A dissipação do herbicida 14C-atrazina do solo foi estudada por extrações com solventes, cromatografia em camada delgada e técnicas radiométricas. Os resultados apresentados mostram que ela foi diretamente proporcional aos aumentos de temperatura. Quanto maior a temperatura, menos resíduos extraíveis e mais resíduos ligados foram detectados. Ao final dos períodos de incubação, os extratos de solo mantidos a 10ºC e a 20ºC continham atrazina mas também seu derivado hidroxi, e a 30ºC e 40ºC, mais hidroxiatrazina do que atrazina. A energia de ativação de Arrhenius calculada foi muito alta (96 kJ. mol-1), provando a predominância de reações químicas que favoreceram a hidrólise. Análises exploratórias dos resíduos ligados ao solo detectaram mais de 90% como hidroxiatrazina, em todas as amostras de diferentes temperaturas. Os resultados sugerem que em solo com as características do aqui estudado e a temperaturas maiores que 20ºC, a atrazina não seria um contaminante livre porque a degradação química resultaria somente no metabólito não fitotóxico hidroxiatrazina, ou como resíduo disponível ou como resíduo ligado.The soil dissipation of the herbicide 14C-atrazine was studied by solvent extraction, thin-layer chromatography and radiometric techniques. Results here presented show it was directly proportional to the temperature increases. As the temperature increased, less extractable and more bound residues were detected. At the end of the incubation period, soil extracts contained mainly atrazine but also its hydroxyderivative at 10ºC and 20ºC, and more hydroxyatrazine than atrazine at 30ºC and 40ºC. The calculated Arrhenius activation energy was very high (96 kJ. mol-1) proving the predominance of chemical reactions favouring the hydrolysis. Exploratory analysis of the soil bound residues detected more than 90% as hydroxyatrazine, in all different temperature samples. Results suggest that in a soil with the characteristics of the soil here studied and at temperatures higher than 20ºC, atrazine would not be a free contaminant because chemical degradation would result only in the non-phytotoxic hydroxyatrazine, either as available or as bound residues

Barifouse Matallo, Marcus

Luchini, Luiz Carlos

Mercedes de Andréa, Mara

Yuri Tomita, Rúbia

The soil dissipation of the herbicide 14C-atrazine was studied by solvent extraction, thin-layer chromatography and radiometric techniques. Results here presented show it was directly proportional to the temperature increases. As the temperature increased, less extractable and more bound residues were detected. At the end of the incubation period, soil extracts contained mainly atrazine but also its hydroxyderivative at 10ºC and 20ºC, and more hydroxyatrazine than atrazine at 30ºC and 40ºC. The calculated Arrhenius activation energy was very high (96 kJ. mol-1) proving the predominance of chemical reactions favouring the hydrolysis. Exploratory analysis of the soil bound residues detected more than 90% as hydroxyatrazine, in all different temperature samples. Results suggest that in a soil with the characteristics of the soil here studied and at temperatures higher than 20ºC, atrazine would not be a free contaminant because chemical degradation would result only in the non-phytotoxic hydroxyatrazine, either as available or as bound residues.A dissipação do herbicida 14C-atrazina do solo foi estudada por extrações com solventes, cromatografia em camada delgada e técnicas radiométricas. Os resultados apresentados mostram que ela foi diretamente proporcional aos aumentos de temperatura. Quanto maior a temperatura, menos resíduos extraíveis e mais resíduos ligados foram detectados. Ao final dos períodos de incubação, os extratos de solo mantidos a 10ºC e a 20ºC continham atrazina mas também seu derivado hidroxi, e a 30ºC e 40ºC, mais hidroxiatrazina do que atrazina. A energia de ativação de Arrhenius calculada foi muito alta (96 kJ. mol-1), provando a predominância de reações químicas que favoreceram a hidrólise. Análises exploratórias dos resíduos ligados ao solo detectaram mais de 90% como hidroxiatrazina, em todas as amostras de diferentes temperaturas. Os resultados sugerem que em solo com as características do aqui estudado e a temperaturas maiores que 20ºC, a atrazina não seria um contaminante livre porque a degradação química resultaria somente no metabólito não fitotóxico hidroxiatrazina, ou como resíduo disponível ou como resíduo ligado

