HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (16) Citing Articles via Google Scholar Google Scholar Articles by Staddon, W. J. Articles by Zablotowicz, R. M. Search for Related Content PubMed Articles by Staddon, W. J. Articles by Zablotowicz, R. M. GeoRef GeoRef Citation Agricola Articles by Staddon, W. J. Articles by Zablotowicz, R. M. Related Collections Structure and Properties Soil Biochemistry

DIVISION S-3—SOIL BIOLOGY & BIOCHEMISTRY

Microbiological Characteristics of a Vegetative Buffer Strip Soil and Degradation and Sorption of Metolachlor

^a Dep. Biological Sciences, Eastern Kentucky Univ., Richmond, KY 40475 and formerly, USDA-ARS, SWSRU
^b USDA-ARS, Southern Weed Science Research Unit, P.O. Box 350, Stoneville, MS 38776

* Corresponding author (mlocke{at}ars.usda.gov)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 
Numerous studies have documented efficacy of vegetated buffer strips (VBS) in removing herbicides from surface runoff. Little is known about the fate of herbicides after deposition in buffer strip soil. Soil samples (0- to 2-cm depth) were collected from a buffer strip and an adjacent bare field (BF). Soil organic C was two-fold higher in VBS than in BF, and VBS soil maintained about 0.7 log(10) greater propagule density of total fungi and bacteria and 2 log(10) greater gram-negative bacteria and fluorescent pseudomonads. Corresponding with enhanced microbial populations, VBS exhibited higher endogenous levels of alkaline phosphatase, tetrazolium chloride dehydrogenase, aryl acylamidase, and fluorescein diacetate hydrolytic activity (1.6- to 3.8-fold greater than BF). Batch studies of metolachlor[2-chloro-N-(2-ethyl-6-methyphenyl)-N-(2-methoxy-1-methylethyl)acetamide] sorption showed greater capacity to sorb metolachlor in VBS soil than in BF (K_d 2.25 vs. 1.60 mL g^-1). Soil treated with ¹⁴C metolachlor (1.25 mg kg^-1) was incubated for 46 d in a laboratory study. Limited mineralization (<4%) was observed for both VBS and BF. Less ¹⁴C (43%) was extracted from VBS samples 46 d after treatment. Extractable fractions consisted primarily of metolachlor, although increasing amounts of polar (e.g., sulfonic acid) and nonpolar metabolites were recovered over time, especially in VBS. Metolachlor half-life was 10 and 23 d for soils from VBS and BF, respectively, attributed to higher levels of organic matter and microbial activity in VBS soils. Data suggest retention and enhanced degradation of metolachlor as it passes through VBS strips may limit further transport.

Abbreviations: BF, bare field • FDA, fluorescein diacetate • LSC, liquid scintillation counting • NT, no-tillage • OC, organic carbon • TTC, tetrazolium chloride • TLC, thin-layer chromatography • VBS, vegetated buffer strip

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 
METOLACHLOR is used for pre- and postemergence control of grasses and some broadleaf weeds in a variety of crops including corn (Zea mays L.) and cotton (Gossypium spp.) (WSSA, 1994). In soils, metolachlor is metabolized by microorganisms (Miller et al., 1997) and binds to organic matter and clay minerals through hydrogen bonding and hydrophilic or lipophilic interactions (Peter and Weber, 1985; Chesters et al., 1989). Studies indicated that this degradation and sorption did not prevent movement of metolachlor and its metabolites to aquatic systems, as evidenced by the presence of parent compound and/or its metabolites in streams, ponds, and wells (Frank et al., 1990a,b; Kolpin et al., 1997; Kalkhoff et al., 1998). Kolpin et al. (1997) have associated rising levels of metolachlor in Iowa municipal wells with increased use of the herbicide. Studies suggested that metolachlor can reach water supplies through surface runoff or by leaching (Bowman et al., 1994; Funari et al., 1998). Metolachlor is not readily degraded in aquatic environments (Liu et al., 1995), enhancing concern about its presence in these systems.

Considerable research has been devoted to decreasing the levels of herbicides and their metabolites in the environment. The use of VBS is one strategy currently used for reducing herbicide levels in surface runoff. Numerous studies have demonstrated the efficacy of VBS for herbicide removal (Klöppel et al., 1997; Lowrance et al., 1997; Patty et al., 1997) including metolachlor (Arora et al., 1996; Misra et al., 1996; Webster and Shaw, 1996; Mersie et al., 1999). However, little is known about the fate of herbicides in soil after entering VBS. While infiltration of surface runoff in grass filter strips appears to be the primary mechanism for lowering outflow concentrations of herbicides, sorption to soil and vegetative material may also be a factor (Arora et al., 1996; Misra et al., 1996).

