SECTION
5: Health Hazards of Chemicals
Introduction (top)
The decisions you make concerning the use of chemicals in the laboratory
should be based on an objective analysis of the hazards, rather than merely
the perception of the risks involved. Once this has been accomplished, a
reasonable means of controlling the hazards through experimental protocol,
work practices,
ventilation,
use of protective
clothing, etc., can be determined.
In order to assess the hazards of a particular chemical, both the physical
and health hazards of the chemical must be considered.
Before using any chemical, the material
safety data sheet (MSDS) or other appropriate resource should be reviewed
to determine what conditions of use might pose a hazard. Accidents
with hazardous chemicals can happen quickly and may be quite severe.
The key to prevention of these accidents is awareness. Once the hazards
are known, the risk of an accident may be reduced significantly by using
safe work practices.
Basic
Toxicology (top)
The health effects of hazardous chemicals are often less clear than the
physical hazards. Data on the health effects of chemical exposure, especially
from chronic exposure, are often incomplete. When discussing the health
effects of chemicals, two terms are often used interchangeably - toxicity
and hazard. However, the actual meanings of these words are quite
different. Toxicity is an inherent property of a material, similar
to its physical constants. It is the ability of a chemical substance to
cause an undesirable effect in a biological system. Hazard is the
likelihood that a material will exert its toxic effects under the conditions
of use. Thus, with proper handling, highly toxic chemicals can be used
safely. Conversely, less toxic chemicals can be extremely hazardous if handled
improperly.
RISK = TOXICITY ´
EXPOSURE
The actual health risk of a chemical is a function of the toxicity and
the actual exposure. No matter how toxic the material may be, there is
little risk involved unless it enters the body. An assessment of the toxicity
of the chemicals and the possible routes of entry will help determine
what protective measures should be taken.
Routes
of Entry (top)
Skin
and Eye Contact
 The simplest way for
chemicals to enter the body is through direct contact with the skin or eyes.
Skin contact with a chemical may result in a local reaction, such as a burn
or rash, or absorption into the bloodstream. Absorption into the bloodstream
may then allow the chemical to cause toxic effects on other parts of the
body. The MSDS usually includes information regarding whether or not skin
absorption is a significant route of exposure.
The absorption of a chemical through intact skin is influenced by
the health of the skin and the properties of the chemical. Skin that
is dry
or cracked or has lacerations offers less resistance. Fat-soluble
substances, such as many organic solvents, can easily penetrate skin
and, in some
instances, can alter the skin’s ability to resist absorption of other
substances.
Wear gloves
and other protective clothing to minimize skin exposure. See Personal
Protective Equipment for more information. Symptoms of skin exposure
include dry, whitened skin, redness and swelling, rashes or blisters,
and itching. In the event of chemical contact on skin, rinse the affected
area with water for at least 15 minutes, removing
clothing while rinsing, if necessary. Seek medical attention if symptoms
persist.
Avoid use of solvents for washing skin. They remove the natural protective
oils from the skin and can cause irritation and inflammation. In some
cases, washing with a solvent may facilitate absorption of a toxic chemical.
Chemical contact with eyes can be particularly dangerous, resulting in
painful injury or loss of sight. Wearing safety
goggles or a face shield can reduce the risk of eye contact. Eyes
that have been in contact with chemicals should be rinsed immediately
with water continuously for at least 15 minutes. Contact lenses should
be removed while rinsing—do not delay rinsing to remove the lenses.
Medical attention is necessary if symptoms persist.
Inhalation
 The respiratory
tract is the most common route of entry for gases, vapors, particles,
and aerosols (smoke, mists and and fumes). These materials may be
transported
into the lungs and exert localized effects, or be absorbed into the
bloodstream. Factors that influence the absorption of these materials
may include the
vapor pressure of the material, solubility, particle size, its concentration
in the inhaled air, and the chemical properties of the material.
