Diffuse atrazine pollution in German aquifers

Until its prohibition in Germany in 1991, atrazine was the mostfrequently applied herbicide in maize cultivation. Moreover, it was used in orchards andvineyards and as a total herbicide on non-cultivated grounds (railways, factory grounds).Later on, atrazine was substituted mainly by terbutylazine. Terbutylazine and terbutrynare the only s-triazines presently permitted in Germany. Nevertheless, atrazine and itsmetabolite desethylatrazine are by far the most abundant herbicides detected in near surfacegroundwater. This might be due to wash-outs from the pools of atrazine and its metabolitesfrom the soil into the groundwater or continuing illegal applications. Samples takenfrom maize fields in 1994 showed that 6.2% of 471 fields tested were treated with atrazinedespite the prohibition of its use. Nevertheless, the overall trend is in fact a slow decreasein atrazine concentrations where it is detected in groundwater and, simultaneously often aslight increase in desethylatrazine concentrations. But this is not the case forall sampling points, and increasing concentrations in several aquifers are observedas well. Factors governing the adsorption, degradation, persistence and the possible transferinto the aquifer and the current situation concerning atrazine occurrence in German aquiferswill be discussed.     

Chemical Fate and Transport of Atrazine in Soil Gravel Materials at Agrichemical Distribution Facilities

The gravel commonly used to cover parking lots and roadways at retail agrichemical facilities may contain relatively large concentrations of pesticides that resulted from past management problems. These pesticides may threaten groundwater quality. Previous studies, however, suggested that the pesticides had not moved from the gravel in several sample profiles. Excavations at a closed facility revealed tremendous variability in pesticide distribution within the site. Pesticides were present below the gravel in two profiles, but the mechanism(s) for their movement were not clear. The objectives of this study were to investigate how the physical and chemical properties of the gravel influence the environmental fate of atrazine. All of the gravel samples collected and characterized contained atrazine and sufficient organic C to adsorb significant amounts of atrazine, thus retarding its movement through the gravel. Laboratory column leaching experiments, however, suggested that much of the atrazine should leach from the gravel within a year or two. A field-scale test plot was constructed to study how atrazine moves through the gravel under controlled conditions. Atrazine was “spilled” in the test plot. Atrazine moved from the gravel both vertically and horizontally. It appears that formulated product spilled on gravel will leach. A single discrete spill can give rise to phantom spills whose occurrence and distribution is not related to any specific pesticide-management practice. The apparent lack of atrazine leaching from gravel appeared to be a transient phenomenon and/or the result of sampling limitations in previous studies. The contaminated gravel clearly poses a risk to groundwater quality.     

Atrazine,desethylatrazine (DEA) and desisopropylatrazine (DIA) degradation by Pleurotus ostreatus INCQS 40310

Abstract

Atrazine is the most common herbicide applied in crops of economic relevance, such as sugar cane, soybean, and corn. Atrazine and its derivatives desethylatrazine (DEA) and desisopropylatrazine (DIA) are toxic to the environment, affecting animal and human health. Thus, this study aimed to evaluate the degradation of atrazine and its derivatives by the fungus Pleurotus ostreatus INCQS 40310, as well as the potential of the enzymes involved in this process. P. ostreatus INCQS 40310 was able to degrade atrazine (82%), DEA (71%), and DIA (56%) over 22?days of fungal cultivation. Proteomic analysis indicated the participation of hydrolases and peroxidases during the degradation process. Additionally, resting cells of the fungus were tested to verify the action of intracellular enzymes in the degradation process, suggesting the participation of cytochrome P450 enzymatic complex. Resting cells experiments promoted the degradation of 50% of atrazine, 36% of DIA, 30% of DEA. So far, this is the first work evaluating the biodegradation of DEA and DIA by fungus.     

