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Atrazine is the most widely used herbicide in the U.S. and has been detected in surface water and groundwater. Technologies are needed for onsite and in situ remediation of water and soil containing atrazine. We investigated the potential of using fine-grained, zero-valent iron (Fe0) to remove atrazine and promote its degradation in contaminated water and soil. Atrazine loss from aqueous solution increased with increasing Fe0concentration (w/v). Agitating 20 μg14C-ring-labeled atrazine L−1with 10% Fe0(w/v) removed 92% of the14C from solution within 48 h. Only about 4% of the14C lost from solution was extractable from the iron with 3 mM CaCl2(readily available pool), 81% was extractable with CH3CN (potentially available pool), and 11% was unextractable residues. A companion experiment indicated that most of the14C extracted from the iron with 3 mM CaCl2after the 48-h Fe0treatment was unaltered atrazine, while the CH3CN extract contained approximately 33% atrazine and 48% was unidentified atrazine transformation products. Treating a highly contaminated solution (20 mg atrazine L−1) with 20% Fe0(w/v) removed 88% of the14C (added as14C-ring-labeled atrazine) from solution within 48 h. Deethylatrazine was the main atrazine transformation product detected in solution after treatment, but small amounts of deisopropylatrazine, didealkylatrazine, and hydroxyatrazine were also found. Treating Sharpsburg surface soil containing 1 mg atrazine kg−1with Fe0(2%, w/w) increased atrazine mineralization from 4.1 to 11.2% after 120 d. Pyrite (4% FeS2, w/w) also increased atrazine mineralization in surface soil, but was less effective in the presence of NO3−or SO42−(100 mg kg−1soil). Adding 2% Fe0(w/w) and 100 mg NO3−kg−1to contaminated subsurface soil increased atrazine mineralization from 0.4 to 8.2% within 120 d, and unextractable residues increased from 4.6 to 9.8%. These results indicate iron can sorb atrazine and promote its transformation in water and soil.

Efficacy, movement, and degradation of dithiopyr and pendimethalin were monitored after application to perennial ryegrass turf in 1990 and 1991. Dithiopyr at 0.6 kg ai ha−1reduced large crabgrass infestation by ≥ 90% up to 87 DAT in both years, while pendimethalin at 1.7 kg ai ha−1provided similar control up to 59 DAT in 1 of 2 yr. Turf thinning due to disease and insect damage in 1990 allowed more herbicide to reach the thatch, mat, and underlying soil in 1991. In both years, more pendimethalin but less dithiopyr was found in thatch 7 DAT than 1 DAT, suggesting greater pendimethalin retention in verdure and thatch. Precipitation was greater after herbicide application in the second year, and concentration in the mat layer reached a maximum by 7 DAT compared to 14 DAT in 1990. Maximum concentrations of dithiopyr and pendimethalin in soil at 0 to 5 cm deep were 20 and 56 μg kg−1, respectively, measured 7 DAT in 1991. Herbicide concentration 5 to 10 cm deep was ≤ 5 μg kg−1at all sampling dates in 1990. In 1991, dithiopyr and pendimethalin concentrations 5 to 10 cm deep did not exceed 4 and 20 μg kg−1, respectively, measured within 1 DAT. Neither herbicide was detected 10 to 20 cm deep, nor in samples collected 30 cm outside of the experimental plots in either year. At 126 DAT (final sampling date), little herbicide was detected in verdure, but residues were found in most thatch and all mat samples. The estimated time for a 50% reduction in detectable residues (DT50) of dithiopyr and pendimethalin from the sampling zone was 35 and 23 days, respectively.

