Herbicide Concentrations In Solution Research Articles

Rice and wheat straw ashes: Characterization and modeling of pretilachlor sorption kinetics and adsorption isotherm

The rice straw ash (RSA) and wheat straw ash (WSA) were explored as low cost adsorbent for pretilachlor removal from water. The ashes were characterized and sorption behavior of pretilachlor was evaluated. Kinetics study suggested that the modified Elovich model best explained the pretilachlor sorption on both the ashes. The adsorption data were analyzed using 2-, 3- and 4-parameter models and nine error functions were used to compute the best fit isotherm by nonlinear regression analysis. The pretilachlor was more sorbed onto the RSA (22.0–92.2%) than the WSA (11.4–61.4%) and percent adsorption decreased with increase in the herbicide concentration in solution. Isotherm model optimization analysis suggested that the Freundlich and the Temkin isotherms were the best models to predict the pretilachlor adsorption onto the RSA and the WSA. The error analysis suggested that the reciprocal of the observed squared (ROS) and the reciprocal of the predicted squared (RPS) error functions provided the best determination of the adsorption constants for the Freundlich and the Temkin isotherms, respectively. The RSA, which exhibited higher pretilachlor sorption potential, can be utilized as low cost adsorbent for pesticide removal from contaminated water.

Effect of deashing on physico-chemical properties of wheat and rice straw biochars and potential sorption of pyrazosulfuron-ethyl

Wheat (WBC) and rice straw biochars (RBC) prepared at 400 and 600 °C and their deashed counterparts were characterized for their physico-chemical properties using CHN analysis, Brunauer–Emmett–Teller (BET), X-ray fluorescence (XRF), scanning electron microscopy (SEM), 13C-nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) techniques. Pyrazosulfuron-ethyl sorption data on normal and deashed biochars could be well fitted to the Freundlich model. The characteristics of biochars and their adsorption capacities for pyrazosulfuron-ethyl were affected by the pyrolysis temperature and nature of feedstock. Rice biochars had higher sorption capacities than the wheat biochars. Deashing of biochars further enhanced their herbicide adsorption potential by a factor of 2–3. Sorption of herbicide on both normal and deashed biochars was concentration dependent (1/n < 1) and decreased with increase in the herbicide concentration in solution, indicating a saturation of sorption sites. The non-linearity of the isotherms increased with increasing pyrolysis temperature and deashing. Furthermore, adsorption of pyrazosulfuron-ethyl was affected by the pH, surface area and pore volume of biochars. Results of this study suggested that the mineral fraction of biochars significantly affected pyrazosulfuron-ethyl sorption.

Adsorption and Leaching Behaviour of Bispyribac-Sodium in Soils

Adsorption-desorption of the herbicide bispyribac-sodium was studied in four Indian soil types. Bispyribac-sodium was poorly adsorbed in the four soils and adsorption decreased with an increase in the herbicide concentration in solution. Freundlich adsorption coefficient (Kf) values for bispyribac-sodium ranged between 0.37 and 0.87. Slope (1/n) values varied from 0.2 to 0.31 suggesting that bispyribac-sodium adsorption was highly dependent on its initial concentration in solution. Bispyribac-sodium adsorption showed a positive correlation with soil pH (r = 0.809) and clay content (r = 0.699) while no correlation was observed with the organic carbon (r = 0.063) content. Sorbed herbicide was completely desorbed during a single desorption step suggesting that the herbicide was bound by weak adsorptive forces. Leaching studies of herbicide in soil 1 packed column indicated complete loss of soil applied herbicide under a simulated rainfall equivalent to 162 mm.

Towards the D1 Protein Application for the Development of Sensors Specific for Herbicides

One of the most widespread groups of pesticides are the triazine herbicides. These substances inhibit photosynthesis by blocking electron transport in plant chloroplasts. The possibility of the chloroplast D1 protein application for determination of the herbicide concentration in solution was investigated. Potentiometry and cyclic voltammetry have been selected to monitor specific interaction between the D1 protein and herbicide. It was found that membranes with well-defined structure, like Langmuir-Blongett film are more suitable for sensitive sensor construction than cross-linked membranes. After addition of atrazine, the current through these multilayers appeared to increase 5 fold. The effect was found to be fast and irreversible. It has been proposed that the toxic action of herbicides on chloroplasts, traditionally interpreted by inhibition of electron flow along the chloroplast membrane, may also be the result of the thylakoid membrane depolarization.