Degradation of contrasting pesticides by white rot fungi and its relationship with ligninolytic potential

The capacity of nine species of white rot fungus from a variety of basidiomycete orders to degrade contrasting mono-aromatic pesticides was investigated. There was no relationship between degradation of the dye Poly R-478, a presumptive test for ligninolytic potential, and degradation of the highly available pesticides diuron, metalaxyl, atrazine or terbuthylazine in liquid culture. However, there were significant positive correlations between the rates of degradation of the different pesticides. Greatest degradation of all the pesticides was achieved by Coriolus versicolor, Hypholoma fasciculare and Stereum hirsutum. After 42 days, maximum degradation of diuron, atrazine and terbuthylazine was above 86%, but for metalaxyl less than 44%. When grown in the organic matrix of an on-farm "biobed" pesticide remediation system, relative degradation rates of the highly available pesticides by C. versicolor, H. fasciculare and S. hirsutum showed some differences to those in liquid culture. While H. fasciculare and C. versicolor were able to degrade about a third of the poorly available compound chlorpyrifos in biobed matrix after 42 days, S. hirsutum, which was the most effective degrader of the available pesticides, showed little capacity to degrade the compound.     

An improved high-performance liquid chromatography–tandem mass spectrometric method to measure atrazine and its metabolites in human urine

We report an improved solid-phase extraction-high-performance liquid chromatography–tandem mass spectrometry method with isotope dilution quantification to measure seven atrazine metabolites in urine. The metabolites measured were hydroxyatrazine (HA), diaminochloroatrazine (DACT), desisopropylatrazine (DIA), desethylatrazine (DEA), desethylatrazine mercapturate (DEAM), atrazine mercapturate (ATZM), and atrazine (ATZ). Using offline mixed-mode reversed-phase/cation-exchange solid-phase extraction dramatically increased recovery and sensitivity by reducing the influence of matrix components during separation and analysis. DACT extraction recovery improved to greater than 80% while the other analytes had similar extraction efficiencies as previously observed. Limits of detection were lower than our previous method (0.05–0.19 ng/mL) with relative standard deviations less than 10%. The total runtime was shorter (18 min) than the previous on-line method, thus it is suitable for large-scale sample analyses. We increased the throughput of our method twofold by using the newer extraction technique.     

Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l^?1 of atrazine in less than 72 h of incubation at the rate of 0.42 mg l^?1 h^?1 and 0.35 mg l^?1 h^?1, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g^?1 of soil compared with 480 mg g^?1 of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.     

阿特拉津及其降解菌的使用对土壤微生物群落的影响

比较了阿特拉津及降解菌株BTAH1的使用对土壤微生物的影响.结果表明,在实验周期内阿特拉津对土壤微生物的代谢作用有较明显的刺激作用,与空白土壤(未施用阿特拉津和降解菌)相比,对照土壤(施用50mg·kg^-1土阿特拉津)呼吸强度显著增加,且土壤中的阿特拉津浓度对土壤NH₄⁺-N和NO₃^--N浓度的影响显著.降解菌BTAH1可在1周内降解土壤中98%以上的阿特拉津,从而使土壤呼吸强度有所下降,土壤中NH₄⁺-N和NO₃^--N的浓度基本与空白土壤持平,对微生物量C和微生物量N影响不显著;放线菌和真菌数量也基本与空白持平,细菌数量较高.对土壤细菌的16SrDNA文库的ARDRA分析发现,阿特拉津及其降解菌的使用对土壤细菌群落结构有一定程度的影响,阿特拉津的使用会降低细菌群落的多样性,而降解菌的使用会恢复土壤细菌的多样性.     

Toxicity of a dichlorvos containing insecticide formulation and an atrazine containing herbicide formulation in chicken embryos after individual administration