Pendimethalin dissipation was studied following annual 1.7 kg ai ha7l applications to 3-yr-old Kentucky bluegrass turf growing on a Sharpsburg silty clay loam soil and an 85/15 by volume sand/Sharpsburg soil mixture in 150-cm-deep rhizotron containers. Plant tissue, thatch, and soil were sampled periodically between application and 168 days after treatment (DAT). Soil and leachate were collected to monitor pendimethalin movement. Most of the herbicide appeared to remain within the turfgrass system. Pendimethalin concentration was highest in plant tissue and thatch. The 4-hydroxymethyl pendimethalin metabolite was detected in turfgrass tissue up to 42 DAT. No pendimethalin was detected at the 30-, 60-, or 120-cm depths in the rhizotron containers. Traces (?0.003 mg kg-1) of pendimethalin detected in rhizotron leachate collected between 6 and 14 days after heavy rainfall (88 and 95 DAT, respectively) were attributed to gravitational displacement of soil colloids containing adsorbed herbi- cide. Pendimethalin application to established turfgrass would not appear to pose a high risk of groundwater contamination. Nomenclature: Pendimethalin, N-(1-ethyl- propyl)-3,4-dimethyl-2,6-dinitrobenzenamine; Kentucky bluegrass, Poa pratensis L. Additional index words. Pendimethalin metabolite, thatch

Laboratory and greenhouse studies were con- ducted to determine imazaquin and imazethapyr adsorp- tion, mobility, and efficacy in Sharpsburg silty clay loam, Holdrege silt loam, and Tripp sandy loam soils after adjusting pH to 5, 6, and 7. Both herbicides were more strongly absorbed, less mobile, and less efficacious at a lower pH. Observations were attributed to ionic bonding resulting from protonation of basic functional groups on the herbicide molecules as pH decreased. Adsorption was greatest in the silty clay loam and least in the sandy loam soil. Conversely, the herbicides were more efficacious and mobile in the more coarse-textured soils. Imazethapyr was less mobile, more highly adsorbed, and more phytotoxic than imazaquin. Greater adsorption of imazethapyr was attributed to a stronger basic pKa and steric factors. Nomenclature: Imazethapyr, (?)-2-(4,5-dihydro-4-methyl- 4-(1-methylethyl)-5-oxo-lH-imidazol-2-yl)-5-ethyl-3-pyrid- inecarboxylic acid; imazaquin, 2-(4,5-dihydro-4-methyl- 4-(1-methylethyl)-5-oxo-lH-imidazol-2-yl)-3-quinolinecar- boxylic acid. Additional index words. Sorption, leaching, phytotoxicity, AC-252,214, AC-263,499.

The dissociation constant for chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in aqueous solution measured by spectrophotometric titration is 3.58 ± 0.05. Chlorsulfuron was more strongly adsorbed on IRA-400-Cl strong anion exchange resin than on IR-4B-OH weak anion exchange resin or Al2O3 anionotropic adsorbent. Hydrogen bonding was probably responsible for the adsorption observed on IR-120-Na(H) cation exchange resin. No chlorsulfuron was adsorbed on Al2O3 cationotropic absorbent, technical montmorillonite, illite, or kaolinite. Adsorption did occur on organic matter derived from a histosol. Chlorsulfuron was strongly adsorbed on activated charcoal but had little affinity for α-cellulose. Adsorption onto hydrophobic polymeric XAD-2 adsorbent at pH 5.2 was not significant for chlorsulfuron concentrations below 30 μM. No significant adsorption occurred on a variety of mineral soils low in organic matter. Adsorption on a Sharpsburg silty clay loam was inversely related to solution pH. Hydrogen bonding and charge transfer bonds were postulated as the major mechanisms responsible for chlorsulfuron adsorption in soil.

Experiments were conducted in 1982, 1983, and 1984 to determine whether herbicides can effectively control weeds in annual statice (Limonium sinuatumMill.) without reducing the marketability of the crop. A greenhouse evaluation of chlorpropham (1-methylethyl 3-chlorophenylcarbamate), napropamide [N,N-diethyl-2-(1-naphthalenyloxy)propanamide], EPTC (S-ethyl dipropyl carbamothioate), oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyi)-1,3,4-oxadiazol-2-(3H)-one}, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] indicated that preemergence applications of the latter three herbicides resulted in the most effective weed control and least statice injury. Oxadiazon was the most effective for broadleaf and grass ed control in field-grown statice. Yield and quality were greatest in oxadiazon-treated plots and exceeded those of the handweeded controls. Annual statice was most sensitive to trifluralin.

