Fritz Führ

A wind tunnel for measuring the gaseous losses of environmental chemicals from the soil/plant system under field-like conditions

Volatilization from treated areas is a major source of pesticide residues in air, fog, and rain. This may lead to long-range transport of pesticide residues to remote areas. Up to now most information on pesticide volatilization has come from laboratory experiments under controlled conditions. A new system has been designed and developed to measure the volatile losses of14C-labelled chemicals after application; the method compares with agricultural practice of treating soils or plants grown in lysimeters. Sensitive analytical methods guarantee a distinction between residues of unchanged pesticide, its metabolites or14CO2 as a mineralization product released into the air.

Photodegradation and volatility of pesticides

Background and ObjectivesAmong the factors affecting the environmental fate of surface-applied pesticides several biological as well as abiotic factors, such as volatilization and photochemical transformations are of particular interest. Whereas reliable measurement methods and models for estimating direct photodegradation are already available for the compartments of water and atmosphere and individual subprocesses have already been described in detail, there is still a need for further elucidation concerning the key processes of heterogeneous photodegradation of environmental chemicals on surfaces.MethodsIn order to systematically examine the direct and indirect photodegradation of14C-labeled pesticides on various surfaces and their volatilization behavior, a new laboratory device (‘photovolatility chamber’) was designed according to US EPA Guideline §161-3. Model experiments under controlled conditions were conducted investigating the impact of different surfaces, i.e. glass, soil dust and radish plants, and environmental factors, i.e. irradiation and atmospheric ozone (O3), on the photodegradation and volatilization of surface-deposited [phenyl-UL-14C] parathion-methyl (PM).Results and DiscussionDepending on the experimental conditions, parathion-methyl was converted to paraoxon-methyl, 4-nitrophenol, unknown polar products and14CO2. With respect to the direct photodegradation of PM (experiments without O3), the major products were polar compounds and14CO2, due to the rapid photochemical mineralization of 4-nitrophenol to14CO2. Paraoxon-methyl and 4-nitrophenol formation was mainly mediated by the combination of light, O3, and -OH radicals. In radish experiments PM photodegradation was presumably located in the cuticle compartment, which exhibited a sensitized photodegradation, as more unknown products were yielded compared to the glass and soil dust experiments. This could be explained by intensifying the inherent PM degradation in the dark with the same product spectrum. Due to photochemical product formation, which is an antagonistic process to the volatilization of parent compound, the volatilization of unaltered parathion-methyl from each surface generally decreased in the presence of light, particularly in combination with increasing O3 concentrations and OH radical production rates.ConclusionFirst results demonstrated that the photovolatility chamber provides a special tool for the systematic evaluation of (a) photodegradation of surface-located pesticide residues, i.e. measuring qualitative aspects of direct and indirect photodegradation together with relative photodegradation rates, and (b) volatilization of pesticides on surfaces by including and optionally varying relevant parameters such as light, atmospheric O3 concentration, surface temperature, air temperature, air flow rate.OutlookThe experimental facility represents an important complement to lysimeter and field studies, in particular for experiments on the volatilization of pesticides using the wind tunnel system. With the photovolatiliry chamber special experiments on photodegradation, volatilization and plant uptake can be conducted to study key processes in more detail and this will lead to a better understanding of the effects of certain environmental processes on the fate of released agrochemicals contributing to an improved risk assessment.

Long-term fate of the herbicide cinosulfuron in lysimeters planted with rice over four consecutive years