A 50% dichlorvos containing insecticide formulation (Unifosz 50 EC) and a 50% atrazine containing herbicide formulation (Hungazin PK 50 WP) were studied in chicken embryos after administration as single compounds. Applied concentrations of dichlorvos were 0.1% (corresponding to the plant protection practice), 0.05%, 0.02%, 0.01%. Applied concentrations of atrazine were 0.66% (corresponding to the plant protection practice), 0.33%, 0.132%, 0.066%. The test materials were injected directly into the air-chamber of eggs on day 0 of the hatching period and evaulation was carried out on day 19 of incubation. The chicken embryos were examined for the following: rate of embryo mortality, body mass, type of developmental anomalies. After the single administrations of dichlorvos containing insecticide formulation and atrazine containing herbicide formulation on day 0 of incubation, the average body weight of chicken embryos significantly did not decrease as compared to the control. After the individual administrations of pesticides the incidence of developmental anomalies was sporadic. The embryonic mortality markedly increased at the highest concentrations of pesticides. The rate of embrio mortality were 61% (dichlorvos insecticide containing formulation) and 52% (atrazine containing herbicide formulation). In summary, the 50% dichlorvos containing insecide formulation (Unifosz 50 EC) and the 50% atrazine containing herbicide formulation (Hungazin PK 50 WP) were toxic to the developing chicken embryos at the highest concentration in our study. The toxic effect was expressed in the high rate of embrio mortality.     

Effects of biochar amendment on the sorption and degradation of atrazine in different soils

ABSTRACT

Sugarcane top-derived biochar was added to an alluvial soil, a moist soil and a paddy soil at the rate of 0.2% and 0.5% (w/w). After the addition of 0.2% and 0.5% biochar, the sorption coefficients (K_d) of atrazine (Ce = 10 mg L^?1) were increased by 26.97% and 79.58%, respectively, in the moist soil with a low level of total organic carbon (TOC), while it increased by 31.43% and 60.06%, respectively, in the paddy soil with a high TOC content. The half-time persistence values of atrazine in the alluvial soil, moist soil and paddy soil were 28.18, 23.74 and 39.84 d, respectively. In the 0.2% biochar amended soils, the corresponding half-times of atrazine for the alluvial soil, moist soil and paddy soil were extended by 10.33, 11.81 and 1.42 d, and they were prolonged by 16.83, 17.52 and 14.74 d, respectively, in the 0.5% biochar amended soils. Atrazine degradation products (deisopropylatrazine and desethylatrazine) decreased after they accumulated to 3.2 and 1 mg kg^?1, respectively. Generally, increasing sorption was accompanied by decreasing degradation of atrazine which is found in biochar-amended soils.     

Bacterial endophyte-enhanced phytoremediation of the organochlorine herbicide 2,4-dichlorophenoxyacetic acid

2,4-Dichlorophenoxyacetic acid is a selective systemic herbicide for the control of broad-leaved weeds, which is widely used throughout the world. The persistence of its residues and its potential to migrate in the soil make it necessary to reduce its concentrations in contaminated soil and groundwater. The nature of this compound makes it particularly toxic to the broad-leaved plants, such as the poplar (Populus) and willow (Salix), which are often used in phytoremediation projects. We describe the inoculation of a model plant, the pea (Pisum sativum), with a genetically tagged bacterial endophyte that naturally possesses the ability to degrade 2,4-dichlorophenoxyacetic acid. The results showed that this strain actively colonized inoculated plants internally (and in the rhizosphere). Inoculated plants showed a higher capacity for 2,4-dichlorophenoxyacetic acid removal from soil and showed no 2,4-dichlorophenoxyacetic acid accumulation in their aerial tissues. This demonstrates the usefulness of bacterial endophytes to enhance the phytoremediation of herbicide-contaminated substrates and reduce levels of toxic herbicide residues in crop plants.     

Atrazine movement in soil: Comparison of field observations and PRZM simulations

The predictive capability of the pesticide root zone model (PRZM) was investigated for herbicide atrazine [2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine] in corn production under no‐till (NT) and conventional‐till (CT) management practices. Simulation values of atrazine residues obtained using our site‐specific soil and environmental data were compared with the actual values measured in soil samples taken from the root zones of the NT and CT plots during three growing seasons: 1986, 1987, and 1988. The mean concentration of atrazine in soil at each sampling time and depth after application, for each tillage treatment plot (NT or CT), was estimated based on the type of distribution (i.e., normal or lognormal). Overall, the PRZMs simulated concentrations for the top 10 cm of soil compared well with the atrazine residues measured in the CT plots, but overestimated measurements in NT plots. For example, in 1986 the mean atrazine concentration measured in soil samples taken 6 d after application from the top 10 cm of CT plots was 548 μg/kg (S.E. 198 μg/kg), and the PRZM predicted value was 690 μg/kg. In contrast, the mean atrazine concentration for the same soil depth increment in NT plots was 385 μg/kg (S.E. 154 μg/kg), with a PRZM predicted value of 674 μg/kg. Although the PRZM prediction was closer to the measured mean for atrazine concentrations in the top 10 cm of the CT system, the model did not transport atrazine to the lower soil depths, as the actual values have indicated in all 3 years. The results of this model comparison, especially for the lower soil depths (20 to 30 cm) in the NT practice, indicated that the PRZM model does not account for the preferential transport of, and, consequently, underestimates the atrazine residue levels in the lower soil profile under NT management systems.     

