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Toxicology Glossary - M

macrophage: Large (10-20 mm diameter) amoeboid and phagocytic cell found in many tissues, especially in areas of inflammation; macrophages are derived from blood monocytes and play an important role in host defence mechanisms

macroscopic (gross) pathology: Study of changes associated with disease that are visible to the naked eye without the need for a microscope

Mad Hatter syndrome: See SN mercurialism

Magnusson and Kligman test: See SN guinea-pig maximisation test

mainstream smoke (tobacco smoking): Smoke that is inhaled
WHO, 1989a
RT sidestream smoke

malaise: Vague feeling of bodily discomfort

malignancy: Population of cells showing both uncontrolled growth and a tendency to invade and destroy other tissues; a malignancy is life-threatening
RT cancer, metastasis, tumour.

malignant:

1. Tending to become progressively worse and to result in death if not treated
2. In cancer, cells showing both uncontrolled growth and a tendency to invade and destroy other tissues
   AN benign

mania: Emotional disorder (mental illness) characterized by an expansive and elated state (euphoria), rapid speech, flight of ideas, decreased need for sleep, distractability, grandiosity, poor judgement and increased motor activity

margin of exposure (MOE), margin of safety (MOS): Ratio of the no-observed-adverse-effect level (NOAEL) to the theoretical or estimated exposure dose (EED) or concentration (EEC)
RT therapeutic index

mass mean diameter: Diameter of a particle with a mass equal to the mean mass of all the particles in a population

mass median diameter: Diameter of a particle with the median mass of all the particles in a population
IAEA, 1978

material safety data sheet (MSDS): Compilation of information required under the US OSHA Hazard Communication Standard on the identity of hazardous substances, health and physical hazards, exposure limits, and precautions
PS hazard communication standard, safety data sheet

maximum allowable (admissible, acceptable) concentration (MAC): Regulatory value defining the concentration that if inhaled daily (in the case of work people for 8 hours with a working week of 40 hours, in the case of the general population 24 hours) does not, in the present state of knowledge, appear capable of causing appreciable harm, however long delayed during the working life or during subsequent life or in subsequent generations
RT permissible exposure limit, threshold limit value

maximum average daily concentration of an atmospheric pollutant: Highest of the average daily concentrations recorded at a definite point of measurement during a certain period of observation
SN peak daily average concentration of an air pollutant
IRPTC, 1982

maximum contaminant level (MCL): Under the Safe Drinking Water Act (USA), primary MCL is a regulatory concentration for drinking water which takes into account both adverse effects (including sensitive populations) and technological feasibility (including natural background levels): secondary MCL is a regulatory concentration based on "welfare", such as taste and staining, rather than health, but also takes into account technical feasibility. MCL Goals (MCLG) under the Safe Drinking Water Act do not consider feasibility and are zero for all human and animal carcinogens

maximum exposure limit (MEL): Occupational exposure limit legally defined in GB under COSHH as the maximum concentration of an airborne substance, averaged over a reference period, to which employees may be exposed by inhalation under any circumstances, and set on the advice of the HSC Advisory Committee on Toxic Substances
RT ceiling value

maximum permissible concentration (MPC): See SN maximum allowable concentration

maximum permissible daily dose: Maximum daily dose of substance whose penetration into a human body during a lifetime will not cause diseases or health hazards that can be detected by current investigation methods and will not adversely affect future generations

maximum permissible level (MPL): Level, usually a combination of time and concentration, beyond which any exposure of humans to a chemical or physical agent in their immediate environment is unsafe
RT maximum allowable concentration

maximum residue limit (MRL) for pesticide residues: Maximum contents of a pesticide residue (expressed as mg/kg fresh weight) recommended by the Codex Alimentarius Commission to be legally permitted in or on food commodities and animal feeds. MRL's are based on data obtained following good agricultural practice and foods derived from commodities that comply with the respective MRL's are intended to be toxicologically acceptable
Codex Alimentarius Commission, 1989

maximum residue limit (MRL) for veterinary drugs: Maximum contents of a drug residue (expressed as mg/kg or g/kg fresh weight) recommended by the Codex Alimentarius Commission to be legally permitted or recognized as acceptable in or on food commodities and animal feeds. The MRL is based on the type and amount of residue considered to be without any toxicological hazard for human health as expressed by the acceptable daily intake (ADI) or on the basis of a temporary ADI that uses an additional uncertainty factor. It also takes into account other relevant public health risks as well as food technological aspects
Codex Alimentarius Commission, 1989