When VBS are established, continuous vegetation is maintained, and soils take on characteristics of grassland soils compared with adjacent cultivated areas. Without tillage, a litter layer from decaying above-ground vegetation and a massive network of roots alters patterns of organic matter accumulation that should substantially stimulate soil microbiological processes such as herbicide degradation. As described by Benoit et al. (1999), the highest isoproturon degradation was observed in vegetative buffer soils that also had the greatest mineralization rates of soil organic matter. Mississippi Delta soils managed under practices that enhance plant residue accumulation in surface soils (no tillage and herbicide-desiccated cover crops) provide an environment for enhanced microbial populations and soil enzyme activity (Wagner et al., 1995; Zablotowicz et al., 1998a) and more rapid degradation of the phenylurea herbicide, fluometuron (1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl) urea) (Zablotowicz et al., 1998a). The present study was conducted to assess the fate of metolachlor (degradation and sorption) and microbiological characteristics (populations and enzymatic activity) of surface soils from a 6-yr-old VBS in comparison with an adjacent cultivated cotton field. This information is needed to assess critically the fate of herbicides that are retained within VBS soils.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 
The study site was on a farmer's field adjacent to Beasley Lake in Sunflower County, Mississippi (an oxbow lake formed from a former channel of the Sunflower River), with a Dundee silt loam (fine-silty, mixed, thermic Aeric Ochraqualf) soil. A VBS and an adjacent BF were examined. The BF area was under long-term (at least 8 yr continuous) cotton production and had been exposed to metolachlor (last application in the spring of 1997). The VBS area was established as hairy vetch (Vicia villosa Roth) at least 6 yr prior to sampling. Predominant species in the VBS at the time of sampling included Poa annua L., Capsella bursa-pastoris (L.) Medicus, Lamium amplexicaule L., Lepidium virginicum L., Vicia villosa Roth, and Stellaria media (L.) Cyrillo. Surface soil samples (0–2 cm) were collected from six 1-m² area plots within each area (VBS or BF) on 2 April 1998. The six VBS sampling locations were spaced approximately 30 m apart and were 10 to 20 m from the edge of Beasley Lake. The corresponding BF locations were 30 to 40 m farther up the slope from the lake. One week prior to the sampling date, the BF was tilled in preparation for planting. Sample material from the VBS was shaken during collection to reduce inclusion of root material in the samples. Ten subsamples were obtained and composited for each plot. Any visible plant tissue was removed before passing samples through a 4-mm sieve. Samples were stored in a cold room at 4°C until further processing. Soil pH (1:1 w/v, 0.01 M CaCl₂), soil organic carbon (OC) (Walkley-Black, Nelson and Sommers, 1996), and particle size distribution (hydrometer method; Gee and Bauder, 1986) were determined for the soils.

Microbiological and Enzyme Assays
Total bacteria, total fungi, gram-negative bacteria, and fluorescent pseudomonads were enumerated by serial dilution on media described elsewhere (Reddy et al., 1995). Briefly, total bacteria were determined on dilute tryptic soy agar with cycloheximide and total fungi with Rose Bengal potato dextrose agar (Martin, 1950). Tryptic soy broth with crystal violet was used for gram-negative bacteria while fluorescent pseudomonads were quantified by means of S-1 media (Gould et al., 1985).

Fluorescein diacetate (FDA) was used as a substrate to estimate total microbial, heterotrophic (esterase, lipase, protease) activity (Schnürer and Rosswall, 1982). Soil (2 g) was incubated with fluorescein diacetate (0.5 mg) in 20 mL phosphate buffer (0.1 mM, pH 7.8) at 20°C for 1 h (150 rpm). The FDA hydrolysis reaction was terminated with the addition of 20 mL of acetone. The reaction mixtures were shaken for 5 min before centrifuging at 8000 x g for 10 min. Fluorescein in the supernatant was quantified spectrophotometrically at 490 nm with an extinction coefficient of 80.3 mM^-1 cm^-1. Microbial metabolic activity was estimated by triphenyl-tetrazolium chloride (TTC) dehydrogenase activity (Casida et al., 1964). Soil (2 g) was incubated statically with 4 mL of 3% (w/v) TTC for 24 h at 37°C. A second set of reactions was performed with the addition of TTC fortified with 0.1% (w/v) yeast extract (Casida, 1977). The TTC reaction was terminated with 12 mL of methanol, and the product, triphenyl-formazan, was extracted by shaking for 30 min. After centrifugation the optical density of the supernatant was measured at 485 nm and corrected for soil incubated without a substrate. Alkaline phosphatase activity was determined as described by Tabatabai (1994). Briefly, the release of p-nitrophenol from p-nitrophenyl phosphate was monitored spectrophotometrically (410 nm). Aryl acylamidase activity (Zablotowicz et al., 1998b) was estimated by monitoring hydrolysis of 2-nitroacetanilide (1 g of soil with 4 mL of 2 mM 2-NAA in phosphate buffer, 0.05 M, pH 8.0). Release of 2-nitroaniline was determined spectrophotometrically (410 nm) after 24 h of incubation at 30°C by extraction with 4 mL of methanol and centrifugation.

