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«: 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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DENITRIFICATION IN SOIL.

Experiments were conducted to evaluate the effects of the herbicide atrazine on denitrification in two soils, Yolo loam from California, United States of America, and S. Cataldo silt loam from Italy. The rates of denitrification and amounts of N2 and N 2 0 gases produced during denitrification were measured from incubation experiments and from miscible displacement experiments on the transport and transformation of 1SN03 in soil with and without incorporated atrazine. The amount of 1SN03 appearing in the effluent of the soil columns was measured as a function of time and fitted to analytical solutions of the transport and transformation equation in order to determine the constants for first order kinetics. The soil columns were also equipped with a means of flowing He and N2 perpendicular to the water and N 0 3 flow, in order to slowly purge the evolved N 2 0 and 1 5 N2 gases from the soil columns. At 25 ppm atrazine, denitrification was substantially inhibited during the first 8 days of incubation. However, at 5 ppm atrazine, denitrification remained the same as with no atrazine or was slightly stimulated. The presence of atrazine in the soil during N 0 3 transport greatly inhibited the reduction of N 2 0 to N2, resulting in small N 2 / N 2 0 ratios. Thus, atrazine, at concentrations reasonable for field application, resulted in a slight increase in the nitrate reduction rate over that without herbicide. The results also show that atrazine can have a profound effect on the enzyme systems that are responsible for reduction of N 2 0 to N2 during denitrification. Thus, the presence of atrazine in the soil may result in increased evolution of N2 О from fertilizer-applied N during time periods when field soils become anoxic.

* The abstract only is published here, since it is intended that the full paper will appear in the IAEA-TECDOC Series (unpriced publication).

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INFLUENCE OF A HERBICIDE ON CERTAIN METABOLIC AND SYMBIOTIC

ACTIVITIES OF A Rhizobium.

The influence of Basalin (a pre-emergence herbicide) on the metabolism and symbiosis of a Rhizobium sp. (strain P 47) with cowpea ( Vigna unguiculata var. С 152) was studied.

The herbicide was applied at 2, 5 and 10 ppm levels to simulate the recommended and higher accumulated levels, respectively. Basalin reduced the in vitro growth of the Rhizobium at 5 and 10 ppm, while oxidation of 14C-glucose by the bacterium was significantly affected at all three levels. At 2 and 5 ppm Basalin did not affect the oxidation of acetate, pyruvate, succinate and fumarate, while citrate oxidation alone was enhanced at the 2 ppm level.

However, the 10 ppm level of the herbicide significantly reduced oxidation of the above TCA-cycle intermediates. Soil application of Basalin significantly suppressed plant growth as well as nodulation (nodule number and weight per plant) at 5 and 10 ppm, but not at the 2 ppm level. Reduction in the dry matter production and total nitrogen content of plants was also observed in plants raised in soil treated with 5 and 10 ppm of the herbicide. Both nodular respiration and leghaemoglobin content of nodules were adversely affected by all three levels of the herbicide, whereas the nitrogenase activity was reduced significantly at 5 and 10 ppm.

Translocation of foliar applied 14C-glucose to roots and nodules was suppressed in cowpea plants raised in Basalin-incorporated soil. In general, the results indicated that, while the recommended level (2 ppm) of the herbicide Basalin was less harmful, the higher accumulated levels (5 and 10 ppm) were highly toxic to the metabolic and symbiotic activity of the cowpea Rhizobium.

* This work was partly supported by the IAEA under Research Contract No. 1660/R3/IND. The abstract only is published here, since it is intended that the full paper will appear in the IAEA-TECDOC Series (unpriced publication).

Poster Presentation IAEA-SM-263/10

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К. WETZEL, H. FAUST Central Institute o f Isotope and Radiation Research, Academy o f Sciences o f the G D R, Leipzig, German Democratic Republic Techniques using the stable isotope 15N have been widely used in agricultural research and are also going to gain wide application in medical research and diagnostics. Therefore, our Central Institute o f Isotope and Radiation Research has made many efforts to develop simple and highly automated methods for analysing this isotope. These have resulted in two commercial emission spectrometrical devices: the 1SN analysers NOI-5 and Isonitromat 5201, which have been developed in co-operation with the VEB Statron, Fürstenwalde, German Democratic Republic. During the last few years we have designed and constructed a third, not yet commercial, device for this purpose, which we have named NOI-6. It is the aim here to describe the technical parameters o f these devices and to discuss the results o f our investigations on the accumulation o f (2-chloroethyl) trimethylammoniumchloride (CCC) in the nodes o f wheat plants, using an emission spectrometrical 1SN analyser.