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EFFECT OF TEMPERATURE Ot'l DISSIPATION OF [14C]-ATRAZINE IN A BRAZILIAN SOIL1 MARA MERCEDES DE ANDRÉA 2, MARCUS BARIFOUSE MATALL0 3, RÚBIA VURI TOMITA4 and LUIZ CARLOS LUCHINI' ÃBSTRACT - The soll dissipation of lhe herbicide "C-atrazine was studied by solvent extraction, thin-!ayer chromatography and radiometric techniques. Resu!ts here presented show it was direct!y proportional to lhe temperature increases. As lhe temperature increased, !ess extractable and more bound residues were detected. At lhe end of lhe incubation period, soll extracts contained main!y atrazlne but also lis hydroxyderivative at 10°C and 20°C, and more hydroxyatrazine than atrazine at 30°C and 40°C. The calcu!ated Arrhenius activation energy was ver)' high (96 Id. moI 4 ) proving the predominance of chemical reactions favouring lhe hydro!ysis. Exp!oratory ana!ysis of the soll bound residues detected more than 90% as hydroxyatrazine, in a!i difíerent temperature samp!es. Resu!ts suggest that in a soll with lhe characteristics of the soll here studied and at temperatures higher than 20°C, atrazine wou!d not be a free contaminant because chemical degradation wou!d resu!t on!y in the non-phytotoxic hydroxyatrazine, either as avai!able or as bound residues. Index terms: dissipation, chemical degradation, residues, sol! contamination. EFEITO DA TEMPERATURA NA DISSIPAÇÃO DE [4  C]-ATRAZINA EM SOLO BRAS!LE!RO RESUMO - A dissipação do herbicida ' 4C-atrazina do solo foi estudada por extrações com so!ventes, cromatografla em camada delgada e técnicas radiométricas. Os resultados apresentados mostram que ela foi diretamente proporcional aos aumentos de temperatura. Quanto maior a temperatura, menos resíduos extraíveis e mais resíduos !igados foram detectados. Ao final dos períodos de incubação, os extratos de so!o mantidos a 10°C e a 20°C continham atrazina mas também seu derivado hidroxi, e a 30°C e 40°C. mais hidroxiatrazina do que atrazina. A energia de ativação de Arrhenius calcu!ada foi muito alta (96 Id. moE'), provando a predominância de reações químicas que favoreceram a hidró!ise. Análises exploratórias dos resíduos ligados ao solo detectaram mais de 90% como hidroxiatrazina, em todas as amostras de diferentes temperaturas. Os resultados sugerem que em so!o com as característi-cas do aqui estudado e a temperaturas maiores que 20°C. a atrazina não seria um contaminante !ivre porque a degradação química resu!taria somente no metabó!ito não fitotóxico hidroxiatrazina, ou como resíduo disponível ou como resíduo ligado. Termos para indexação: dissipação, degradação química, resíduos, contaminação do so!o. Accepted for pub!ication on August 9, 1996. 2 Biól., Dfl., !nstituto Biológico, Centro de Radioisótopos, Cai-xa Postal 7119, CEP 01064-970 São Paulo, SP, Brasil. Eng. Agr., M.Sc., Instituto Biológico. Seção de llerbicidas, Caixa Postal 70, CEP 13001-970 Campinas, SP, Brasil. Biól., !nstituto Biológico, Centro de Radioisótopos. Qulmico, Dr., Instituto Bio!