Metolachlor Degradation and Sorption
Two laboratory studies were conducted simultaneously to determine the effects of VBS on metolachlor degradation in soil. Field moist soils (25 g oven-dry weight equivalent) from each of the six field plots in the VBS and BF areas were added to 250-mL Nalgene bottles (in Study I) or 250-mL biometer flasks (in Study II) and brought to 300 g kg^-1 soil moisture (gravimetric) with deionized water. In Study II, biometer flasks were used to assess metolachlor mineralization to ¹⁴CO₂. Otherwise, conditions for the two studies were the same. A mixture of ¹⁴C-ring labeled metolachlor (spec. act. 3.05 x 10⁵ kBq mmol^-1) (96% purity by TLC, Novartis, Greensboro, NC)¹ and technical grade metolachlor (99% purity, Chem Service, West Chester, PA) was applied uniformly to the soil surface (1.25 mg metolachlor kg^-1 soil; 3.3 kBq radioactivity per sample). Soils were incubated in the dark at 25°C. Water was added periodically to compensate for evaporation. In Study II, evolved ¹⁴CO₂ (mineralized) was trapped in the sidearm of the biometer flask by means of 10 mL 1 M NaOH and quantified by liquid scintillation counting (LSC) (Packard TriCarb 4000 Series, Packard Instruments, Meriden, CT) using Hionic-Fluor (Packard, Meriden, CT) (Bartha and Palmer, 1965; Locke and Harper, 1991). To avoid saturation by CO₂, the NaOH was replaced on sampling days. Soils from both studies were destructively sampled at nine sampling points throughout the 46-d incubation. At each sampling time, soils were extracted with methanol (50 mL per extraction). Samples were shaken at room temperature (24 h for the first extraction, 2.5 h for the second). Bottles were centrifuged at 6000 x g for 10 min and the supernatants from each extraction were pooled. Radioactivity in the extracts was quantified by LSC by Ecolume (ICN, Costa Mesa, CA). After extraction, air-dried soils were combusted to measure nonextractable ¹⁴C (Oxidizer Model 306, Packard Instruments, Downers Grove, IL). Extract volumes were reduced with a rotary evaporator. Samples were diluted in 100 mL of ultra-pure water and acidified below pH 3 prior to passing through conditioned C₁₈ solid-phase extraction columns (J.T. Baker, Phillipsburg, NJ). Metolachlor and metabolites were eluted from the column with 3 mL of methanol. Aliquots (90-µL) were spotted on thin-layer chromatography (TLC) plates (20 by 20 cm, 250-µm silica gel, Whatman, Clifton, NJ). A hexane:ethyl acetate:methylene chloride (6:3:1) solvent system (Liu et al., 1989; Locke et al., 1996) was used to develop the plates to 10 cm, and they were analyzed with a Bioscan System 200 Imaging Scanner (Bioscan, Washington, DC). Metolachlor migrated with an R_f of approximately 0.71. The presence of the sulfonic acid metabolite of metolachlor (Novartis, Greensboro, NC) was corroborated by means of two additional solvent systems (butanol:acetic acid: water 12:3:5 and butanone:acetic acid:water 10:1:1, Lamoureux and Rusness, 1989). Each study consisted of duplicate samples from each of six field plots.

For sorption studies, 5-g (oven-dried equivalent) soil samples were added to 25-mL Corex centrifuge tubes with Teflon caps. Container controls were used to correct for sorption to tubes and caps (sorption was <0.25%). ¹⁴C-metolachlor solutions (597 kBq L^-1) were prepared in 0.01 M CaCl₂ with metolachlor concentrations of 0.85, 7.85, and 35.55 µmol L^-1. Ten milliliters of solution were added to each tube, and samples were shaken for 24 h. Samples were centrifuged (8000 x g) and two 1-mL subsamples of supernatant were counted by LSC as described previously. Desorption was performed under similar conditions (5 g soil, oven-dried equivalent; 10 mL of solution). The starting concentration was 15 µmol L^-1 with 1510 kBq L^-1. Tubes were shaken for 24 h, centrifuged (8000 x g), after which 5 mL were removed and replaced with 5 mL fresh 0.01 M CaCl₂. Two 1-mL subsamples of the supernatant were removed for counting. The desorption procedure was repeated three times. The sorption–desorption experiment included five replications and was repeated once.

