| Chemical Abstract Number (CAS #) |
1918021
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| Synonyms | Picloram |
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4-Amino-3,5,6-trichloro-2-pyridinecarboxylic acid |
| Analytical Methods |
EPA Method 515.1 |
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EPA Method 515.2 |
EPA Method 555 |
EPA Method 644 |
EPA Method 8151 |
| Molecular Formula | C6H3Cl3N2O2 |
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| Use | SYSTEMIC HERBICIDE
PICLORAM & ITS SALTS ARE HERBICIDES MOST BROADLEAVED CROPS,
EXCEPT CRUCIFERS, ARE SENSITIVE; MOST GRASSES ARE RESISTANT.
EFFECTIVE IN CONTROLLING ANNUAL WEEDS; USED ALONE OR IN
COMBINATION WITH 2,4-D AGAINST DEEP-ROOTED PERENNIALS ON NON-CROP
LAND; AS PELLETS OR IN COMBINATION WITH 2.4-D OR 2,4,5-T BRUSH
CONTROL.
AT EXTREMELY LOW DOSAGES, ACTS AS A GROWTH REGULATOR ON APRICOTS,
FIGS, CHERRIES, ETC.
Picloram is used to control bitterweed, knapweed, leafy spurge, locoweed, larkspur, mesquite,
prickly pear, and snakeweed on rangeland in the western states.
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| Apparent Color | COLORLESS POWDER ; CRYSTALS
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| Odor | CHLORINE-LIKE
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| Melting Point | 218-219 DEG C
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| Molecular Weight | 241.48
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| Sensitivity Data | SKIN--MILD IRRITANT, NOT A SKIN SENSITIZER TO HUMANS.
EYES--MODERATE IRRITATION WHICH HEALS READILY. INHALATION--DUSTS
MAY BE SOMEWHAT IRRITATING
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| Environmental Impact | Picloram is released to the environment primarily from its application as a herbicide and
its use is restricted in the U.S. If released to land it will not adsorb to the soil, hydrolyze, or
evaporate from soils or surfaces. It will be subject to leaching to groundwater and may be subject
to significant biodegradation in soils and groundwater. If released to water it will not be expected
to adsorb to sediments, to bioconcentrate in aquatic organisms, to evaporate, or to appreciably
hydrolyze. It will be subject to significant near surface photolysis with reported half-lives ranging
from 2.3-41.3 days. Based on biodegradation in soils and groundwater, it may be subject to
degradation in surface waters. As an aromatic amine, its rate of degradation in water and soil may
be increased due to oxidation by free radicals, adsorption to humic materials followed by
oxidation, and catalytic oxidation by cations, although no experimental data specific to picloram
were found. If released to the atmosphere it will be subject to significant deposition and washout
due to its low vapor pressure (will adsorb to particulate matter) and significant water solubility. It
may also be subject to significant direct photolysis. The estimated vapor phase half-life in the
atmosphere is 12.21 days as a result of reaction with photochemically produced hydroxyl radicals.
General human exposure will occur mainly through its manufacture and use as a herbicide.
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| Environmental Fate | TERRESTRIAL FATE: SORPTION OF PICLORAM BY ORGANIC MATTER &
CERTAIN CLAYS HAS BEEN DEMONSTRATED. HOWEVER, PICLORAM SALT
FORMULATIONS ARE WATER SOLUBLE & LEACHING MAY OCCUR IN SANDY
SOILS LOW IN ORGANIC MATTER.
/TERRESTRIAL FATE: DEGRADATION STUDIES OF PICLORAM IN SOIL WAS
CONDUCTED. T/2= 0.693/K. IN REGINA HEAVY CLAY, AT 25 DEG C & AT MOISTURE
HOLDING CAPACITY T/2= 68 - 10 DAYS.
/Aquatic Fate: it is decomposed in water to negligible levels within 180 days. In a study a
standing pond was sprayed at a rate of 4 lb/acre, which resulted in 2400 ppb at time 0, 700 ppb at
day 1, & 6 ppb at 180 days.
TERRESTRIAL FATE: PICLORAM IS THE MOST PERSISTANT HERBICIDE OF THE
GROUP CHLOROBENZOIC ACIDS/.
TERRESTRIAL FATE: If picloram is released to soil it will not be expected to adsorb to the soil
and may leach to groundwater, a conclusion supported by the detection of picloram in some
groundwater samples. However, picloram is an aromatic amine, and some aromatic amines have
been shown to bind to humic materials which may be present in some moist soils; this binding may
decrease leaching processes (see also ABIO). It will not be expected to hydrolyze or evaporate
from soils or surfaces. It may be subject to significant biodegradation with reported half-lives in
soils ranging from 55-100 days or more.
