Organophosphorothioates and synergised synthetic pyrethroids as grain protectants on bulk wheat

Organophosphorothioates and synergised synthetic pyrethroids were used in duplicate field trials carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays using malathion-resistant strains of insects were carried out on samples of treated grain at intervals over 9 months. These established that all treatments were generally effective. Deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ fenvalerate (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1), fenitrothion (12 mg kg^?1)+ phenothrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) and pirimiphos-methyl (4 mg kg^?1)+ permethrin (1 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) controlled common field strains of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.). Against a highly resistant strain of S. oryzae, deltamethrin (2 mg kg^?1)+ piperonyl butoxide (8 mg kg^?1) was superior to the remaining treatments. All treatment combinations completely prevented progeny production in Tribolium castaneum (Herbst), T. confusum Jacquelin du Val and in Ephestia cautella (Walker). Residues of deltamethrin, fenvalerate, permethrin and phenothrin were determined and shown to be highly persistent on stored wheat. During milling, residues accumulated in the bran fractions and were reduced in white flour. They were not significantly reduced during baking.     

Organophosphorus and synergised synthetic pyrethroid insecticides as grain protectants for stored sorghum

A field experiment was carried out on bulk sorghum stored for 26 weeks in concrete silos in South Queensland. No natural infestation occurred. Laboratory bioassays of treated grain, in which malathion-resistant strains of insects were added to grain samples, indicated that all the treatments were generally effective. Deltamethrin (2mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹), fenitrothion (12mg kg⁻¹)+fenvalerate (1 mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹), and fenitrothion (12mg kg⁻¹)+phenothrin (2mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹) controlled typical malathion-resistant strains of Sitophilus oryzae (L.), Rhyzopertha dominica (F.), Tribolium castaneum (Herbst) and Ephestia cautella (Walker). Pirimiphos-methyl (6mg kg⁻¹)+permethrin (1mg kg⁻¹)+piperonyl butoxide (8mg kg⁻¹) allowed some survival of adults and progeny production by S. oryzae after 12 weeks, and by one strain of R. dominica throughout. Chemical assays established that the residues and rates of breakdown of these grain protectants on sorghum conformed to the general pattern on other cereal grains. Residues at the conclusion of the experiment were below the individual Maximum Residue Limits recommended by the Codex Alimentarius Commission.     

Fenitrothion plus (1R)-phenothrin,and pirimiphos-methyl plus carbaryl,as grain protectant combinations for wheat

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 9 months, using malathion-resistant strains of insects, established that treatments were generally effective. Fenitrothion (12 mg kg^?1)+ (1R)-phenothrin (2 mg kg^?1) was more effective than pirimiphos-methyl (6 mg kg^?1) + carbaryl (10 mg kg^?1) against Sitophilus oryzae (L.) and Ephestia cautella (Walker); the order of effectiveness was reversed for S. granarius (L.). Against Rhyzopertha dominica (F.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.), both treatments effectively prevented the production of progeny. The order of persistence was pirimiphos-methyl> (1R)-phenothrin>carbaryl or fenitrothion. During processing from wheat to white bread, residues were reduced by 98% for carbaryl, >44% for (1R)-phenothrin, 98% for fenitrothion and 85% for pirimiphosmethyl.     

Extensive pilot use of the grain protectant combinations,fenitrothion plus bioresmethrin and pirimiphos-methyl plus bioresmethrin

Each of the combinations, bioresmethrin (1 mg kg^?1) plus pirimiphos-methyl(6 mg kg^?1) or fenitrothion (12 mg kg^?1), was applied in 1976 to grain in 21 commercial storages. Grain condition and protectant residues were regularly monitored. Three storages became infested with Rhizopertha dominica (F.), but all storages remained free of other insect species. In two of the three infested storages, application of protectant was uneven, and the third became infested only after 8 months of storage. Despite some variations in recovered residues between sites, the mean residue levels were accurately described by predictive models. Falls in temperature during storage varied considerably, and were related to factors other than climate and bin size. There was a marked effect by aeration with ambient cold air on both the grain temperature and the rate of loss of residues. Results of collaborative studies on the determination of residues indicate a need for regular check programmes of analysis, and confirm previous conclusions that residues of fenitrothion and pirimiphos-methyl can be accurately and conventionally determined.     