Degradation and Sorption Models and Statistical Analysis
Degradation of chloroacetamide herbicides such as alachlor and metolachlor occurs primarily via cometabolism, thus there is little adaptation of microorganisms to facilitate biodegradation (Stampor and Tuovinen, 1998; Zablotowicz et al., 1998c). The disappearance of total extractable ¹⁴C and metolachlor was evaluated by mans of the power rate equation and assumptions considered by Hamaker, 1972.

(1)

(2)

where C is the concentration of extractable ¹⁴C or metolachlor at time t, C_o is the initial concentration of metolachlor, n is the order of reaction, and k is the rate constant.

Sorption of metolachlor to soils was described by the average distribution sorption coefficient for the three concentrations (Hamaker and Thompson, 1972; Green and Karickhoff, 1990; Cleveland, 1996). Desorption was described by the average distribution desorption coefficient for two concentrations.

(3)

where S is the amount of metolachlor sorbed to the soil (µmol kg^-1), K_d is the distribution sorption (or desorption) coefficient, and C is concentration of metolachlor in solution at equilibrium (µmol L^-1).

Nonlinear regression analysis of Eq. [1] and [2], analysis of variance, and other statistical tests were performed by SAS ver. 4.10 (SAS Institute Inc., 2000). Degradation, sorption, and desorption studies were repeated, and after statistical analysis determined no differences between data sets, the data were pooled.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 
Soil and Microbial Parameters
The surface (0–2 cm) soils from the VBS and BF had similar texture (silt loam) (Table 1). The VBS had more than twice as much OC and half a unit lower pH than the BF (1.17% vs. 0.54%; 4.8 and 5.3, respectively). Culturable populations of all microbial taxa examined were greater in the VBS than the BF (Table 2). Differences in total bacteria were likely due to gram-negative bacteria such as fluorescent pseudomonads, as was observed in some cover crop soils (Wagner et al., 1995; Zablotowicz et al., 1998a).

Sorption and Desorption
A higher sorption K_d value for the VBS soil indicates a greater capacity to sorb metolachlor (Table 4). The desorption K_d value for the VBS was moderately higher than the BF, indicating a greater equilibrium shift in favor of sorption for the VBS soil (Table 4). Again, this results from the larger sorption capacity in the VBS soil. Higher organic carbon in the VBS is one of the most significant factors in relation to greater sorption in these soils (Obrigawitch et al., 1981; Braverman et al., 1986; Wood et al., 1987; Locke, 1992; Miller et al., 1997). These results are consistent with the observations of Mersie et al. (1999) and support the hypothesis that enhanced metolachlor retention in VBS may reduce further mobility.

Degradation and Metabolite Formation
Extractable ¹⁴C decreased over the course of the experiment for both soils (Fig. 1a) and was described by a first-order model (Table 5). Half-lives for the extractable ¹⁴C fraction were 18 and 38 d for the VBS and BF, respectively (Table 5). After 46 d of incubation, 28% of the initial ¹⁴C could be extracted from the VBS soils while 48% was recovered from the BF soils. Conversely, nonextractable ¹⁴C increased with time and was significantly higher for the VBS (LSD =0.05) after Day 1 with the exception of Day 26 (Fig. 1b). The extractable-bound results are consistent with the sorption experiment and likely reflect the higher levels of organic matter and microbial activity in the VBS soils. Total CO₂ evolution did not differ between VBS and BF, and did not account for more than 4% of the total ¹⁴C for either soil (Fig. 1b). Limited mineralization of metolachlor has been observed by others (Levanon et al., 1994; Miller et al., 1997; Stampor and Tuovinen, 1998) including in rhizosphere soils (Anderson and Coats, 1995). Locke et al. (1996) also found low rates of mineralization for another chloroacetamide, alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide]. In contrast to our mineralization results, Benoit et al. (1999) found that ¹⁴C-CO₂ release from isoproturon was dramatically higher in grass buffer soils (15% in upper 2 cm soil) than those from an adjacent field (2%) suggesting more complete mineralization in the former. Metolachlor has double ortho substitution in the aniline ring and N-alkyl substitution that hinders mineralization of the aniline ring (Villareal et al., 1994).

