Atrazine

Composition Tech. is ³96% pure. Mol. wt. 215.7 M.f. C₈H₁₄ClN₅ Form Colourless powder. M.p. 175.8 ºC B.p. 205.0 °C/101 kPa V.p. 3.85 ´ 10^-2 mPa (25 ºC) (OECD 104) K_OW logP = 2.5 (25 ºC) Henry 1.5 ´ 10^-4 Pa m³ mol^-1 (calc.) S.g./density 1.23 (22 °C) Solubility In water 33 mg/l (pH 7, 22 ºC). In ethyl acetate 24, acetone 31, dichloromethane 28, ethanol 15, toluene 4.0, n-hexane 0.11, n-octanol 8.7 (all in g/l, 25 ºC). Stability Relatively stable in neutral, weakly acidic and weakly alkaline media. Rapidly hydrolysed to the hydroxy derivative in strong acids and alkalis, and at 70 ºC in neutral media; DT₅₀ (pH 1) 9.5, (pH 5) 86, (pH 13) 5.0 d. pKa 1.7, v. weak base

USES Atrazine

Uses Pre- and post-emergence control of annual broad-leaved weeds and annual grasses in maize, sorghum, sugar cane, pineapples, chemical fallow, grassland, macadamia nuts, conifers, industrial weed control. In Europe, use is concentrated in maize and sorghum. Used also in combinations with many other herbicides. Phytotoxicity Phytotoxic to many crops, including most vegetables, potatoes, soya beans, and peanuts. Formulation types FW; GR; SC; WG; WP. Selected tradenames: 'AAtrex' (USA) (Syngenta); 'Agri-atrazina' (Cequisa); 'Aktikon' (Nitrokémia); 'Atranex' (Makhteshim-Agan); 'Atrataf' (Rallis); 'Atratylone' (Agriphar); 'Atrazol' (Sipcam); 'Coyote' (Milenia); 'Dhanuzine' (Dhanuka); 'Fogard' (Caffaro); 'Mebazine' (Aventis); 'Sanazine' (Sanachem); 'Surya' (Nagarjuna Agrichem); 'Triaflow' (Inquiport); 'Vectal' (Aventis); 'Zeazin S 40' (Istrochem);

MAMMALIAN TOXICOLOGY Atrazine

IARC ref. 53, 73 class 3 Oral Acute oral LD₅₀ for rats 1869-3090 mg tech./kg, mice >1332-3992 mg/kg. Skin and eye Acute percutaneous LD₅₀ for rats >3100 mg/kg. Mild skin irritant; non-irritating to eyes (rabbits). Skin sensitiser in guinea pigs, but not in humans. Inhalation LC₅₀ (4 h) for rats >5.8 mg/l air. NOEL (2 y) for rats 10 mg/kg diet (0.5 mg/kg daily), for dogs 150 mg/kg diet (3.75 mg/kg daily), for mice 10 mg/kg diet (1.4 mg/kg daily). ADI 0.005 mg/kg b.w. Water GV 2 mg/l (TDI 0.5 mg/kg b.w.). Toxicity class WHO (a.i.) III (Table 5); EPA (formulation) III EC hazard (Xn; R48/22| R43| N; R50 R53)

ECOTOXICOLOGY Atrazine

Birds Acute oral LD₅₀ varies from 940 mg/kg for bobwhite quail to >2000 mg/kg for mallard ducks and 4237 mg/kg for adult Japanese quail. Dietary LC₅₀ (8 d) for Japanese quail (chicks) >5000, (adults) >1000 mg/kg. Fish LC₅₀ (96 h) for rainbow trout 4.5-11.0, bluegill sunfish 16, carp 76, catfish 7.6, guppies 4.3 mg/l. Daphnia LC₅₀ (24 h) 87 mg/l. Algae EC₅₀ (72 h) for Scenedesmus subspicatus 0.043 mg/l, (96 h) for Selenastrum capricornutum 0.13 mg/l. Bees LD₅₀ (oral) >97 mg/bee; (contact) >100 mg/bee. Worms LC₅₀ (14 d) for Eisenia foetida 78 mg/kg soil.

ENVIRONMENTAL FATE Atrazine

Animals In mammals, following oral administration, atrazine is rapidly and completely metabolised, primarily by oxidative dealkylation of the amino groups (R. Ikonen et al., Toxicol. Lett., 1988, 44, 109; Bull. Environ. Contam. Toxicol., 1989, 43, 199; Y. Deng et al., J. Agric. Food Chem., 1990, 38, 1411), and by reaction of the chlorine atom with endogenous thiols. Diaminochlorotriazine is the main primary metabolite, which readily conjugates with glutathione. More than 50% of the dose is eliminated in the urine and around 33% in the faeces within 24 h. Plants In tolerant plants, atrazine is readily metabolised to hydroxyatrazine and amino acid conjugates, with further decomposition of hydroxyatrazine by degradation of the side-chains and hydrolysis of the resulting amino acids on the ring, together with evolution of CO₂. In sensitive plants, unaltered atrazine accumulates, leading to chlorosis and death. Soil/Environment Major metabolites under all conditions are desethylatrazine and hydroxyatrazine. Field DT₅₀ 16-77 d (median 41 d), the longer values being from cold or dry conditions. In natural waters, DT₅₀ 10-105 d (mean 55 d). DT₅₀ under groundwater conditions 105->200 d, depending on test system (M. J. Wood et al. in: A Walker (Ed.), Pesticides in soils and water: current perspectives (BCPC Monograph 1991, 47, 175-182)). K_d 0.2-18 ml/g, K_oc 39-173 ml/g; desalkylated metabolites had values similar to those of atrazine, while hydroxyatrazine was much more strongly adsorbed.

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