HRAC C3 WSSA 6; phenylpyridazine

NOMENCLATURE
Common name pyridate (BSI, E-ISO, (m) F-ISO, WSSA)
IUPAC name 6-chloro-3-phenylpyridazin-4-yl S-octyl thiocarbonate
Chemical Abstracts name O-(6-chloro-3-phenyl-4-pyridazinyl) S-octyl carbonothioate
CAS RN [55512-33-9] EEC no. 259-686-7 Development codes CL 11 344 (Agrolinz)

PHYSICAL CHEMISTRY
Mol. wt. 378.9 M.f. C19H23ClN2O2S Form Colourless crystals; (tech., brown, oily liquid). M.p. 27 oC; (tech., 20-25 oC) B.p. 220 oC/0.1 mmHg (tech.) V.p. 4.8 ′ 10-4 mPa (20 oC) (tech.) KOW logP = 4.01 Henry 1.21 ′ 10-4 Pa m3 mol-1 (20 °C) (calc.) S.g./density 1.16 (20 oC) (tech.) Solubility In water c. 1.5 mg/l (pH 7, 20 oC). Readily soluble in most organic solvents. Stability Hydrolysis DT50 89 h (pH 5), 58.5 h (pH 7), 6.2 h (pH 9) (all 25 oC). F.p. 131 °C

COMMERCIALISATION
History Herbicide reported by A. Diskus et al. (Proc. Br. Crop Prot. Conf. - Weeds, 1976, 2, 717). Introduced by Chemie Linz AG (now DSM Chemie Linz), who (as Agrolinz Melamin GmbH) sold it to Sandoz AG (now Syngenta AG) in 1994. Patents AT 326409 Manufacturers DSM Chemie Linz

APPLICATIONS
Biochemistry Photosynthetic electron transport inhibitor at the photosystem II receptor site. Mode of action Selective contact herbicide, absorbed predominantly by the leaves. Uses Post-emergence control of annual broad-leaved weeds, especially Solanum spp., Chenopodium spp., Galium aparine, Kochia scoparia and Amaranthus retroflexus (triazine-resistant biotypes), and some grass weeds, in maize, sweet corn, oilseed rape, cereals, rice, peanuts and vegetables, at 0.9 kg a.i./ha. Often used in combination with a triazine or other product, to extend the spectrum of activity. Phytotoxicity Should not be applied in mixture with, or within 14 days of, any other product which may result in de-waxing of crop foliage. Formulation types EC; WP. Selected tradenames: 'Lentagran' (Syngenta); 'Pirate' (Barclay)

OTHER TRADENAMES
'Tough' (USA) (Syngenta); 'Zintan' (Syngenta) mixtures: 'Lido' (+ terbuthylazine) (Syngenta); 'Sailor' (+ sulcotrione) (Syngenta, Bayer) Discontinued names: 'Barclay Pirate' * (Barclay)

ANALYSIS
Product analysis by hplc with u.v. detection (CIPAC Handbook, 1995, G, 137-142). Residues determined by hplc. Details available from Syngenta.

MAMMALIAN TOXICOLOGY
Oral Acute oral LD50 for male and female rats >2000, male mice c. 10 000, female mice >10 000 mg/kg. Skin and eye Acute percutaneous LD50 for rabbits 32000 mg/kg. Moderately irritating to skin; non-irritating to eyes (rabbits). Evidence of sensitisation in guinea pigs, but no symptoms observed in man (applicators, technicians, workers). Inhalation LC50 (4 h) for rats >4.37 mg/l air. NOEL (28 mo) for rats c. 18 mg/kg b.w. daily; (12 mo) for dogs 30 mg/kg b.w. daily (oral gavage). ADI 0.18 mg/kg (Novartis proposed); 0.35 mg/kg (WHO, 1992). Water GV 100 mg/l (TDI 35 mg/kg b.w.). Other Tests for carcinogencity, mutagenicity, and teratogenicity were negative. Toxicity class WHO (a.i.) III; EPA (formulation) III EC hazard (R43)

ECOTOXICOLOGY
Birds Acute oral LD50 for bobwhite quail 1269-1502 mg/kg. Dietary LC50 (8 d) for Japanese quail, bobwhite quail and mallard ducks >5000 mg/kg b.w. Fish LC50 (96 h) for catfish 48, rainbow trout >1.2 to 81, bluegill sunfish >2.12 to >100, carp >100 mg/l. Daphnia LC50 0.83 mg/l; in simulated field, 3.3-7.1 mg/l. Algae IC50 for Scenedesmus subspicatus 82.1 mg/l. Bees Non-toxic to honeybees. LD50 (oral and contact) >100 mg/bee. Worms LC50 for earthworms 799 mg/kg soil. Other beneficial spp. Harmless to beneficial arthropods such as Poecilus and Aleochara ('Lentagran' 450EC). No effect on soil respiration, ammonification and nitrification.

ENVIRONMENTAL FATE
Animals In animals, following oral administration, pyridate is rapidly and completely hydrolysed to its principal metabolite 3-phenyl-4-hydroxy-6-chloropyridazine, which is detoxified by formation of O- and, depending on species, N- glucuronides. The principal metabolite and the conjugates are rapidly and completely excreted. No cumulative effect after repeated administration. Plants In plants, pyridate is hydrolysed into its principal metabolite 3-phenyl-4-hydroxy-6-chloropyridazine, with a half-life ranging from a few minutes to days. This metabolite itself forms conjugates as O- and N-glycosides, which do not possess herbicidal activity. Soil/Environment Rapidly degraded in soil, DT50 <2.8 d. The principal metabolite is 3-phenyl-4-hydroxy-6-chloropyridazine, which typically has DT50 7-21 d (field), 15-43 d (lab.); DT90 47-143 d (lab.). In biologically-active water, pyridate is rapidly transformed into the same metabolite as in soil, decomposition of which is accelerated by photodegradation, DT50 16 d. Pyridate is not leached from soil; although its metabolite is less strongly bound to soil (Kd 0.3-26), lysimeter, water monitoring and field dissipation studies indicate it is unlikely to leach in practice.