«: AGROCHEMICALS: FATE IN FOOD AND THE ENVIRONMENT PROCEEDINGS OF A SYMPOSIUM, ROME, 7 - 1 1 JUNE 1982 JOINTLY ORGANIZED BY IAEA AND FAO l^J I N T E R ...»
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EFFECTS OF FERTILIZERS, FUNGICIDES AND HERBICIDES ON THE FATE OF14 C-PARATHION AND 14 C-FONOFOS IN SOILS AND CROPS.
Metabolism and translocation of 14C-parathion and 14 C-fonofos deposits in and from an agricultural loam soil into oat or corn plants growing in an open agro-ecosystem were significantly affected by the presence of organic and inorganic fertilizers as well as by the fungicide captafol (Difolatan) and the herbicide atrazine. Utilizing another soil type in a closed system, the interaction of selected fungicides, herbicides and N-fertilizers with microorganisms in cranberry soils and their effects on the degradation of 14C-phenyl-parathion were investigated. Soil microorganisms were responsible for the oxidative as well as reductive degradation of the insecticide.
Incubation of soils with parathion or p-nitrophenol for 4 d, followed by the addition of 14 Cparathion resulted after 24 h in an enhanced degradation of the insecticide to 14C02 (34—39% of the applied radiocarbon as opposed to 2% in controls), and also in an increased binding of 14 C to the soil. The fungicide captafol inhibited the degradation of soil-applied 14C-parathion as evidenced by a reduction of both 14C02 evolution and 14C-bound residues. Maneb and benomyl suppressed the degradation of 14C-parathion to 1 4 C02 but not the formation of bound residues. PCNB had no effect. Addition of 2, 4D to 14C-parathion-treated soil also resulted in an increased persistence of the insecticide. Studies conducted with the insecticide and (NH4)2S04, NH4NO3, KNO3 or urea showed that under all experimental conditions the total amounts of 14 C recovered were similar, yet the distribution of 14C-compounds into benzene-soluble, watersoluble and bound residues was not. This possibly indicated a change in the pathway of 14 Cparathion degradation. The insecticide was most persistent in soils containing ( N H ^ S O, }, as demonstrated by a recovery of 29% of the applied radiocarbon in benzene-soluble form. Analyses by TLC of this benzene extraction phase revealed the presence of 14C-parathion, 14C-p-aminophenol and 14C-aminoparathion. It appears that the form of the N-soil amendment and not the N amendment as such affected the degradation of 14C-parathion. Results reported here stress the importance of investigating the environmental fate of a particular pesticide in relation to the presence of other agricultural chemicals.
* The abstract only is published, since it is intended that the full paper will appear in the IAEA-TECDOC Series (unpriced publication).
FATE OF 2, 4D HERBICIDE IN SOIL/PLANT ECOSYSTEMS.
The behaviour of 2, 4D herbicide was investigated in soil/plant ecosystems under laboratory, greenhouse and field conditions, using isotope tracer techniques. Laboratory studies included: (a) Degradation of 14 C-2,4D in three different soils by incubating them in closed systems and collecting the evolved 14 СОг in sodium hydroxide. Four weeks after incubation 18.7, 19.7 and 24.6% of the applied 14 C activity were recovered from the three soils in the alkaline solution, (b) Degradation o f 2, 4 D a t room temperature with three different moisture contents (10, 15 and 20%) was studied in open systems. Within 4 weeks 9 4. 0 - 9 6. 0 % of the applied herbicide was degraded and-the degradation rate was higher at the 20% moisture content. Greenhouse investigations included: Distribution of 2, 4 D in soil/plant ecosystems in two soil types with barley, wheat and oats. After extracting the herbicide from the soil samples, the bound residues in the soil were determined by using the wet combustion method. Uptake of 2, 4 D in the two soils by barley, wheat and oats during 4 weeks under these conditions was very low and most of the herbicide remained in the soil.
