Liquid–liquid extraction or solid-phase extraction followed by gas chromatography (GC) or high-performance liquid chromatography are traditional herbicide residue determination methods for ...environmental samples. Solid-phase microextraction (SPME) is a solventless, fast, and sensitive alternative herbicide residue extraction method that can be applied to numerous environmental matrices. The objective of this paper was to review SPME literature regarding extraction theory, extraction modes, fiber types, and method optimization in conjunction with present and future SPME applications for herbicide determination in environmental samples.
Herbicides applied to soils potentially affect soil microbial activity. The quantity and frequency of Roundup Ultra RU; N-(phosphonomethyl)glycine; Monsanto, St. Louis, MO applications have escalated ...with the advent of Roundup-tolerant crops. The objective of this study was to determine the effect of Roundup Ultra on soil microbial biomass and activity across a range of soils varying in fertility. The isoproplyamine salt of glyphosate was applied in the form of RU at a rate of 234 mg active ingredient kg(-1) soil based on an assumed 2-mm glyphosate-soil interaction depth. Roundup Ultra significantly stimulated soil microbial activity as measured by C and N mineralization, as well as soil microbial biomass. Cumulative C mineralization as well as mineralization rate increased above background levels for all soils tested with addition of RU. There were strong linear relationships between C and N mineralized, as well as between soil microbial C and N (r2 = 0.96 and 0.95, respectively). The slopes of the relationships with RU addition approximated three. Since the isopropylamine salt of glyphosate has a C to N ratio of 3:1, the data strongly suggest that RU was the direct cause of the enhanced microbial activity. An increase in the C mineralization rate occurred the first day following RU addition and continued for 14 d. Roundup Ultra appeared to be rapidly degraded by soil microbes regardless of soil type or organic matter content, even at high application rates, without adversely affecting microbial activity.
Although the effectiveness of vegetative filter strips (VFS) for reducing herbicide runoff is well documented, a comprehensive review of the literature does not exist. The objectives of this article ...are to denote the methods developed for evaluating herbicide retention in VFS; ascertain the efficacy of VFS regarding abating herbicide runoff; identify parameters that affect herbicide retention in VFS; review the environmental fate of herbicides retained by VFS; and identify future research needs. The retention of herbicide runoff by VFS has been evaluated in natural rainfall, simulated rainfall, and simulated run-on experiments. Parameters affecting herbicide retention in VFS include width of VFS, area ratio, species established in the VFS, time after establishment of the VFS, antecedent moisture content, nominal herbicide inflow concentration, and herbicide properties. Generally, subsequent transport of herbicides retained by VFS is reduced relative to adjacent cultivated soil because of enhanced sorption and degradation in the former.
In this study, a double-tube centrifuge method was employed to determine the effects of soil moisture on the bioactivity of cafenstrole, pretilachlor, benfuresate, oxyfluorfen and simetryn. In ...general, the available herbicide concentration in soil solution (ACSS) showed little change as soil moisture increased for herbicides. The total available herbicide in soil solution (TASS) typically increased as soil moisture increased for all herbicides. The relationship between TASS and % growth rate based on dry weight showed strong linear relationships for both cafenstrole and pretilachlor, with r2 values of 0.95 and 0.84, respectively. Increasing TASS values were consistent with increasing herbicide water solubility, with the exception of the ionizable herbicide simetryn. Plant absorption and % growth rate exhibited a strong linear relationship with TASS. According to the results suggested that TASS was a better predictor of herbicidal bioactivity than ACSS for all herbicides under unsaturated soil moisture conditions.