Evidence of atrazine mineralization in a soil from the Nile Delta: Isolation of Arthrobacter sp. TES6, an atrazine-degrading strain

The s-triazine herbicide atrazine was rapidly mineralized (i.e., about 60% of ¹⁴C-ring-labelled atrazine released as ¹⁴CO₂ within 21 days) by an agricultural soil from the Nile Delta (Egypt) that had been cropped with corn and periodically treated with this herbicide. Seven strains able to degrade atrazine were isolated by enrichment cultures of this soil. DNA fingerprint and phylogenetic studies based on 16S rRNA analysis showed that the seven strains were identical and belonged to the phylogeny of the genus Arthrobacter (99% similarity with Arthrobacter sp. AD38, EU710554). One strain, designated Arthrobacter sp. strain TES6, degraded atrazine and mineralized the ¹⁴C-chain-labelled atrazine. However, it was unable to mineralize the ¹⁴C-ring-labelled atrazine. Atrazine biodegradation ended in a metabolite that co-eluted with cyanuric acid in HPLC. This was consistent with its atrazine-degrading genetic potential, shown to be dependent on the trzN, atzB, and atzC gene combination. Southern blot analysis revealed that the three genes were located on a large plasmid of about 175 kb and clustered on a 22-kb SmaI fragment. These results reveal for the first time the adaptation of a North African agricultural soil to atrazine mineralization and raise interesting questions about the pandemic dispersion of the trzN, atzBC genes among atrazine-degrading bacteria worldwide.     

Impact of roots on ground water quality

Preferential flow is perhaps the major chemical transport process influencing the rapid and typically unexpected movement of agricultural chemicals to ground water. Plant roots are a major contributor to preferential flow mechanics as they form spatial voids which can be used as preferential flow pathways. Chemical transport of atrazine, deethylatrazine, and bromide solutions concentrations under tilled and no-tilled corn fields was evaluated below the active root zone. Additionally, the impact of roots on flow pathways was visualized using a soluble dye (Brilliant Blue FCF). Pictures of the dye-stained pattern were subsequently digitized to determine the cross-sectional area used for transport as a function of depth. Bromide transit times through the field soils were not influenced by tillage practice, whereas atrazine transport was strongly influenced by tillage practice. Under no-till field conditions, atrazine was rarely detected but deethylatrazine concentrations were greater than those observed under tilled field conditions. Visual observation indicated that the dye under no-tillage was more predominant in the corn row, indicative of transport through void root channels. No-tillage practices may decrease the likelihood of ground water contamination through leaching due to the formation of stable root channels where an organic carbon source and microbial population are preferentially located to degrade pesticides.     

The impact of two pesticides on olfactory-mediated endocrine function in mature male Atlantic salmon (Salmo salar L.) parr

