Quantcast Toxicity and Volatility

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AFM 91-19 / TM 5-629 / NAVFAC MO-314
24 May 1989
9
behaves like a plant hormone. It accumulates
b. The relative toxicity of chemicals is deter-
mostly in areas of rapidly dividing cells, up-
mined in small animal tests. Unfortunately,
setting the normal metabolism of the plant
humans do not always react the same as small
and causing death of the cells. Foliar applica-
animals. It is always possible that a human will
tions of translocated herbicides are of great
be poisoned by a smaller dose of a given
practical value because small amounts are effec-
chemical than results with animals would indi-
tive and they can be applied in small volumes of
cate, or vice versa. The extremely toxic herbi-
water.
cides included in this publication are acrolein
c. Soil-Sterilant versus Preemergence Herbi-
and endothall, and the general-purpose fumi-
cides. These both act through the soil but are
gant, methyl bromide. They must be handled
used in different sites and situations.
with particular care.
c. Volatility refers to the tendency of a liquid
(1) A soil-sterilant herbicide makes a soil
or solid to change to vapor. Vapors of some
incapable of supporting higher plant life; but it
herbicides kill plants. This is an important
generally does not kill all life in the soil, such as
consideration in purchasing herbicides such as
fungi, bacteria, and other micro-organisms; nor
2,4-D or other phenoxy herbicides. When using
does it kill ungerminated seeds. Its toxic effects
volatile herbicides, the use must be aware of
may remain for only a short time or for years.
temperature as well as wind speed and direction.
Persistent residual toxicity depends on the nature
Volatility generally increases as temperature
of the chemical and its rate of decomposition or
rises. When vapors from the herbicide are likely
leaching, the colloidal and chemical properties
to injure adjacent crops or other plants, an
of the soil, the relative tolerance among weed
amine salt or a low-volatile ester formulation
species, and the rate of application.
should be used.
(2) Herbicides vary in their rate of disap-
d. Esters of 2,4-D are classified as being of
pearance from the soil because of differences in
high or low volatility according to the degree of
their volatility, susceptibility to decomposition
vaporization that occurs. In general, methyl,
by soil micro-organisms, sensitivity to sunlight,
ethyl, isopropyl, butyl, and amyl esters are
chemical reactions, and solubility. For example,
considered highly volatile and should not be
some of the carbamates are volatile at moder-
used. The high molecular weight esters are low
ately high temperatures and rapidly lose their
in volatility and include: butoxyethyl, butoxye-
toxic effect during the summer months. Certain
thoxypropyl, ethoxyet hoxypropyl, propylene gly-
soil micro-organisms effectively decompose her-
col butyl ether, and isooctyl esters.
bicides such as 2,4-D in a short time. Amitrole
is soluble in water and is readily leached.
Section D -- Hazards to Non-Target Organisms
(3) Some herbicides are readily adsorbed by
mineral and organic colloids in the soil and are
rendered unavailable, or only slowly available,
1-9. General Information. Nearly all herbicides
for plant absorption. For example, diuron is
are potentially dangerous in one way or another,
adsorbed on clay colloid particles, making leach-
but they are not likely to cause injury if used
ing difficult. Paraquat is completely inactivated
properly and if recommended precautions are
by soil because its positively charged cations
observed. Because several kinds of danger are
react with the negatively charged clay minerals
associated with handling and applying herbi-
to form complexes. The fertility and pH of a
cides, and possible injury is not limited to the
soil also influence the persistence and availability
operator, consider the potential effects on all of
of certain chemicals.
the following: operator and handler, livestock,
desirable plants, fish and wildlife, water quality,
and equipment.
1-8. Toxicity and Volatility:
a. Toxicity ratings are described in attachment
3, and the toxicities of herbicides and plant
1-10. Operator and Handler. The person who
hauls, mixes, and applies the herbicidal spray, or
Those herbicides rated extremely toxic (low
spreads the dry product, could be poisoned from
L D50) must be handled with great care (while
swallowing the herbicide, by skin absorption, or
those rated as slightly toxic (high LD50) require
by inhalation. In each case, there is greater
less special attention). The dermal toxicity rating
danger from the concentrated material than
is also given, and the same precautions are
from the diluted spray solution or suspension.
required.
Be sure to read the label for each chemical used.





 


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