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The fate of the urea-herbicide linuron was studied in experimental ditches. Eight ditches were sprayed three times at monthly intervals, while two served as controls. As a simulation of spray drift, four doses (nominal: 0.5; 5; 15 and 50 pg.dni3) were applied in duplicate. After each herbicide application, the ditches were kept stagnant for a week, followed by a flow period of three weeks with fresh water. No clear stratifican n of linuron could be found in the water compartment. During the stagnant period, half-lives ‘a for the disappearance of linuron in the water compartment ranged from 7.2 to 11.8 days. The rate of disappearance was slower in the ditches treated with the highest dose and in colder treatment periods. A maximum of 6% of the linuron dose was found in the sediment and 1% in the macrophyte compartment. Approximately 20% of the fraction in the sediment compartment was present in the pore water. 01998 Else&r Science Ltd. All rights reserved

A treatment procedure was developed to mimic spray drift deposition of pesticides on the water surface of outdoor experimental ditches. The performance of this procedure was evaluated in two studies (using the pesticides chlorpyrifos and linuron, respectively) by testing the capability to apply pesticides to the ditches accurately, without contaminating adjacent control ditches. This was done by measuring the volume and concentration of the spray, by chemical analysis of the compounds in the ditch water and by measuring spray deposition on the water surface. After the first study some slight modifications were made to the treatment procedure. In the second study, in which eight ditches were treated with a fixed volume of spray of varying pesticide concentrations, it could be shown that the actual volumes dosed closely matched the intended volume (mean value per treatment within 1% of intended value; coefficient of variation

Simple compartmental models can be used to predict the fate of pesticides in aquatic systems. However, often the process parameters needed in these models are lacking. The objective of this study was to see whether experiments in laboratory micro-ecosystems can provide these parameters. The fate of the insecticide chlorpyrifos was investigated in derived micro-ecosystems composed of water and sediment. Chlorpyrifos was measured in sediment and water, at exponential time intervals during an incubation period of 64 days. A two-compartmental model was used to describe the mass of chlorpyrifos in both water and sediment. The rate constants for transformation and transport were estimated. These rate constants were used to simulate the dynamics of chlorpyrifos in water and sediment of an experimental pond. The simulation results were compared with measured concentrations. The parameters obtained from the micro-ecosystems could not be used to predict the fate of chlorpyrifos under field conditions with this model. Only with adjustments for the rate constant for transformation in water, the fate of chlorpyrifos could be simulated adequately during the first 5 days after application.

Data on the adsorption and transformation rates of diazinon, parathion, tetrachlorvinphos and triazophos in soils were collected from a survey of the literature. As little information is available on their mobility, the adsorption of tetrachlorvinphos and triazophos on three soils was measured in a slurry experiment. Properties of diazinon were introduced into a computer model simulating glasshouse soil systems in a simplified way. The leaching of diazinon from the root zone was calculated to be zero. The properties of the other three organophosphates indicate that in similar computations leaching from the root zone would have been even lower. Samples from tile drains and water courses in areas with many glasshouses were analysed by gas-liquid chromatography. The concentration of the four organophosphate insecticides in almost all of the samples of water from tile drains was below the detectable limit. However in samples from the water courses, pesticide residues were found regularly, sometimes at fairly high concentrations. Thus contamination of water courses would seem to be produced not by leaching of pesticides through the soil but by other pathways.

The transformation of metham‐sodium into methyl isothiocyanate and the further transformation of the latter active compound were measured in incubation studies with moist soils in gastight flasks at 15°C. Soils were collected from seven “problem” fields, from six frequently fumigated glasshouses and from nine trials with plots treated annually and plots left untreated. Metham‐sodium was transformed to methyl isothiocyanate to a high extent (more than 90 %) in all soils tested, and the maximum amounts of methyl isothiocyanate were measured within 0.1 to 1 day after addition of metham‐sodium. The transformation rate of methyl isothiocyanate varied considerably: the time for 50 % transformation ranged from 0.5 to 50 d. In general, methyl isothiocyanate was transformed appreciably faster in soils that had previously been treated frequently. However, in soils from two trial plots, that had been treated 13 times or more, no clearly enhanced rate of transformation was measured. Poor nematode control on ...

Adsorption of ethoprophos, tetrachlorvinphos and etridiazole onto rock-wool was found to be much weaker than adsorption onto soils. The rates of transformation in water and in water plus rock-wool at 20°C were low. The concentration of etridiazole was measured in a nutrient-film system with recirculating nutrient solution. The decrease was rapid in the first few hours but was more gradual afterwards, to low values at 8 days after application. Etridiazole penetrated poorly into the lower part of a rock-wool system when the solution was trickled near the stem-base of the tomato plants.

Inadequate nematode control on some loamy soils after fumigation with 1,3-dichloropropene prompted further study of transformation in these soils. The rate of transformation of (Z)- and (E)-1,3-dichloropropene was measured in moist soils incubated at 15 degrees C in fumigant-tight systems. In six loamy soils, transformation was gradual and pseudo first-order during 3 to 6 days but thereafter it was very fast. At an initial content in dry soil of 62-80 mg/kg the remaining amounts were less than 0.2% of the dose after a week. The greatly accelerated transformation after a short time lag suggests that the soils contained microorganisms that can transform 1,3-dichloropropene effectively. The fast transformation was measured in soil from fields once or twice fumigated previously as well as from fields never treated. In one of these loamy soils, a fast transformation (less than 0.2% remaining after 7 days) was measured at initial contents of 3.7, 18 and 92 mg/kg. But when the initial content was 470 mg/kg, the transformation rate was markedly suppressed (half-life 33 days). In another loamy soil, which showed no accelerated transformation patterns, the pseudo half-lives substantially increased from 4.3 to 36 days when the initial content of 1,3-dichloropropene was raised from 3.7 to 470 mg/kg. (Abstract retrieved from CAB Abstracts by CABI’s permission)