In order to elucidate the long-term fate of the sulfonylurea herbicide cinosulfuron, the 14C-labelled chemical was applied to a clay loam soil, encased in two lysimeters, 22 days after rice (Oryza sativa L.) transplanting, and rice plants were grown for four consecutive years. Throughout the experimental period, leaching through soil profiles, absorption and translocation by rice plants, and distribution of 14C by downward movement in the soil layers were clarified. The total volume of leachates collected through the lysimeter soil over the four years amounted to 168 and 146 L in lysimeters I and II, respectively. The leachates contained 2.43% and 2.99% of the originally applied 14C-radioactivity, corresponding to an average concentration of 0.29 and 0.41 microg/L as the cinosulfuron equivalent in lysimeters I and II, respectively. The total 14C-radioactivity translocated to rice plants in the third and fourth year was 0.69% and 0.60% (lysimeter I), and 1.02% and 0.84% (lysimeter II) of the 14C applied, respectively. Larger amounts of cinosulfuron equivalents (0.54-0.75%) remained in the straw in the fourth year than in any other parts. The 14C-radioactivities distributed down to a depth of 70 cm after four years were 56.71-57.52% of the 14C applied, indicating the continuous downward movement and degradation of cinosulfuron in soil. The non-extractable residues were more than 88% of the soil radioactivity and some 45-48% of them was incorporated into the humin fraction. The 14C-radioactivity partitioned into the aqueous phase was nearly 30% of the extractable 14C, suggesting strongly that cinosulfuron was degraded into some polar products during the experimental period. It was found out in a supplemental investigation that flooding and constant higher temperature enhanced mineralization of [14C]cinosulfuron to 14CO2 in soil, indicating the possibility of chemical hydrolysis and microbial degradation of the compound in the flooded lysimeter soil.

Comparative Studies on the Formation of Bound Residues in Soil in Outdoor and Laboratory Experiments

Abstract To evaluate the formation of bound residues in soil, standardized degradation experiments were designed with soil-plant systems such as pot experiments in the greenhouse and lysimeter experiments under outdoor conditions using 14C-labelled metamitron, and methabenzthiazuron. During the experiments different losses of 14C occurred due to mineralization of the labelling positions. More than 80% of the remaining radioactivity applied in pot and lysimeter experiments was detected in the 0–10 cm soil layer. Thirteen weeks after application of 14C-metamitron, 20% of the applied 14C remained in the lysimeter soils after extraction with organic solvents or 0.01 M CaCl2 solution while 50% remained unextractable in the soils kept at 22°C and 50% of the maximum water holding capacity of the soil. In the case of methabenzthiazuron, 25% of the applied radioactivity could not be extracted from the lysimeter soils with organic solvents, whereas, 30–40% remained in the soils of the laboratory studies. The result...

Characterisation of soil-bound residue fractions of the fungicide dithianon by gel permeation chromatography and polyacrylamide gel electrophoresis.

The degradation of the (14)C-labelled fungicide dithianon in an orthic luvisol was investigated under standardized conditions in comparison to stimulated microbial activity by an amendment of maize straw. The compound is characterized by mineralization losses of approximately 33% and the formation of non-extractable bound residues of approximately 63% in 64 days. Despite the major role of microorganisms in mineralizing this compound, the formation of bound residues is not biotically induced. Gel permeation chromatography and polyacrylamide gel electrophoresis, as different size separation techniques of the humic acids fractions, showed differences in the distribution patterns of non-extractable residues depending on the addition of straw material. The results presented support the existence of humic substances in soil as a micellar system rather than as a biopolymer.

Formation and bioavailability of bentazon residues in a German and Korean agricultural soil

Abstract Benzene-ring-labelled 14C-bentazon incubated aerobically in a German and a Korean soil at application rates of 5.51 and 25.05 mg/kg was mineralized to 14CO2 at average rates of 0.6 % and 0.2 % week , respectively, in both soils. Distilled water was the most suitable solvent for the extraction of bentazon-residues. Extraction results disclosed that after 15 weeks of incubation higher percentages of non-extractable residues were formed in soils with the lower bentazon concentration of 5.51 mg/kg. In the carbon rich Korean soil the non extractable bound residues amounted to 57 % of the 14C applied. About 2 % of this remaining radioacarbon was taken up by maize plants during a 3 weeks growing period compared to 8–14 % from soils containing aged bentazon residues and 36 to 43 % which were found predominantly in the roots when the 14C-bentazon was mixed into the soil immediately before planting the maize.