maximum tolerable concentration (MTC): Highest concentration of a substance in an environmental medium that does not cause death of test organisms or species (denoted by LC_o)
WHO, 1979

maximum tolerable dose (MTD): Highest amount of a substance that, when introduced into the body, does not kill test animals (denoted by LD_o)

maximum tolerable exposure level (MTEL): Maximum amount or concentration of a substance to which an organism can be exposed without leading to an adverse effect after prolonged exposure time

maximum tolerated dose (MTD): High dose used in chronic toxicity testing that is expected on the basis of an adequate subchronic study to produce limited toxicity when administered for the duration of the test period. It should not induce (a) overt toxicity, for example appreciable death of cells or organ dysfunction, or (b) toxic manifestations that are predicted materially to reduce the life span of the animals except as the result of neoplastic development or (c) 10% or greater retardation of body weight gain as compared with control animals. In some studies, toxicity that could interfere with a carcinogenic effect is specifically excluded from consideration

mean life: Average lifetime of a molecular, atomic, or nuclear system in a specified state. For an exponentially decaying system, it is the average time for the number of molecules, atoms or nuclei in a specified state to decrease by a factor of e, the base of natural logarithms
SN mean time
RT turnover time
ISO, 1972

mean time: See SN mean life

median effective concentration (EC₅₀): Statistically derived concentration of a substance in an environmental medium expected to produce a certain effect in 50% of test organisms in a given population under a defined set of conditions

median effective dose (ED₅₀): Statistically derived dose of a chemical or physical agent (radiation) expected to produce a certain effect in 50% of test organisms in a given population or to produce a half-maximal effect in a biological system under a defined set of conditions

median lethal concentration (LC₅₀): Statistically derived concentration of a substance in an environmental medium expected to kill 50% of organisms in a given population under a defined set of conditions

median lethal dose (LD₅₀): Statistically derived dose of a chemical or physical agent (radiation) expected to kill 50% of organisms in a given population under a defined set of conditions.

median lethal time (TL₅₀): Statistically derived average time interval during which 50% of a given population may be expected to die following acute administration of a chemical or physical agent (radiation) at a given concentration under a defined set of conditions

median narcotic concentration (NC₅₀): Statistically derived concentration of a substance in an environmental medium expected to cause narcotic conditions in 50% of a given population under a defined set of conditions

median narcotic dose (ND₅₀): Statistically derived dose of a substance expected to cause narcosis in 50% of test animals under a defined set of conditions

meiosis:

1. Process of "reductive" cell division, occurring in the production of gametes, by means of which each daughter nucleus receives half the number of chromosomes characteristic of the somatic cells of the species
   RT chromosome,diploid, gamete, haploid
2. See miosis

mercurialism: Chronic poisoning caused by the excessive use of mercury, by breathing its vapour, or by exposure in mining or smelting processes.
SN Mad Hatter syndrome

mesocosm: See RT microcosm

mesothelioma: Malignant tumour of the mesothelium of the pleura, pericardium or peritoneum, that may be caused by exposure to asbestos fibres and some other fibres
BT tumour
RT malignant

metabolic activation: Biotransformation of a substance of relatively low toxicity to a more toxic derivative
BT activation, biotransformation
NT lethal synthesis
SN bioactivation

metabolic half-life (half-time): Time required for one half of the quantity of a substance in the body to be metabolically transformed into a derivative or to be eliminated
SN metabolic half-time
RT clearance, elimination

metabolic model: Analysis and theoretical reconstruction of the way in which the body deals with a specific substance, showing the proportion of the intake that is absorbed, the proportion that is stored and in what tissues, the rate of breakdown in the body and the subsequent fate of the metabolic products, and the rate at which it is eliminated by different organs as unchanged substance or metabolites
WHO, 1989a

metabolic transformation: Biochemical transformation of a substance that takes place within an organism
SN biotransformation

metabolism: Sum total of all physical and chemical processes that take place within an organism; in a narrower sense, the physical and chemical changes that take place in a given substance within an organism. It includes the uptake and distribution within the body of chemical compounds, the changes (biotransformation) undergone by such substances, and the elimination of the compounds and of their metabolites
WHO,1989a
RT biotransformation

metabolite: Any intermediate or product resulting from metabolism
After Nagel et al. (eds), 1991
RT biotransformation

metaplasia: Abnormal transformation of an adult, fully differentiated tissue of one kind into a differentiated tissue of another kind
RT hyperplasia, neoplasia

metastasis:

