IDENTIFICATION
Common name: Clopyralid
Chemical abstracts name: 3,6-dichloro-2-pyridinecarboxylic acid
Type: Herbicide
CAS RN: [1702-17-6]
M.F.: C6H3Cl2NO2
Mol Wt: 192.0
PHYSICAL CHEMISTRY
Form (appearance): Colourless crystals.
M.P.: 151-152℃
V.P.: 1.33 mPa (pure, 24℃); 1.36 mPa (tech., 25℃)
F.P.: No flashing exhibited in ignition test
S.G.: 1.57 (20℃)
Solubility: Pure (99.2%) 7.85 (in distilled water), 118 (pH 5), 143 (pH 7), 157 (pH 9) (all in g/l, 20℃). In acetonitrile 121, n-hexane 6, methanol 104 (all in g/kg). Forms water-soluble salts, for example potassium, solubility >300 g/l (25℃).
Stability: Decomposes above m.p. Stable in acidic media and to light; on hydrolysis, DT50>30 d at pH range 5-9 (25℃) in sterile water.
KowlogP: - 1.81 (pH 5), -2.63 (pH 7), -2.55 (pH 9),1.07 (unionised, 25℃)
Pka: 2
APPLICATION
Formulation types: SL
Biochemistry: Synthetic auxin (acting like indolylacetic acid).
Mode of action: Selective systemic herbicide, absorbed by the leaves and roots, with translocation both acropetally and basipetally, and accumulation in meristematic tissue. Exhibits an auxin type reaction. Acts on cell elongation and respiration.
Uses: Post-emergence control of many annual and perennial broad leaved weeds of the families Polygonaceae, Compositae, Leguminosae, and Umbelliferae, in sugar beet, fodder beet, oilseed rap(maize, brassicas, onions, leeks, strawberries, flax and grassland. Provides particularly good control of creeping thistle (Cirsium arvense), perennial sow-thisde, coltsfoot, mayweeds, and Polygonum spp.
Phytotoxicity: Good crop tolerance of graminaceous, cruciferous crops.
MAMMALIAN TOXICOLOGY
Oral: Acute oral LD50 for male rats 3738, female rats 2675 mg/kg.
Skin and eye: Acute percutaneous LD50 for rabbits >2000 mg/kg; a severe eye irritant, not a skin irritant.
Inhalation: LC50 (4 h) for rats >0.38 mg/l.
Noel: (2 y) for rats 15, male mice 500, female mice >2000 mg/kg b.w. daily.
ADI: 0.15 mg/kg.
Other Non-carcinogenic, non-mutagenic, non-teratogenic, and produces no significant toxicological effects on reproductive parameters.
Toxicity: WHO (a.i.) III (Table 5); EPA (formulation) IV
EC hazard: Xl; R41| N; R51, R53
ECOTOXICOLOGY
Birds: Acute oral LD50 for mallard ducks 1465, bobwhite quail >2000 mg/kg. Dietary LC50 (5 d) for mallard ducks and bobwhite quail >4640 mg/kg diet.
Fish: LC50 (96 h) for rainbow trout 103.5, bluegill sunfish 125.4 mg/l.
Daphnia: EC50 (48 h) 225 mg/l. EC50 (21 d) immobilisation 69, reproduction 80 mg/l; NOEC 17 mg/l.
Algae: EC50 (96 h) for Selenastrum capricornutum, cell count 6.9, cell volume 7.3 mg/h
/Other aquatic spp. EC50 (14 d) for Lemna gibba 89 mg/l.
Worms: LC50 (14 d) for earthworms >1000 mg/kg soil.
/ Bees: Non-toxic to bees. LD50 (48 h, oral and contact) >100 μg/bee;
/ Other beneficial spp. No effect on nitrification, nitrogen fixation or degradation of cellulose, starch, protein and leaf material at 1-10 ppm.
ENVIRONMENTAL FATE
Plant: Clopyralid is not metabolised in plants.
Animals: In rats, following oral administration, there is rapid and almost quantitative unchanged elimination in the urine.
Soil/Environment: In soil, microbial degradation occurs; slow degradation occurs in sterile soil. The major product is CO2; only traces of one other metabolite have been recorded. Aerobic soil degradation depends on initial concentration (DT50 range 7 at 0.0025 ppm to 435 at 2.5 ppm, sandy loam), soil temperature and soil moisture; DT50 (BBA guidelines) 14-56 d; DT50 (USA guidelines) 2-94 d. Mean Koc 4.64 (range 0.4-12.9), mean Kd 0.0412 (range 0.0094-0.0935); when aged in loam soil for 30 d, Koc was c. 30 ml/g, suggesting clopyralid would be more tightly sorbed. Although data indicate potential for leaching, field dissipation and lysimeter studies demonstrate fairly rapid degradation and limited downward movement. Field dissipation DT50 was 8-66 d (19 sites), with downward movement confined to 18 in. In lysimeter studies, the centre of mass movement ranged from 6-18 in. after 12 months, and cumulative (2 y) leachate concentrations were 0.002-0.14 ppb (0.1-0.6% of applied). |