View larger version (26K): [in this window] [in a new window]   Fig. 1. Fate of 14C during the course of the experiment. Results for extractable 14C are shown in (a) with curves representing nonlinear regression fits of the first-order equation. Symbols for (a) are • VBS extractable and BF extractable. The nonextractable and mineralized components are illustrated in (b). Symbols for (b) are VBS Mineralized, BF Mineralized, • VBS nonextractable, and BF nonextractable.

TLC analysis indicated that most of the extracted ¹⁴C was metolachlor during the first 17 d of incubation (Fig. 2a). More metolachlor (LSD = 0.05) was extracted from the BF soils throughout the course of the experiment. First-order kinetics described metolachlor degradation for both soils, and the half-lives were 10 and 23 d, respectively, for the VBS and BF (Table 5). At the end of the experiment, 7% of initial metolachlor remained extractable in the VBS while 26% could still be recovered from the BF. More metolachlor was extracted from the BF soils on and after Day 5. For BF, metolachlor was the primary constituent of the extracts throughout the study period (Fig. 2). In the VBS, metolachlor was the dominant compound in the extract until Day 26 when the amount of metabolites was equivalent to or greater than metolachlor (Fig. 2). Significantly more nonpolar metabolites (those which migrated between 0.2 to 0.6 in the hexane:ethyl acetate:methylene chloride solvent) were isolated from the VBS soils on Days 13, 19, and 26. Polar compounds (those which remained at the origin of the TLC plate) were similar for both soils during most of the incubation period, but more polar compounds were recovered from the BF soils during the last 2 wk (Fig. 2b). This may be due to slower degradation rates in the BF soils, resulting in an accumulation of non-polar compounds. Combining polar and nonpolar values revealed significantly higher metabolite accumulation early in the incubation (Days 5, 9, 13, and 19) from VBS soil. The presence of the sulfonic acid metabolite was confirmed using the two polar solvent systems in several samples from Day 19. Sulfonic acid comprised between 26 and 60% of the total polar metabolites in these later samples. Studies by Locke et al. (1996) indicated that sulfonic acid was the major metabolite of the chloroacetamide alachlor during degradation in soil. Polar metabolites of the chloroacetamides may also result from glutathione conjugation mediated by gram-negative bacteria (Zablotowicz et al., 1994). Overall, our results are similar to those of Anderson et al. (1994) who found enhanced degradation of metolachlor in rhizosphere soils. Further, Mersie et al. (1999) found little metolachlor in leachate from a tilted-bed runoff experiment, suggesting that degradation, sorption, or both had taken place.

View larger version (28K): [in this window] [in a new window]   Fig. 2. TLC analysis of methanol extractable 14C. Disappearance of metolachlor over time (a) with curves representing nonlinear regression fits of the first-order equation. Symbols for (a) are • VBS metolachlor and BF metolachlor. Appearance of non-polar and polar metabolites are shown in (b). Symbols for (b) are • VBS non-polar, BF non-polar, VBS polar, and BF polar.

	ACKNOWLEDGMENTS

 
The authors extend their appreciation to Earl Gordon for technical support, Charles Bryson for identifying the plants and Debbie Boykin for assistance with data analysis. The ¹⁴C metolachlor and metabolites were kindly provided by Novartis, Greensboro, NC.

	NOTES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 
¹ Mention of a product or manufacturer is for information only and does not constitute endorsement by the USDA.

Received for publication July 21, 2000.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS NOTES RESULTS AND DISCUSSION REFERENCES

 

