clay and isoproturon

During pesticides degradation, biogenic non-extractable residues ("apparent NER") may not share the same environmental fate and risks with the "real NER" that are bound to soil matrix. It is not clear how microbial community (MC) inoculation for pesticides degradation would influence the NER composition. To investigate degradation efficiency of pesticides Isoproturon (IPU) and NER composition following MC inoculation, clay particles harboring MC that contains the IPU degrading strain, Sphingomonas sp., were inoculated into soil receiving

Topics: Aluminum Silicates; Biodegradation, Environmental; Clay; Pesticide Residues; Phenylurea Compounds; Soil; Soil Microbiology; Soil Pollutants; Sphingomonas

We present a set of adsorption coefficients measured on various Eocene and Quaternary materials sampled from the vadose zone of a catchment in Northern France for three herbicides, atrazine, isoproturon and metamitron. Some vadose zone materials were found to have higher adsorption coefficients than the topsoil. The adsorption coefficients were strongly dependent on the clay content of the material. From 83% to 97% of the variability in the adsorption coefficients could be explained by a linear relationship to the clay content. Adsorption coefficients normalized for clay content, Kclay, ranged between 1.6 and 17.6 litre kg(-1) for atrazine. Neglecting the adsorption properties of the vadose zone and relying exclusively on Koc values to predict mobility may bias regional or local risk assessment of groundwater contamination by pesticides. More information on the adsorption properties of geological materials should be collected to improve our ability to predict pesticide concentrations in groundwaters.

Topics: Adsorption; Agriculture; Aluminum Silicates; Atrazine; Clay; France; Fresh Water; Herbicides; Phenylurea Compounds; Soil; Soil Pollutants; Solubility; Triazines

The influence of five rainfall treatments on water and solute leaching through two contrasting soil types was investigated. Undisturbed lysimeters (diameter 0.25 m, length 0.5 m) from a sandy loam (Wick series) and a moderately structured clay loam (Hodnet series) received autumn applications of the radio-labelled pesticide isoproturon and bromide tracer. Target rainfall plus irrigation from the end of November 1997 to May 1998 ranged from drier to wetter than average (235 to 414 mm); monthly rainfall was varied according to a pre-selected pattern or kept constant (triplicate lysimeters per regime). Leachate was collected at intervals and concentrations of the solutes were determined. Total flow (0.27-0.94 pore volumes) and losses of bromide (3-80% of applied) increased with increasing inputs of water and were larger from the Wick sandy loam than from the Hodnet clay loam soil. Matrix flow appeared to be the main mechanism for transport of isoproturon through the Wick soil whereas there was a greater influence of preferential flow for the Hodnet lysimeters. The total leached load of isoproturon from the Wick lysimeters was 0.02-0.26% of that applied. There was no clear variation in transport processes between the rainfall treatments investigated for this soil and there was an approximately linear relationship (r2 = 0.81) between leached load and total flow. Losses of isoproturon from the Hodnet soil were 0.03-0.39% of applied and there was evidence of enhanced preferential flow in the driest and wettest treatments. Leaching of isoproturon was best described by an exponential relationship between load and total flow (r2 = 0.62). A 45% increase in flow between the two wettest treatments gave a 100% increase in leaching of isoproturon from the Wick soil. For the Hodnet lysimeters, a 35% increase in flow between the same treatments increased herbicide loss by 325%.

Topics: Aluminum Silicates; Bromides; Clay; Fresh Water; Herbicides; Methylurea Compounds; Models, Biological; Pesticide Residues; Phenylurea Compounds; Porosity; Rain; Seasons; Silicon Dioxide; Soil; Solutions; Water

The uncalibrated predictive ability of four preferential flow models (CRACK-NP, MACRO/MACRO_DB, PLM, SWAT) has been evaluated against point rates of drainflow and associated concentrations of isoproturon from a highly structured and heterogeneous clay soil in the south of England. Data were available for four plots for a number of storm events in each of three successive growing seasons. The mechanistic models CRACK-NP and MACRO generally gave reasonable estimates of drainflow over the three seasons, but under-estimated concentrations of isoproturon over a prolonged period in the first season and over-estimated them in the two remaining seasons. CRACK-NP simulated maximum concentrations of isoproturon over the first two events of each of the three seasons of 156, 527 and 24.4 micrograms litre-1, respectively, and matched the observed data (465, 65.1 and 0.65 micrograms litre-1) slightly better than MACRO (69.1, 566 and 58.5 micrograms litre-1). Automatic selection of parameters from soils information within MACRO_DB reduced the emphasis on preferential flow relative to the stand-alone version of MACRO. This gave a poor simulation of isoproturon breakthrough and simulated maximum concentrations were 0, 50.1 and 35.1 micrograms litre-1, respectively. The capacity model PLM gave the best overall simulation of total drainflow for the first two events in each season, but over-estimated concentrations of isoproturon (967, 808 and 51.3 micrograms litre-1). The simple model SWAT represented total drainflow reasonably well and gave the best simulation of maximum isoproturon concentrations (140, 80.2 and 8.2 micrograms litre-1). There was no clear advantage here in using the mechanistic models rather than the simpler models. None of the models tested was able to simulate consistently the data set, and uncalibrated modelling cannot be recommended for such artificially drained heavy clay soils.

Topics: Aluminum Silicates; Clay; Computer Simulation; England; Herbicides; Methylurea Compounds; Permeability; Phenylurea Compounds; Porosity; Rheology; Risk Assessment; Seasons; Soil; Soil Pollutants; Water; Water Pollutants; Water Pollution, Chemical

Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural tilth or a finer topsoil tilth. The influence of topsoil tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h-1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequently drainage event. Analysis of covariance showed a significant effect of topsoil tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer tilth. However, generation of the fine tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains.

Topics: Aluminum Silicates; Bromides; Clay; Herbicides; Hydrogen-Ion Concentration; Linuron; Methylurea Compounds; Particle Size; Pesticide Residues; Phenylurea Compounds; Seasons; Soil; Soil Pollutants; Time Factors; Water; Water Pollutants, Chemical