Modelling penetration of plant cuticles by crop protection agents and effects of adjuvants on their rates of penetration

Schönherr, Jörg; Baur, Peter

doi:10.1002/ps.2780420308

Cited by 144 publications

(148 citation statements)

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“…Later, Baur (1993) and SchSnherr and Baur (1994) pointed out that correlations between log k* (or log D) and log Vx are purely descriptive and have no physical meaning, while the slopes and y-intercepts of the graphs log k* vs. Vx have definite physical meaning. The y-intercept (k *~ represents the mobility of a hypothetical molecule of zero molar volume while the slope of the graph [3'(13' = [3/2.3) is a measure of size selectivity of the barrier and its reciprocal value is related to the free volume of diffusion.…”

Section: Discussionmentioning

confidence: 98%

Mobilities of organic compounds in plant cuticles as affected by structure and molar volumes of chemicals and plant species

Baur

Marzouk

Schönherr³

et al. 1996

Planta

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Abstract. Solute mobilities of 28 compounds in isolated cuticular membranes (CM) from Capsicum annuum L. fruit, Citrus aurantium L. and Pyrus communis L. leaves were studied using unilateral desorption from the outer surface. First-order rate constants of desorption (k*), which are directly proportional to the diffusion coefficient in the waxy outer limiting skins of cuticles were measured. When log k* was plotted vs. molar volumes of test compounds linear graphs were obtained. The y-intercepts of these graphs (k *~ represent the mobility of a hypothetical molecule having zero molar volume and the slopes of the graphs (13') represent the size selectivity of the barrier and are related to the free volume available for diffusion. Thus, solute mobilities in cuticles are composed of two independent terms which are subtractive. If k *~ and 13' are known, k* can be estimated for any solute from its molar volume (Vx) using the equation log k*= log k *~ 13'Vx. These parameters were used to analyse the effects of plant species, extraction of cuticular waxes and molecular structure of solutes on solute mobilities in plant cuticles. For aliphatic solutes, k *~ was a factor of 10 smaller than for cyclic compounds, while 13' was 0.011 and 0.012, respectively. The k*-values for CM of the three species were very similar, but 13' was higher for bitter-orange CM (0.012) than for those 9 f pepper fruits and pear leaves (0.009). This has the consequence that differences in solute mobilities (k *~ among cuticles from different plan species increase with increasing molar volumes of solutes. Our data and our analysis provide evidence that constituents of cuticular waxes are mobile, at least in the solid amorphous wax fraction, but mobility decreases rapidly with increasing molar volume. For instance, if 13' amounts to 0.01, mobilities of wax monomers decrease by a factor of 10 for every increase in molar volume of 100 cm 3. mol-1. Thus, hexaAbbreviations: CM = cuticular membrane(s); 2,4-D = 2,4-dichlorophenoxyacetic acid; LAB = lactic acid buffer; MX = polymer matrix membranes; UDOS = unilateral desorption from the outer surface Correspondence to: P. Baur; FAX: 49 (5066) 82 61 1 l decanoic acid is quite mobile in the amorphous wax fraction of Citrus (k* = 1.5 x 10 -6. s-l), but for dotriacontane having twice the molar volume, k* was only 2.5 x 10-9. s-a, which is almost three orders of magnitude smaller. Wax esters have even higher molar volumes and their mobilities will be even smaller (about 4 x 10-12. s-1 for a C4s-ester). Since low chain mobilities are a prerequisite for low mobilities and permeabilities, the selective advantage of high-molecular-weight wax monomers in plant cuticular waxes becomes obvious. Extracting cuticular waxes from pear leaf CM increased solute mobilities by a factor of 182, but it had no effect on size selectivity. We interpret this result as evidence to the effect that cuticular waxes reduce mobility by increasing tortuosity of the diffusion path, rather than by decreasing the mean free path of diffusiona...