1. Movement of bacteria or body cells, especially cancer cells, from one part of the body to another, resulting in change in location of a disease or of its symptoms from one part of the body to another
2. Growth of pathogenic micro-organismsor of abnormal cells distant from the site of their origin in the body

methaemoglobinaemia: Presence of methaemoglobin (oxidized haemoglobin) in the blood in greater than normal proportion

methaemoglobin-forming substance: Substance capable of oxidising directly or indirectly the iron(II) in haemoglobin to iron(III) to form methaemoglobin, a derivative of haemoglobin that cannot transport oxygen

microalbuminuria: Chronic presence of albumin in slight excess in urine

microcosm: Artificial test system that simulates major characteristics of the natural environment for the purposes of ecotoxicological assessment: such a system would commonly have a terrestrial phase, with substrate, plants and herbivores, and an aquatic phase, with vertebrates, invertebrates and plankton. The term "mesocosm" implies a more complex and larger system than the term "microcosm" but the distinction is not clearly defined
SN experimentalmodel ecosystem

micromercurialism: Effects of exposure to mercury detected at the lowest exposure levels producing a measurable reaction
RT mercurialism

microsome: Artefactual spherical particle, not present in the living cell, derived from pieces of the endoplasmic reticulum present in homogenates of tissues or cells: microsomes sediment from such homogenates when centrifuged at 100 000 g and higher: the microsomal fraction obtained in this way is often used as a source of mono-oxygenase enzymes
RT cytochrome P-420, cytochrome P-448, cytochrome P-450, endoplasmic reticulum, mono-oxygenase, phase 1 reactions

micturitic: See SN diuretic

Minamata disease: Neurological disease caused by ingestion of methylmercury-contaminated fish, first seen at Minamata Bay in Japan

mineralization: Complete conversion of organic substances to inorganic derivatives

minimum lethal concentration (LC_min): Lowest concentration of a toxic substance in an environmental medium that kills individual organisms or test species under a defined set of conditions
SN lowest lethal concentration found
WHO, 1979

minimum lethal dose (LD_min): Lowest amount of a substance that, when introduced into the body, may cause death to individual species of test animals under a defined set of conditions

miosis: Abnormal contraction of the pupil of the eye to less than 2 mm. Alternative spelling (obsolete): meiosis

miscible: Liquid substances capable of mixing without separation into two phases; refers to liquid mixtures

mitochondri/on (pl -a): Eukaryote cytoplasmic organelle that is bounded by an outer membrane and an inner membrane; the inner membrane has folds called cristae that are the centre of ATP synthesis in oxidative phosphorylation in the animal cell and supplement ATP synthesis by the chloroplasts in photosynthetic cells. The mitochondrial matrix within the inner membrane contains ribosomes, many oxidative enzymes, and a circular DNA molecule that carries the genetic information for a number of these enzymes

mitogen: Substance that induces lymphocyte transformation or, more generally, mitosis and cell proliferation
RT transformation

mitosis: Process by which a cell nucleus divides into two daughter nuclei, each having the same genetic complement as the parent cell: nuclear division is usually followed by cell division
After Nagel et al. (eds), 1991

mixed function oxidase: See SN mono-oxygenase

modifying factor (MF): As used by the USEPA, uncertainty factor that is greater than zero and less than, or equal to 10; the magnitude of the factor depends upon the professional assessment of scientific uncertainties of a study or database not explicitly treated with the standard uncertainty factors (for example the completeness of the overall database and the number of animals tested); the default value for the factor is 1
BT uncertainty factor
IRIS, 1986

molluscicide: Substance intended to kill molluscs
SN limacide

monitoring: Continuous or repeated observation, measurement, and evaluation of health and/or environmental or technical data for defined purposes, according to prearranged schedules in space and time, using comparable methods for sensing and data collection. Evaluation requires comparison with appropriate reference values based on knowledge of the probable relationship between ambient exposure and adverse effects
NT ambient monitoring, biological effect monitoring, biological monitoring, environmental monitoring, health surveillance, personal monitoring.
After Berlin, Yodaiken, and Henman,1984; WHO, 1980; Zielhuis and Henderson, 1986

monoclonal: Pertaining to a specific protein from a single clone of cells, all molecules of this protein being the same

