Definition of Terms Physico/Chemical Properties

Atmospheric pressure

The pressure above any area in the Earth’s atmosphere caused by the weight of air.  Standard atmospheric pressure or "the standard atmosphere" (1atm) is defined as 101.325 kilopascals (kPa). This standard pressure is a purely arbitrary representative value for pressure at sea level, and real atmospheric pressures vary from place to place and moment to moment everywhere in the world.

Acidity

An acid is traditionally considered to be any chemical compound that when dissolved in water, gives a solution with a pH of less than 7.

Alkaline

A solution is traditionally considered to be alkalline when the pH is found to be greater than 7.

Autoflammability (liquid)

Commonly called the AutoIgnition (Temperature (AIT) is the lowest temperature of a hot surface that can ignite a vapour.

Boiling Point

The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid.

Density

(symbol: ρ - Greek: rho) is a measure of mass per unit of volume. The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass divided by its total volume. A denser object (such as iron) will have less volume than an equal mass of some less dense substance (such as water).

The SI unit of density is the kilogram per cubic metre(kg/m3)

where
ρ is the object's density (measured in kilograms per cubic metre)
m is the object's total mass (measured in kilograms)
V is the object's total volume (measured in cubic metres)

Dissociation Constant

In chemistry and biochemistry, a dissociation constant or an ionization constant is a specific type of equilibrium constant used for dissociation (ionizationation) reactions. That means that it refers to the extent to which a complex, molecule, or salt separates or splits into smaller molecules, ions, or radicals in a reversible manner. The dissociation constant is represented by the symbol Kd.

Given the reaction:
AxBy <=> xA + yB

It is given by the expression:

Kd = [A]x×[B]y×[AxBy]-1

Where [A], [B], and [AxBy] indicate the concentrations of A, B, and AxBy, respectively.

Equilibrium

The condition of a system in which competing influences are balanced.

Equilibrium Constant

In chemistry, the equilibrium constant is a theoretically-calculated number associated to a reaction which is an useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs.

Evaporation

The process whereby atoms or molecules in a liquid state (or solid state if the substance sublimes) gain sufficient energy to enter the gaseous state. The thermal motion of a molecule must be sufficient to overcome the surface tension of the liquid in order for it to evaporate, that is, its kinetic energy must exceed the work function of cohesion at the surface. Evaporation therefore proceeds more quickly at higher temperature and in liquids with lower surface tension. Since only a small proportion of the molecules are located near the surface and are moving in the proper direction to escape at any given instant, the rate of evaporation is limited. Also, as the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases.

If the evaporation takes place in a closed vessel, the escaping molecules accumulate as a vapour above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapour increases. When the process of escape and return reaches an equilibrium, the vapour is said to be "saturated," and no further change in either vapour pressure and density or liquid temperature will occur.

Explosive

Any explosive material has the following characteristics:

• It is chemically or otherwise energetically unstable.
• The initiation produces a sudden expansion of the material accompanied by the production of heat and large changes in pressure (and typically also a flash or loud noise) which is called the explosion.

Flammable in contact with water

A material that, through contact with water, is liable to become spontaneously flammable or to give off flammable or toxic gas at a rate greater than 1 liter per kilogram of the material, per hour, when tested.

Flammable solids

Materials that can burn rapidly as a powder layer.

Flammability

Flammable or Flammability refers to the ease at which a substance will ignite, causing fire or combustion. Materials that will ignite at temperatures commonly encountered are considered flammable, with various specific definitions giving a temperature requirement.

Freezing point

When considered as the temperature of the reverse change (See Melting point, it is referred to as the freezing point.

Gas

Like liquids, gases are fluids: they have the ability to flow and do not resist deformation, although they do have viscosity. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but instead expand to fill whatever space they occupy. The kinetic energy in a gas is the second greatest of the states of matter (afterplasma). Because of this increased kinetic energy, gas atoms and molecules tend to bounce off of any containing surface and off one another, the more powerfully as the kinetic energy is increased. A common misconception is that the collisions of the molecules with each other is essential to explain gas pressure, but in fact their random velocities are sufficient to define that quantity.

The word "gas" was probably coined by a Flemish chemist as a re-spelling of his pronunciation of the Greek word chaos.

Hydrophobicity

Hydrophobe (from the Greek (hydros) "water" and (phobos) "fear") in chemistry refers to the physical property of a molecule that is repelled by water. Hydrophobic molecules in water often cluster together. Hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. Hydrophobic is often used interchangeably with "oily" or "lipophilic". Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar from polar compounds.

Hydrophilicity

Hydrophile, from the Greek (hydros) "water" and φιλια (philia) "friendship", refers to a physical property of a molecule that can bond with water.  A hydrophilic molecule or portion of a molecule is one that typically is electrically polarized and capable of hydrogen bonding, enabling it to dissolve more readily in water than in oil or other "non-polar" solvents.