Chlorpyrifos-methyl plus bioresmethrin; Methacrifos; Pirimiphos-methyl plus bioresmethrin; and synergised bioresmethrin as grain protectants for wheat

Field trials with various pesticide combinations were carried out on bulk wheat in commercial silos in Queensland, South Australia and Western Australia. Laboratory bioassays on samples of treated grain at intervals over 8 months using malathion-susceptible and malathion-resistant strains established the following orders of efficacy: against Sitophilus oryzae (L.), chlorpyrifos-methyl 10 mg kg^?1 + bioresmethrin 1 mg kg^?1 = methacrifos 15 mg kg^?1 in aerated storage > pirimiphos-methyl 4 or 6 mg kg^?1 + bioresmethrin 1 mg kg^?1 = bioresmethrin 4 mg kg^?1 + piperonyl butoxide 16 mg kg^?1; against Rhyzopertha dominica (F.), bioresmethrin 4 mg kg^?1 + piperonyl butoxide 16 mg kg^?1 > methacrifos 15 mg kg^?1 > chlorpyrifos-methyl 10 mg kg^?1 + bioresmethrin 1 mg kg^?1 = pirimiphos-methyl 4 or 6 mg kg^?1 + bioresmethrin 1 mg kg^?1. All treatments completely prevented production of progeny in Sitophilus granarius (L.), Tribolium castaneum (Herbst), T. confusum Jackquelin du Val and Oryzaephilus surinamensis (L.). The biological efficacy of methacrifos was greater and the rate of degradation lower in aerated than in non-aerated storage. Residue levels of all compounds were determined chemically and were below proposed international residue levels to be considered by the Codex Alimentarius Commission.     

Synergised cyfluthrin and cypermethrin as grain protectants on bulk wheat

Duplicate field trials were carried out on bulk wheat in commercial silos in Queensland and New South Wales. Laboratory bioassays on samples of treated grain at intervals over 8 or 9 months storage using malathion-resistant strains of insects established that treatments were generally effective. Cyfluthrin (2 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) and cypermethrin (4 mg kg^?1) plus piperonyl butoxide (10 mg kg^?1) completely controlled two strains of Sitophilus oryzae L. Control of a third strain by the cypermethrin combination was incomplete after 11/2 months and neither controlled a multi-resistant laboratory strain. Both combinations were effective against Rhyzopertha dominica F., Tribolium castaneum Herbst and Ephestia cautella Walker. No natural infestation developed in the treated grain in any silo. Mean residues of cyfluthrin and cypermethrin after 9 months storage were 58% and 52% of the calculated application rates, respectively. Compared with overall concentrations in the wheat, residue levels were higher in bran and pollard and lower in white flour. During baking, residues decreased by up to 29%. Operators experienced respiratory irritation associated with exposure to both combinations and alternative formulations would be required for use of these materials in grain storage.     

The persistence and activity of insecticide spary deposits on woven polypropylene fabric

Wettable powder formulations of the organophosphorus insecticides, fenitrothion and pirimiphos-methyl, and the pyrethroids, permethrin and deltamethrin, have been compared for persistence and activity on woven polypropylene fabric; the residues produced in maize kept under the test sheets have also been measured. The test insects were Sitophilus oryzue (L.) and Tribolium custuneum (Herbst). Permethrin at 41 and 83 mg m^?2 was completely effective for the full 12 weeks of the experiment. Deltamethrin at 6.2 and 12.5 mg m^?2 was almost equally effective but after 4 weeks the deposit was slower acting against S. oryzae. The organophosphorus compounds were effective only up to 2 weeks at 250 mg m^?2 and up to 4 weeks at 500 mg m^?2. No residues could be detected under the pyrethroids but the organophosphorus insecticides gave residues of 2–4 mg kg^?1 on a thin layer of grain. This residue was biologically effective against the test insects.     

