E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Some trade names include Kerb, Propyzamide, RH-315 and Benzamide.
The U.S. Environmental Protection Agency (EPA) restricts the use of all
pronamide formulations, except those in water-soluble packets, due to their
oncogenicity, or potential to cause tumor growth (2). Restricted Use
Pesticides (RUP) may be purchasedand used only by certified applicators.
Check with specific state regulations for local restrictions which may apply
(9). Products containing pronamide must bear the signal word "Caution" (16).
Pronamide is an herbicide used either before weeds emerge
(preemergence), and/or after weeds come up (postemergence). It controls a
wide range of annual and perennial grasses, as well as certain annual
broadleaf weeds. Pronamide is usually incorporated into the soil by
cultivation, irrigation, or rain immediately following application (14). The
toxic action of this herbicide is selective, meaning that it kills specific
target plants while sparing other, desirable plants. It is used primarily on
lettuce and alfalfa crops, as well as on blueberries, ornamentals, fruit
trees, forage legumes, and on fallow lands. It is available in wettable
powder and granular formulations (11, 16).
Pronamide is classified by EPA as a slightly poisonous herbicide.
Mixers and applicators are expected to receive the most exposure to this
material through skin contact. To protect workers from potential eye and
mucous membrane irritation, precautionary statements on manufacturing-use
product labels warn: "Harmful if absorbed through the skin or inhaled.
Causes moderate eye irritation. Avoid contact with the skin, eyes, or
clothing. Avoid breathing dust" (11).
The dose of a chemical that causes death in one-half (50%) of test
animals when it is given to them by mouth, is referred to as its acute oral
lethal dose fifty, or LD50. The oral LD50 for pronamide ranges from 5620
mg/kg in female rats, to 8,350 mg/kg in male rats. In dogs, its LD50 is
10,000 mg/kg (1). When applied to the skin of rabbits, it produced slight
local irritation, but no systemic intoxication. The acute dermal toxicity of
pronamide is greater than 3160 mg/kg (4, 11, 14).
When dogs were fed a diet containing approximately 0, 11, 34, or 100
mg/kg pronamide for 3 months, decreases in weight gain and food consumption,
changes in blood chemistry, and increased liver weights were observed at 100
mg/kg. No adverse effects occurred at 34 mg/kg. In a similar study of rats
fed 0, 0.5, 7.5, 22.5, 67.5 or 202.5 mg/kg/day for 3 months, liver weight
changes occurred in females at 7.5 mg/kg/day (22).
In a 2-year feeding study with dogs, the addition of pronamide to the
diet at doses of 0, 0.75, 2.5 or 7.5 mg/kg/day caused no adverse health
effects at any of the doses tested. A NOAEL of 7.5 mg/kg/day, the highest
dose tested, was established for this study (22).
The EPA has established a Lifetime Health Advisory (LHA) level of 50
micrograms per liter (ug/l) for pronamide in drinking water. This means that
EPA believes that water containing pronamide at or below this level is
acceptable for drinking every day over the course of one's lifetime, and does
not pose any health concerns. However, consumption of pronamide at high
levels well above the LHA level over a long period of time has been shown to
cause liver damage in animal studies (21).
When pregnant rabbits were given doses of 0, 5, 20 or 80 mg/kg/day
during days 7 to 19 of gestation (18 rabbits per dose), no effects on
development or reproduction were observed at or below the 20 mg/kg dose. At
80 mg/kg, there was an increased incidence of liver lesions, one maternal
death, five abortions, and a decrease in maternal weight gain (22). In a 3-
generation rat reproduction study, no effects on reproduction were observed at
300 ppm (15 mg/kg/day), the highest dose tested (20, 22).
No teratogenic effects were found when doses as high as 15 mg/kg/day
were administered to pregnant rabbits (22).
Several tests for mutagenicity involving bacterial or mammalian cell
cultures, or live animals have been performed. All test results have been
negative (22, 23).
Pronamide is classified as a possible human carcinogen by the EPA (21).
A material is classified as a possible human carcinogen when there is limited
or uncertain evidence that it has caused cancer in animals receiving high
doses of the chemical over the course of their lifetimes. Pronamide has
caused tumors in male rats at dosages of 150 mg/kg and 300 mg/kg in the diet.
Cancerous tumors, 'carcinomas,' of the liver, as well as an increased
incidence of tumors in all organs, were induced in male mice fed 50 or 100
mg/kg of pronamide for 18 months (7, 19). In a 2-year rat feeding study, the
NOEL was 15 mg/kg and no evidence of tumor formation was observed at feeding
levels of 1.5, 5 or 15 mg/kg/day (20).
The EPA has concluded that this herbicide poses a limited oncogenic risk
for applicators which can be reduced through the use of protective measures,
such as protective clothing and water-soluble packaging (10).
Consumption of pronamide at high levels well above the Lifetime Health
Advisory level over a long period of time has been shown to cause liver damage
in animal studies (21).
Fate in Humans and Animals
Pronamide is not readily absorbed into the bloodstream from the
gastrointestinal tracts of rats and cows. After oral doses of radio labeled
Kerb to rats, unmetabolized Kerb accounted for 54 ad 0.6% of the radioactivity
recovered in feces and urine, respectively. Unmetabolized Kerb did not appear
in the urine of a cow treated orally with radio labeled Kerb (22). Traces of
pronamide were found in the milk of cows given feed that contained five ppm
doses of formulation (7). Pronamide has a low potential for bioaccumulation
in animal tissues (18).
