NOTE: GENERAL PROPERTIES OF ORGANIC SOLVENTS

The organic solvents share several properties. They are all volatile. They are generally neurotoxic or anaesthetic as a result of fat solubility and potential for entering and altering the function of neuronal phospholipids in membranes. Many irritate the respiratory tract and defat or damage the skin.

Some are hepatotoxic and to a lesser extent nephrotoxic. The prototypical solvent in the toxicology literature is carbon tetrachloride. Think also of those you are familiar with from everyday use: e.g. paraffin, petrol, alcohol, nail polish remover, paint thinners and strippers, turpentine, Tippex, etc.

Class vs. specific effects:

Organic solvents are a heterogeneous group of chemical compounds widely used in industry. Exposures occur in many different settings. Some of these exposures, such as painting, printing, degreasing or dry cleaning, are obvious. Other exposures may not be obvious. Organic solvents have the common property of being able to dissolve organic compounds, although they may not be used for this purpose in industry. They may be chemical intermediates in other processes, so that it is the manufacturing worker rather than the end user who is exposed.

It is impossible to remember all of the various solvents let alone their effects. You should start by ensuring that you know the class effects. These are effects that many solvents have and that you would think of first in doing a risk assessment.

Then, you need to know some of the more important associations of specific solvents or classes of solvents.

Physical determinants of dose: exposure and absorption of organic solvents:

Absorption depends on concentration, duration of exposure (dependent on physicochemical properties), route of entry, blood/gas partition coefficient, liphophilic characteristics (and for inhalation, depth and rate of respiration).

Physicochemical properties:

• Evaporation Rate - the time required to change a given volume of liquid to vapour.
• Vapour Pressure - the pressure of vapour in equilibrium with the liquid at a given temperature.
• Boiling Point - temperature at which solvent's vapour pressure is equal to atmospheric pressure.
• Flash Point - the lowest temperature at which the vapour pressure of a substance is sufficient for it to ignite in air when exposed to flame.
• Explosive Limits - the lowest and highest proportions of vapour to air that have potential for explosion. (Note that many solvents present explosion hazards).

Routes of entry:

• Inhalation - Usually the most important in determining dose in occupational settings.
• Percutaneous - In certain settings the skin represents the major route of exposure and uptake. Depends on the chemical features of the solvent and the conditions of use.
• Ingestion - A poor route of absorption of organic solvents, but aspiration can easily occur, (for example after paraffin ingestion) with consequent severe damage to the lungs.

Blood-gas partition coefficients:

For anaesthetics a high blood/gas partition coefficient implies a longer time needed to go into and come out of anaesthesia. The same principle applies to occupational exposure.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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