Ethyl formate plus methyl isothiocyanate--a potential liquid fumigant for stored grains

BACKGROUND: Methyl bromide is being phased out for use on stored commodities, as it is listed as an ozone‐depleting substance, and phosphine is the fumigant widely used on grains. However, phosphine resistance occurs worldwide, and phosphine fumigation requires a long exposure period and temperatures of > 15 °C. There is an urgent requirement for the development of a fumigant that kills insects quickly and for phosphine resistance management. This paper reports on a new fumigant formulation of 95% ethyl formate plus 5% methyl isothiocyanate as an alternative fumigant for stored grains. RESULTS: The formulation is stable for at least 4 months of storage at 45 °C. A laboratory bioassay with the formulation showed that it controlled all stages of Sitophilus oryzae (L.), Sitophilus granarius (L.), Tribolium castaneum (Herbst), Rhyzopertha dominica (F.), Trogoderma variabile Ballion and Callosobruchus maculatus (Fabricius) in infested wheat, barley, oats and peas at 80 mg L^?1 for 5 days, and in canola at both 40 mg L^?1 for 5 days and 80 mg L^?1 for 2 days at 25 ± 2 °C. After an 8–14 day holding period, residues of ethyl formate and methyl isothiocyanate in wheat, barley, peas and canola were below the experimental permit levels of 1.0 and 0.1 mg kg^?1. However, fumigated oats needed an 18 day holding period. CONCLUSIONS: The findings suggest that the ethyl formate plus methyl isothiocyanate formulation has potential as a fumigant for the control of stored‐grain insect pests in various commodities. Copyright © 2011 Society of Chemical Industry     

Combinations of pirimiphos-methyl and carbaryl for stored grain protection

In laboratory experiments, whole wheat was treated with pirimiphos-methyl or carbaryl or combinations of these two insecticides; the treated grain was then adjusted to a 12% moisture content and stored at 25°C for bioassay at various intervals over a period of 39 weeks. Pirimiphos-methyl at 5.1 mg kg^?1 effectively controlled Sitophilus granarius (L.) and Tribolium confusum Jacquelin du Val but was ineffective against Rhyzopertha dominica (F.) CRD 118, a strain showing malathion resistance. Conversely, carbaryl at 6.5 mg kg^?1 (but not at 3.1 mg kg^?1) was effective against R. dominica, but ineffective against the other two species. A combination of pirimiphosmethyl + carbaryl, at 1.8 + 5.1 mg kg^?1, controlled S. granarius and R dominica but not T. confusum, whilst a 4.2 + 3.4 mg kg^?1 combination was relatively more effective against T. confusum but less so against R. dominica. In a separate experiment, whole wheat was treated with carbaryl at 2.5, 5.0 and 7.5 mg kg^?1 (nominal rates). Samples were stored and, at various times after the treatments, were bioassayed with R. dominica CRD 2, at 20, 25, 30 and 35°C. The results were comparable with those for the CRD 118 strain, but efficacy was reduced at higher temperatures. The combination of pirimiphos-methyl at 4–5 mg kg^?1 and carbaryl at 5–6 mg kg^?1 is suggested as a potentially useful grain protectant where R. dominica is a problem and long term storage is required. These results are discussed in relation to the protection of stored grain in Australia.     

Fungal invasion and mycotoxin contamination of stored sorghum grain as influenced by threshing methods

Sanitation from harvest to storage is a key factor in eliminating sources of infection and reducing levels of mycotoxigenic fungal invasion, and thereby mycotoxin contamination. This study was conducted at Haramaya University, Eastern Ethiopia to investigate the effects of threshing methods on fungal invasion and mycotoxin contamination of sorghum grain. The methods included threshing on bare ground, cow-dung-painted ground, concrete asphalt and canvas. The threshed grain was kept separately in bags in three replications in a completely randomized design and stored for five months. The results revealed that all the sorghum grain samples taken from different threshing methods were contaminated with both Aspergillus and Fusarium species. There were variations in fungal invasion between samples taken immediately after threshing and stored samples. The level of Aspergillus spp. invasion was much higher in the latter in sorghum grain threshed on bare ground. The concentration of aflatoxin B₁ was gradually increased, whereas the total fumonisin concentration was decreased with the storage duration both in 2013 and 2014. On stored sorghum grain, the highest (1.97 µg kg^?1) and the lowest (0.70 µg kg^?1) mean aflatoxin B₁ concentrations were recorded from sorghum grains threshed on bare ground and on canvas, respectively. Sorghum grain obtained from canvas threshing method had significantly lower mean total fumonisin content (142.5, 54.9 µg kg^?1) than grain from the other methods at threshing. The current work clearly demonstrated the effect that threshing might have on fungal invasion and mycotoxin contamination of sorghum grains. .     