ógico, Centro de Radioisótopos. hSttI]I1IIWS(IX] The herbicide atrazine is recommended for pre--emergence app!ication iii soil for crop p!ants as com, sugar-cane, sorghum, soya, etc. (Esser etal., 1975), and it is pointed as the herbicide contaminant most found iii ground water (Hance, 1987). In lhe sou!, the herbicide undergo degradation by chemical and bio!ogicai (main!y microbio!ogical) activities Pesq. agropec. bras., Brasilia, v.32, n.l, p.95-100,jan. 1997 96 	 M.M. DE ANDRÉA etal. (Hance, 1987). Kaufman & Kearney (1970) stated that chemical hydro!ysis of chioro-s-triazines occurs faster than the microbial degradation resulting in the corresponding hydroxy-s-triazines. The hydrolysis is a detoxication reaction because hydroxyatrazine is a non-phytotoxic metabolite (Esser et ai., 1975). Thereafter, availabi!ity and bioactivity of herbicides in soil are also associated with the degradation process. Factors leading to production of non-phytotoxic substances are importantto neutralize phytotoxic effects; but, a too fast degradation process may decrease the weed control (Reinhardt et ai., 1990). Some ofthe factors responsibie for the hydro!ysis of atrazine are soil pH (Hance, 1987; Reinhardt et ai., 1990) and temperatures higher than 30°C (Kaufinan & Keamey, 1970). Thus, as pointed by Waiker & Weich (1989), weather conditions and edaphic factors shouid have influence on atrazine persistence. Since Brazi!ian climatic conditions may reach temperatures as high as 40°C and soll pH is mostly acid, this study aimed to verify the behaviour of atrazine appiied te soil incubated under temperatures ranging from 10°C te 40°C, for different periods of thte. MATERIAL AND METHODS Herbicide Commercial atrazine 12-ch!oro.4-(ethy!amino)-6--(isopropylamino)-s-triazinel was supp!ied by CIBA--GEIGY S.A., Brazil, and analysed by the Chemical Section of the Instituto Biológico as 490.5 g . L' of atrazine. The corresponding radiolabc!!ed, atrazine-ring- was obtained from Sigma Chemical Company, USA, with speciflc activity of 270 MBq - mmoI' (7.3 mCi. mmot'). Before using, the ' 4C-atrazine 95% purity was checked by thin-Iayer chromatography (TLC) and radioscanner, as described bellow. Sol! A GIey llumic soll sample, loamy textured (63% sand; 9.0% silt; 27.9% clay; 2.1% carbon, and p1-! (11 30) 4.6), was coflected at 0-30 cm depth from an agricultural arca used for grecn stuff and com crops in So Paulo State. Pesq. agropec. bras., Brasilia, v.32, nt, p.95-10O,jan. 1997  The soll was air dried and passed through 2.0 mm sieve for homogenization. Sol! treatment A 500 g soil sample was treated with a mixture of atrazine (2.18 mg) and C]-atrazine (12.5 J1Ci) in 165 ml ofwater (equivalent te 33% of fle!d capacity). The total "4C app!ied was dctermined by combustion of(Sx) 0.5 g soil samples (dry weight basis) in a Ilarvey Oxidizer OX-600. The "C01 from soll combustion was trapped in 3 ml of ethanolamine in a !iquid scinti!!ation solution consisting of 4g PPO, 0.2 g POPO?. 670 ml toluene and 330 ml Renex" (Mesquita & Rüegg, 1984) plus meDiano! (6:4 1  scintillation so!ution:methanol) and quantified by liquid scintillation counting (LSC) in a Beckman LS-5801. The remaining treated soll was then divided in equal portions of 140 g which were submitted te different incubation time and temperature treatments (Table 1). The soil water contcnt was adjusted two times per week. Degradation studies Dissipation was studied by ana!ytical detemiinations after 14C-atrazine application to sei!, for estimating the degradation process and products fornied with time at different temperatures. At each fixed incubation time (2x) 10 g of treated sol! (dry weight basis) were Soxhlet extracted with 70 ml methano! for 8 hours. Extractable radioactivity was determined by LSC of(2x) 2 ml methanol aliquota ofeach replicate. Another (2x) 15 ml methanol aliquots from soll extracts were concentrated by roto-evaporation (Buchi) at 55°C, the residue was redissolved in (3 x 1 ml) acetone which was chromatographed in TLC p!ates (silica ge!