PESTICIDES
You have
heard it.
Pesticides are poisons. Pesticides can
be converted to chemical warfare agents. The pesticides
themselves can be used as chemical warfare agents. The same
technology (e.g. crop dusters) for dispersing pesticides
can be used to disperse chemical warfare agents.
These
statements are a mixture of truths, exaggerations, or
are mostly false.
Let us take a look at these chemicals and what
they can do.
What is a
Pesticide?
A
pesticide is an agent used to destroy pests. Pesticides
include insecticides (destroys insects), herbicides
(destroys plants), arachnicides (destroys spiders,
mites, ticks), larvacides (destroys immature stages of
insects such as grubs and caterpillars), fungicides
(destroys fungus), rodenticides (kills mice, rats),
molluscocides (destroys clams, snails, etc.) and
fumigants.
Sometimes insect repellents (such as DEET) and
plant growth regulators are lumped in with discussions
of pesticides. The agent
is usually a chemical that destroys the unwanted pest,
but the agent could also be a naturally occurring plant
extract or bacteria that inflict a fatal disease on the
targeted pest.
Much
effort is spent developing new pesticides that are
specific to the targeted pest but do not harm other life
including humans.
After the pesticide has accomplished its intended
purpose, it should not persist in the environment. Some of
the older pesticides developed decades ago have been
since found to harm birds and other life, or were very
poisonous to humans, and have been outlawed for use in
the United
States. Some may
be produced or used in other countries for special use,
such as use of DDT for control of mosquitoes where
malaria is prevalent.
Pesticides may be applied to
crops, to soils where crops are grown, buildings were
crops are stored, ponds, forested areas, grasslands,
applied topically to animals including humans, or put in
cattle feed.
In lieu
of pesticides, environmentally conscious people may
advocate (1) control practices such as drainage of
containers or ditches where mosquitoes may breed, (2)
encouragement or addition of natural predators to
control the unwanted pests, (3) crop rotation and (4)
inclusion of “wild areas” within agriculture land. The wild areas
provide a home for natural predators.
Pesticide Classifications
Pesticide
formulations as used by the consumer contain one or more
active ingredients plus various “inert”
ingredients.
The inert ingredients are there to give the
formulation the desired physical characteristics so the
pesticide can be easily and safely applied. Sometimes
the formulations are mixed with fertilizers. Most
formulations sold to the public are pellets, which are
relatively dust free and release the active ingredient
slowly.
However some are applied as dusts or as
aerosolized liquid droplets. Some are
fumigants and are released as vapors or gases. Some are
poison bait and are used for rodents, birds,
cockroaches, etc..
Pesticides are classified
into either chemical classes or use classes according to
the active ingredient. The U.S.
Environmental Protection Agency recognizes 1000+ active
ingredients and almost 90,000 different brand name
formulations. Roughly 40
new active ingredients are approved each year. Some active
ingredients have been withdrawn from use in the
United States
because of harm to people or the environment. A complete list
is at
http://www.epa.gov/pesticides/science/models_db.htm#databases
The PEAC tool lists approximately 250 active ingredients
including a few that have been withdrawn from use. The
approximately 250 selected for display in the PEAC tool
are or were either widely used or are relatively toxic.
Pesticide
names (for active ingredients) are assigned by the
International Organization for Standardization
(England). The names
assigned are unique and internationally recognized. The U.S.
Environmental Protection Agency and California
Department of Pesticide Regulation maintains a listing
of brand name formulations.
Examples
of Pesticide Use Classes
- Insecticides
and arachnicides
- Herbicides
- Fungicides
- Molluscicides
- Avicides
- Rodenticides
- Growth
hormones
Examples
of Chemical Classes
- Carbamates
- Organophosphates
- Chlorinated
hydrocarbons (Organochlorine pesticide)
- Bromated
hydrocarbons
- Botanicals
(natural pesticides derived from plants)
- Triazine
and Triazoles
- Ureas
- Thiocarbamates
- Dithiocarbamates
- Dinitrophenols
- Substituted
amides
- Bipyridilium
pesticides
- Phenoxys
- Pyridines
- Inorganic
A more
complete listing of classifications with specific
pesticide examples may be found at the EXTOXNET website
developed by several state cooperative extension offices
and maintained by Oregon State University, at http://extoxnet.orst.edu/tibs/pestgrp.htm
.
The U.S.
Department of Transportation classifies pesticides by
chemical classes.
UN (United Nations) shipping numbers reflect
this.