Acaricides and their residues in Spanish commercial beeswax

BACKGROUND: The purpose of this work was to determine residues of acaricides in recycled Spanish beeswax. RESULTS: Chlorfenvinphos, fluvalinate, amitraz, bromopropylate, acrinathrin, flumethrin, coumaphos, chlorpyrifos, chlordimeform, endosulfan and malathion residues were determined by GC‐µECD/NPD/MS detection. Owing to the extreme instability of amitraz, this analyte was transformed into the stable end‐metabolite 2,4‐dimethylaniline, later derivatised with heptafluorobutyric anhydride and determined by GC‐µECD/MS. Recoveries from spiked samples ranged from 86 to 108%, while quantification limits varied from 0.10 to 0.30 mg kg^?1 using GC‐µECD/NPD, and from 12 to 85 µg kg^?1 by GC‐MSD. Of a total of 197 samples analysed, only eight samples (4%) were free of residues of chlorfenvinphos (0.019–10.6 mg kg^?1), fluvalinate was present in 93.6% of samples analysed (0.027 –88.7 mg kg^?1), while coumaphos was confirmed in only five of the 134 samples analysed at concentrations of less than 195 µg kg^?1. The remaining acaricides were identified with different levels of incidence at concentrations from 12 to 231 µg kg^?1. CONCLUSIONS: Residues of acaricides were found in an extensive number of beeswax samples. The contamination with chlorfenvinphos and tau‐fluvalinate was very relevant, particularly as chlorfenvinphos is not legally authorised for use in beekeeping. The possible impacts of the main acaricides detected on larval and adult honey bees are discussed. Copyright © 2010 Society of Chemical Industry     

The behaviour of residues of benzoylprop-ethyl and its breakdown products in wheat

Samples of wheat grain and straw have been analysed from trials with the wild oat herbicide benzoylprop-ethyl ( I ) in several countries. Following recommended commercial treatments (application of 1.0–1.6 kg ha^?1 at Feekes growth stage G-J), total residues of I and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL - alanine (free and conjugated) were low and in the majority of instances they were < 0.01 mg kg^?1 in samples of grain from the UK, although rather higher residues were detected in some grain samples from other countries. Residues in straw were higher, but normally did not exceed 2 mg kg^?1, and were rather variable, possibly as a result of differences in agricultural practice.     

The behaviour of residues of flamprop-isopropyl and its breakdown products in barley

Residue data are reported for flamprop-isopropyl ( I ) in barley grain and straw samples following applications of the herbicide to crops grown in eight countries. The samples were analysed for I and its hydrolysis product N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL -alanine ( II ). Following recommended applications (normally 1 kg ha^?1 at Feekes scale G-I/J), residues of I and II in the grain were low (90% were <0.02 mg kg^?1 for I , 86% were <0.06 mg kg^?1 for II , levels which were essentially the limits of determination). Residues in straw were higher and more variable, but again 63 and 77% of samples were below 1 mg kg^?1 for I and II , respectively.     