Behaviour of carbofuran in a rice plant-grown lysimeter throughout four growing seasons

When the systemic insecticide 14C-carbofuran was applied to a lysimeter transplanted with rice plants by the conventional method (1.2 kg a. i./ha), altogether 0.30% of the originally applied 14C-radioactivity leached out of the 1.00 m undisturbed soil core up to the 167th week after the application. The radioactivities detected in the brown rice grain harvested in 4 succeeding growing seasons amounted to 0.17, 0.02, 0.03, and 0.02 ppm carbofuran equivalents in the four years, respectively, being below the MRL of 0.2 ppm carbofuran set by FAO/WHO. The 14C-activities detected in the 0–10, 10–20, 20–30, and 30–40cm soil layer were 19.85, 11.52, 4.55, and 1.97% of the originally applied 14C, respectively, after 2 years, whereas those down to the 70 cm soil layer after 4 years were reduced a lot, suggesting strongly the possible loss of 14C in soil through mineralization to 14CO2.

Seasonal changes of [phenyl-U-14C]methabenzthiazuron loads in soil solution under practical farming conditions

Abstract In a two-year lysimeter experiment with methabenzthiazuron herbicide applied in accordance with good agricultural practice in an orthic luvisol, the dissolved active ingredient fractions in the soil solutions and leaching behaviour were examined with the aid of suction candles. The highest active ingredient concentrations of the first experimental year were determined in the soil solution immediately after pre-emergence application in autumn. The active ingredient concentrations decreased continuously during subsequent sampling. After turning the soil for the succeeding crop, high methabenzthiazuron concentrations were again determined in the soil solutions of the A p horizon and, for the first time, the major metabolite demethyl methabenzthiazuron also occurred. Below 40 cm soil depth neither methabenzthiazuron nor a metabolite was found in the soil solution. The development of active ingredient concentrations in the soil solution could be divided into three phases for this lysimeter experiment. Methabenzthiazuron was also characterized in the leachates. The mechanisms assumed were, on the one hand, a preferential flow with relatively high methabenzthiazuron concentrations, but small leachate volumes. On the other hand, a mass flow caused an extremely small input of trace amounts of active ingredient into the leachate below the drinking water limit of 0.1 μg L −1 .

Volatilization and Mineralization of [3-14C]Fluoranthene After Soil Incorporation and Soil Surface Application

Abstract The gaseous losses of [3-14C]fluoranthene from bare soil were measured in a glass wind tunnel under field-like conditions. Four experiments of 14 days each were performed under individual climatic situations. In two studies. [3-14C]fluoranthene was incorporated into the 0–1 cm soil layer (approx. 670 μg kg−1), in the other two experiments [3-14C]fluoranthene was sprayed onto the soil surface (approx. 120 g ha−1). The data obtained will be used for validation of the HESP computer model (Human Exposure of Soil Pollutants). In all experiments the major fraction of radioactivity (60.0–97.6% of the applied radioactivity (AR)) was recovered in the 0–2 cm soil layer. The mineralization of [3-14C]fluoranthene was strongly temperature dependent and slightly higher for surface application (σ 6.6 and 3.3% AR) than for soil incorporation (σ 1.9 and 5.3% AR), possibly because of stronger adsorption in the soil and the resulting lower availability for microbial degradation. After surface application, the volat...

Fate of the herbicide bentazon in rice plant‐grown lysimeters over four consecutive cultivation years+

Abstract When the herbicide benzene‐ring‐14C‐bentazon was applied onto two 0.25 m2 lysimeters by the conventional method(1.6 kg a.i./ha) in Korea and rice plants were grown over four consecutive years, 3.16(lysimeter I) and 17.27%(lysimeter II) of the originally applied radioactivities leached in total up to the 167th week after the application. The 14C activities translocated into rice straw in the first year ranged from 1.4 to 2.2% of the originally applied amount, reducing remarkably in the second year, and those into brown rice grain were below the MRL of 0.1 ppm bentazon set by FAO/VHO. The 14C activities remaining in the 0∼10, 10∼20, 20∼30, and 30∼40 cm soil layer were approximately 14.07, 16.45, 27.53, and 21.28%(lysimeter I) and 4.37, 10.06, 10.45, and 9.34%(lysimeter II), of the originally applied 14C, respectively, after 2 years, amounting to a total of 79.33 and 34.22%, respectively. After 4 years the residual radiocarbon in the 0—60 cm soil layer was reduced, indicating that 26.60(lysimeter I)...