Liquid

A fluid whose volume is fixed under conditions of constant temperature and pressure; and, whose shape is usually determined by the container it fills. Furthermore, liquids exert pressure on the sides of a container as well as on anything within the liquid itself; this pressure is transmitted undiminished in all directions.

If a liquid is at rest in a uniform gravitational field, the pressure p at any point is given by;

p = ρgz

where ρ is the density of the liquid (assumed constant) and z is the depth of the point below the surface. Note that this formula assumes that the pressure at the free surface is zero, relative to the surface level.  

Liquids have traits of surface tension and capillarity; they generally expand when heated, and contract when cooled. Objects immersed in liquids are subject to the phenomenon of buoyancy.

Liquids at their respective boiling point change to gases, and at their freezing point, change to a solid. Via fractional distillation, liquids can be separated from one another as they vaporise (evaporate) at their own individual boiling points. Cohesion between molecules of liquid is insufficient to prevent those at free surface from evaporating.

Melting Point

The melting point of a solid is the temperature at which it changes state from solid to liquid.

Oxidising

Substances that have the ability to oxidise other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidisers. Put in another way, the oxidant removes electrons from the substance. Oxidants are usually chemical substances in high oxidation numbers (e.g.H2O2, MnO4-, CrO3, OsO4) or highly electronegative substances that can gain one or two extra electrons by oxidizing a substance (O2, O3, F2, Cl2,Br2).

Partition Coefficient

LogP is a measure of differential solubility of a compound in two solvents. The log ratio of the concentrations of the solute in the solvent is called LogP or the Partition Coefficient. The most well known of these partition coefficients is the one based on the solvents Octanol and water. The octanol-water partition coefficient is a measure of the hydrophobicity and hydrophilicity of a substance. In the context of drug-like substances, hydrophobicity is related toabsorbtion, bioavailability, hydrophobic drug-recepto interactions, metabolism and toxicity.

Pressure

(symbol: p or P) is the measure of the normal component of force that acts on a unit area.:

where: p is the pressture,  F is the normal component of the force and A is the area.

Often F is taken to be the magnitude of the mean vector force normal to the surface of area A upon which it exerts; the "surface" not necessarily being a that of a body, but for example the cross sectional area of a conduit.  Pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are sometimes called gauge pressure. An example of this is the air pressure in a tire of a car, which might be said to be "thirty PSI", but is actually thirty PSI above atmospheric pressure. In technical work, this is often written as "30 PSIG" or, more commonly, "30 psig", though other methods which avoid attaching this information to the unit of pressure are preferred.

Pyrophoric

Also known as Spontaneously combustible material. A pyrophoric material is a liquid or solid that, even in small quantities and without an external ignition source, can ignite after coming in contact with air.

pH

A measure of the activity of hydrogen ions (H+) in a solution and, therefore, its acidity or alkalinity. In aqueous systems, the hydrogen ion activity is dictated by the dissociation constant of water (Kw = 1.011 × 10−14 at 25 °C) and interactions with other ions in solution. Due to this dissociation constant a neutral solution (hydrogen ion activity equals hydroxide ion activity) has a pH of approximately 7. Aqueous solutions with pH values lower than 7 are considered acidic, while pH values higher than 7 are considered alkaline.

Relative density

(also known as specific gravity) is a measure of the density of a material. It is dimensionless, equal to the density of the material divided by the density of water (or, sometimes used for gases, of air).

Since water's density is 1.0 × 103 kg/m3 in SI units, the relative density of a material is approximately the density of the material measured in kg/m3 divided by 1000 (the density of water). There are no units of measurement.

Solid

A solid is a phase of matter, characterized by resistance to deformation and changes of volume. At the microscopic scale, a solid has these properties:

• The atoms or molecules that comprise the solid are packed close together.
• These constituent elements have fixed positions in space relative to each other.  This accounts for the solid's rigidity.
• If sufficient force is applied, either of these properties can be violated, causing permanent deformation.
• Because any solid has some thermal energy, its atoms vibrate. However, this movement is very small and very rapid, and cannot be observed under ordinary condition

Solubility

A substance is soluble in a fluid if it dissolves in the fluid. The dissolved substance is called the solute and the dissolving fluid (usually present in excess) is called thesolvent, which together form a solution. The process of dissolving is called solvation, or hydration if the solvent is water.

Substance

In relation to the NONS regulations a substance is a chemical element or compound in the natural state or obtained by any production process, including any additive necessary to preserve the stability of the product and any impurity deriving from the process used, but excluding any solvent which may be separated without affecting the stability of the substance or changing its composition. A preparation, i.e. a deliberate mixture of such substances, is not subject to these regulations, but one or more of its constituents may be.

