Toxic Effects of Chemicals
All chemicals have toxic effects at some dose level for some route of exposure. It is therefore wise to minimize exposure to chemicals. Chemicals can have local or systemic effects. Local toxicity refers to the direct action of chemicals at the point of contact. Systemic toxicity occurs when the chemical agent is absorbed into the bloodstream and distributed throughout the body, affecting one or more organs. Toxic effects are also classified as acute or chronic. Acute effects are observed shortly after exposure. Chronic effects result from long term exposures or appear after a latency period.
Routes of Exposure
Dermal Contact: One of the most frequent exposures to chemicals is by contact with the skin. Spills and splash can result in overt contamination of the skin. Also, laboratory personnel may unconsciously contaminate themselves when they touch work surfaces, glassware, or equipment which become contaminated during experimental activity. A common result of skin contact is localized irritation or dermatitis. However, a number of materials are absorbed through the skin to produce systemic poisoning. The main portals of entry for chemicals through the skin are the hair follicles, sebaceous glands, sweat glands, and cuts or abrasions of the outer layers of the skin. The follicles and glands are supplied with blood vessels, which facilitate the absorption of chemicals into the body. Chemicals can also gain entrance into the body when contaminated hands touch the mouth, nose eyes, sores, or cuts.
Inhalation: Inhalation of toxic vapors, mists, gases, or dusts can produce poisoning by absorption through the mucous membrane of the mouth, throat, and lungs and can seriously damage these tissues, by local action. Inhaled gases or vapors may pass rapidly into the capillaries of the lungs and be carried into the circulatory system. The degree of injury resulting from inhalation of toxic substances depends on the toxicity of the material, its solubility in tissue fluids, its concentration, and the duration of exposure.
Inhalation hazards are often associated with gases and volatile chemicals but solids and non volatile liquids can also present an inhalation hazard for laboratory personnel. Laboratory chemicals in the form of dusts and particulates can become airborne when transferred from one container to another. Grinding and crushing procedures can also produce aerosols. Splash created from spills and during vigorous shaking and mixing also results in aerosol formation. Many of the generated during such procedures do not settle out but remain suspended in the air and are carried about by air currents in the room. Some of these are capable of being inhaled and deposited in the respiratory tract. For many operations it is not obvious that an aerosol is being generated and laboratory personnel may not be aware that a hazardous situation exists. Actually, all laboratory operations involving an open vessel will result in the release of an aerosol. Such operations include weighing, stirring, pouring, injections with a needle and syringe, animal handling, and removing caps and stoppers. Alert laboratory personnel will take care not to create unnecessary aerosols.
Ingestion: Ingestion of toxic materials in the laboratory can also occur when contaminated hands come in contact with the mouth or with food items which are placed in the mouth. Food items and utensils themselves can become contaminated when stored in the laboratory. The practice of mouth can result in aspiration of toxic materials.
Injection: Accidents involving needles and syringes can result in injection of contamination through the skin. The needle and syringe is one of the most hazardous items used in the laboratory especially when combined with the task of inoculating an uncooperative animal. Also, containers of toxic chemicals may break resulting in hazard from contact with broken contaminated glass.
The eyes are of particular concern because they are so sensitive to irritants. Ocular exposure can occur via splash or when contaminated hands rub the eyes. Few substances are innocuous in contact with the eyes and a considerable number are capable of causing burns and loss of vision. The eyes are very vascular and provide for rapid absorption of many chemicals.
Safe Handling Practices for Toxic Materials
Access Control: Access to laboratories, which have extremely toxic chemicals, should be controlled by the faculty member. The laboratory door should be kept closed while experiments are in progress. This not only protects those people who might otherwise enter the laboratory, but also reduces interruptions to laboratory staff, which could lead to accidents.
Personnel Practices: Personnel should wash their hands immediately after completion of any procedure involving toxic chemicals and when they leave the laboratory. The use of liquid soap dispensers, preferably foot operated, is recommended.
Eating, drinking, smoking, chewing of gum, application of cosmetics, or storage of utensils, food, or food containers should not be allowed in laboratories where toxic materials are used. The practice of mouth pipetting should also not be allowed. Mechanical pipettes aids are to be used for all procedures.
Decontamination of Work Surfaces: Work surfaces should be protected from contamination by using disposable plastic backed paper or stainless steel trays. Other items and equipment, which become contaminated during experimental activity, should be decontaminated with an appropriate solvent.
Minimizing Aerosols: Since all procedures involving an open vessel of liquids or powders generate aerosols, the laboratory worker should develop techniques which might include discharging liquids form pipettes as close as possible to the fluid level of the receiving vessel, or allowing the contents to run down the wall of the receiving vessel. Dropping the contents from a height will generate greater aerosol. Rapid mixing of liquids with pipettes by alternate suction and expulsion or forcibly expelling material from a pipette should be avoided. Care should also be taken when discarding gloves or plastic backed absorbent paper used to cover the work surface so that contamination is not aerosolized in the process. Dry sweeping or dry mopping contaminated laboratory floors could spread contamination. Floors should be cleaned with a wet mop or with a vacuum cleaner equipped with a HEPA filter.