All our 1SN analysers are based on the same principle:

(1) Chemical reaction between nitrogen compounds (ammonium compounds, amines, amides) and ammonium hypobromite to form gaseous nitrogen (2) Purification o f nitrogen (3) Introduction o f purified nitrogen into a discharge tube (4) High frequency excitation to effect light emission (С 3 7Г-В 3 7г) (5) Separation o f the bands emitted by the isotopic molecules by a monochromator (6) Recording the intensity o f the isotopic bands by a secondary electron multiplier (7) Calculation o f the relative abundance o f 1SN.





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0.90 0.20 0.27 0.12 0.33 0.06 0.04 0.07 0.13 0.07 2 S N excess abundance in the ear: 0.20 at.%.

The 15 N analyser NOI-5 only performs steps 4, 5 and 6; our 15 N analysers, NOI-6 and Isonitromat 5201, perform steps 1 to 6. The additional advantage o f Isonitromat 5201 is the possibility to hold up to 380 test samples that are sampled and introduced into the analyser automatically. Both NOI-6 and Isonitromat 5201 calculate the relative 1SN abundances by an analogous computer and then print them. Our new 15 N analyser NOI-6 combines most o f the advantages o f NOI-5 and Isonitromat 5201, particularly the high accuracy and small amounts o f nitrogen needed which are characteristic o f NOI-5 and part o f the high degree o f automation o f Isonitromat 5201.

As is known synthetic CCC is a growth-retarding substance used for stem shortening o f wheat, particularly when applying large amounts o f nitrogen fertilizers. Former investigations at our institute and other research institutions on the uptake and transport o f CCC in wheat have proved that it is rather effectively accumulated in the stem. The stem-shortening effect might be associated with differences in the CCC concentration in different parts of the plants showing different responses to the biologically active substance. Therefore, we studied the distribution and persistence o f CCC in the stems o f wheat plants, using 15 N-labelled CCC and the analytical procedures already described.

Spring wheat was grown in a water culture using Zinsadse I nutrient solution.

When the plants had reached a height o f 25 cm their roots were dipped into an aqueous 7 X 10~ 4 M solution o f 15 N-labelled CCC for 6 h (the 15 N abundance used was 50.7 at.%). After a further period o f 7 weeks, when the ears had emerged, the plants were harvested. The main shoots o f the harvested plants were divided into different parts to determine the CCC content by the inverse isotope dilution technique.

298 POSTER PRESENTATIONS Fresh samples were treated with alcohol, resulting in a 'soluble N' fraction and a precipitate 'protein fraction'. Nitrogen-15 was determined by our emission spectrometric method. The results o f these experimental investigations are shown in Table I.

No 1SN excess abundance was found in the protein fraction, indicating that the CCC molecule was virtually not metabolized. Therefore, we can conclude that the 15 N excess abundance is representative o f the CCC content.

Usually the upper region of the wheat plant exhibits the highest 15 N abundance, values decreasing in the basipetal direction. Moreover, the nodes show considerably higher 1SN abundances and higher CCC contents, respectively, than the neighbouring internodes and subnodes.

POSTER PRESENTATIONS

Poster Presentations IAEA-SM-263/8

ACCUMULATION A N D MIGRATION

OF H E A V Y METALS IN SOILS

A N D CONTAMINATION TO G R O U N D W A T E R

AS A RESULT OF LONG-TERM

APPLICATION OF URBAN WASTES

N. EL BASSAM Institut für Pflanzenbau und Pflanzenziichtung, Bundesforschungsanstalt für Landwirtschaft, Braunschweig-Vôlkenrode, Federal Republic o f Germany Standards for waste utilization in soil improvement and crop production should provide reasonably high levels o f public health protection. By utilization o f waste water, sewage sludge and municipal waste compost on farmland, heavy metals and other constituents accumulate in the soil to a different degree.

T o investigate their behaviour in the soil over long periods different sites

were selected for investigation and sampling o f undisturbed soil columns:

(a) Sewage farm in operation for 85 years (b) Field experiments with sewage sludge (c) Field experiments with municipal waste compost.