Previous studies have indicated that dissolved-phase metolachlor 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methoxy-1-methylethyl) acetamide transported in surface runoff is retained by vegetative filter ...strips to a greater degree than either metolachlor oxanilic acid 2-(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino-2-oxoacetic acid (OA) or metolachlor ethanesulfonic acid 2-(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl-1)amino-2-oxoethanesulfonic acid (ESA), two primary metabolites of metolachlor. Adsorption-desorption of ESA and OA in vegetated filter strip soil (VFSS) has not been evaluated, yet these data are required to assess the mobility of these compounds in VFSS. The objective of this experiment was to compare metolachlor, ESA, and OA adsorption and desorption parameters between VFSS and cultivated soil (CS). Adsorption and desorption isotherms were determined using the batch equilibrium procedure. With the exception of a 1.7-fold increase in organic carbon content in the VFSS, the evaluated chemical and physical properties of the soils were similar. Sorption coefficients for metolachlor were 88% higher in VFSS than in CS. In contrast, sorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, sorption coefficients for ESA and OA were at least 79% lower in both soils. Metolachlor desorption coefficients were 59% higher in the VFSS than in the CS. Desorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, desorption coefficients for ESA and OA were at least 66% lower in both soils. These data indicate that the mobility of ESA and OA will be greater than metolachlor in both soils. However, higher organic carbon content in VFSS relative to CS may limit the subsequent transport of metolachlor from the vegetated filter strip.
Vegetated filter strips (VFS) potentially reduce the offsite movement of herbicides from adjacent agricultural fields by increasing herbicide mass infiltrated (M(inf)) and mass adsorbed (M(as)) ...compared with bare field soil. However, there are conflicting reports in the literature concerning the contribution of M(as) to the VFS herbicide trapping efficiency (TE). Moreover, no study has evaluated TE among atrazine (6-chloro-N-ethyl-N'-isopropyl-1,3,5triazine-2,4-diam ine) and atrazine metabolites. This study was conducted to compare TE, M(inf), and M(as) among atrazine, diaminoatrazine (DA,6-chloro- 1,3,5triazine-2,4-diamine), deisopropylatrazine (DIA, 6-chloro-N-ethyl-1,3,5triazine-2,4-diamine), desethylatrazine (DEA, 6-chloro-N-isopropyl-1,3,5triazine-2,4-diamine), and hydroxyatrazine (HA,6-hydroxy-N-ethyl-N'-isopropyl- 1,3,5triazine-2,4-diamine) in a buffalograss VFS. Runoff was applied as a point source upslope of a 1- x 3-m microwatershed plot at a rate of 750 L h(-1). The point source was fortified at 0.1 micrograms mL(-1) atrazine, DA, DIA, DEA, and HA. After crossing the length of the plot, water samples were collected at 5-min intervals. Water samples were extracted by solid phase extraction and analyzed by high performance liquid chromatography (HPLC) photodiode array detection. During the 60-min simulation, TE was significantly greater for atrazine (22.2%) compared with atrazine metabolites (19.0%). Approximately 67 and 33% of the TE was attributed to M(inf) and M(as), respectively. These results demonstrate that herbicide adsorption to the VFS grass, grass thatch, and/or soil surface is an important retention mechanism, especially under saturated conditions. Values for M(as) were significantly higher for atrazine compared with atrazine's metabolites. The M(as) data indicate that atrazine was preferentially retained by the VFS grass, grass thatch, and/or soil surface compared with atrazine's metabolites.
The study was conducted to investigate the effects of water potential on bioavailability of the nano-unit 14C-cafenstrole, 14C-pretilachlor, 14C-benfuresate, 14C-simetryn and 14C-oxyfluorfen applied ...with or without dimepiperate or daimuron under various water potential conditions. The highest bioavailable concentration in soil solution (BCSS) was found at 60% soil moisture, while the lowest occurred at 50% soil moisture for soil-applied alone or in combination. All water potential conditions differed significantly from each other with variations in total bioavailable amount in soil solution (TBSS) when either dimepiperate or daimuron were added to the soil, and changes were directly proportional to variations in water potential. Across all treatments, TBSS at 80% soil moisture was three to four times greater than that at 50% soil moisture when applied alone or in combination with dimepiperate or daimuron. Cafenstrole and simetryn had distribution coefficient (Kd) values <64 ml g-1 and a TBSS ranging from 10 to 44 ng g-1 soil, regardless of water potential conditions applied alone or in combination. Pretilachlor and benfuresate had Kd values <15 ml g-1 and a TBSS range of 38 to 255 ng g-1 soil when applied with or without dimepiperate or daimuron.