Scanning electron microscopy (SEM) was used to study alachlor microcapsule morphology and the effects of straw age and moisture on herbicide release. Microcapsule diameter in the formulation ranged from 2 to 15 μm. The polyurea encapsulating material was stable in water over time. Diffusion was suggested as the primary mode of alachlor release, with diffusion rate controlled by herbicide and salt concentration gradients between the microcapsule and the surrounding aqueous solution. Alachlor release was promoted by drying the microcapsules before addition to water. Microcapsule morphology was unchanged 48 h after application to dry straw, and microcapsules did not appear to adhere to the straw surface. Microcapsules applied to overwintered wet straw were shriveled at 48 h after treatment, indicating herbicide loss. Capsule walls were broken and appeared brittle after application to fresh wet straw. Organic constituents of the fresh straw cuticle may affect capsule wall integrity.

Much of the success of modern agriculture is due to pesticide technology. Because weeds pose the greatest threat to crop yields, the largest class of pesticides used today is herbicides. Herbicides include products whose active ingredients represent a wide range of chemical families; yet most constitute a minimal potential hazard to man and the environment. Criteria typically used to determine potential hazard are mammalian and piscine toxicity, persistence, and bioaccumulation. By evaluating these criteria and assigning numerical values it is possible to devise a ranking of pesticides such as that developed by Weber (51). This list identifies those pesticides most likely to have some undesirable activity, either before or after they are applied. All herbicides ranked well below organochlorine insecticides in hazard rating and most were less hazardous than the organophosphate and carbamate insecticides. However, any substance, when used improperly, has the potential to cause problems, and for this reason all chemicals should be handled with caution.

Atrazine [2chloro-4(ethyla.mino)6(isopropylamino)-s-triazine] retention by standing and flat wheat (Triticum aestivum L.) stubble was determined over time. Immediately following an application of 1.7 kg/ha atrazine, approximately 60% of the herbicide had been intercepted by the stubble and 40% was found in the underlying soil. After 3 weeks and 50 mm of rainfall, atrazine on standing and flat stubble had decreased by 90 and 63%, respectively, while atrazine in the soil increased nearly twofold. No atrazine was found in stubble 9 weeks after application, and only 17% of that originally applied remained in the upper 4 cm of the soil. Successive alternate-day applications of 12.5, 25, or 50 mm water on 1 4C-atrazine retention by stubble was determined. Atrazine loss from stubble was greatest during the first water application, but there was no linear relationship between water application rate and retention of the herbicide. Atrazine loss from stubble decreased significantly following the second water application in all treatments. The amount of water applied did not influence atrazine loss following the third washing. Subsequent loss after the fourth, fifth, sixth, and seventh washings was 'Received for publication January 24, 1983 and in revised form July 5, 1983. Published as Paper No. 7077, Journal Series, Nebraska Agric. Exp. Stn. Research reported was part of senior author's Ph.D. Thesis. 2Grad. Student and Asst. Prof., Dep. Agron., Univ. of Nebraska, Lincoln, NE 68583 and Prof., Dep. Agron., Univ. of Nebraska, North Platte Station, North Platte, NE 69101. not significant at any water application volume. After the seventh washing, atrazine residues were greatest on stubble which had received the least amount of water. Additional index words. Minimum till, crop residue, stubble mulch.