A New Substance is one that does not appear on the EINECS inventory, with the exception of polymers in which less than 2% in combined form is a new substance.

Surface tension

An effect within the surface layer of a liquid that causes the layer to behave as an elastic sheet. Surface tension is caused by the attraction between the molecules of the liquid, due to various intermolecular forces. In the bulk of the liquid each molecule is pulled equally in all directions by neighbouring liquid molecules, resulting in a net force of zero. At the surface of the liquid, the molecules are pulled inwards by other molecules deeper inside the liquid, but there are no liquid molecules on the outside to balance these forces, so the surface molecules are subject to an inward force of molecular attraction which is balanced by the resistance of the liquid to compression. There may also be a small outward attraction caused by air molecules, but as air is much less dense than the liquid, this force is negligible.  Surface tension is measured in newtons per metre (N·m-1), is represented by the symbol σ or γ or T and is defined as the force along a line of unit length perpendicular to the surface or work done per unit area.

Temperature

The physical property of a system which underlies the common notions of "hot" and "cold"; the material with the higher temperature is said to be hotter. Temperature is a measure of the average kinetic energy of the particles in a sample of matter.

Vapour

Although vapour and gas are frequently used interchangeably, vapor often carries the connotation of gaseous matter in a state of equilibrium with identical matter in a liquid or solid state below its boiling point. A liquid or solid does not have to boil to release a vapor.

Vapour pressure

The pressure (if the vapor is mixed with other gases, the partial pressure ) of a vapour. At any given temperature, for a particular substance, there is a pressure at which the vapor of that substance is in equilibrium with its liquid or solid forms. This is the equilibrium vapor pressure or saturation vapour pressure of that substance at that temperature. The term vapour pressure is often understood to mean saturated vapour pressure. A substance with a high vapor pressure at normal temperatures is often referred to as volatile.

Definition of Terms Toxicity & Ecotoxicity Properties

Acute Toxicity

A property of a substance that has toxic effects on a living organism, when that organism is exposed to a lethal dose of a substance once. In other words, basically a short term version of chronic toxicity.

Acute exposure

A single exposure to a toxic substance which may result in severe biological harm or death; acute exposures are usually characterized as lasting no longer than a day.

Ames test

A biological assay used in genetics, generally genetic toxicology, to test for mutagenic properties of a chemical compound. A compound is said to be mutagenic if it causes a change in the DNA (deoxyriboneucleic acid) of a living cell or organism. The test is named after its inventor, Bruce Ames.

Biodegredation

The term biodegradation is often used in relation to sewage treatment, environmental remediation (bioremediation) and to plastic materials although biodegradation is perhaps better regarded as the closing of the loop commencing with photosynthesis. Whereas photosynthesis is the process of creating growing matter through the conversion of carbon dioxide (CO2) and water (H2O) into plant material through the action of sunlight, biodegradation is the process of converting organic materials back into CO2 and H2O through microbial action.  Biodegradable matter is material that will biodegrade.

Carcinogen

Any substance or agent that promotes cancer. Carcinogens are also often, but not necessarily, mutagens or teratogens.

Chromosome Aberration

The gain or loss of chromosome material can lead to a variety of genetic disorders.

Chronic exposure

continuous exposure to a toxin over an extended period of time, often measured in months or years.

Hydrolysis

A chemical process in which a molecule is split into two parts by the addition of a molecule of water.

In vitro

(Latin: "within glass") is an experimental technique where the experiment is performed in a test tube, or generally outside a living organism or cell.

In vivo

(Latin for (with)in the living). In vivo is used to indicate the presence of a whole/living organism, in distinction to a partial or dead organism, or a computer model.

Lethal dose (LD)

An indication of the lethality of a given substance or type of radiation. Because resistance varies from one individual to another, the 'lethal dose' represents a dose (usually recorded as dose per kilogram of subject body weight) at which a given percentage of subjects will die.

The most commonly-used lethality indicator is the LD50 (or LD50), a dose at which 50% of subjects will die. LD measurements are often used to describe the power of venoms in animals such as snakes.

Animal-based LD measurements are a commonly-used technique in drug research, although many researchers are now shifting away from such methods.

LD figures depend not only on the species of animal, but also on the mode of administration. For instance, a toxic substance inhaled or injected into the bloodstream may require a much smaller dosage than if the same substance is swallowed.

LD50

Refers to the dose of a toxic substance that kills 50 percent of a test population (typically rats or other surrogates when the test concerns human toxicity). LD50 estimations in animals became obsolete in 1991 and are no longer required for regulatory submissions as a part of pre-clinical development package.