Herbicide Retention by Vegetative Buffer Strips from Runoff under Natural Rainfall

Effectiveness of vegetative buffer strips for herbicide retention from agricultural runoff was evaluated in a two-year natural rainfall study. A source area of 0.41 ha (mainly Canisteo silty clay loam soil), having an average slope of 3%, was fall chisel-plowed, spring disked, and planted to corn. Three herbicides (atrazine, metolachlor, and cyanazine) were applied to the source area in each spring. Six vegetative buffer strips, 1.52 m wide 20.12 m long, were isolated with metal borders downslope of the source area in a well established bromegrass (Bromus inermis) waterway. These strips provided for three replications of two drainage to buffer area ratio treatments of 15:1 and 30:1. Herbicide retention was dependent on the antecedent moisture conditions of the strips. These retentions ranged from 11 to 100% for atrazine, 16 to 100% for metolachlor, and 8 to 100% for cyanazine. Herbicide retention by the buffer strips for the two treatments were not significantly different for the observed storm events. Herbicide concentrations in solution in outflow from the strips were less than the inflow concentrations for all the three herbicides. Infiltration was the key process for herbicide retention by the buffer strips, although there was some adsorption to in-place soil and/or vegetation. Metolachlor concentrations in sediment increased in outflow for the two treatments; however, the opposite was true for atrazine and cyanazine. Herbicide retention by sediment deposition in the strip represented about 5% of the total herbicide retention by the buffer strips. The buffer strips were found to have high percent sediment retention, ranging from 40 to 100%; thus, the strips would be more effective for retaining strongly adsorbed herbicides.

The effect of chlorsulfuron and diclofop-methyl on the uptake and utilization of zinc by wheat

The effects of the herbicides Hoegrass and Glean on the uptake of zinc by wheat were examined in two glasshouse experiments. Application of the active ingredients chlorsulfuron and diclofop-methyl decreased shoot weight, root weight and zinc uptake similarly to the herbicides Glean and Hoegrass. It can therefore be concluded that the effects of Hoegrass and Glean on zinc uptake in wheat can be attributed to these active ingredients and not to other constituents of the commercial herbicide preparations. Effects of chlorsulfuron on zinc uptake in soil were different from those obtained in solution. In soil, chlorsulfuron decreased both zinc concentrations in the youngest emerged blade and zinc content of shoots, while in solution where uptake is not likely to be limited by the rate of zinc diffusion to sites of absorption, there were no significant effects on zinc uptake. However, in both soil and solution, shoot and root weights were decreased by herbicide, particularly at low rates of zinc supply. Roots were shorter and thicker when herbicide concentrations in solution were increased.

Use of a Mathematical Model to Determine the Fate of Atrazine in Barley (Hordeum vulgare) Plants

A model of the pharmacokinetics of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] in barley (Hordeum vulgare L. ‘Escourgnon’) plants has been described. Uptake of atrazine conforms to a first-order kinetic model. Roots play a small role as a sink for atrazine. Metabolism of the herbicide conforms to a second-order kinetic model. Using this model, the amount of atrazine in leaves can be evaluated at any time if the concentration of herbicide in solution is known.

Effects of Concentration and Time of Exposure on the Phytotoxicity of Linuron

When seedlings of lettuce and turnip were grown in nutrient solutions containing different concentrations of linuron, the concentration in the shoot at the time when toxicity symptoms appeared was related to the solution concentration. With lettuce, for example, symptoms were recorded after 7 d at 0.15 μg/ml and the shoot concentration was 2.7 μg/g fresh wt. At 0.06 μg/ml, symptoms appeared after 10 d and the shoot concentration was then 1.1 μg/g fresh wt. If grown for different periods in solutions containing linuron and then transferred to fresh nutrient solutions containing no herbicide, turnip or lettuce seedlings which had accumulated 0.7–0.8 μg linuron/g fresh wt developed toxicity symptoms 4 to 6 d later. Seedlings were also treated with linuron after they had grown for different periods in control nutrient solutions. The shoot concentrations attained before toxicity symptoms appeared were higher in those seedlings which were larger when herbicide treatment began. These results show that the herbicide concentration in solution, time of exposure, and age of seedling are interrelated in determining linuron phytotoxicity.

Herbicide Equilibrium in Soils in Relation to Soil Water Content

The concept of herbicide partition into adsorbed and solution phases in the soil was utilized to predict the effect of soil water content on the concentration of herbicide in solution. Calculated predictions based on measured partition coefficients and water contents were tested experimentally by equilibrating 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) with soil from three horizons of a latosolic soil at four water contents (45 to 60%). The effects of adsorption and water content were predicted with reasonable accuracy when only that water held at tensions less than 15 bars was considered available for equilibration with the applied herbicide. Only on low adsorption soils will water content variations alter significantly herbicide concentration in the soil solution. The principal effect of soil water content on herbicide phytotoxicity probably is associated with herbicide transport, which is more sensitive to changes in water content than is the concentration of herbicide in soil solution.