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Appendix I: Safety Readings 1
Appendix I: Safety Readings
CHEMICAL HYGIENE and SAFETY in the LABORATORY
Reading 1. TOXICOLOGY: Routes of Entry and Dose
References:
Safety in Academic Chemistry Laboratories, American Chemical Society, Washington, D.C.:
2003, pp.10-11.
Working Safely with Chemicals in the Laboratory, 2nd Ed., Genium Publishing, Schenectady,
NY: 1994, pp. 5-9.
(Copies ofthese references are in the laboratories. They may not be removed.)
"What is it that is not poison? All things are poison and nothing is
without poison. It is the dose only that makes a thing not a poison",
Paracelsus, 15th Century AD
When anything is ingested in sufficient quantity, it can be lethal. Toxicity is subdivided into
acute and chronic effects. Acute poisons produce an immediateeffect, usually from a single
dose. Chronic effects result from low doses accumulated over long periods of time. Any
substance can be harmful to living things. But, just as there are degrees of being harmful, so are
there also degrees of being safe. A complex relationship exists between a material and its
biological effects in humans that involves considerations of dose, the length of time ofexposure,
the route of exposure, and other, more individual factors, e.g., age, gender, allergies, lifestyle,
etc.
A chemical is considered hazardous if it is
• determined to be carcinogenic, toxic, corrosive, an irritant, a strong sensitizer,
flammable, or reactive, and thereby poses a threat to health and the environment;
• assigned a threshold limit value (TLV) by the American Conference ofGovernmental
Industrial Hygienists;
• specifically listed under the OSHA Act, 29 CFR part 1910, Subpart Z.
Routes of Entry:
There are four main routes by which hazardous chemicals enter the body:
(1) Inhalation: gases and vapors can be absorbed through the respiratory tract
(lungs). Once in the lungs, air contaminants can enter the bloodstream and
circulate throughout your body. Gasessoluble in water, e.g., ammonia and
Appendix I: Safety Readings 2
hydrogen chloride, readily dissolve in the moisture found in the nose and upper
respiratory tract, causing irritation. Gases insoluble in water, e.g., nitrogen dioxide
and phosgene (COCl2), are not absorbed in the upper tract, but still reach the
lungs and cause pulmonary edema (fluid in the lungs). Carbon monoxide, once in
thelungs, absorbs into the blood and can affect other parts of your body.
Particulate matter, such as dust from powdered solids or fumes from burning
chemicals can be inhaled and cause irritation or damage. Particle size determines
how far into the respiratory tract the particles go and the subsequent injury that
results. Larger particles (10 μ , μ = micron) are caught in your nose; smallerparticles (1-5 μ ) can continue down the throat and airways where they are trapped
in mucous. Tiny hairs called cilia will move the mucous containing these particles
up to the throat, where they are either swallowed or coughed out. The smallest
particles (less than 1 μ) reach the air sacs (alveoli) in the lungs. Microphages in
the lungs can engulf and destroy some of these particles: substances likecrystalline silica (SiO2), asbestos, and beryllium will remain indefinitely and may
cause respiratory disease or cancer.
(2) Ingestion: Eating, drinking, smoking, biting fingernails, etc. with contaminated
hands or in contaminated work areas can lead to absorption through the digestive
tract. Chemists never perform taste tests of unknown chemicals. Examples of
toxic materials that can beingested include lead, mercury, cyanides, and arsenic.
Any toxic material you handle can be ingested.
(3) Skin Contact and Absorption: This is the most common cause of occupational
disease (dermatitis). Hazardous chemicals can react with your skin’s chemical
components and disrupt protein and lipid structures, which produces local
irritation and rashes, chemical burns, and/or permanent damage....