The vapor
pressure is an indicator of how quickly a substance evaporates into
the air and how high the concentration in air can become – higher
concentrations in air cause greater exposure in the lungs and greater
absorption in the
bloodstream.
Most chemicals have an odor that is perceptible at a certain concentration,
referred to as the odor threshold; however, there is no relationship between
odor and toxicity. There is considerable individual variability in the
perception of odor. Olfactory fatigue may occur when exposed to high concentrations
or after prolonged exposure to some substances. This may cause the odor
to seem to diminish or disappear, while the danger of overexposure remains.
Symptoms of over-exposure may include headaches, increased mucus production,
and eye, nose and throat irritation. Narcotic effects, including confusion,
dizziness, drowsiness, or collapse, may result from exposure to some substances,
particularly many solvents. In the event of exposure, close containers
or otherwise increase ventilation, and move to fresh air. If symptoms
persist, seek medical attention.
Volatile hazardous materials should be used in a well-ventilated area,
preferably a fume hood, to reduce the potential of exposure. Occasionally,
ventilation
may not be adequate and a fume hood may not be practical, necessitating
the use of a respirator.
The Occupational Safety and Health Administration Respiratory Protection
Standard regulates the use of respirators; thus, use of a respirator is
subject to prior review by EHS according to University policy. See Personal
Protective Equipment for more information.
Ingestion
The gastrointestinal tract is another possible route of entry for toxic
substances. Although direct ingestion of a laboratory chemical is unlikely,
exposure may occur as a result of ingesting contaminated food or beverages,
touching the mouth with contaminated fingers, or swallowing inhaled particles
which have been cleared from the respiratory system. The possibility of
exposure by this route may be reduced by not eating, drinking, smoking,
or storing food in the laboratory, and by washing hands thoroughly after
working with chemicals, even when gloves were worn.
Direct ingestion may occur as a result of the outdated and dangerous
practice of mouth pipetting. In the event of accidental ingestion, immediately
go to McCosh Health Center or contact the Poison Control Center, at 800-962-1253
for instructions. Do not induce vomiting unless directed to do so by a
health care provider.
Injection
The  final
possible route of exposure to chemicals is by injection.
Injection
effectively bypasses the protection provided by intact skin and provides
direct access
to the bloodstream, thus, to internal organ systems. Injection may
occur through mishaps with syringe needles, when handling animals,
or through
accidents with pipettes, broken glassware or other sharp objects that
have been contaminated with toxic substances.
If injection has occurred, wash the area with soap and water
and seek medical attention, if necessary. Cautious use of any sharp object
is always important. Substituting cannulas for syringes and wearing gloves
may also reduce the possibility of injection.
Toxic Effects of Chemical Exposure
(top)
In addition to the dose, the outcome of exposure is determined
by (1) the way the chemical enters the body, (2) the physical properties
of the chemical, and (3) the susceptibility of the individual receiving
the dose.
Toxic
Effects of Chemicals
The toxic effects of a chemical may be local or systemic.
Local injuries involve the area of the body in contact with the chemical
and are typically caused by reactive or corrosive chemicals, such as strong
acids, alkalis or oxidizing agents. Systemic injuries involve tissues or
organs unrelated to or removed from the contact site when toxins have been
transported through the bloodstream. For example, methanol that has been
ingested may cause blindness, while a significant skin exposure to nitrobenzene
may effect the central nervous system.
Certain chemicals may affect a target organ. For example, lead primarily
affects the central nervous system, kidney and red blood cells; isocyanates
may induce an allergic reaction (immune system); and chloroform may cause
tumors in the liver and kidneys.
It is important to distinguish between acute and chronic exposure and
toxicity. Acute toxicity results from a single, short exposure.
Effects usually appear quickly and are often reversible. Chronic
toxicity results from repeated exposure over a long period of time. Effects
are usually delayed and gradual, and may be irreversible. For example,
the acute effect of alcohol exposure (ingestion) is intoxication, while
the chronic effect is cirrhosis of the liver. Acute and chronic effects
are distinguished in the MSDS, usually with more information about acute
exposures than chronic.