Short-term exposure of the olfactory epithelium of mature male Atlantic salmon parr to either the pesticide simazine (concentrations 1.0 and 2.0 microg l(-1)) or the pesticide atrazine (concentration 1.0 microg l(-1)) significantly reduced the olfactory response to the female priming pheromone, prostaglandin F(2alpha). In addition, the reproductive priming effect of the pheromone on the levels of expressible milt was also reduced after exposure to the individual pesticides (simazine 0.1, 0.5, 1.0 and 2.0 microg l(-1) and atrazine 0.5 and 2.0 microg l(-1)). When the olfactory epithelium was exposed to a mixture of simazine and atrazine, (concentrations of 0.5:0.5 and 1.0:1.0 microg l(-1)), there was no significant reduction in the olfactory response when compared to the single pesticides at equivalent concentrations. In addition, exposure to a mixture of simazine and atrazine had no synergistic effect on the priming response, and plasma levels of testosterone, 11-ketotestosterone and 17,20beta-dihydroxy-4-pregnen-3-one were similar in the groups of male parr exposed to the individual pesticides. Although the levels of expressible milt were reduced in all groups, there were no significant differences between the different pesticide treatments. The results of the study suggest that the two s-triazine pesticides have an additive and not a synergistic impact on olfactory-mediated endocrine function in mature male salmon parr.     

Growth Response of Coyote Willow (Salix exigua) Cuttings in Relation to Alluvial Soil Texture and Water Availability

A common approach to re‐establishing cottonwood–willow habitat along regulated rivers is through installing dormant, rootless cuttings, yet there is little published information exploring floodplain characteristics that optimize growth of southwestern riparian willows planted in this manner. The goal of this project was to evaluate relationships between growth attributes of Salix exigua and soil texture and soil water availability. Monitoring plots were established in five willow swales planted with dormant S. exigua cuttings along the banks of the Middle Rio Grande in central New Mexico. Data analysis revealed significantly higher aerial cover, height, and stem density for S. exigua plants installed in plots with intermediate levels (15–25%) of fine textured soils distributed through the soil profile. Similar relationships were found in relation to soil water availability. Regression analysis of percent fines and available water at different depth increments provided limited explanation of variability in willow growth attributes at different plots. Findings indicate that S. exigua plants established from cuttings can achieve heights and aerial cover values similar to naturally established willow bars if the floodplain soil profile contains intermediate levels of fine textured soils and the maximum depth to groundwater is within 1.5 m of the ground surface. Where sites are dominated by coarse sand, S. exigua growth may be improved if maximum depth to groundwater is within 1 m of the ground surface.     

Effects of Propagule Phenology (Non-Dormant Versus Dormant) and Planting System (Vertical Versus Horizontal) on Growth Performance of Willow Clones Grown Under Different Weeding Regimes

To assess the effects of propagule phenology and planting system on growth performance of three willow clones grown under different weeding regimes, a field experiment was performed in central Sweden 2014–2016. Freshly harvested (non-dormant) and cold-stored (dormant) cuttings (planted vertically) and billets (planted horizontally) from willow clones Tordis, Tora, and Jorr were planted in weeded and in unweeded plots. Sprouting was significantly higher for willows grown from non-dormant (74%) than dormant (58%) propagules and for cuttings (84%) compared with billets (42%). Survival was higher for willows from non-dormant propagules in weeded (71%) compared with unweeded (63%) plots, willows from dormant propagules in weeded (72%) compared with unweeded (60%) plots, and for willows from cuttings (93%) compared with billets (39%). During 2014–2016, aboveground biomass production was significantly higher for willows from cuttings (11.71 t DW ha^?1) than from billets (6.13 t DW ha^?1), grown in weeded (15.29 t DW ha^?1) than in unweeded (2.55 t DW ha^?1) plots, and differed significantly among willow clones (11.48, 9.27, and 6.01 t DW ha^?1 for Tordis, Tora, and Jorr, respectively). In this study, (i) planting with cold-stored and freshly harvested willow propagules was equally successful and therefore cold storage could be potentially avoided and replaced with planting of freshly harvested propagules in early spring; however, (ii) in terms of measured growth performance parameters, willows grown from cuttings performed better than grown from billets; and (iii) weed competition significantly reduced survival and aboveground biomass production, confirming that weed control during establishment of willow is crucial.     