-60 E 254 ). Developing system was first!y ethylether (15 cm) to separate atrazine and two of its metabo!ites (deisopropylatrazine and deethylatrazine). The plate was again unidimensiona!!y developed in toluene:acetic acid:acetone (7:2:1) for 5 cm, to separate the hydroxyatrazine. The R 1s from standards of TABLE 1. Soil treatments after herbicide addition. Temperatura (°C) 	 Incubation time (.ays) 10 	 20 	 40 	 70 	 100 	 140 20 	 20 40 60 	 80 	 100 30 	 10 20 30 	 50 	 70 40 	 10 20 30 	 40 	 50 EFFECT OF TEMPERATURE 	 97 hydroxyatrazine, deisopropylatrazine, deethylatrazine and atrazine were 0.16, 0.51, 0.57 and 0.68, respectively, determined under UV light (254 nm) and radioscanner in a TLC Scanner II LII 2723 (Berthold). The chromatograms were divided into strips and lhe sulca gel was scrapped off for LSC. Samples (2 x 0.5 g)  of each extracted soil sample were combusted as described above, for determination of soll bound residues. RESULTS AND DISCUSSION Results on radiocarbon balance are presented in Table 2. The extractable residues decreased with time of incubation ia ali temperature treatments. The decrease was more pronounced as the temperature increased, as also reported by Rosário (1989). At 30°C, only 10 days were required for 71% recovery as extractable residues, but at 20°C and 10°C, 40 or 100 days respectiveiy, were needed for the sarne recovery. The extractable residues detected at 20°C after 100 days (39%) were higher than the recovered after only 10 days at 40°C (30% - Table 2). The arnounts of bound residues increased with time ia ali temperatures, and the higher the temperature the highest the arnount detected  (Table 2). Only lO days were enough for 26% and 55% ofbound residues formation at 30°C and 40°C, respectively. At 10°C, only about 8% were detected as bound residues after 20 days, and thereafter the increase was slow, reaching 9.8% after 140 days. At 20°C, the increase of bound residues formation was more pronounced and 41% were detected after 100 days, in agreement with reports of Capriel et ai. (1985), and Khan & Behki (1990). However, in samples incubated at 30°C, about haif of the radiocarbon was detected as bound residues at the end of the 70 days, and rnost of the radiocarbon was detected as bound afier only 50 days ia samples kept aI 40°C (Table 2). Total recoveries generaily decreased from the initial to the end ofthe experiment, under different temperatures, probably due to CO 2 evolution or volatilization with time (Kaufhian & Keamey, 1970). TLC ofthe soil extracts showed little degradation ofatrazine to the phytotoxic deisopropylatrazine and deethylatrazine. Their amounts varied from 0.8% (at 40°C, 40 days) to 3.1% (at 20°C, 60 days), and from 0.1% (aI 40°C, 40 days) to 3.7% (at 20°C, 20 days), respectively. However, the amounts of hydroxyatrazine and atrazine varied much more and were related with increases of temperature and incubation time (Figs. 1 and 2). TABLE 2. Radiocarbon recoveries according to temperature treatment and time of incubation (in % of applied). Tempera. 	 Product' 	 Incubation time (days) ture (°C) 	 lO 	 20 	 30 	 40 	 50 	 60 	 70 	 80 	 100 	 140 lO E 84.3 - 86.5 . 78.6 - 	 73.1 	 61.7 B - 7.7 - 9.6 - 	. 10.7 - 	 11.5 	 9.8 T - 92.0 - 96.1 . 	- 89.3 - 	 84.6 	 71.5 20 E - 83.4 - 71.2 . 	 59.7 - 51.4 	 39.1 	 - 13 - 17.9 - 27.1 29.9 33.2 	 41.2 	 - T - 1013 - 98.3 . 	 89.6 . 84.5 	 80.3 	 - 30 E 70.7 57.1 49.3 - 40.1 	- 33.2 - 	 - 	 - II 26.0 35.9 42.3 - 45.5 	 - 46.7 - 	 - 	 - T 96.7 93.0 91.6 - 85.6 	- 79.9 - 	 - 	 - 40 E 30.1 23.8 15.1 16.8 19.5 	 - - - 	 - 	 - II 55.3 68.8 81.0 72.1 81.5  T 85.4 92.6 96.1 88.9 101.0  1 E - extraclables; B - bound residues; T - total reeovered 2 Nol analysed. Pesq. agropec. bras,. Brasilia, v.32, n.I, p.95-I00,jan. 1997 t 20 e Is o lo o te x 98 	 M.M. DE ANDRÉA et ai. Aithough amounts of extractable hydroxyatrazine did not exceed 23%, there was a slow increase with time in ali different temperatures (Fig. 1). At 10°C, the hydroxyatrazine detected ranged from 1.2% (20 days) to 2.2% (140 days), white the amounts of atrazine decreased from 77% to 54% (Fig. 2) and fite bound residues increased from 7.7% to 9.8% (Table 2) in the sarne period o! time. At 20°C, the arnounts of the hydroxy derivative increased frorn 5.0% (20 days) to 11% (100 days - Fig. 1), but atrazine recoveries decreased from 71.6% to 10.5%, in the sarne period (Fig. 2). The sarne 11% of hydroxyatrazine were detected within only lO days under 