Mutagen

(Latin, literally origin of change) is an agent that changes the genetic information (usually DNA) of an organism and thus increases the number of mutations above the natural background level. Mutagens are usually chemical compounds or ionizing radiation. The Ames test is one method to determine how mutagenic an agent is.

Organs

In biology, an organ (Latin: organum, "instrument, tool") is a group of tissues that perform a specific function or group of functions. Common animal organs include the heart, lungs, brain, eye, stomach, spleen, pancreas, kidneys, liver, intestines, skin, uterus, bladder, bone, etc.

Organism

In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life.

Poisons

Poisons are substances that can cause injury, illness, or death to organisms, usually by chemical reaction or other activity on the molecular scale.

Pre-clinical development

A stage in the development of a new drug that begins before clinical trials (testing in humans) can begin, and during which important safety and pharmacology data is collected.

Terratogen

Teratogenesis is a medical term from the Greek, literally meaning monster-making, which derives from teratology, the study of the frequency, causation, and development of congenital malformations—misleadingly called birth defects. Teratogenesis has gained a more specific usage for the development of abnormal cell masses during fetal growth (see pregnancy), causing physical defects in the fetus.

Toxicity

(from Greek τοξικότητα - poisonousness) is a measure to the degree to which something is toxic or poisonous. The study of poisons is known as toxicology. Toxicity can refer to the effect on a whole organism, such as a human or a bacterium or a plant, or to a substructure, such as the liver.

Toxicology

(from the Greek words toxicon and logos) is the study of the adverse effects of chemicals on living organisms. It is the study of symptoms, mechanisms, treatments and detection of poisoning, especially the poisoning of people. The chief criterion regarding the toxicity of a chemical is the dose, i.e. the amount of exposure to the substance. It is safe to say that almost all substances are toxic under the right conditions.

Legislative Terminology

Biocidal Product Directive

The Biocidal Products Directive or 98/8/EC was introduced into European legislation in 1998 and all Member States had to implement the Directive by 14th May 2000.  The legislation covers Biocidal Products that are used in a variety of industries to control unwanted organisms, such as animals, insects, bacteria, viruses and fungi.  They are intended to kill or otherwise exert a controlling effect by chemical or biological means.

Cosmetic Products Directive

Council Directive 76/768 of 27 July 1976 on the approximation of the laws of the Member States relating to cosmetic products. The Directive contains the "7th amendment" and some subsequent technical adaptations (up to 28 January 2005). A ‘cosmetic product’ shall mean any substance or preparation intended to be placed in contact with the various external parts of the human body (epidermis, hair system, nails, lips and external genital organs) or with the teeth and the mucous membranes of the oral cavity with a view exclusively or mainly to cleaning them, perfuming them, changing their appearance and/or correcting body odours and/or protecting them or keeping them in good condition.

Dangerous Substances Directive

The common name for EC Directive 67/548/EEC. This directive sought to regulate the classification, packaging and labelling of dangerous substances.

EINECS

An acronym for the European INventory of Existing Commercial Chemical Substances. This is a list of commercial substances which were marketed in the EC at some time between 1 January 1971 and 18 September 1981. The substances on this list are exempt from the Notification Of New Substances regulations.

ELINCS

An acronym for the European LIst of Notified (New) Chemical Substances. This is a list of those substances which have passed through the notification process in one or more of the EC member states.

Good Laboratory Practice

Generally refers to a system of management controls for laboratories and research organisations to ensure the consistency and reliability of results as outlined in ICH Guidelines.

Global Harmonised System or The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH)

A project that brings together the regulatory authorities of Europe, Japan and the United States and experts from the pharmaceutical industry in the three regions to discuss scientific and technical aspects of pharmaceutical product registration.

The purpose of ICH is to reduce or obviate the need to duplicate the testing carried out during the research and development of new medicines by recommending ways to achieve greater harmonisation in the interpretation and application of technical guidelines and requirements for product registration.

Harmonisation would lead to a more economical use of human, animal and material resources, and the elimination of unnecessary delay in the global development and availability of new medicines while maintaining safeguards on quality, safety, and efficacy, and regulatory obligations to protect public health.

NONS

The Notification Of New Substances regulations are formally known as EC Directive 92/32/EEC (Also see Seventh Amendment).

Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH)

The European Commission’s (EC) White Paper of 2001 on a ‘future chemical strategy’ proposed a system called REACH that requires chemicals manufactured in quantities of greater than 1 tonne to be Registered, those manufactured in quantities greater than 100 tonnes to be Evaluated and certain substances of high concern (eg carcinogenic, mutagenic and toxic to reproduction (CMR’s)) to be Authorised.

Seventh Amendment

A name commonly given to EC Directive 92/32/EEC. This was the seventh time that EC Directive 67/548/EEC, the Dangerous Substances Directive, had been amended. It forms the basis of the Notification of New Substances regulations 1993.