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Introduction
Scope of the
Problem
Effect of
Pesticides on Exposed Workers
Medical
Monitoring
Tracking
Information
Clinical Manifestations
Exposure
Management
Summary
Publications
Web Sites
Introduction
Pesticide exposure is an issue for occupational health
professionals in many parts of this country and around
the world. Pesticides include any substance intended
for preventing, destroying, or otherwise mitigating
the effects of pests. Pests may be insects, rodents,
weeds, or any other undesirable living thing.
Therefore, the term “pesticides” is utilitarian rather
than scientific.
Scope of the Problem
Agricultural workers across the country are exposed to
pesticides on a daily basis. This exposure also exists
for those who handle and transport the pesticides. In
California alone, pesticide management has substantial
implications for agriculture. In 1999-2000 the gross
cash income for that industry exceeded $27.2 billion
and more than 70% derived from vines, trees, and row
crops, most of which were sprayed with chemicals to
combat pests. Analysis of state pesticide use data
shows that between 1991 and 1998 more than 1.5 billion
pounds of pesticides were applied in California.
Because of the toxicity of many of the commonly
applied pesticides, California and many other states
mandate monitoring of agricultural workers exposed to
these substances. The cholinesterase-inhibiting
insecticide group of organophosphates and carbamates
are among the most commonly used and monitored. At the
Federal level, workers are protected by the EPA’s
Worker Protection Standard, which is aimed at reducing
the risk of pesticide poisonings and injuries among
the three and a half million people who work with
pesticides at 560,000 workplaces. States often have
more stringent requirements to protect workers. Basic
EPA requirements are:
• Protection during applications
• Restricted entry intervals
• Personal protective equipment
• Notification of workers
• Decontamination supplies
• Emergency assistance
• Pesticide safety training and safety posters
• Access to labeling and site-specific information
Effect of Pesticides on Exposed
Workers
Organophosphates and carbamates exert pesticidal
action by inhibiting acetyl cholinesterase (AChE), an
enzyme essential for proper neuromuscular
coordination. In normal neurotransmission,
acetylcholine (ACh) is released at synapses in
response to action potentials along nerve fibers.
After acting on receptors on the membrane of the
postsynaptic cell, the ACh is normally instantly
hydrolyzed and inactivated by acetyl cholinesterase.
Organophosphates and carbamates bind the AChE through
phosphorylation, thus reducing its availability. The
subsequent loss of enzyme function allows accumulation
of the impulse transmitter ACh at parasympathetic
neuroeffector junctions (causing muscarinic effects)
and at skeletal myoneural junctions and central
nervous system (CNS) synapses (causing nicotinic
effects).
Medical Monitoring
Category I (labeled “Danger”) and category II (labeled
“Warning”) are the most toxic pesticides. The
categorization of pesticides as I, II, and III is
based on the mean lethal dose of the pesticide,
category III being the least toxic. Medical monitoring
is based upon cholinesterase levels, measured in both
the red blood cells (RBC) as well as serum, and
observing for decreased levels. At the outset of the
farming season, blood specimens are obtained and RBC
and serum cholinesterase levels measured for workers
anticipated to be exposed to category I or II
chemicals at least seven days in a 30-day period. A
second specimen is drawn 3–14 days later. As long as
the RBC and serum levels of the two draws are within
15%, an adequate baseline is considered to have been
obtained.
After the base level is determined, blood specimens
are obtained monthly for at least three months and RBC
and serum cholinesterase levels are compared to the
baseline. If levels drop to 80% of the baseline,
retesting is required. If the RBC cholinesterase level
drops to less than 70% of the baseline, or serum to
less than 60%, the employee must be removed from
exposure.
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Tracking Information
Tracking software such as StolaSystem® or SYSTOC®
assists the busy occ med clinic by facilitating
management of measured cholinesterase levels (see
figure above). Baselines and subsequent values are
compared and the clinician is signaled when a
dangerous decrease occurs. For clinics whose customers
include agricultural employers using organophosphate
or carbamate pesticides, cholinesterase monitoring is
a valuable service.
Clinical Manifestations
Muscarinic Signs:
Salivation
Tearing
Sweating
Nausea and vomiting
Diarrhea
Respiratory secretions
Bronchospasm
Bradycardia
Nicotinic Signs:
Voluntary muscle weakness
Voluntary muscle fasciculations
Paralysis
Tachycardia
Central Nervous System Signs:
Headache
Anxiety
Confusion
Psychosis
Seizures
Stupor
Coma
Exposure Management
Occasionally, occupational medicine clinics need to
treat employees that come in contact with
organophosphate pesticides. The event may occur when
workers in processing plants contact the substance in
the course of processing, haulers are exposed to
containers that leak in transit, field workers are
sprayed, and other circumstances.
Emergency treatment includes removing any remaining
pesticide, e.g., contaminated clothing or materials,
by undressing the employee and showering or hosing.
Employees showing clinical evidence of organophosphate
or carbamate intoxication are managed based upon the
severity of their subjective and physical findings. If
indicated, respiratory and/or circulatory support may
be needed. Intravenous atropine or pralidoxime is used
if the patient shows signs of instability.
Mild poisoning causes flu-like symptoms that the
patient may even dismiss as a viral infection.
Laboratory testing typically demonstrates a
cholinesterase value of no less than 75% of baseline,
and clinical management consists primarily of removal
from exposure. If no additional exposure occurs,
cholinesterase regenerates at about 1% per day.
Moderate poisoning will include muscarinic, nicotinic
and/or central nervous system (CNS) manifestations
listed below and treatment may require atropine or
pralidoxime.
Severe cases may call for cardiovascular or
respiratory support, gastrointestinal decontamination,
seizure control or other measures. Hospitalization is
required.
Summary
If employers in your area manufacture, transport, or
use organophosphate or carbamate pesticides, consider
initiating a monitoring program to meet the needs of
those employers. If you investigate what regulations
may apply to your particular state and design a
program that meets those requirements, you will be
providing a valuable service. To market your program
successfully, consider conducting seminars for
employers to discuss pesticide management.
Publications
Keifer, Matthew C., “State of the Art Reviews: Human
Health Effects of Pesticides,” Hanley and Belfus,
Inc., Volume 12, Number 2, April–June, 1997.
Reigart, J. Routt, Recognition and Management of
Pesticide Poisonings, U.S. Environmental Protection
Agency, Fifth Edition, 1999.
Guidelines for Physicians, California Environmental
Protection Agency, Third Edition, 1995.
Web Sites
ace.orst.edu/info/npic/gen.htm
vm.cfsan.fda.gov/~lrd/pestadd.html
www.ent.iastate.edu/list/pesticides_and
_regulations.html
www.epa.gov/opptsmnt/
www.epa.gov/pesticides/
www.extension.umn.edu/pesticides
www.pesticide.org/
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