30°C, and it increased until 22.7% (70 days - Fig. 1). The amounts of atrazine detected at 30°C (Fig. 2) varied from 54% (10 days) to 6.3% (70 days) and fite bound residues forrnation increased from 26% to 47% iii the sarne sarnpiing tirnes (Table 2). At 40°C, 16% were detected as hydroxyatrazine 10 days afier the treatment, and thereafter it did not change very much (Fig. 1), but the arnounts of atrazine decreased frorn about 12% to oniy 0.43% Ti~ (dop.) IO,C 	 - t't 	 30'C 	 - 400 FIG. 1.Extractable "C-hydroxyatrnine tormed from "C-atrazine applied to sou. Ti.. (da,.) tot - •0 - 401 FIG. 2. Extractable ' 1C-atrazine ia sou under different temperatures. Pcsq. agropec. bras., Brasilia, v.32, nt, p.95-10O,jan. 1997 (Fig. 2). Atthe end of the experiments, fite recovered products were as foilow: atrazine>bound> hydroxyatrazine at 10°C; bound> atrazine = hydroxyatrazine at 20°C, and bound>hydroxyatra-zine>atrazine at 30°C and 40°C. Tbus, the ternperature treatments were highly and inverseiy related to extractable residue recoveries, but directly related to bound residues formation (Tabie 2) and degradation to hydroxyatrazine (Fig. 1). The quickness of atrazine degradation foliowed a ftrst order kinetics (Fig. 2). According to Waiker (1987), this aliows the calculation of half-lives and degradation rate constants at dif'ferent ternperatures, by the linear regression analysis of logarithrns of the rernaining concentration against time o! incubation (Table 3). The calculation showed that each 10°C increase itt the ternperature decreased the half-life by a factor o!, at Ieast, 3. Rate constant values were plotted against 1 /Temperature (°K) and resulted in a straight une (Fig. 3) characterized by the Arrhenius equation, TABLE 3. Degradation rate constante and hal!--lives of atrazine in sou at different temperaturcs. Temperatura 	 Rata constants 	 Half-life (°C) 	 (days-I) 	 (days) 10 0.00279 248.7 20 0.01223 56.7 30 0.03506 19.8 40 0.15350 4.5 0.0031 	 0.0032 	 0.0033 	 0.0034 	 0.0035 lIA b,oI,t. tem pera tur. ('o) 	t,p.,lm.otol d'lo 	 -a-- ....... FIG. 3.Activation energy of atrazine in soU under different temperatures. EFFECT OF TEMPERATURE 	 99 which resuits in the activation energy: In K = in A - - EaIRT, where K is the degradation rate constant values, A is a soil constant which characterizes the dependence of haif-iife to temperature, R is the universal gas constant, Ea is the activation energy, and T is the temperature in °K (Waiker & Brown, 1985; Waiker, 1987; Rosário, 1989; Lehmann et ai., 1993). The caicuiated Arrehnius activation energy was about 96 kJ . mot', which is very high compared with other herbicides and soiis (Wallcer & Srown, 1983; Waiker, 1987; Vega et ai., 1992), and is characteristic of predom'inance of chemical reactions for degradation of atrazine (Vega et ai., 1992). This high value is due to the temperature effect, but may also be associated with the low soil pH, favouring atrazine hydroiysis to the hydroxy derivative detected in these experiments even at temperatures of 10°C and 20°C (Hance, 1987; Reinhardt et ai., 1990; Reinhardt & Nei, 1993). The characterization of some sampies of sou bound residues perforrned at the Centre for Land & Bioiogicai Resources (Agricuiture Canada) is presented in Tabie 4. Oniy hydroxyatrazine and atrazine were detected and no evidence was obtained for the presence of any deaikyiated toxic products. Hydroxyatrazine represented more than 90% of the bound residues in ali anaiysed samples. Therefore, atrazine is tiot a probabie free contaminant for crops in soiis w'ith the characteristics of the soil here studied and suitabie water content under the warm Brazilian weather conditions, because the predominance of chemicai reactions resuited mainly in the non-phytotoxic hydroxyatrazine. TABLE 4. Rccovery of soil bound residues from 1 4C-atrazine. Sample 	 Bornid residues 	 OH-atraz. 	 Atraz. (% ofapplied) 	 -- --- CONCLUSIONS 1.The availabihty ofatrazine in the soil solution decreases with time independentiy of lhe tem perature. 