However the UN numbers also take into account the
“inert ingredients” because they affect whether the
pesticide is shipped as a liquid or solid, and the
flammability of the liquid. The
following pesticide classes and corresponding UN#s are
listed in the 2004 Emergency Response Guidebook:
Specific
Listings
- Aluminum
phosphide pesticide, UN# 3048
- Methyl
parathion, liquid, UN#3018
- Methyl
parathion, solid, UN#2783
- Parathion,
UN#2783
- Parathion
and compressed gas mixture, UN#1967
- Zinc
phosphide, UN# 1714
Table 1. Pesticide
classes and UN Shipping Numbers
|
Pesticide Class |
Solid, toxic |
Liquid, toxic |
Liquid, toxic,
flammable |
Liquid, flammable,
toxic |
|
Arsenical
pesticide |
2759 |
2994 |
2993 |
2760 |
|
Benzoic derivative
pesticide |
2769 |
3004 |
3003 |
2770 |
|
Bipyridilium
pesticide |
2781 |
3016 |
3015 |
2782 |
|
Carbamate
pesticide |
2757 |
2992 |
2991 |
2758 |
|
Copper based
pesticide |
2775 |
3010 |
3009 |
2776 |
|
Coumarin derivative
pesticide |
3027 |
3026 |
3025 |
3024 |
|
Dithiocarbamate
pesticide |
2771 |
3006 |
3005 |
2772 |
|
Organochlorine
pesticide |
2761 |
2996 |
2995 |
2762 |
|
Organophosphorus
pesticide |
2783 |
3018 |
3017 |
2784 |
|
Organotin
pesticide |
2786 |
3020 |
3019 |
2787 |
|
Pesticide,
n.o.s. |
2588 |
2902 |
2903 |
3021 |
|
Phenoxyacetic acid
derivative pesticide |
3345 |
3348 |
3347 |
3346 |
|
Phenoxy
pesticide |
2765 |
3000 |
2999 |
2766 |
|
Phenyl urea
pesticide |
2767 |
3002 |
3001 |
2768 |
|
Phthalimide derivative
pesticide |
2773 |
3008 |
3007 |
2774 |
|
Pyrethroid
pesticide |
3349 |
3352 |
3351 |
3350 |
|
Thiocarbamate
pesticide |
2771 |
3006 |
3005 |
2772 |
|
Triazine
pesticide |
2763 |
2998 |
2997 |
2764 |
There are
also generic listings for insecticide gases.
- Insecticide
gas, n.o.s., UN# 1968
- Insecticide
gas, toxic, flammable, n.o.s., UN#3355
- Insecticide
gas, toxic, n.o.s., UN#1967
- Insecticide
gas, flammable, n.o.s., UN#1954 or UN#3354
The words
“toxic” and “poisonous” are synonymous in the 2004
Emergency Response Guidebook, and n.o.s. means “not
otherwise specified”.
However, “Liquid, toxic”, “Liquid, toxic,
flammable” and “Liquid, flammable, toxic” have different
meanings as defined by DOT:
- Liquid,
flammable, toxic: flash point
less than 23oC
[23oC = 73.4oF]
- Liquid,
toxic, flammable: flash point
between 23oC and 61oC
- Liquid,
toxic:
flash point over 61oC
[141.8oF]
Parathion
and methyl parathion also fall into the general
classification of organophosphorous pesticides.
How
Toxic are Pesticides to Humans?
It
depends upon the particular pesticide. Some are
highly toxic and some are practically nontoxic. Some
may be acutely toxic but display no long-lasting effects
if and when the person recovers. Exposure
to other pesticides may increase the risk of cancer or
motor impairment later in life.
The U.S.
National Library of Medicine maintains a data base on
toxicity of chemicals including pesticides. To access
this, go to http://toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB,
and enter the pesticide name or its CAS number.
Acute
toxicity is measured in terms of exposure of the
chemical to a test animal, usually a rat. The dosage (mg
of chemical per kilogram of body weight) which kills 50%
of the test animals is called LD50 . Exposure
may be by ingestion, skin contact (a patch containing
the chemical is attached to the animal), or by
inhalation.
LC50 is the concentration of chemical
in the air that kills 50% of the animals over a
specified time period, usually 1 or 4 hours. The
inference is made that the animal toxicity data can be
transferred to humans.
Pregnant females and the very young are often
more susceptible.
Table 2. Toxicity data
for seven of the more toxic pesticides:
|
Pesticide |
Pesticide Chem
Class |
Ingestion,
LD50, mg/kg body wt. |
Dermal,
LD50, mg/kg body wt. |
Inhalation,
LC50, mg/m3 |
|
Aldrin |
Organochlorine |
39
to 45 (rat); human child death at 8 mg/kg |
90
to 150 |
|
|
Dieldrin |
Organochlorine |
65
(human); 38 (rat) |
120
to 215 |
|
|
Endrin |
Organochlorine |
7.5
to 18 |
12
to 60 |
|
|
Lindane |
Organochlorine |
76 to 190
rat; human 120 |
50
to 1000 |
|
|
Paraquat |
Bipyridilium |
35
(human); 110 to 150 (rat) |
80
to 325 |
|
|
Parathion |
Organophosphorus |
|