clay and mesotrione

A natural Cameroonian smectite-type clay (SaNa) was exchanged with cationic surfactants, namely cetyltrimethylammonium (CTA) and didodecyldimethyl ammonium (DDA) modifying its physico-chemical properties. The resulting organoclays that have higher adsorption capacity for mesotrione than the pristine SaNa clay, have been used as modifiers of glassy carbon electrode for the electrochemical detection of this herbicide by square wave voltammetry. The stripping performances of SaNa, SaCTA and SaDDA modified electrodes were therefore evaluated and the experimental parameters were optimized. SaDDA gives the best results in deoxygenated acetate buffer solution (pH 6.0) after 2 min accumulation under open circuit conditions. Under optimal conditions, the reduction current is proportional to mesotrione concentration in the range from 0.25 to 2.5 μM with a detection limit of 0.26 μM. The fabricated electrode was also applied for the commercial formulation CALLISTO, used in European maize market.

Topics: Aluminum Silicates; Carbon; Clay; Cyclohexanones; Electrochemistry; Electrodes; Glass; Herbicides; Hydrogen-Ion Concentration; X-Ray Diffraction

In field experiments carried out during the 1997-2001 period on four different soil types (sand, sandy loam, heavy sandy loam and clay) in Flanders (Belgium), the persistence of the three 4-HPPD inhibiting maize herbicides mesotrione (100 and 150 g ha-1), sulcotrione (300 and 450 g ha-1) and isoxaflutole (75 and 125 g ha-1) was studied. Therefore, soil samples were taken at regular intervals from application in spring and frozen. When all samples had been taken, greenhouse bioassays were set up to detect herbicide residues in the different soil types. Therefore, two extremely sensitive test plants, sugarbeet (Beta vulgaris L. spp. altissima Doell. var. saccharifera Deck.-Dill) and red clover (Trifolium pratense L.) were sown in the soil samples. Test plants were harvested after 2 (sugarbeet) and 3 (red clover) weeks and foliage fresh weight per plant was determined. This parameter was expressed relatively to the average fresh weight per plant of the plants sown in the control soil samples taken at each sampling date. The bioassays revealed several factors that influence the persistence of the herbicide tested. First, there is a remarkable influence of the experimental year due to variation in weather conditions (especially rainfall and temperature during the first weeks after spraying). Secondly, a different soil texture results in a highly different persistence: the shortest biological persistence was noticed each year in clay, followed by heavy sandy loam; the longest persistence was recorded in sandy and sandy loam soil types. Thirdly, there are important differences between the three herbicides tested: isoxaflutole (a member of the isoxazole chemical family) was shown to be less persistent than sulcotrione and mesotrione (both members of the triketone family). Remarkably, this was not the case in clay, where a longer persistence could be seen for isoxaflutole compared to sulcotrione and mesotrione. This study also revealed that applying a low rate results in a shorter persistence period compared to the higher rate. All these factors work together in a complex way which determines the persistence of the three herbicides tested.

Topics: 4-Hydroxyphenylpyruvate Dioxygenase; Aluminum Silicates; Belgium; Beta vulgaris; Clay; Cyclohexanones; Herbicides; Isoxazoles; Mesylates; Pesticide Residues; Plant Leaves; Rain; Silicon Dioxide; Soil; Soil Pollutants; Temperature; Trifolium; Weather