2. The higher the temperature Iess extractabie and more bound residues are detected. 3. Degradation of atrazine in hydroxyatrazine is reiated to increases in temperature and incubation time, and the process involved is mainly chemicai degradation. 4. The half-life of atrazine iii soil decreases with increases in temperature. ACKNOWLEDGEMENTS To Dr. A. Waiker (AFRC Institute ofHorticuiturai Research, Weiiesbourne, U.K.) for vaivabie suggestions, and Dr. S. U. Khan (Centre for Land & Biological Resources, Agricuiture Canada, Otawa, Ontario, Canada) for expioratory analysis of sou bound residues. This paper is part of a Technicai Cooperation Research Contract (BRA/51023) with IAEA - lntemationai Atomic Energy Agency. REFERENCES CAPRIEL, P.; HAISCU, A.; KHAN, S.U. Distribution and nature of bound (nonextractable) residues of atrazine in a mineral soil nine years after lhe herbicide application. Journal of Agriculture and Food Chemistry, Washington, v.33, p.567-569, 1985. ESSER, H.D.; DUPUIS, CL; EBERT, E.; MARCO, G.; VOGEL, C. s-Triazines. in: KEARNEY, P. C.; KAUFMAN, D.A. (Eds.). Herbicides, chemistry, degradation, and mode ofaction. 2. ed. NewYork: Marcel Dekker, 1975. p.I29-2O8. HANCE, RI. ilerbicide behaviour in lhe sou, with 10°C, 140 days 9.8 0.46 0.042 particular reference to the potential for ground water 20°C. 100 days 41.2 0.96 0.132 contamination. In: HUTSON, D.H.; ROBERTS, 30°C, 70 days 46.7 1.64 0.172 T.R. (Eds.). Herbicides. New York: John Wiley & 40°C, 	 50 days 81.5 2.97 0.242 Sons, 1987. p.223-247. Pesq, agropec. bras., Brasilia, v.32, n.l, p.95-100,jan. 1997 100 	M.M. DE ANDRÉA etal. KAUFMAN, D.A.; KEARNEY, P.C. Microbial degradation of s-triazine herbicides. Residue Reviews, New York, v.32, p.235-265, 1970. KIIAN, S.U.; BEIIKI, R.M. Effects of ?seudomonas species on thc release of bound "C residues from soil treated with [' 4C] atrazine. Journal of Agriculture and Food Chemistry, Washington, v.38, p.2090-2093, 1990. LEHMANN, R.G.; FONTAINE, D.D.; OLBERDING, E.L. Soil degradation of flumetsulam at different temperatures in the laboratory and fie!d. Weed Rescarch, Oxford, v.33, p187495, 1993. MESQUITA, T.B.; RÜEGO, E.F. Influência de agentes tenso-ativos na detecção da radiação beta. Ciência e Cultura, São Paulo, v.36, p.446-450, 1984. REINHARDT, C.F.; EHLERS, 1.0.; NEL, P.C. Persistence of atrazine as affected by sciccted soU properties. S. Afr. Tydskr. Plant Grond, South Africa, v.7, p.182-187, 1990. REINI-IARDT, C.F.; NEL, P.C. The influence of sou type, soil water content and temperature on atrazine persistence. S. Afr. J. Plant Sou, South Africa, v. lO, p.45-49, 1993. ROSÁRIO, M.F.M.R.L. Comportamento dos resíduos da atrazina em solos portugueses. Lisboa: Universidade Técnica de Lisboa, 1989. 437p. Tese de Doutorado. VEGA, D.; BASTIDE, 1.; POULAIN, C. Dégradation chirnique ou microbiologique des sulfony!urées dans le sol. II. Cas du metsulforon méthyle. Weed Research, Oxford, v.32, p.149-l$$,  1992. WALKER, A. Evaluation of a simulation model for prediction of chiorsuifliron persistence in soil. Weed Research, Oxford, v.27, p.143-l52, 1987. WALKER, A.; BROWN, P.A. Measurement and prediction of chlorsulfuron persistence in sou. Builetin of Environmental Contamination and Toxicology, New York, v.30, p.365-372, 1983. WALKEL A.; BROWN, P.A. The relative persistence in soil of five acetanilide herbicides. Builetin o! Environmental Contaminntion and Toxicology, New York, v.34, p.143-149, 1985. WALKER, A.; WELCH, S.J. The relative movement and persistence in soil of chlorsulfuron, metsulfuron-methyl and triasulfuron. Weed Research, Oxford, v.29, p.375-383, 1989. Pesq. agropec. bras., Brasilia, v.32, n.l, p.95100,jan. 1997 

Efeito da temperatura na dissipação de [14C]-atrazina em solo Brasileiro

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Effect of temperature on dissipation of [14C]-atrazine in a Brazilian soil

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