Biological Remediation of Groundwater Containing Both Nitrate and Atrazine

Due to its high usage, mobility, and recalcitrant nature, atrazine is a common groundwater contaminant. Moreover, groundwaters that are contaminated with atrazine often contain nitrate as well. Nitrate interferes with the biological degradation of atrazine and makes it more difficult to use in situ biological methods to remediate atrazine contaminated groundwater. To solve this problem we used two reactors in sequence as models of in situ biobarriers; the first was a vegetable-oil-based denitrifying biobarrier and the second an aerobic reactor that oxygenated the denitrifying reactor’s effluent. The reactors were inoculated with an atrazine-degrading microbial consortium and supplied with water containing 5 mg l⁻¹ nitrate–N and 3 mg l⁻¹ atrazine. Our hypothesis was that the denitrifying barrier would remove nitrate from the flowing water and that the downstream reaction would remove atrazine. Our hypothesis proved correct; the two reactor system removed 99.9% of the atrazine during the final 30 weeks of the study. The denitrifying barrier removed ~98% of the nitrate and ~30% of the atrazine while the aerobic reactor removed ~70% of the initial atrazine. The system continued to work when the amount of nitrate–N in the influent water was increased to 50 mg l⁻¹. A mercury poisoning study blocked the degradation of atrazine indicating that biological processes were involved. An in situ denitrifying barrier coupled with an air injection system or other oxygenation process might be used to remove both nitrate and atrazine from contaminated groundwater or to protect groundwater from an atrazine spill.     

Field-scale remediation of atrazine-contaminated soil using recombinant Escherichia coli expressing atrazine chlorohydrolase

We performed the first field-scale atrazine remediation study in the United States using chemically killed, recombinant organisms. This field study compared biostimulation methods for enhancing atrazine degradation with a novel bioaugmentation protocol using a killed and stabilized whole-cell suspension of recombinant Escherichia coli engineered to overproduce atrazine chlorohyrolase, AtzA. AtzA dechlorinates atrazine, producing non-toxic and non-phytotoxic hydroxyatrazine. Soil contaminated by an accidental spill of atrazine (up to 29 000 p.p.m.) supported significant populations of indigenous microorganisms capable of atrazine catabolism. Laboratory experiments indicated that supplementing soil with carbon inhibited atrazine biodegradation, but inorganic phosphate stimulated atrazine biodegradation. A subsequent field-scale study consisting of nine (0.75 m³) treatment plots was designed to test four treatment protocols in triplicate. Control plots contained moistened soil; biostimulation plots received 300 p.p.m. phosphate; bioaugmentation plots received 0.5% (w/w) killed, recombinant E. coli cells encapsulating AtzA; and combination plots received phosphate plus the enzyme-containing cells. After 8 weeks, atrazine levels declined 52% in plots containing killed recombinant E. coli cells, and 77% in combination plots. In contrast, atrazine levels in control and biostimulation plots did not decline significantly. These data indicate that genetically engineered bacteria overexpressing catabolic genes significantly increased degradation in this soil heavily contaminated with atrazine.     

Organic Amendments to Enhance Atrazine and Metamitron Degradation in Two Contaminated Soils with Contrasting Textures

Among all types of xenobiotics, pesticides such as herbicides play a significant role in soil and water pollution due to their wide usage all over the world. This study addresses the ability of organic amendments to enhance atrazine and metamitron degradation in two herbicide-contaminated soils with contrasting textures under laboratory conditions. Soil samples were collected from surface soils with textures of sandy loam and silty clay, from northeastern Iran. Initial concentration of herbicides was 50 mg · kg^{? 1} soil. Contaminated soil samples were treated with manure, compost and vermicompost at rates of 0, 0.5, and 2% (w/w). Residual concentrations of atrazine and metamitron were determined by HPLC at the end of incubation periods of 20, 40, and 60 days. Residual concentrations of atrazine were 46.5, 38.9, and 36.2 mg · kg^{? 1} after 20, 40, and 60 days incubation, respectively. Residual metamitron concentrations were clearly lower than atrazine. After 20, 40, and 60 days, concentrations of metamitron were 2.9, 1.0, and 0.6 mg · kg^{? 1}, respectively. Organic amendments at the rates of 0.5 and 2% showed similar effects on the enhancement of herbicide degradation in soils. However, no statistically significant effect was observed among types of organic amendments (α = 0.05). Degradation was affected by soil textures. Residual concentrations of herbicides were higher in sandy loam than in silty clay soil.