• Anderson, T.A., and J.R. Coats. 1995. Screening rhizosphere soil samples for the ability to mineralize elevated concentrations of atrazine and metolachlor. J. Environ. Sci. Health B30:473–484.
• Anderson, T.A., E.L. Kruger, and J.R. Coats. 1994. Biological degradation of pesticide wastes in the root zone of soils collected at an agrochemical dealership. p. 199–209. In T.A. Anderson and J.R. Coats (ed.) Bioremediation through rhizosphere technology. ACS Symposium Series 563. American Chemical Society, Washington, DC.
• Arora, K., S.K. Mickelson, J.L. Baker, D.P. Tierney, and C.J. Peters. 1996. Herbicide retention by vegetative buffer strips from runoff under natural rainfall. Trans. ASAE 39:2155–2162.
• Bartha, R., and D. Pramer. 1965. Features of a flask and method for measuring the persistence and biological effects of pesticides in soil. Soil Sci. 100:68–70.
• Benoit, P., E. Barriuso, Ph. Vidon, and B. Réal. 1999. Isoproturon sorption and degradation in a soil from grassed buffer strip. J. Environ. Qual. 28:121–129.[Abstract/Free Full Text]
• Bollag, J.-M., L.L. McGahen, R.D. Minard, and S.Y. Liu. 1986. Bioconversion of alachlor in an anaerobic stream sediment. Chemosphere 15:153–162.
• Bowman, B.T., G.J. Wall, and D.J. King. 1994. Transport of herbicides and nutrients in surface runoff from corn cropland in southern Ontario. Can. J. Soil. Sci. 74:59–66.
• Braverman, M.P., T.L. Lavy, and C.J. Barnes. 1986. The degradation and bioactivity of metolachlor in soil. Weed Sci. 34:479–484.
• Burns, R.G. 1982. Enzyme activity in soil: Location and possible role in soil ecology. Soil Biol. Biochem. 14:423–427.
• Casida, L.E., Jr. 1977. Microbial metabolic activity in soil as measured by dehydrogenase determinations. Appl. Environ. Microbiol. 34:630–636.[Abstract/Free Full Text]
• Casida, L.E., Jr., D.A. Klein, and T. Santoro. 1964. Soil dehydrogenase activity. Soil Sci. 98:371–376.
• Chesters, G., G.V. Simsiman, J. Levy, B.J. Alhajjar, R.N. Fathulla, and J.M. Harkin. 1989. Environmental fate of alachlor and metolachlor. Rev. Environ. Contam. Toxicol. 110:1–74.[ISI][Medline]
• Cleveland, C.B. 1996. Mobility assessment of agrichemicals: Current laboratory methodology and suggestions for future directions. Weed Technol. 10:157–168.
• Frank, R., H.E. Braun, B.S. Clegg, B.D. Ripley, and R. Johnson. 1990a. Survey of farm wells for pesticides, Ontario, Canada, 1986 and 1987. Bull. Environ. Contam. Toxicol. 44:410–419.[ISI][Medline]
• Frank, R., H.E. Braun, B.D. Ripley, and B.S. Clegg. 1990b. Contamination of rural ponds with pesticide, 1971–85, Ontario, Canada. Bull. Environ. Contam. Toxicol. 44:401–409.[ISI][Medline]
• Funari, E., L. Barbieri, P. Bottoni, G. Del Carlo, S. Forti, G. Giuliano, A. Marinelli, C. Santini, and A. Zavatti. 1998. Comparison of the leaching properties of alachlor, metolachlor, triazines, and some of their metabolites in an experimental field. Chemosphere 36:1759–1773.
• Gee, G.W., and J.W. Bauder. 1986. Particle-size analysis. p. 383–411. In A. Klute (ed.) Methods of soil analysis. Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
• Gould, W.D., C. Hagedorn, T.R. Bardinelli, and R.M. Zablotowicz. 1985. New selective media for enumeration and recovery of flourescent pseudomonads from various habitats. Appl. Environ. Microbiol. 49:28–32.[Abstract/Free Full Text]
• Green, R.E., and S.W. Karickhoff. 1990. Sorption estimates for modeling. p. 79–101. In H.H. Cheng (ed.) Pesticides in the soil environment: Processes, impacts, and modeling. SSSA Book Ser. 2. SSSA, Madison, WI.
• Hamaker, J.W. 1972. Decomposition: Quantitative aspects. p. 253–279. In C.A.I. Goring and J.W. Hamaker (ed.) Organic chemicals in the soil environment. Vol. I. Marcel Dekker, New York.
• Hamaker, J.W., and J.M. Thompson. 1972. Adsorption. p. 49–143. In C.A.I. Goring and J.W. Hamaker (ed.) Organic chemicals in the soil environment. Vol. I. Marcel Dekker, New York.
• Hsu, T.-S., and R. Bartha. 1974. Interaction of pesticide-derived chloroaniline residues with soil organic matter. Soil. Sci. 116:444–452.
• Kalkhoff, S.J., D.W. Kolpin, E.M. Thurman, I. Ferrer, and D. Barcelo. 1998. Degradation of chloroacetanilide herbicides: The prevalence of sulfonic and oxanilic acid metabolites in Iowa groundwaters and surface waters. Environ. Sci. Technol. 32:1738–1740.
• Klöppel, H., W. Kördel, and B. Stein. 1997. Herbicide transport by surface runoff and herbicide retention in a filter strip—Rainfall and runoff simulation studies. Chemosphere 35:129–141.
• Kolpin, D.W., D. Sneck-Fahrer, G.R. Hallberg, and R.D. Libra. 1997. Temporal trends of selected agricultural chemicals in Iowa's groundwater, 1982–1995: Are things getting better? J. Environ. Qual. 26:1007–1017.[Abstract/Free Full Text]
• Lamoureux, G.L., and D.G. Rusness. 1989. Propachlor metabolism in soybean plants, excised soybean tissues, and soil. Pestic. Biochem. Physiol. 34:187–204.
• Levanon, D., J.J. Meisinger, E.E. Codling, and J.L. Starr. 1994. Impact of tillage on microbial activity and the fate of pesticides in the upper soil. Water Air Soil Pollut. 72:179–189.
• Liu, D., J. Maguire, G.J. Pacepavicius, I. Aoyama, and H. Okamura. 1995. Microbial transformation of metolachlor. Environ. Toxicol. Water Qual. 10:249–258.
• Liu, S.-Y., Z. Zheng, R. Zheng, and J.-M. Bollag. 1989. Sorption and metabolism of metolachlor by a bacterial community. Appl. Environ. Microbiol. 55:733–740.[Abstract/Free Full Text]
