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Pesticide Residue, Tolerance,and Registration |
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Pesticide Residue, Tolerance,and RegistrationThe use of pesticides is strictly controlled in the United States. Every chemical which has possible use as a pesticide is closely tested and reviewed before it is marketed. The laws controlling the use of pesticides on food or feed crops are more strict. The amount of pesticide remaining on the crop at harvest is carefully regulated.
The pesticide which is on the leaves, skin, or other surface right
after application is the deposit. Sometimes the deposit
can be easily seen, as with many dusts or wettable powders. At
other times it cannot be seen with the naked eye. If the pesticide
deposit remains on the surface for a period of time, it is called
a residue. Some pesticides leave little or no residue. Heat, light,
moisture, soil organisms, and other chemical reactions in the
environment quickly break them down. Other pesticides are not
quickly broken down. They leave a residue on the crop or in the
environment for weeks, months, or years. Depending on how and
where it is used, each pesticide will vary in how long a residue
remains on the crop or surface. Therefore, information on residues
is required on each crop the pesticide is applied to. Unfortunately,
a pesticide may drift over from a nearby field and leave a residue
on a crop or surface.
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A long-lasting residue may be desirable because the pesticide
is effective for a longer period of time. It need not be applied
as often and thus may be cheaper to use. However, long-lasting
residues are not always desirable. The chemicals may remain on
food or feed and be hazardous to those eating them. The residues
may remain in the soil to interfere with crops that are planted
at a later date. Or they may remain on the surface and injure
workers or others who reenter the treated area. Clearly it is
important to know what residue, if any, remains after a period
of time. Food, in fact, may have no residue because it may never
have been treated, or it was treated at less than the maximum
dose and the residues may have degraded.
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Many times residues remain on food or feed crops at harvest
time. Since these crops are to be eaten, safe amounts of residues
must be established. The maximum amount of residue which may remain
on a harvested crop is called a tolerance. Federal law requires
that a tolerance be set for every
food or feed use of each pesticide before it is registered. The
tolerances vary from crop to crop depending on the many safety
factors involved. If the residue exceeds the set tolerance, the
crop may not be marketed or sold. It is subject to condemnation
and seizure by federal or state regulatory agencies.
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How Tolerances Are Set. Much information is gathered and studied before a tolerance is set. Studies on test animals are done to determine the acute and chronic toxicity of the chemical. Toxicity to fish, birds, and mammals is also determined. The length of time the pesticide remains in the environment is measured. Possible long-term effects such as buildup in animals or in the environment are studied. All these factors (and others) are taken into account before setting a tolerance. The tolerance is usually set at least 100 times smaller than the highest dose which has no effect in test animals. For example, 200 parts per million of pesticide A have no effect on test animals. Then the tolerance for pesticide A on any food or feed crop could be no higher than 2 parts per million (ppm). The "safety factor" is 100 times. The tolerances for pesticide A may not be as high as 2 ppm. Field tests may show that acceptable pest control is achieved using doses and methods that result in a residue much less than 2 ppm. Then the tolerance would be set at 1 ppm. [The tolerance is stated in parts per million (ppm) by weight. That is, one part of pesticide to one million parts of crop or meat.]
Negligible Residue Tolerances. A residue
may be on a food or feed crop even though no pesticide was ever
directly applied to it. These residues result from indirect
contact with the chemical. The residue may be found, for example,
in livestock which have eaten sprayed forage and grass. Edible
meat of livestock containing residues must have a negligible
residue tolerance. Or when a herbicide is applied before a
crop emerges, a residue may be left in the soil. As the crop grows
it may pick up a small amount of the herbicide. If the residue
is still in the crop at harvest, a negligible residue tolerance
must be set. A negligible residue tolerance (usually just "negligible
residue") is set when a very small residue is likely to be
on food or feed at harvest. Negligible means small or minor. The
negligible residue is usually one tenth (0.1) of a part per million
or less. It is far below any toxic level.
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Finite Tolerances. When a pesticide will be applied directly
on a food or feed crop and animal, a finite tolerance is set.
A finite tolerance (often just "tolerance") is usually
larger than a negligible residue. However, it is still well below
possible toxic levels. To be eaten, a tolerance must have been
set, unless it is exempt from tolerance.
Most pesticides break down in the environment. As they break
down, the residue on the crop or animal becomes smaller. Therefore,
the residues remaining at harvest depend on how long before harvest
the pesticide is applied. "Days to Harvest" is the least
number of days between the last pesticide application and the
harvest day. ("Days to Slaughter" is used with livestock.)
Both are listed on the label. For example, when pesticide A is
applied on the day of harvest, it leaves a residue of 10 ppm.
However, when it is applied 7 days before harvest, it leaves a
residue of only 2 ppm. If acceptable pest control is possible
by applying 7 days before harvest, EPA will often set the tolerance
at 2 ppm and the "Days of Harvest" at 7 days.
If days to harvest, recommended dosages and other label instructions
are followed, the residue on the crop should be under the set
tolerance.
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Even though a tolerance is set for a pesticide on a specific
crop, it still cannot be legally used until registered. Every
pesticide and every use must be registered federally by the Environmental
Protection Agency (EPA). EPA reviews all the required information
on the pesticide. This includes toxicity studies, wildlife and
environmental studies, breakdown and residue studies, chemical
studies, etc. Registration will be granted only if the Administrator
finds that the benefits of its use outweigh the risks. EPA also
reviews and registers all statements which appear on the pesticide
label. (See Chapter XIV, The Label.) No pesticide may be bought,
sold, or used in the United States until it has federal registration
for the product, the use, and the label.
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It is up to you, the applicator, to help make sure that all
food complies with established tolerances. Only you can
be sure that no illegal residues remain on food crops. Follow
label directions carefully. Do not be responsible for seizure
of your customer's or his neighbor's crop!
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