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Section: Discussionmentioning

confidence: 98%

Mobilities of organic compounds in plant cuticles as affected by structure and molar volumes of chemicals and plant species

Baur

Marzouk

Schönherr³

et al. 1996

Planta

Self Cite

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“…The higher the pesticide persistence in the fruit, the higher the potential risk to the consumer via food intake. For this reason, studies of the effects of the cuticle and waxes on pesticide persistence can provide important data for the refinement of consumer risk assessment, and inform possible options for the mitigation of pesticide residues in the transport limiting barrier of the cuticle has a large tortuosity which is reduced or removed upon the removal of waxes (Schönherr and Baur, 1994;and Baur et al, 1996).…”

Section: Introductionmentioning

confidence: 99%

Effect of surface waxes on the persistence of chlorpyrifos-methyl in apples, strawberries and grapefruits

Riccio

Trevisan

Capri

2006

Food Additives and Contaminants

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To cite this version:Rossella Riccio, Marco Trevisan, Ettore Capri. Effect of surface waxes on the persistence of chlorpyrifos-methyl in apples, strawberries, and grapefruits. Food Additives and Contaminants, 2006, 23 (07) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 Figure 5. Total amount of chlorpyrifos methyl residues measured in the whole fruit and in four fractions of fruit, A grapefruit, B apple, C strawberry. AbstractThe effects of the cuticle and epicuticular waxes of grapefruit, strawberry and apple on the photodegradation and the penetration of chlorpyrifos-methyl were studied. Photodegradation experiments were conducted by exposing the insecticide to the light of a xenon lamp in the presence of a film of wax extracted from the fruit surface. The half-life of chlorpyrifos-methyl irradiated in absence of waxes was 9.6 min. The half-lives of pesticide irradiated in the presence of wax extracts of apple, grapefruit and strawberry were 83, 34, and 26 min respectively. In penetration studies, fruit with and without wax layers were treated with an aqueous suspension of pesticide. The penetration of the pesticide from the cuticle to the pulp was measured after 24 hours. Samples without wax contained a higher total amount of insecticide than those with wax. No pesticide was detected in samples of apple and grapefruit pulp. Residues were detected in all fractions of strawberry. The waxes and cuticle appear to have some effect on the photodegradation and penetration of chlorpyrifos-methyl in fruit samples.

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“…Low permeability of leaf and fruit cuticles for organic compounds often limits the rates of foliar uptake of pesticides and growth regulators (e.g. Hull 1971;Kirkwood 1987;Schonherr & Baur 1994).…”

Section: Introductionmentioning

confidence: 99%

Lognormal distribution of water permeability and organic solute mobility in plant cuticles

Baur

1997

Plant Cell & Environment

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It is shown that water permeabilities and organic solute mobilities in plant cuticles have a lognormal distribution. Seven-hundred and fifty values for rate constants of desorption (^mobility) of 2,4-D from isolated Citrus aurantium L. cuticles from a population of leaves were pooled and analysed. A histogram of the rate constants of individual cuticles showed a skew distribution with a strong tail to higher values. Cuticular membranes with high values did not differ from others in visual appearance and were not leaky. After log-transformation of original data an almost perfect normal distribution was obtained. Statistical tests showed that a normal distribution of original values is not acceptable. Inspection of older data for water permeability in the same species and experiments using large samples of cuticles from leaves of Pyrus communis L. and Stephanotis floribunda Brongn. and from fruits of Capsicum annuum L. showed a similar distribution, as did inspection of data for experiments with organic solutes. A lognormal distribution was found for cuticles of plants from growth chambers, glasshouses and outdoors as well as for water permeability of intact leaves of Hedera helix L. For small samples the overestimation from using the arithmetic mean of original data can be high, but use of the geometric mean or the median leads to smaller deviations. Removing cuticular waxes from cuticles produced normally distributed samples. A normal distribution was also obtained when organic compounds which increase solute mobility were sorbed into cuticles.

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Modelling penetration of plant cuticles by crop protection agents and effects of adjuvants on their rates of penetration

Cited by 144 publications

References 30 publications

Mobilities of organic compounds in plant cuticles as affected by structure and molar volumes of chemicals and plant species

Mobilities of organic compounds in plant cuticles as affected by structure and molar volumes of chemicals and plant species

Effect of surface waxes on the persistence of chlorpyrifos-methyl in apples, strawberries and grapefruits

Lognormal distribution of water permeability and organic solute mobility in plant cuticles

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