Insecticidal efficacy of fipronil against four stored‐product insect pests: influence of commodity,dose, exposure interval,relative humidity and temperature

BACKROUND: Fipronil is an insecticidal pyrazole that is commonly used as an insecticide in field crops, urban pesticide and veterinary medicine, but there are no reports of its evaluation against stored‐product insects. Three series of laboratory bioassays were conducted to assess fipronil as a potential grain protectant against adults of Sitophilus oryzae (L.), Tribolium confusum Jacquelin du Val, Rhyzopertha dominica (F.) and Prostephanus truncatus (Horn). Factors such as dose (0.01, 0.1, 1 and 10 mg fipronil kg^?1 grain), exposure interval (24 h, 48 h, 7 days and 14 days), temperature (20, 25 and 30 °C), relative humidity (RH; 55 and 65%) and commodity (wheat, maize, barley and paddy rice) were evaluated with regard to their impact on the insecticidal activity of fipronil. Progeny production was assessed after 64 days of exposure. RESULTS: At doses of < 1 mg fipronil kg^?1 grain, efficacy of fipronil was enhanced by an increase in temperature from 20 to 25 °C against S. oryzae or R. dominica for exposures of > 48 h and against T. confusum or P. truncatus for exposures of > 24 h. A further increase in temperature from 25 to 30 °C, although it enhanced efficacy at doses of < 1 mg fipronil kg^?1 grain against S. oryzae at all exposure intervals and against T. confusum after 7 days of exposure, it was negatively associated with efficacy against R. dominica or P. truncatus for exposures of > 24 h. By contrast, increase in RH did not have a significant impact on efficacy of fipronil. Although the performance of fipronil among the tested commodities was species dependent, this substance appeared to be less effective in paddy rice than in barley, maize and wheat. Regardless of the treated commodity, progeny production of all the tested species was almost suppressed with doses higher than 0.1 mg fipronil kg^?1 grain. CONCLUSIONS: Fipronil appeared to be a very effective alternative to the existing substances in stored‐grain protection at doses equal to or higher than 1 mg fipronil kg^?1 grain, and thus these doses require further evaluation in terms of safety for the consumer and residues on stored products. Copyright © 2010 Society of Chemical Industry     

Efficacy of Surface Dust Treatments of Pirimiphos-Methyl and Etrimfos when Applied to Commercially Stored Wheat and Barley

Commercially stored wheat and barley were surface treated with dust formulations of pirimiphos-methyl and etrimfos at the manufacturer's recommended application rate. Samples were taken at four-weekly intervals for 32 and 16 weeks for wheat and barley respectively. Pesticide efficacy was determined using insect bioassays and chemical analysis of residues. There was no evidence to suggest a decline in residue levels of either pesticide over the experimental period. However, considerable variation was observed in the residue levels recorded at different sample points and also between residue levels recorded for the same point over the trial period. Control of susceptible strains of Tribolium castaneum (Herbst), Oryzaephilus surinamensis (L.) and Sitophilus granarius (L.) was achieved where recovered pesticide residues remained above 1 mg kg⁻¹ pirimiphos-methyl and 1·6 mg kg⁻¹ etrimfos.     

Potential of piperonyl butoxide‐synergised pyrethrins against psocids (Psocoptera: Liposcelididae) for stored‐grain protection

BACKGROUND: Piperonyl butoxide (PB)‐synergised natural pyrethrins (pyrethrin:PB ratio 1:4) were evaluated both as a grain protectant and a disinfestant against four Liposcelidid psocids: Liposcelis bostrychophila Badonnel, L. entomophila (Enderlein), L. decolor (Pearman) and L. paeta Pearman. These are key storage pests in Australia that are difficult to control with the registered grain protectants and are increasingly being reported as pests of stored products in other countries. Firstly, mortality and reproduction of adults were determined in wheat freshly treated at 0.0, 0.75, 1.5, 3 and 6 mg kg^?1 of pyrethrins + PB (1:4) at 30 ± 1 °C and 70 ± 2% RH. Next, wheat treated at 0.0, 1.5, 3 and 6 mg kg^?1 of pyrethrins + PB (1:4) was stored at 30 ± 1 °C and 70 ± 2% RH and mortality and reproduction of psocids were assessed after 0, 1.5, 3 and 4.5 months of storage. Finally, the potential of synergised pyrethrins as a disinfestant was assessed by establishing time to endpoint mortality for adult psocids exposed to wheat treated at 3 and 6 mg kg^?1 of synergised pyrethrins after 0, 3, 6, 9 and 12 h of exposure. RESULTS: Synergised pyrethrins at 6 mg kg^?1 provided 3 months of protection against all four Liposcelis spp., and at this rate complete adult mortality of these psocids can be achieved within 6 h of exposure. CONCLUSION: Piperonyl butoxide‐synergised pyrethrins have excellent potential both as a grain protectant and as a disinfestant against Liposcelidid psocids. Copyright © State of Queensland, Department of Employment, Economic Development and Innovation, 2010. Published by John Wiley and Sons, Ltd.     