• Locke, M.A. 1992. Sorption-desorption kinetics of alachlor in surface soil from two soybean tillage systems. J. Environ. Qual. 21:558–566.[Abstract/Free Full Text]
• Locke, M.A., and S.S. Harper. 1991. Metribuzin degradation in soil: I. Effects of soybean residue amendment, metribuzin level, and soil depth. Pestic. Sci. 31:221–237.
• Locke, M.A., L.A. Gaston, and R.M. Zablotowicz. 1996. Alachlor biotransformation and sorption in soil from two soybean tillage systems. J. Agric. Food Chem. 44:1128–1134.
• Lowrance, R., G. Vellidis, R.D. Wauchope, P. Gray, and D.D. Bosch. 1997. Herbicide transport in a managed riparian forest buffer system. Trans. ASAE 40:1047–1057.
• Martin, J.P. 1950. Use of acid, rose bengal and streptomycin in the plate method for enumerating soil fungi. Soil Sci. 69:215–232.
• Mersie, W., C.A. Seybold, C. McNamee, and J. Huang. 1999. Effectiveness of switchgrass filter strips in removing dissolved atrazine and metolachlor from runoff. J. Envrion. Qual. 28:816–821.
• Miller, J.L., A.G. Wollum III, and J.B. Weber. 1997. Degradation of carbon-14-atrazine and carbon-14-metolachlor in soil from four depths. J. Environ. Qual. 26:633–638.[Abstract/Free Full Text]
• Misra, A.K., J.L. Baker, S.K. Mickelson, and H. Shang. 1996. Contributing area and concentration effects on herbicide removal by vegetative buffer strips. Trans. ASAE 39:2105–2111.
• Nelson, D.W., and L.E. Sommers. 1996. Total carbon, organic carbon, and organic matter. p. 961–1010. In J.M. Bigham (ed.) Methods of soil analysis. Part 3. Chemical methods. SSSA Book Ser. No. 5. SSSA, Madison, WI.
• Obrigawitch, T., F.M. Hons, J.R. Abernathy, and J.R. Gipson. 1981. Adsorption, desorption and mobility of metolachlor in soils. Weed Sci. 29:332–336.
• Patty, L., B. Réal, and J.J. Gril. 1997. The use of grassed buffer strips to remove pesticides, nitrate and soluble phosphorus compounds from runoff water. Pestic. Sci. 49:243–251.
• Peter, C.J., and J.B. Weber. 1985. Adsorption, mobility, and efficacy of alachlor and metolachlor as influenced by soil properties. Weed Sci. 33:874–881.
• Prueger, J.H., J.L. Hatfield, and T.J. Sauer. 1999. Field-scale metolachlor volatilization flux estimates from broadcast and banded application methods in Central Iowa. J. Environ. Qual. 28:75–81.
• Reddy, K.N., R.M. Zablotowicz, and M.A. Locke. 1995. Chlorimuron adsorption, desorption, and degradation in soils from conventional tillage and no-tillage systems. J. Eviron. Qual. 24:760–767.
• SAS Institute Inc. 2000. Windows Version 4.10. SAS Institute, Inc., Cary, NC.
• Schnürer, J., and T. Rosswall. 1982. Fluorescein diacetate hydrolysis as a measure of total microbial activity in soil and litter. Appl. Environ. Microbiol. 43:1256–1261.[Abstract/Free Full Text]
• Stampor, D.M., and Tuovinen. 1998. Biodegradation of the acetanilide herbicides alachlor, metolachlor, and propachlor. Crit. Rev. Microbiol. 24:1–22.[ISI][Medline]
• Tabatabai, M.A. 1994. Soil enzymes. p. 775–833. In R.W. Weaver et al. (ed.) Methods of soil analysis. Part 2—Microbiological and biochemical properties. SSSA Book Ser. 5. SSSA, Madison, WI.
• Villareal, D.T., R.F. Turco, and A. Konopka. 1994. A structure activity study with aryl acylamidases. Appl. Environ. Microbiol. 60:3939–3944.[Abstract/Free Full Text]
• Wagner, S.C., R.M. Zablotowicz, M.A. Locke. R.J. Smeda, and C.T. Bryson. 1995. Influence of herbicide-desiccated cover crops on biological soil quality in the Mississippi Delta. p. 86–89. In W.L. Kingery and N.W. Buehring (ed.) Proceedings of the Southern Conservation Tillage Conference for Sustainable Agriculture. Mississippi Agric. Forestry Exp. Stn. Spec. Bull. 88-7.
• Webster, E.P., and D.R. Shaw. 1996. Impact of vegetative filter strips on herbicide loss in runoff from soybean (Glycine max). Weed Sci. 44:662–671.
• WSSA. 1994. Herbicide handbook. 7th ed. Weed Science Society of America, Champaign, IL.
• Wood, L.S., H.D. Scott, D.B. Marx, and T.L. Lavy. 1987. Variability in sorption coefficients of metolachlor on a captina silt loam. J. Environ. Qual. 16:251–255.
• Zablotowicz, R.M., R.E. Hoagland, and M.A. Locke. 1994. Glutathione S-transferase activity in rhizosphere bacteria and the potential for herbicide detoxification. p. 184–198. In T.A. Anderson and J.R. Coats (ed.) Bioremediation through rhizosphere technology. ACS Symposium Series 563, American Chemical Society, Washington, DC.
• Zablotowicz, R.M., M.A. Locke, and R.J. Smeda. 1998a. Degradation of 2,4-D and fluormeturon in cover crop residues. Chemosphere 37:87–101.
• Zablotowicz, R.M., R.E. Hoagland, and S.C. Wagner. 1998b. 2-Nitroacetanilide as substrate for determination of aryl acylamidase activity in soils. Soil Biol. Biochem. 30:679–686.
• Zablotowicz, R.M., R.E. Hoagland, and M.A. Locke. 1998c. Biostimulation: Enhancement of cometabolic processes to remediate pesticide-contaminated soils. p. 217–250. In P. Kearney and T. Roberts (ed.) Pesticide remediation in soils and water. John Wiley & Sons, Ltd., Chichester, UK.
• Zablotowicz, R.M., R.E. Hoagland, W.J. Staddon, and M.A. Locke. 2000. Effects of pH on chemical stability and de-esterification of fenoxaprop-ethyl by purified enzymes, bacterial extracts, and soils. J. Agric. Food Chem. 48:4711–4716.[ISI][Medline]