AQUATIC FATE: If picloram is released to water it will not be expected to adsorb to sediments,
to bioconcentrate in aquatic organisms, to evaporate, or to appreciably hydrolyze. As an aromatic
amine, however, it may bind to humic materials (see also ABIO and KOC). It will be subject to
significant near-surface direct photolysis with reported half-lives for irradiation by sunlight under
various conditions ranging from 2.3-41.3 days. No information concerning the biodegradation in
surface waters was found; however, degradation reported in lab tests with groundwater samples
and soils suggest that biodegradation in water may occur.
ATMOSPHERIC FATE: If picloram is released to the atmosphere it will probably be subject to
significant deposition and washout due to its very low vapor pressure and significant water
solubility. It may also be subject to direct photolysis based on its ready photolysis in aqueous
solutions. The estimated vapor-phase half-life in the atmosphere is 12.21 days as a result of
reaction with photochemically produced hydroxyl radicals.
/Terrestrial Fate: Studies on the persistence, metabolism, and toxicity of heterocyclic pesticides
are reviewed. Picloram is highly persistent in soil, but is rapidly degraded by UV light in aqueous
solutions. It does not suppress soil microorganisms, and has low toxicity in aquatic organisms.
The herbicide picloram was applied to control spotted knapweed in the northern Rockies to
determine persistence in soils and vegetation, losses by photodegradation, rainfall induced
migration, and potential contamination of surface and groundwater. Two sites were selected to
represent best case and worst case conditions for on site retention of picloram. A valley bottom
terrace was treated with 0.28 kg/ha of picloram in the spring of 1985, and sampled over the
following 445 days. In the spring of 1986, 1.12 kg/ha of picloram was applied to both sides of a
minimal construction logging road extending 4 km along a stream draining a granitic upper
mountain watershed. Of the 17.1 sq km watershed, 0.15% was sprayed. Vegetation, soils, surface
water, and groundwater near the road were sampled during the 90 days following application. At
the valley bottom site, 36, 13, and 10.5% of the picloram applied persisted after 90, 365, and 445
days. At the mountain watershed site, 78% persisted after 90 days. Picloram was not detected in
the surface or groundwater during the 90 days after application. Loss by photodegradation during
the first 7 days after treatment was important at both sites.
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| Drinking Water Impact | GROUNDWATER: Riesel, TX, 1971-73, subsurface water after treatment of 1:1
mixture of picloram and 2,4,5-T, 90 samples, 13% pos, not detected (nd)-trace; well water, 8
wells, 10 samples, 30% pos, nd-trace; drainage lysimeter water, 126 samples, 86% pos, nd-4
ppb .
Picloram was aerially applied to a longleaf pine (Pinus palustris L) site in the upper coastal plain
of Alabama to control kudzu. Pellets (10% ai) were spread at the rate of 56 kg/ha on loamy sand
Typic Kanhapludult soils. Movement of the herbicide was monitored with mineral soil samples,
tension-cup lysimeters, flow-proportional streamflow samplers, and discrete samplers. Picloram
levels in the upper 15 cm of mineral soil peaked at 0.96 to 2.25 mg/kg 225 days after application,
depending on slope position, and declined to 0.13 to 0.29 mg/kg one year later. In soil solution,
picloram was detected at a depth of 0.4 m between 26 and 273 days after application. Only 4 of
15 lysimeters consistently contained detectable residues. Maximum picloram levels in soil solution
were 130, 450, and 191 mg/cu m for ridge, midslope, and toe-slope positions, respectively.
Downstream monitoring began 4 days after the herbicide application, and an initial concentration
of 68 mg/cu m of picloram was detected. The maximum downstream concentration of 77 mg/cu
m occurred 18 days after the application, immediately after the second storm event. Downstream
levels dropped to <10 mg/cu m after 90 days and to <2 mg/cu m after 200 days. Following
localized retreatment along the stream more than a year after the initial treatment, levels climbed
again into the 20 to 30 mg/cu range. Most of the initial off-site movement came from a perennial
stream that had been inadvertently treated, but subsequently storm runoff was the largest
contributor to stream contamination. Picloram residues in this stream were similar to those
observed downstream, but they were higher (up to 241 mg/cu m) and dropped faster to below 2
mg/cu m after day 150.
EFFL: Reisel, TX, 1970-72, runoff water from fields treated with 1:1 mixture of picloram and
2,4,5-T, 13 day period after spraying, 21 samples, 100% pos, 15-830 ppb, avg 464 ppb; 40-110
days after spraying, 22 samples, 91% pos, not detected-3 ppb .
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