Evaluation of microbial inoculation and vegetation to enhance the dissipation of atrazine and metolachlor in soil

Four greenhouse studies were conducted to evaluate the effects of native prairie grasses and two pesticide-degrading bacteria to remediate atrazine and metolachlor in soils from agricultural dealerships (Alpha site soil, northwest Iowa, USA; Bravo site soil, central Iowa, USA). The Alpha soil contained a low population of atrazine-degrading microorganisms relative to the Bravo soil. Each soil freshly treated with atrazine or metolachlor was aged for a short or long period of time, respectively. An atrazine-degrading bacterium, Agrobacterium radiobacter strain J14a; a metolachlor-degrading bacterium, Pseudomonas fluorescens strain UA5-40; and a mixture of three native prairie grasses-big bluestem (Andropogon gerardii Vitman), yellow Indian grass (Sorghastrum nutans [L.] Nash), and switchgrass (Panicum virgatum L.)-were added to the soils after the soils were aged for long periods of time. The soils aged for short periods of time were treated with J14a, the prairie grasses, or both after aging. The J14a and the grasses significantly reduced the concentration of atrazine in Alpha soil when the soil was aged for a short period of time. However, these treatments had no statistically significant effect when the soil was aged for a long period of time or on atrazine in Bravo soil. Inoculation with UA5-40 did not enhance metolachlor dissipation in either soil, but vegetation did increase metolachlor dissipation. Our results indicate that the dissipation of atrazine by J14a is affected by the presence of indigenous atrazine-mineralizing microorganisms and probably by the bioavailability of atrazine in the soil.     

固相萃取–高效液相色谱法测定肉及肉制品中莠去津和西玛津

目的:探讨同时测定肉和肉制品中莠去津和西玛津的方法。方法:利用固相萃取处理方法,高效液相色谱仪进行分离,同时测定莠去津和西玛津。结果:莠去津和西玛津0.1 mg/ml～5.0 mg/ml范围内线性关系良好(r值均≥0.999),加标回收率为88%～103%,RSD为1.3%～7.8%,检出限分别为0.02μg/ml和0.04μg/ml。结论:用固相萃取-高效液相色谱法,同时测定肉和肉制品中莠去津和西玛津,操作简便,准确性和重现性均满足试验要求。     

ELISA and HPLC methods for atrazine and simazine determination in trophic chains samples

The aim of the research was to determine optimal conditions for atrazine determination in trophic chain samples by means of an antigen-coated tube enzyme-linked immunosorbent assay (ELISA). The ELISA method was used for analysis of a selection of samples and the results and method requirement compared with HPLC. The 2 h competitive ELISA showed a minimum detection limit of 0.05 ng mL⁻¹ and a dynamic range 0.1–2 ng mL⁻¹. Investigation of atrazine concentration in a selection of trophic chain samples indicated that the content of atrazine (μg kg⁻¹) in soil samples was 3.2–85.4, vegetable roots 32.9–148.9, green parts of plants 67.7–136.4, cereals 42.4–91.5 and samples of animal origin 1.3–8.4. The correlation between results obtained by HPLC and ELISA methods was 0.97. In addition, simazine content was determined by the HPLC method in which the detection limits were 0.2 μg g⁻¹ for atrazine and 0.3 μg g⁻¹ for simazine. The content (μg kg⁻¹) of simazine in soil samples was 13.5–15.5, in vegetables roots 29.5–93.7, in green parts of plants 34.6–72.6 and in cereals 158–189.The study demonstrates the utility and convenience of the simple, practical and cost-effective ELISA method in a non-immunoassay laboratory for the analysis of food and environmental samples. The method is ideal for the rapid screening of large numbers of samples in laboratories where access to HPLC facilities is limited or lacking. In addition the investigation demonstrates the presence of significant levels of atrazine and simazine in trophic chain samples collected from different areas of the region. As expected, the highest concentration of both herbicides was found in plants.     

