PHYSICAL CHEMISTRY Clopyralid

Mol. wt. 192.0 M.f. C 6 H 3 Cl 2 NO 2 Form Colourless crystals. M.p. 151-152 oC V.p. 1.33 mPa (pure, 24 oC); 1.36 mPa (tech., 25 oC) K OW logP = -1.81 (pH 5), -2.63 (pH 7), -2.55 (pH 9), 1.07 (unionised, 25 °C) S.g./density 1.57 (20 oC) Solubility Pure (99.2%) 7.85 (in distilled water), 118 (pH 5), 143 (pH 7), 157 (pH 9) (all in g/l, 20 oC). In acetonitrile 121, n -hexane 6, methanol 104 (all in g/kg). Forms water-soluble salts, for example potassium, solubility >300 g/l (25 oC). Stability Decomposes above m.p. Stable in acidic media and to light; on hydrolysis, DT 50 >30 d at pH range 5-9 (25 oC) in sterile water. pKa 2 F.p. No flashing exhibited in ignition test

clopyralid-olamine

Mol. wt. 253.1 M.f. C 8 H 10 Cl 2 N 2 O 3 Solubility In water 560 g/l (25 oC).

COMMERCIALISATION Clopyralid

History Herbicide reported by T. Haagsma ( Down Earth, 1975, 30 (4), 1). Introduced in France (1977) by Dow Chemical Co. (now Dow AgroSciences). Patents US 3317549

APPLICATIONS Clopyralid

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.

clopyralid

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 rape, maize, brassicas, onions, leeks, strawberries, flax and grassland. Provides particularly good control of creeping thistle ( Cirsium arvense ), perennial sow-thistle, coltsfoot, mayweeds, and Polygonum spp. Phytotoxicity Good crop tolerance of graminaceous, cruciferous crops. Formulation types SL. Selected tradenames: 'Clio' ( Agriphar ); 'Cyronal' ( Aventis ); 'Diclopyr' ( Agrimix ); mixtures: 'Scorpion' (+ benazolin + dimefuron ) ( Aventis )

ANALYSIS Clopyralid

Product analysis by glc. Residues determined by glc of a derivative (A. J. Pik & G. W. Hodgson, J. Assoc. Off. Anal. Chem., 1976, 59, 264). Details available from Dow AgroSciences.

MAMMALIAN TOXICOLOGY

clopyralid

Oral Acute oral LD 50 for male rats 3738, female rats 2675 mg/kg. Skin and eye Acute percutaneous LD 50 for rabbits >2000 mg/kg; a severe eye irritant, not a skin irritant. Inhalation LC 50 (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 class WHO (a.i.) III (Table 5); EPA (formulation) IV EC hazard Xi; R41| N; R51, R53

ECOTOXICOLOGY

clopyralid

Birds Acute oral LD 50 for mallard ducks 1465, bobwhite quail >2000 mg/kg. Dietary LC 50 (5 d) for mallard ducks and bobwhite quail >4640 mg/kg diet. Fish LC 50 (96 h) for rainbow trout 103.5, bluegill sunfish 125.4 mg/l. Daphnia EC 50 (48 h) 225 mg/l. EC 50 (21 d) immobilisation 69, reproduction 80 mg/l; NOEC 17 mg/l. Algae EC 50 (96 h) for Selenastrum capricornutum , cell count 6.9, cell volume 7.3 mg/l. Other aquatic spp. EC 50 (14 d) for Lemna gibba 89 mg/l. Bees Non-toxic to bees. LD 50 (48 h, oral and contact) >100 m g/bee. Worms LC 50 (14 d) for earthworms >1000 mg/kg soil. Other beneficial spp. No effect on nitrification, nitrogen fixation or degradation of cellulose, starch, protein and leaf material at 1-10 ppm.

ENVIRONMENTAL FATE Clopyralid

Animals In rats, following oral administration, there is rapid and almost quantitative unchanged elimination in the urine. Plants Clopyralid is not metabolised in plants. Soil/Environment In soil, microbial degradation occurs; slow degradation occurs in sterile soil. The major product is CO 2 ; only traces of one other metabolite have been recorded. Aerobic soil degradation depends on initial concentration (DT 50 range 7 at 0.0025 ppm to 435 at 2.5 ppm, sandy loam), soil temperature and soil moisture; DT 50 (BBA guidelines) 14-56 d; DT 50 (USA guidelines) 2-94 d. Mean K oc 4.64 (range 0.4-12.9), mean K d 0.0412 (range 0.0094-0.0935); when aged in loam soil for 30 d, K oc 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 DT 50 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).