The metabolism of tefluthrin in the goat

A goat was dosed orally with [¹⁴C]tefluthrin, twice daily for 4 days, at a rate equivalent to 10.9 mg kg^?1 in its diet. Within 16 h of the final dose, 70.1% of the dose had been excreted (urine 41.4%, faeces 28.7%). Extensive metabolism occurred in the goat by ester cleavage and oxidation at a variety of positions on the molecule. Low radioactive residues were detected in the milk (0.076 mg kg^?1), fat (0.076 mg kg^?1) and muscle (0.016 mg kg^?1), with tefluthrin as the largest individual component of the residue (milk 66.5%, fat 76.7%, muscle 34.2%). Higher residues were present in the kidney (0.3 mg kg^?1) and liver (1.0 mg kg^?1) and only a small percentage of this residue was due to tefluthrin (kidney 3.4%, liver 6.1%). The remainder of the residue in the kidney and liver was a complex mixture of metabolites. Most of the kidney metabolites were identified, but a high proportion of the liver residue was due to six unidentified polar compounds.     

Effects of N, P and K on Striga asiatica (L.) Kuntze seed germination and infestation of sorghum

Sorghum (Sorghum bicolor (L.) Moench) plants were grown in pots with 12.5 and 50 mg applied N kg^?1 soil. With an increase of soil N, the Striga asiatica (L.) Kuntze infestation, as well as the sorghum shoot dry matter losses due to infestation, decreased. The relative differences in stimulant capacity to induce Striga seed germination among the four sorghum genotypes were not consistent over the 0 to 150 mg N 1^?1 range. The sorghum root exudate was considerably more active at 0 mg N 1^?1, than at 30 mg N 1^?1, and the stimulant produced at 150 mg N 1^?1 failed to induce Striga seed germination. Presence of N in the growth medium considerably reduced the effectiveness of the stimulating substance produced by sorghum roots, whereas K promoted stimulant activity only in the absence of N. The presence or absence of P in the growth medium did not affect Striga seed germinability, probably due to the inability of this element to interfere with the production or activity of the stimulating substance from the host plants. It can be concluded, therefore, that sorghum plants seem to produce active root exudate only in conditions of N deficiency.     

The chemical control of the lesser date moth,Batrachedra amydraula meyr., and residue levels of organophosphate insecticides in dates

Larvae of the lesser date moth (Batrachedra amydraula Meyr.) cause damage to dates in Iraq. A formulation based on a mixture of equal parts of wheat flour and pollen grains and containing either chlorpyrifos, fenitrothion or pirimiphos-methyl (all at 5 mg kg^?l) was dusted (5 g formulation bunch^?1) onto female clusters of dates at the time of pollination. Numbers of larvae, yield of dates and insecticide residues were monitored over a three-month period. Results showed that, by this technique, all three insecticides were effective in controlling the pest but that fenitrothion and chlorpyrifos were better than pirimiphos-methyl.     

Comparative purification methods for determination of triadimenol residues in plant material

Two procedures are described for the determination of residues of triadimenol and compared on cereal material. After extraction, purification is carried out by Florisil column chromatography in method I and by semi-preparative High-Performance Liquid Chromatography in method II. Triadimenol residues are quantified by gas chromatography with a thermoionic detector. With method I, interference was observed but not with method II. This specific procedure has been tested on other plant materials. Recoveries in the range of 90–98% indicate that this procedure is suitable for residue analysis of this fungicide with detection limits of 0·008 mg kg^?1 in wheat grains, 0·03 mg kg^?1 in wheat straw and 0·004–0·008 mg kg^?1 in other plants. Maximum residue limits in France are: 0·1 mg kg^?1 in grain, 2·0 mg kg^?1 in straw and 1·0 mg kg^?1 in other vegetables and fruit.