Effect of sediment on the fate of metolachlor and atrazine in surface water

In aquatic environments, pesticides can partition between the dissolved phase and particulate phase depending on the type of suspended sediment present and the physical and chemical properties of the pesticides and water. Particulate matter and sediment can alter the bioavailability of contaminants to organisms and therefore influence their toxicity and availability for microbial degradation. Experiments were conducted to determine the degradation of atrazine (6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2.4-diamine) and metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methooxyprop-2-yl)acetamide) in surface water, and to evaluate the contribution of sediment to their dissipation. Sediment significantly reduced concentrations of atrazine and metolachlor in the surface water as a result of greater degradation, evident by increased quantities of degradates in the surface water, and the partitioning of the herbicide or herbicide degradates in the sediment. First-order 50% dissipation time (DT50) values for atrazine and metolachlor were 42 and 8 d in the surface water-sediment incubation systems, which were almost four times less than the DT50s calculated for the sediment-free systems. The results of this research illustrate the importance of sediment in the fate of pesticides in surface water. Greater comprehension of the role of sediment to sequester or influence degradation of agrichemicals in aquatic systems will provide a better understanding of the bioavailability and potential toxicity of these contaminants to aquatic organisms.     

Degradation and persistence of metolachlor in soil: effects of concentration,soil moisture,soil depth,and sterilization

The present study evaluated the influence of soil depth, soil moisture, and concentration on the persistence and degradation of metolachlor in soil. Greater percentages of metolachlor persisted in subsurface soils than in surface soil regardless of the soil moisture or initial herbicide concentration. Larger quantities of bound residues and extractable degradation products were found in the surface soils as a result of the increased soil sorption and biodegradation of metolachlor associated with the surface soil, which had more organic matter. Saturated soil favored the dissipation of metolachlor and the formation of soil-bound residues. Significantly greater quantities of a dechlorinated metabolite were measured in the saturated surface soil compared to the unsaturated soil. Mineralization of metolachlor to CO2 and volatilization of metolachlor or metolachlor degradates was minimal in surface and subsurface soils at both soil moistures and herbicide concentrations. Increased metolachlor concentrations did not inhibit microbial activity; however, the greater rate of application did result in the reduced percentage of applied [14C]metolachlor that was bound to surface or subsurface soil. A significant reduction in the quantity of extractable metolachlor degradates and unextractable soil-bound residues in sterile soil revealed the significance of biodegradation to the dissipation of metolachlor in soil.     

Effect of subsurface drainage on runoff losses of atrazine and metolachlor in Southern Louisiana

Joint Contribution from the U.S. Dept. of Agriculture, ARS and Louisiana Agricultural Experiment Station, Louisiana State University     

Effect of simulated sunlight on atrazine and metolachlor toxicity of surface waters.

Atrazine and metolachlor are the two most widely used herbicides in the United States; through non-point-source runoff both herbicides may cause toxicity to aquatic organisms. Toxicity changes were measured for atrazine and metolachlor in surface waters after exposure to simulated sunlight (0, 20, and 40 kJ/m2) using a Xenon Weather-Ometer. A Microtox toxicity test, using the marine luminescent bacterium Vibrio fischeri, was conducted on deionized, river, and bay water samples mixed with atrazine or metolachlor herbicide (12 mg/liter) after exposure to simulated sunlight. Microtox test (EC50%) results demonstrated that the toxicity decreased with increasing light intensity for both herbicides in river and bay water. These results also indicate that the toxicity of the bay water, with high concentrations of organic and suspended matter, was reduced, for both herbicides, compared with the toxicity of the river water, possibly through photodegradation of pesticides.     

Comparision of atrazine and metolachlor affinity for bermudagrass ( Cynodon dactylon L.) and two soils

Given that bermudagrass is being used as one of the grasses of choice in grass filter strip plantings as an acceptable grass to reduce off-target losses of herbicides, laboratory experiments were conducted to determine and compare the relative affinity of bermudagrass, a Weswood soil, and a Houston Black soil for atrazine (6-chloro- N-ethyl- N-isopropyl-1,3,5-triazine-2,4-diamine) and metolachlor (2-chloro- N-(2-ethyl-6-methylphenyl)- N-(2-methoxy-1-methyethyl) acetamide). Experiments were also conducted to determine if the presence of one herbicide affects the relative affinity of the other compound to these sorbents. The experiments were carried out using radiolabeled atrazine and metolachlor. Results were reported in disintegrations min(-1) (dpms) and converted to K(d) to determine and compare relative affinity. Both K(d) values for relative affinity of atrazine (86.2) and metolachlor (131.5) to bermudagrass were significantly greater than those of the two soils, Weswood (atrazine, 20.0 and metolachlor, 28.4) and Houston Black (atrazine, 35.8 and metolachlor, 33.5). The two compounds were also mixed together to mimic the common practice of applying atrazine and metolachlor simultaneously as a tank mix. Relative affinity of atrazine to any of the sorbents was not affected by the presence of metolachlor. Similarly, when comparing the affinity of metolachlor alone to that of metolachlor with atrazine present in the solution, no significant differences were observed for bermudagrass or the Weswood soil. However, on the Houston Black soil, the presence of atrazine significantly increased the soil's affinity for metolachlor.     