Relatively few chemicals have been evaluated for chronic effects, given
the complexity of that type of study. Chronic exposure may have very different
effects than acute exposure. Usually, studies of chronic exposure evaluate
its cancer causing potential or other long-term health problems.
Evaluating
Toxicity Data
Most estimates of human toxicity are based on animal studies, which may
or may not relate to human toxicity. In most animal studies, the effect
measured is usually death. This measure of toxicity is often expressed as
an LD50 (lethal dose 50) – the dose required to kill 50%
of the test population. The LD50 is usually measured in milligrams of
the material per kilogram of body weight of the test animal. The concentration
in air that kills half of the population is the LC50.
To estimate a lethal dose for a human based on animal tests, the LD50
must be multiplied by the weight of an average person. Using this method,
it is evident that just a few drops of a highly toxic substance, such
as dioxin, may be lethal, while much larger quantities of a slightly toxic
substance, such as acetone, would be necessary for the same effect.
Susceptibility
of Individuals
Factors that influence the susceptibility of an individual to the effects
of toxic substances include nutritional habits, physical condition, obesity,
medical conditions, drinking and smoking, and pregnancy. Due to individual
variation and uncertainties in estimating human health hazards, it is difficult
to determine a dose of a chemical that is totally risk-free.
Regular exposure to some substances can lead to the development of an
allergic rash, breathing difficulty, or other reactions. This phenomenon
is referred to as sensitization. Over time, these effects may occur
with exposure to smaller and smaller amounts of the chemical, but will
disappear soon after the exposure stops. For reasons not fully understood,
not everyone exposed to a sensitizer will experience this reaction. Examples
of sensitizers include epoxy resins, nickel salts, isocyanates and formaldehyde.
Particularly
Hazardous Substances
The OSHA Laboratory Standard defines a particularly hazardous substance
as "select carcinogens", reproductive toxins, and substances that have
a high degree of acute toxicity. Further information about working
with Particularly
Hazardous Substances is outlined in Particularly
Hazardous Substances.
Where
To Find Toxicity Information
Toxicity information may be found in Material Safety Data Sheets,
under the "Health Hazard Data" section, on product labels, in the Registry
of Toxic Effects of Chemical Substances (RTECS), or in many other
sources listed in the MSDS
page.
Chemical
Exposure Determination (top)
OSHA establishes exposure limits for several hundred substances. Laboratory
workers must not be exposed to substances in excess of the permissible exposure
limits (PEL) specified in OSHA Subpart Z, Toxic
and Hazardous Substances. PELs refer to airborne concentrations
of substances averaged over an eight-hour day. Some substances also
have "action levels" below the PEL requiring certain actions such as
medical surveillance or routine air sampling.
The MSDS for a particular substance indicates whether any of the chemicals
are regulated through OSHA and, if so, the permissible exposure limit(s)
for the regulated chemical(s). This information is also available in the
OSHA Table Z list of regulated chemicals.
Exposure
Monitoring
Exposure monitoring must be conducted if there is reason to believe
that exposure levels for a particular substance may routinely exceed
either the
action level or the PEL. EHS and the principal investigator or supervisor
may use professional judgment, based on the information available
about
the hazards of the substance and the available control measures, to
determine whether exposure monitoring must be conducted.
When necessary, exposure monitoring is conducted by EHS according to
established industrial hygiene practices. Results of the monitoring are
made available to the individual monitored, his or her supervisor, and
the departmental Chemical
Hygiene Officer within 15 working days of the receipt of analytical
results.
Based on the monitoring results, periodic air sampling may be scheduled
at the discretion of EHS, in accordance with applicable federal, state
and local regulations.
EHS maintains records of all exposure monitoring results. Departmental
Chemical Hygiene Officers should keep records of monitoring conducted
for their department operations.
 Section
6: Controlling Chemical Exposure
 Section
4: Hazard Identification and Chemical Information Resources
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