Effects on Birds
Pronamide is practically non-toxic to birds. The LD50 for pronamide in
Japanese quail is 8,700 mg/kg, and 20,000 mg/kg in mallard ducks (11). The
lethal concentration fifty, or LC50, is a calculated concentration of a
material in air or water which causes death in 50% of an experimental animal
population exposed to it for a specified length of time. The 8-day dietary
LC50 for Kerb Technical Herbicide in bobwhite quail and mallard ducks is
greater than 10,000 ppm (23).
Effects on Fish
Pronamide is practically non-toxic to warmwater fish and slightly toxic
to coldwater fish. The 96-hour LC50 for pronamide in bluegills is 100 mg/l,
72 mg/l in rainbow trout, 350 mg/l in goldfish, 204 mg/l in harlequin fish,
and 150 mg/l in guppies. The 48-hour LC50 for Daphnia magna, a small
freshwater crustacean, is greater than 5.6 mg/l (11, 16, 23).
Effects on Other Animals (Nontarget species)
Pronamide is practically nontoxic to mammals, but may be moderately
toxic to aquatic invertebrates (11). Pronamide is non-toxic to honey bees
Breakdown of Chemical in Soil and Groundwater
Pronamide is readily bound, or adsorbed, to organic matter in soil (Koc
= 990 g/ml) (17). In most soil types, there is very little movement, or
leaching, of pronamide through the ground with soil moisture (14). It is
nearly insoluble in water (15 ug/ml) (17). However, the EPA does consider a
pronamide metabolite (RH24,580) to be one of the pesticide compounds with
greatest potential for leaching into groundwater (8). Leaching of most
pronamide residues in soil occurs in loamy sands and in silt loams (7). It
was not found in groundwater in a national groundwater survey (12).
Pronamide is inactivated by soil organic matter and will not be
effective on muck, peat, or other high-organic content soils (10). Depending
upon soil type and climatic conditions, persistence of pronamide varies from
two to nine months. Residual activity is greater in sandy soils with low
organic matter. Accumulation of the herbicide from repeated annual
applications to the same soil does not appear problematic.
Chemical degradation may be the main route of disappearance from the
soil. Photodecomposition at the soil surface can also occur (18). A moderate
amount of pronamide breakdown is carried out by soil microorganisms. The
herbicide is not active against common soil microorganisms. Some studies
indicate that under very hot and dry conditions, pronamide turns into a
gaseous form, through a process called volatilization (14). The dissipation
half-life for pronamide is 1.5 to 13 weeks in soil (12). Increasing soil
temperature, and to a lesser extent, soil moisture and pH increase the rate of
pronamide degradation in soil (22).
Breakdown of Chemical in Water
In water bodies, pronamide is chemically stable at a neutral pH. It is
slowly degraded chemically, by light, and by aquatic and muck organisms. Loss
from volatilization is not significant (3, 18). Pronamide is thought to be
stable because less than 10% was hydrolyzed, or broken down in water, over a
four week period (12). It is stable to hydrolysis between pH 4.7 and 8.8
Breakdown of Chemical in Vegetation
Crops for which pronamide is not registered must not be planted in
fields that have been given previous treatment with pronamide products (10).
Pronamide primarily inhibits root development in germinating seeds or young
seedlings. In perennial grasses, it interrupts both root and shoot growth.
For pronamide to be effective, it has to move into the root zone of target
weeds. Since it is taken up by the roots, pronamide needs to be carried into
the root zone by rainfall, irrigation, or soil incorporation. Pronamide is
readily translocated from the roots to other plant parts. Absorption of
pronamide through plant leaves is minimal. Pronamide is metabolized slowly by
both tolerant and sensitive plants (11, 14).
PHYSICAL PROPERTIES AND GUIDELINES
Pronamide is a white or off-white crystalline solid with a mild odor
(14). It is relatively stable (11). It should be stored in a cool, dry place
at temperatures between 0 and 50 degrees C. Under normal conditions, there
should be little decomposition of this material (1). Water-soluble packets of
this herbicide significantly reduce the risk of exposure for mixers (11).
Pronamide is noncorrosive under normal use conditions. It is stable
under normal temperatures and pressures, but may pose a slight fire hazard if
exposed to heat or flame. It poses a fire and explosion hazard in the
presence of strong oxidizers. Thermal decomposition of pronamide will release
toxic oxides of nitrogen and carbon and toxic and corrosive fumes of chlorides
Pronamide should not be applied directly to water, nor should water be
contaminated by the cleaning of equipment or disposal of wastes associated
with this material (11). Protective clothing is recommended during the
mixing, loading, or application of end-use products unless water-soluble
packaging is used (11). Pronamide applications should not be allowed to drift
into nontarget areas (14).
Occupational Exposure Limits:
No occupational exposure limits have been established for pronamide by
OSHA, NIOSH or ACGIH (19).
|Specific gravity: ||0.48 gm/cc (22)
|H20 solubility: ||1.5 mg/100 g at 25 degrees C (14)
|Solubility in other solvents (at 25 degrees C): ||33 ppm dimethyl sulfoxide; 15 ppm in methanol; 10 ppm in xylene and kerosene; 5 ppm in nitrobenzene and ethylene dichloride (11).
|Melting point: ||155-156 degrees C (309-313 degrees F) (11)
|Boiling point: ||321 degrees C (18)
|Vapor pressure: ||8.5 x 10 to the minus 5 mmHg at 25 degrees C (14)
|Koc: ||215, 218, 200, 990 (calc) (12)
|Kd: ||0.42-7.98; 0.5-19 (12)
|Chemical Class/Use: ||Substituted benzamide; amide herbicide
Rohm and Haas Co.
Independence Mall West
Philadelphia, PA 19105
Review by Basic Manufacturer:
Comments solicited: October, 1992
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