Surface and subsurface transport of atrazine and alachlor from a Brookston clay loam under continuous corn production

Three tillage practices, conventional, zero, and ridge tillage, were compared for water quality in the first three years of tillage establishment. The tillage treatments were on a poorly drained, Brookston clay loam soil of <1% slope, tiled to a depth of 95 cm. Tillage had no significant effect on runoff volume, distribution between surface and subsurface runoff, herbicide concentration or herbicide loss. The volume of tile discharge exceeded the volume of surface runoff in all years. Triazine losses varied from 1.2 to 7.7% of atrazine applied (1.8 kg/ha) while alachlor losses were less than 0.5% of application (2.5 kg/ha). Herbicide losses were greatest when runoff producing events occurred soon after herbicide application. The dealkylated metabolite, de-ethyl atrazine, was detected in the runoff water at low concentrations throughout the study period consistent with its occurrence as an intermediate metabolite. Herbicide concentrations were higher in surface runoff water than subsurface runoff water which resulted in a greater proportion of herbicide loss from the surface. In most cases more atrazine was lost during the growing season that at other times, however, in drier years losses after harvest may account for a significant proportion of total loss. In all years, alachlor losses occurred during the growing season, because of its shorter persistence in soil relative to atrazine.     

Sorption of acetochlor, S-metolachlor, and atrazine in surface and subsurface soil horizons of Argentina

Understanding herbicide sorption within soil profiles is the first step to predicting their behavior and leaching potential. Laboratory studies were conducted to determine the influence of surface and subsurface soil properties on acetochlor, atrazine, and S-metolachlor sorption. Soil samples were taken from horizons A, B, and C of two loamy soils of the humid pampas of Argentina under no-till management; horizon A was divided into two layers, A(0) (0-5 cm) and A(1) (5 cm to the full thickness of an A horizon). Sorption isotherms were determined from each sampled horizon using the batch equilibrium method and seven concentrations (0, 0.1, 0.5, 2.0, 5.0, 10.0, and 20.0 mg?L(-1)). Sorption affinity of herbicides was approximated by the Freundlich equation. The sorption strength K(f) (mg(1 - 1/n) kg(-1) L(1/n) ) over the soils and horizons studied followed the order S-metolachlor (16.51-29.19)?>?atrazine (4.85-12.34) ≥ acetochlor (5.17-11.97), which was closely related to the hydrophobicity of herbicides expressed as octanol-water partition coefficient (K(OW) ). The K(f) values of the three herbicides were positively correlated with soil organic carbon, with a significance of p < 0.01. Values of K(f) for the three herbicides decreased with depth in the two soils, indicating greater sorption onto surficial soil horizons and possibly a delayed transport toward subsurface soils and subsequent pollution of groundwater.     

Mineralization of aged atrazine,terbuthylazine, 2,4-D,and mecoprop in soil and aquifer sediment

The effect of aging of the herbicides atrazine, terbuthylazine, 2,4-D, and mecoprop on their bioavailability to degrading microorganisms was studied in soil and aquifer sediment. 14C-ring-labeled herbicide (2.5 mg/kg) was added to sterilized soil or aquifer sediment and stored at 10 degrees C for up to 103 d before inoculation with either the atrazine and terbuthylazine-degrading Pseudomonas sp. strain ADP (atrazine-degrading Pseudomonas) or an enriched culture able to mineralize 2,4-D and mecoprop. The initial mineralization rate and recovery of 14CO2 after 62 to 113 d of incubation were used as measures of the availability of the compounds to the microorganisms. Aging in soil reduced the initial mineralization of atrazine. Thus, only 17% of the added 14C-atrazine had been mineralized after 21 h of incubation when aged for 88 d as compared with 33% when the atrazine had been aged for 1 d. 14CO2 recovery was only 58% after 88 d of aging as compared with 81% when aged for 1 d. A similar effect of aging was seen with terbuthylazine. With 2,4-D, the effect of aging in soil on mineralization by the enriched culture was much smaller. Aging had no effect on mineralization of mecoprop in soil or on mineralization of any of the herbicides in aquifer sediment.