Isotope studies and neutron activation analysis were carried out on the accumulation and migration o f antimony, arsenic, cadmium, chromium, mercury, lead, selenium and zinc.

A significant accumulation o f most o f the 27 metals investigated was

detected in the upper layers o f the sewage farm soils:

(a) The concentration o f Cr, Hg and Zn already approached the permissible limit o f elements in soils (b) Relatively high accumulations o f Sb, Ba, Cd, Hg, Pb, Sn and U were also found.

In the event o f adequate water flux, a specific differentiation in the heavy metal migration rate in soils could be identified. The soil and concentration factors were then determined. The order o f mobility observed was Se As Zn Cd Pb Cr.Hg Sb.

–  –  –

An absolutely stationary state was not noticed so that under certain conditions a sudden enhancement o f the mobility could take place. Leaching, as well as contamination o f the surface and groundwater, should be expected.

The length o f time during which a given organic waste can be applied to a soil and the total load without resulting in a metal concentration in excess o f the permissible levels listed in Table I can be calculated according to the following formula

–  –  –

where n is the number o f years till the permissible limits have been reached, M s p is the permissible metal concentration in soils (see Table I), Ms¿ is the initial metal concentration in soils, M w is the metal concentration in waste, and w is the weight o f wastes in kilogram dry matter per hectare per year.

POSTER PRESENTATIONS

IAEA-SM-263/22

–  –  –

W. FABIG Fraunhofer-Institut für Toxikologie und Aerosolforschung, Schmallenberg J.C.G. OTTOW Institut für Bodenkunde und Standortslehre, Universitàt Hohenheim, Stuttgart, Federal Republic o f Germany Many pesticides are halogenated aromatic compounds that are markedly more refractile to microbial attack than non-halogenated aromatics [ 1 ]. It was observed that microbial degradation o f such compounds, especially dehalogenation, occurs more rapidly in flooded anaerobic soils than in aerobic upland soils [2].

Complete mineralization with methane or carbon dioxide as metabolic endproducts was minimal under these conditions. On the contrary, anaerobic conditions support the accumulation o f partially mineralized pesticides such as TDE [3].

Therefore, we examined the possibility o f mineralizing aromatic nuclei in absolutely anaerobic environments only at the expense o f nitrate. We used ring-U- 14 C-benzoate as the carbon and energy source for the utilization by actively denitrifying Pseudomonas sp., Moraxella sp., and a aeruginosa, Acinetobacter consortium o f various bacteria [4]. Experiments were done with the aromatic compound as the only carbon source in the culture medium and with glycerol as an additional carbon source. At the end o f the tests the fate o f the labelled carbon was examined as well as the conversion o f nitrate.

Under absolutely anaerobic conditions, with nitrate as the only terminal electron acceptor, rupture o f the benzene nucleus was not possible, neither with pure strains nor with mixed denitrifying populations. Also, when a second carbon source was present in the culture medium no 14C02 production was detected, indicating that no ring fission occurred. However, if traces o f oxygen were left in the culture vessel, both mineralization o f the aromatic moiety and denitrification could be observed. With increasing amounts o f oxygen, mineralization as well as denitrification was intensified. In the presence o f 10 or 304 POSTER PRESENTATIONS 20% oxygen (vol./vol.) in the culture vessel the relationship between produced C 0 2 and denitrification gases was constant. Only when the oxygen concentration increased to 40% (vol./vol.) did the amount o f released denitrification gases drop relatively to the produced carbon dioxide. These data lead to the conclusion that small quantities o f molecular oxygen are sufficient to activate oxygenases and to rupture the benzene nucleus, and that the aliphatic products are then metabolized immediately by nitrate respiration. With a limited oxygen supply the molecular oxygen is used primarily for the ring fission.

Elimination o f pesticides in soils is favoured by alternating changes between anaerobic and aerobic conditions. An anaerobic environment enables dechlorination, whereas even traces o f molecular oxygen permit fission o f the aromatic ring [5]. For fast and complete mineralization o f the aliphatic components o f the pesticide a sufficient nitrate supply is needed.

REFERENCES

[1] HARTMANN, J. et al., Appl. Environ. Microbiol. 37 (1979) 421.

[2] JAGNOW, G. et al., Arch. Microbiol. 115 (1977) 285.



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