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The degradation rates in soil of 1-benzyltriazole together with six analogues having substituents in the phenyl ring and two commercial triazole fungicides, PP450 and triadimefon, were determined at 15°C and 20 % soil water content. The order of degradation rates of the benzyltriazoles was H > 4-OCH3 > 4-F>4-Cl.4-≥tert-C4Hg3,4-diCl>3-CF3. Thus, in general, persistence was enhanced by electron-withdrawing substituents and by lipophilic groups that increased sorption by soil. Of the commercial fungicides, PP450 was degraded very slowly (half-life 578 days) while triadimefon was quickly converted (half-life 15 days) to the corresponding alcohol, triadimenol, which in turn was degraded very slowly. The effects of temperature and soil water content on rate of degradation were studied for 1-benzyltriazole and 1-(4-fluorobenzyl)triazole. The rate of degradation of 1-benzyltriazole was more sensitive to soil temperature and water content than was that of 1 -(4-fluorobenzyl)triazole. The influence of these results on the input data required by models which simulate persistence in field soil is discussed. [ABSTRACT FROM AUTHOR] more...

The uptake from solution of maleic hydrazide, flamprop and a series of phenoxyacetic acids by roots, and their subsequent translocation to shoots, was measured in barley. Both uptake and translocation increased as the pH of the solution decreased, the magnitude of the change varying amongst the chemicals tested. Uptake by roots could be accounted for by the ion-trap mechanism, which assumes that entry of the chemicals occurs largely by passive diffusion of the undissociated form of the acids, with passage of the anions across the cell membranes being very slow. The ratio of the permeability of the cell membranes to the undissociated and dissociated forms of the acids was estimated from the accumulation in roots, and in the phenoxyacetic acid series this ratio was maximal (4×105) for compounds of intermediate lipophilicity. Maleic hydrazide and flamprop had much lower ratios, 1.8×102 and 103 respectively; the value for flamprop was much less than for phenoxyacetic acids of similar lipophilicity, such as 2, 4- dichlorophenoxyacetic acid, indicating that lipophilicity may not be the sole factor determining the behaviour of weak acids in plants. Translocation to shoots was approximately proportional to the chemical concentrations in the roots. [ABSTRACT FROM AUTHOR] more...

Techniques using R. communis were modified to enable the movement of chemicals in phloem and the factors controlling their distribution in the plant to be described quantitatively. The non-ionised chemicals tested, aminotriazole, O-methylcarbamoyloximes (including aldoxycarb and oxamyl) and phenylureas, spanning a range of lipophilicity of log KOW= −0.87 to +2.27, all freely entered the phloem. However, only the more polar compounds were retained sufficiently in the phloem to be transported over long distances, indicating that polar compounds cross cell membranes more slowly than compounds of intermediate lipophilicity; these findings substantiate the 'intermediate permeability hypothesis' of phloem translocation of xenobiotics. However, the amount of chemical reaching or retained in the sink tissues, especially in the root, was small even for the chemicals that were translocated best in the phloem. [ABSTRACT FROM AUTHOR] more...

Uptake of weak acids by roots of Ricinus communis and their translocation to shoots increased as the pH of the nutrient solution decreased, the behaviour being closely similar to that observed for the same compounds in barley. Phenoxyacetic acids (p Ka ˜3) with log Kow, for the undissociated acid of between 1 and 3 were readily taken up and translocated in phloem to the apical leaf and the upper stem of R. communis following injection into the petioles of mature leaves; strong retention of these chemicals in the stem rapidly depleted their concentration in phloem down the stem so that very little was found in roots. A more polar and a more lipophilic phenoxyacetic acid were poorly translocated from the petioles, and flamprop (pKa 3.7, log Kow, 2.9) was predominantly xylem-mobile. Maleic hydrazide (pKa 5.65, log Kow, −0.6) was taken up from the petioles rather slowly but was readily phloem-translocated from the mature leaves, and little was retained by the stem, permitting appreciable amounts to reach the roots and nutrient solution. Concentrations of these weak acids in leaf phloem were up to ten times higher than in the adjacent leaf cells, and could be predicted reasonably well assuming that accumulation in phloem was purely a physico-chemical process occurring due to the ion-trap effect, taking values obtained from barley roots for the ratio of the permeabilities of membranes to the undissociated and dissociated forms of the acids. [ABSTRACT FROM AUTHOR] more...

The carbamoyloxime pesticides methomyl, oxamyl and aldicarb, together with the oxidation products of aldicarb, are known to break down much more rapidly in certain anaerobic subsoils than in the aerobic topsoils from the same site. Ferrous ions have now been shown to be involved in this reaction. Oxamyl was degraded in aqueous solutions at 30°C containing 250 μg ml−1 Fe2+ with a half-life of about 10 h, independent of pH in the range of 5.65-7.66; the observed products of this reaction were N,N-dimethyl-l-cyanoformamide and methanethiol. These same products, rather than the oximino hydrolysis product observed from degradation in aerobic soils, were rapidly and quantitatively formed from oxamyl in suspensions of anaerobic reduced subsoils (Fe2+ concentration 27-41 μg ml−1 soil water), but oxamyl was rather stable in water-saturated Vredepeel subsoil (Fe2+ concentration 0.65 μg ml−1) in which the redox potential was much higher. Methomyl behaved similarly. The rates of reaction in the suspensions of anaerobic subsoils were greater than expected from the concentrations of Fe2+ in the soil water, but most of the Fe2+ present in soil was bound to the soil particles by cation exchange and this bound Fe2+ may have participated. Breakdown of aldicarb was accelerated both in solutions of Fe2+ and in the suspensions of anaerobic reduced subsoils, though the rate enhancement was less than observed with methomyl and oxamyl; 2-methyl-2-methylthiopropionitrile and 2-methyl-2-methylthiopropionaldehyde were the observed products from aldicarb in anaerobic soil but only the former was produced in Fe2+ solutions; the corresponding nitriles and aldehydes were also yielded by aldicarb sulphoxide and aldicarb sulphone in the anaerobic, reduced subsoils. [ABSTRACT FROM AUTHOR] more...

Two analogues of the aphid alarm pheromone ( E)-β-farnesene, a trifluorofarnesene and a difluoro-1-norfarnesene, were found to be highly active and were more readily detectable than the parent compound. For ( Z)-hexadec-11-enal, a component of some lepidopteran sex attractant pheromones, replacement of the carbonyl oxygen with a difluoromethyl group to give a difluoroheptadecadiene resulted in loss of activity. A trifluoroacetoxyhexadecanolide was a more volatile analogue of the mosquito oviposition pheromone (−)-(5 R,6 S)-6-acetoxy-5-hexadecanolide and was highly active. [ABSTRACT FROM AUTHOR] more...

The polarities of pyrethroids and their performance as knockdown and killing agents against houseflies are discussed. The optimum polarity for knockdown is here shown to be greater than that needed for kill, probably because knockdown depends on relatively rapid penetration through the cuticle into the haemolymph and thence to the site of action. [ABSTRACT FROM AUTHOR] more...