In field studies aimed at studying the degradation and leaching of 2,4D, polyethylene tubes were placed in the field and labelled herbicide was applied to the top of the tubes. After 4 weeks the soil found in each joint of the tube was analysed for the extractable and bound residues. The balance figure of this experiment was 62.9% and the significant loss of herbicide (37.1%) was attributed to degradation. In 4 weeks the chemical was leached to a depth of 25 cm in the soil. In a field experiment aimed at studying the effect on crops and fertilizer of 2,4D, barley, wheat and oats were grown in small boxes in the field and diammonium phosphate fertilizer was mixed with the soil in some of the boxes. After 4 weeks uptake of the herbicide by the plants was very low, in the range of 0. 2 - 0. 9 % of the applied herbicide.
Uptake of the chemical by the plants grown with fertilizer was much lower and was of similar magnitude ( 0. 2 - 0. 7 % ).
* This work was supported by the IAEA under Research Contract No. 2154-R3-SD.
The abstract only is published, since it is intended that the full paper will appear in the IAEA-TECDOD Series (unpriced publication).
BEHAVIOUR OF CARBARYL IN SOILS UNDER THE INFLUENCE OF DIFFERENTCARBON SOURCES.
The effect of adding various carbon sources (microcristalline cellulose, filter paper, sucrose, milk, soy bean leaf and soy bean oil) on the persistence of carbaryl was investigated in samples of Humic Gley soil (43% organic matter; 57% clay; 12% silt; pH 5.7) and Yellow Red Latosol soil (0.36% organic matter; 11% clay; 9% silt, pH 6.4) using radiometric techniques.
For these studies an aqueous solution of 14C-carbaryl labelled on the carbonyl group was added to 10 g of soil after treatment with the carbon sources. Samples were extracted with 20 ml of dichloromethane and analysed by liquid scintillation counting. Extracted carbaryl was identified by thin-layer chromatography by spotting on silica-gel plates with 1 ml extract and using hexane-acetone (4:1) as the solvent system. After extraction, radiocarbon remaining in the soil was determined by wet combustion to COj. Recovery of carbaryl from soils as a function of incubation time and differing carbon sources showed that addition of milk, sucrose and soy bean oil induced in the Humic Gley soil a moderate increase in the rate of degradation of carbaryl, while incubation with the other organic nutrient sources, such as cellulose, filter paper and soy bean leaves, had practically no influence on degradation. In contrast, addition of nutrient sources on the Yellow Red Latosol greatly increased degradation of carbaryl, very little of this compound being left after 6-weeks treatment. Carbaryl was very poorly degraded on the Humic Gley soil, probably due to its higher content of organic matter which causes its higher absorption to the soil particles, thus reducing availability of the insecticide for metabolic processes. Nutrient sources that contribute towards increasing degradation of carbaryl in soils are certainly those readily available for microorganisms. In the studies performed here pure cellulose and filter paper are slowly metabolized and milk and soy bean oil, which are deprived of cellulose, are more efficiently attached by microorganisms than cellulose itself.
* This work was supported by the IAEA under Research Contract No. 2161/SD and the Secretaria de Cooperaçâo Económica e Técnica Internacional (SUBIN), as well as by a Conselho Nacional de Pesquisas (CNPq) scholarship to R. Hirata. The abstract only is published, since it is intended that the full paper will appear in the IAEA-TECDOC Series (unpriced publication).
PESTICIDE METABOLISM IN PLANTS(Session V) Chairman;
METABOLISM OF PESTICIDES IN PLANTS: SOME APPLICATIONS OF NUCLEARTECHNIQUES.
Metabolism of pesticides in plants is reviewed, using selected references to illustrate the development and application of nuclear techniques. The significance of metabolic processes is discussed and some possible developments in the application of nuclear technology.
Radiotracers have been used for investigating the metabolism o f pesticides in plants for over 30 years, and at least one publication exists which dates from 1951 [ 1 ]. There has been a continuous expansion o f the effort to learn the fate o f pesticides in crops and the environment and, while it is possible that the main driving force remains fear o f the unknown, in this case pesticide residues, there are other good reasons for these studies and some may become apparent later.