Raoul Calvet

Sorption of weak organic acids in soils: clofencet, 2,4-D and salicylic acid

The sorption behaviour of a new wheat hybridising agent (clofencet, 2-4-(chlorophenyl)-3-ethyl-2,5-dihydro-5-oxopyridazine-4-carboxylic acid) was investigated in batch equilibrium experiments and compared to that of two other organic acids (2,4-D and salicylic acid). Sorption coefficients Kd for the three compounds were determined in 18 Cambisols and Ferralsols. Kd values for clofencet were 0.3-9.4 l/kg for Cambisols and 2.1-68 l/kg for Ferralsols. Sorption of clofencet was strongly related statistically to that of salicylic acid. Sorption of clofencet and salicylic acid decreased exponentially with increasing solution pH in Cambisols whereas a bell-shaped curve was obtained for the sorption of salicylic acid in Ferralsols. Sorption of 2,4-D (2,4-dichlorophenoxyacetic acid) was not statistically related to the pH of the different soils. Positively charged oxide surfaces were shown to play a significant role in the sorption of clofencet and salicylic acid. The use of simple correlation and multiple linear regressions suggested that the main sorption mechanisms of clofencet in soils were likely to be ligand exchange on oxide surfaces and, to a lesser extent, cation bridging. Differences in the sorption behaviour of clofencet/salicylic acid and 2,4-D might be attributed to the possibility of the two former compounds forming bidentate complexes with metals.

Biosorption characterization of herbicides, 2,4-D and atrazine, and two chlorophenols on fungal mycelium

Biosorption of the 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4-dichlorophenol (2,4-DCP), 4-chlorophenol (4-CP) and 2-chloro-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine) has been studied on the mycelium of Emericella nidulans and Penicillium miczynskii, isolated from composted wheat straw and a soil respectively. Results obtained with inactivated fungal biomass showed that a rapid adsorption on fungal cell walls surfaces was the main sorption phenomenon for the more hydrophobic molecules. This sorption was only partially reversible. With active living mycelia, additional phenomena were responsible for an increased sorption of all chemicals. This process was slow and depended on the chemical concentration. For 4-CP, it was attributed to biodegradation as demonstrated by the presence of degradation products in solution. Bioaccumulation inside the mycelium could also partially explained the results observed with living biomass for 4-CP, 2,4-DCP and 2,4-D.

Sorption of low levels of nonionic and anionic surfactants on soil: effects on sorption of triticonazole fungicide

The sorption of two anionic surfactants and a series of seven nonionic alkylphenolethoxylate surfactants of increasing hydrophilic/lipophilic balance (HLB) in a loamy clay soil was evaluated. The effect of low doses of these surfactants on the sorption characteristics of the fungicide triticonazole was investigated. The critical micellar concentration (CMC) of the surfactants in pure water and soil–water systems, and surfactant sorption were estimated by surface tension measurements using a batch equilibration technique. Triticonazole sorption, alone and in the presence of low doses of surfactants, was also measured by batch equilibration. CMC of the alkylphenol surfactants increased with their HLB. The sorption of surfactants increased with their lipophilicity. CMC in the soil–water systems were considerably higher than in pure water. Sorption of the most lipophilic alkylphenol surfactants at the higher doses significantly increased triticonazole sorption. Proposed mechanisms are modifications of soil surface properties, and increase of soil organic carbon content. Sorption of the other nonionic and anionic surfactants only resulted in monomeric surfactant concentrations in pore water, and did not affect triticonazole sorption.

Influence of adsorption-desorption phenomena on pesticide run-off from soil using simulated rainfall

The surface run-off of a number of pesticides (diuron, isoproturon, atrazine, alachlor, aclonifen, trifluralin, lindane and simazine), chosen for their range of adsorption behaviours, was studied using simulated rainfall applied to small plots over a short time (one hour). Pesticides were applied together onto bare soil using two different sandy loam soils from Jailliere and Coet Dan sites. The surface run-off samples were collected throughout the running of the event and concentrations of pesticides were measured in both liquid and solid phases. Sorption isotherms for isoproturon and diuron on Jailliere soil as well as eroded particles were measured under equilibrium conditions and compared to their partitioning during surface run-off. At the rainfall intensity used, both soils generated a large load of eroded particles. The average run-off flow rate increased with time for the Jailliere soil, while it remained relatively constant at a higher level for the Coet Dan soil. The concentrations of each pesticide in the run-off samples decreased as the experiments proceeded. The pesticides were classified into two types by their partitioning between the solid and liquid phases. Atrazine, simazine, diuron, isoproturon and alachlor were mainly transported in surface run-off water. By contrast, 90% of trifluralin and aclonifen was adsorbed onto eroded particles. Lindane was intermediate, with a 37% adsorption level. When the contribution of eroded particles was minor, the agrochemical concentrations were inversely proportional to the water flow rate. We have proposed a model that describes the mass of chemicals extracted from soil into surface water during a surface run-off event of a given average duration and flow rate. This model takes into account the dilution of the soil solution and the desorption of chemicals through two parameters called, respectively, the dilution factor and the extraction retardation factor. The desorption kinetic was the limiting step in the surface run-off of weakly sorbed chemicals, such as isoproturon.

Influence of adsorption-desorption phenomena on pesticide runoff measured under controlled conditions*

Abstract The surface runoff of isoproturon and diuron is studied using simulated rainfall applied to small 1 m 2 plots of soil. Isoproturon was less adsorbed by soil than diuron and eroded particles did not contribute to the pesticide transfer. A model is then proposed to describe such transfer of pesticide. This model introduces ( i ) a dilution factor a , which seems proportional to the concentration of the soil solution before applying the artificial rain and ( ii ) an extraction retardation factor b , which is inversely proportional to the partition coefficient between the solid and liquid phase of soil.