This article has been cited by other articles:

				F. P. Vinther, U. C. Brinch, L. Elsgaard, L. Fredslund, B.V. Iversen, S. Torp, and C. S. Jacobsen Field-Scale Variation in Microbial Activity and Soil Properties in Relation to Mineralization and Sorption of Pesticides in a Sandy Soil J. Environ. Qual., August 8, 2008; 37(5): 1710 - 1718. [Abstract] [Full Text] [PDF]

				D. Kay, A. C. Edwards, R. C. Ferrier, C. Francis, C. Kay, L. Rushby, J. Watkins, A. T. McDonald, M. Wyer, J. Crowther, et al. Catchment microbial dynamics: the emergence of a research agenda Progress in Physical Geography, February 1, 2007; 31(1): 59 - 76. [Abstract] [PDF]

				D. L. Shaner and W. B. Henry Field History and Dissipation of Atrazine and Metolachlor in Colorado J. Environ. Qual., January 9, 2007; 36(1): 128 - 134. [Abstract] [Full Text] [PDF]

				L. J. Krutz, S. A. Senseman, K. J. McInnes, D. W. Hoffman, and D. P. Tierney Adsorption and Desorption of Metolachlor and Metolachlor Metabolites in Vegetated Filter Strip and Cultivated Soil J. Environ. Qual., May 1, 2004; 33(3): 939 - 945. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (16) Citing Articles via Google Scholar Google Scholar Articles by Staddon, W. J. Articles by Zablotowicz, R. M. Search for Related Content PubMed Articles by Staddon, W. J. Articles by Zablotowicz, R. M. GeoRef GeoRef Citation Agricola Articles by Staddon, W. J. Articles by Zablotowicz, R. M. Related Collections Structure and Properties Soil Biochemistry