Laboratory and field research was conducted to determine the influence of winter wheat (Triticum aestivumL.) stubble on weed control and the dissipation of emulsifiable concentrate formulations (EC) of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], and acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide]; and microencapsulated formulations (ME) of alachlor and acetochlor. EC metolachlor provided better weed control than EC alachlor when applied 28 days before planting sorghum (Sorghum bicolorL.) and similar weed control when applied at 1 or 14 days before planting. This difference was attributed to more rapid EC alachlor dissipation. The order of relative herbicide persistence at 24 C and 33% (w/w) soil moisture in a silty clay loam was ME acetochlor = ME alachlor > EC metolachlor > EC acetochlor = EC alachlor. Acetanilide degradation was affected more by increasing temperature from 15 to 24 C than by increasing soil moisture from 15 to 33%. More herbicide was washed from overwintered than fresh straw in the first 1 cm of simulated rainfall. In the first simulated rainfall event, more herbicide was removed from straw that had been dry than wet at application, but the amount of herbicide remaining on dry and wet straw was similar after four events. Formulation generally did not affect herbicide wash-off.

Adsorption and desorption characteristics of fluridone (1-methyl-3-phenyl-5-[3-txifluoromethyl)phenyl]-4-(1H)-pyridinone} on prepared clays and organic matter were studied in unbuffered and buffered aqueous solutions. In unbuffered aqueous solution the adsorption of fluridone decreased in the order: H-saturated organic matter (H-OM) > Ca-saturated montmorillonite (Ca-mont) > Ca-saturated organic matter (Ca-OM) > kaolinite. Based on the chemistry of fluridone, the nature of the adsorbent, and previously reported studies, the major adsorption mechanisms appear to be pH-dependent adsorption of protonated fluridone and direct protonation of the herbicide at acidic surfaces, supplemented by physical adsorption forces such as van der Waals attractions and charge transfer bonds. The adsorption of fluridone on Norfolk sand (Typic Paleudult; fine-loamy, siliceous, thermic), unmodified (CK), or amended with montmorillonite (HC) or organic matter (HM) at pH 4.0, 5.2, and 7.0 was also studied. Over all adsorption was greatest on HC soil, least on CK soil, and intermediate on the HM soil. In each system adsorption was inversely related to pH. These results were interpreted by comparison with adsorption observed on prepared clay minerals and organic matter.

Residue levels of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} in soil were determined indirectly by measuring the chlorophyll content of wheat (Triticum aestivumL.) grown on a Norfolk sandy loam (Typic paleudult; fine loam, siliceous, thermic) 14, 22, 39, and66days after a preemergence application of the herbicide. The half-life for 0.22 and 0.45 kg/ha of fluridone was estimated to be 18 days. Phytotoxicity increased with increasing pH in newly-treated soils and in soil sampled 14 days after treatment. Higher chlorophyll levels in wheat grown in soil sampled 39 days after fluridone application indicated a decrease in biologically-active herbicide. Soil removed from the field following later cultivation produced small reductions in chlorophyll at pH 4.0 and 5.2, but at pH 7.0 significant fluridone activity was still present in the soil after 66 days. Cultivation may have increased the surface concentration of the herbicide.

Glyphosate [N-(phosphonomethyl)glycine] phytotoxicity to greenhouse-grown wheat (Triticum aestivumL. ‘Centurk’) was greatly reduced by Ca2+in the carrier solution. Addition of ethylenediaminetetraacetic acid (EDTA) restored glyphosate phytotoxicity in hard water and increased phytotoxicity in deionized water. The phytotoxicity of 0.1 kg ae/ha glyphosate plus 1.0% (w/v) EDTA was equal to that observed for 0.2 kg/ha of the herbicide alone in deionized water or 0.4 kg/ha in water containing 200 ppm Ca2+. EDTA was more compatible with glyphosate in combination with X-77 or MON-0011 nonionic surfactant than with cationic surfactant (contained in a commercial formulation). Phytotoxicity could be increased by adding EDTA and nonionic surfactant to the latter formulation. EDTA increased glyphosate phytotoxicity to wheat when applied in water that contained high levels of calcium and bicarbonate. Glyphosate activity was greater at pH 4 than at pH 6 or 10, but EDTA was equally effective at pH 4, 6, or 10 for all levels of calcium tested up to 800 ppm. NaHCO3probably reduced phytotoxicity by increasing the pH of the glyphosate solution.