Attilio A.M. Del Re

Root Uptake and Xylem Translocation of Pesticides from Different Chemical Classes

A pressure-chamber technique was used to study the root uptake and xylem translocation of some fungicides, herbicides and an insecticide from different chemical classes in detopped soybean roots. Physiological parameters such as K + leakage from roots, K + concentrations in the xylem sap, and protein and ATP levels in the root cells were measured so as to evaluate any potential damage of this technique to the root system. HPLC was used to quantify the compounds in the xylem sap. The pressure-chamber technique has proved useful to study the root uptake and translocation of pesticides, does not damage the root system, and allows one to obtain appreciable volumes of xylem sap that can be analysed directly by HPLC, thus avoiding dependence on the availability of radio-labelled compounds. The concentration of each pesticide in the xylem sap showed a steady-state kinetic profile. Non-linear regression analysis was used to calculate the steady-state concentration and the time required to achieve 50% of the steady-state concentration (TSSC 50 ). TSSC 50 was well correlated with log K ow ; the more lipophilic the compound the more time was required to reach the steady-state concentration. The efficiency of translocation was assessed by the transpiration stream concentration factor (TSCF) and a non-linear relationship between TSCF and log K ow was observed. The highest TSCF values were measured for those compounds with log K ow values around 3, a lipophilicity value similar to that reported earlier in an analogous experiment with detopped soybean plants but slightly higher than that reported in earlier experiments with intact barley plants. Lower TSCF values were obtained with chemicals with log K ow values below as well as above 3.

Characterization of Spatial Variability Structure in Three Separate Field Trials on Pesticide Dissipation

Experiments were carried out on three Italian farms to assess the degree of spatial variation of pesticide -eld concentration during treatment and during dissipation trials. Test pesticides were chloridazon and metamitron (both sugar-beet herbicides) applied as a tank mix. The classical statistical technique and geostatistics were used to summarize and evaluate variable spatial data. The results show that the actual values of pesticide concentration for applica- tion rate and initial concentration in all three areas are lower than expected, thus indicating that under -eld conditions only a part of the pesticide reaches the soil during the distribution. The actual values for both herbicides in all three areas expressed as percentage of expected values ranged from 44E1% to 64E2% for application rate and from 40E5% to 99E5% for initial concentration. The coeffi- cient of variation was similar for both pesticides and ranged from 23E 8t o 74 E1 for application rate, 24E1 and 58E8 for initial concentration and 11E1 and 110E0 for dissipation half-lives. The high variability in application rate and initial concen- tration could be ascribed to an uneven herbicide distribution, and in dissipation studies to variation in half-lives for the rate of herbicide loss from soil in di†erent parts of the -eld. Geostatistic analysis indicated little spatial correlation, probably because the sampling sites were widely spaced on the -eld. In all cases, the data were not sufficient to estimate the range of inNuence, probably because of the size of the experimental -elds and the sampling strategy.

Relationships of Pesticide Octanol/Water Partition Coefficients to Their Physicochemical Properties

Chemodynamic theories estimate the fate, distribution, bioaccumulation potential, and approximate residence time of pollutants in the environment, all on the grounds of physicochemical properties. Mathematical models have been developed to use chemodynamic theories for prediction purposes (Mackay and Pater son 1981). Most of these models require input data on the physical and chemical properties of the compounds investigated.

Residues of esfenvalerate in irrigation water, stubble, husked and unhusked rice samples of a paddy-field

Esfenvalerate insecticide was tested to study its behaviour in a rice paddy‐field. Samples of irrigation water, husked and unhusked rice, stubble and suspended matter collected on different days after application, were analysed by GLC. Esfenvalerate residues were detectable only in the suspended matter samples collected one hour after application. Esfenvalerate residues were not detectable in both the husked and unhusked rice and in the stubble.

Conformational Distribution of Dissolved Organic Matter Released from Compost by Repeated Water Extractions

The dissolved organic matter (DOM) released from compost by repeated water extractions was quantified and DOM conformational changes by high performance size-exclusion chromatography (HPSEC) were followed. Three commercial composts were extracted consecutively 4 times with equal water: compost ratios. The total organic carbon content of each DOM sample was analyzed using the chemical oxygen demand method, and the conformational size-distribution assessed by means of HPSEC. Results showed that compost continues to release considerable amounts of DOM with repeated water extractions, and that subsequent DOM extractions resulted in organic matter with increasing molecular dimensions and presumably larger hydrophobicity. This may have important consequences on soil processes and functions such as organic matter dynamics and transport of pollutants.