of the body.
hyperalimentation: Ingestion or administration of nutrients in excess of optimal amounts.
hyperbilirubinaemia: Excessive concentration of bilirubin in the blood.
hypercalcaemia: Excessive concentration of calcium in the blood.
hyperglycaemia: Excessive concentration of glucose in the blood.
hyperkalaemia: Excessive concentration of potassium in the blood.
hypernatraemia: Excessive concentration of sodium in the blood.
hyperparathyroidism: Abnormally increased parathyroid gland activity that affects, and is affected by, plasma calcium concentration.
hyperplasia: Abnormal multiplication or increase in the number of normal cells in a tissue or organ.
RT hypertrophy, neoplasia.
hyper-reactivity: Term used to describe the responses of (effects on) an individual to (of) an agent when they are qualitatively those expected, but quantitatively increased.
hyper-reflexia: Exaggeration of reflexes.
hypersensitivity: State in which an individual reacts with allergic effects following exposure to a certain substance (allergen) after having been exposed previously to the same substance.
PS allergy.
RT cell-mediated hypersensitivity, sensitization.
hypersusceptibility: Excessive reaction following exposure to a given amount or concentration of a substance as compared with the large majority of other exposed subjects.
RT idiosyncrasy.
hypertension: Persistently high blood pressure in the arteries or in a circuit, for example pulmonary hypertension or hepatic portal hypertension.
hypertrophy: Excessive growth in bulk of a tissue or organ through increase in size but not in number of the constituent cells.
RT hyperplasia.
hypervitaminosis: Condition resulting from the ingestion of an excess of one or more vitamins.
hypo-: Prefix meaning under, deficient: when used with the suffix "-aemia" refers to blood and with the suffix "-uria" refers to urine, for example "hypocalcaemia".
hypocalcaemia: Abnormally low calcium concentration in the blood.
hypokalaemia: Abnormally low potassium concentration in the blood.
hyponatraemia: Abnormally low sodium concentration in the blood.
hypovolaemic: Pertaining to an abnormally decreased volume of circulating fluid (plasma) in the body.
hypoxaemia: Deficient oxygenation of the blood.
1. Abnormally low oxygen content or tension.
2. Deficiency of oxygen in the inspired air, in blood or in tissues, short of anoxia. 

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