monoclonal antibody: Antibody produced by cloned cells derived from a single lymphocyte
BT antibody
RT polyclonal antibody

mono-oxygenase: Enzyme that catalyses reactions between an organic compound and molecular oxygen in which one atom of the oxygen molecule is incorporated into the organic compound and one atom is reduced to water; involved in the metabolism of many natural and foreign compounds giving both unreactive products and products of different or increased toxicity from that of the parent compound: such enzymes are the main catalysts of phase 1 reactions in the metabolism of xenobiotics by the endoplasmic reticulum or by preparations of microsomes
SN mixed function oxidase
RT cytochrome P-420, cytochrome P-448, cytochrome P-450, endoplasmic reticulum, microsome, phase 1 reactions

morbidity: Any departure, subjective or objective, from a state of physiological or psychological well-being: in this sense, "sickness", "illness", and "morbid condition" are similarly defined and synonymous. The WHO Expert Committee on Health Statistics noted in its Sixth Report (1959) that morbidity could be measured in terms of three units:

1. Proportion of persons who were ill
2. The illnesses (periods or spells of illnesses) that these persons experienced
3. The duration (days, weeks, etc.) of these illnesses
   NT disease
   Last, 1988

morbidity rate: Term used loosely to refer to incidence or prevalence rates of disease
IPCS, 1978

mordant: Substance that fixes a dyestuff in or on a material by combining with the dye to form an insoluble compound, used to fix or intensify stains in a tissue or cell preparation

mortality: Death as studied in a given population or subpopulation. The word mortality is often used incorrectly instead of mortality rate
IPCS, 1978

mortality rate: See SN death rate

mortality study: Investigation dealing with death rates or proportion of deaths attributed to specific causes as a measure of response
IPCS, 1978

multigeneration study:

1. Toxicity test in which two to three generations of the test organism are exposed to the substance being assessed
2. Toxicity test in which only one generation is exposed and effects on subsequent generations are assessed

multiple (or multiphasic) screening: Procedure that has evolved by combining single screening tests, and is the logical corollary of mass screening. Where much time and effort have been spent by a population in attending for a single test such as mass radiography, it is natural to consider the economy of offering other tests at the same time. Multiple (or multiphasic) screening implies the administration of a number of tests, in combination, to large groups of people
BT screening
WHO, 1989a

multistage cluster sampling: Cluster sampling with more than two stages, each sampling being made on aggregates (or clusters) in which the clusters already obtained by the preceding sampling have been divided.
ISO, 1977

multistage model: Dose-response model for cancer death estimation of the form

P(d) = 1 - exp[-(q_o + q₁d¹+ q₂d² + ........... + q(k)d^k)]

where P(d) is the probability of cancer death from a continuous dose rate, d, the q's are constants, and k is the number of dose groups (or, if less than the number of dose groups, k is the number of biological stages believed to be required in the carcinogenesis process). With the multistage model, it is assumed that cancer is initiated by cell mutations in a finite series of steps. A one-stage model is equivalent to a one-hit model

multistage sampling: Type of sampling in which the sample is selected by stages, the sampling units at each stage being subsampled from the larger units chosen at the previous stage
ISO, 1977

murine: Of or belonging to the family of rats and mice (Muridae)

mutagen: Any substance that can induce heritable changes (mutations) of the genotype in a cell as a consequence of alterations or loss of genes or chromosomes (or parts thereof)

mutagenesis: Introduction of heritable changes (mutations) of the genotype in a cell as a consequence of alterations or loss of genes or chromosomes (or parts thereof)
After Nagel et al. (eds), 1991

mutagenicity: Ability of a physical, chemical, or biological agent to induce heritable changes (mutations) in the genotype in a cell as a consequence of alterations or loss of genes or chromosomes (or parts thereof)

mutation: Any relatively stable heritable change in genetic material that may be a chemical transformation of an individual gene ( gene or point mutation), altering its function, or a rearrangement, gain or loss of part of a chromosome, that may be microscopically visible (chromosomal mutation); mutation can be either germinal and inherited by subsequent generations, or somatic and passed through cell lineage by cell division
RT chromosome, gene
RT clastogenesis, genotoxicity

myasthenia: Muscular weakness

mycotoxin: Toxin produced by a fungus

mydriasis: Extreme dilation of the pupil of the eye, either as a result of normal physiological response or in response to a chemical exposure

myelosuppression: Reduction of bone marrow activity leading to a lower concentration of platelets, red cells and white cells in the blood