The recent introduction of imidazolinone-tolerant rice varieties allow imazethapyr to be used in commercial rice. Little is known about imazethapyr photodegradation in the rice field. Laboratory ...studies were conducted to determine the direct and indirect photolysis rates for imazethapyr and to evaluate the photolysis of imazethapyr in three rice paddy waters. The reaction quantum yield (φ I) for imazethapyr was determined to be 0.023 ± 0.002, while the hydroxyl radical rate constant ( ) was 2.8 × 1013 M-1 h-1. These results show that imazethapyr is susceptible to both direct and indirect photolysis reactions in water. The results also show that imazethapyr photolysis in paddy water will be affected by turbidity because of its impact on the availability of sunlight to drive direct and indirect photolysis reactions.
Atrazine alone and atrazine plus glyphosate were added to soil to determine their effect on soil microbial activity as measured by C and N mineralization (Cmin, Nmin) and soil extractable atrazine ...without the use of radiolabelled isotopes. Atrazine alone was added to soils as a formulated product (Aatrex 4L) at a field rate of 2 x (94 mg kg super(-1)), 4 x (188 mg kg super(-1)), and 6 x (282 mg kg super(-1)) with an assumed soil penetration depth of 58 mm. Glyphosate, as Roundup Ultra, was added along with atrazine to soil in equal amounts bringing the total cumulative herbicide amount to 2 x (188 mg kg super(-1)), 4 x (376 mg kg super(-1)) and 6 x (564 mg kg super(-1)) assuming a 2-mm soil penetration depth for glyphosate. Atrazine plus glyphosate stimulated microbial activity more than atrazine alone. During 56 days of incubation, mineralized C and N were highly correlated (r super(2) = 0.93). In addition, the C and N added from the herbicides were correlated with the amounts of C and N mineralized above the controls and were highly correlated (r super(2) = 0.93 for Cmin and r super(2) = 0.97 for Nmin). Cmin was greatest during the first 7 days of incubation after herbicide application while Nmin was greatest during the day 14 to day 28 period indicating a possible substrate shift from glyphosate to atrazine since atrazine has more N relative to C than glyphosate. Atrazine extracted from soil at four time periods (day 7, 14, 28, and 56) showed similar degradation curves (DT sub(50) = 10.5 days) for the atrazine and atrazine-glyphosate treatments for all rates, with the exception of the 6 x rate after 14 days and the 2 x rate after 28 days of incubation where glyphosate appeared to slightly enhance the degradation of atrazine.
ABSTRACT
Herbicides applied to soils potentially affect soil microbial activity. The quantity and frequency of Roundup Ultra RU; N‐(phosphonomethyl)glycine; Monsanto, St. Louis, MO applications have ...escalated with the advent of Roundup‐tolerant crops. The objective of this study was to determine the effect of Roundup Ultra on soil microbial biomass and activity across a range of soils varying in fertility. The isoproplyamine salt of glyphosate was applied in the form of RU at a rate of 234 mg active ingredient kg−1 soil based on an assumed 2‐mm glyphosate–soil interaction depth. Roundup Ultra significantly stimulated soil microbial activity as measured by C and N mineralization, as well as soil microbial biomass. Cumulative C mineralization as well as mineralization rate increased above background levels for all soils tested with addition of RU. There were strong linear relationships between C and N mineralized, as well as between soil microbial C and N (r2 = 0.96 and 0.95, respectively). The slopes of the relationships with RU addition approximated three. Since the isopropylamine salt of glyphosate has a C to N ratio of 3:1, the data strongly suggest that RU was the direct cause of the enhanced microbial activity. An increase in the C mineralization rate occurred the first day following RU addition and continued for 14 d. Roundup Ultra appeared to be rapidly degraded by soil microbes regardless of soil type or organic matter content, even at high application rates, without adversely affecting microbial activity.
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