The metabolism of the pyrethroid insecticide (±)-α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethyl-cyclopropanecarboxylate,WL 41706, in the rat

The metabolism of the pyrethroid insecticide α-cyano-3-phenoxybenzyl 2,2,3,3-tetramethylcyclopropanecarboxylate (WL 41706) has been studied in rats using two forms of ¹⁴C-labelling (benzyl- and cyclopropyl-). Excretion of benzyl^?14C was rapid, 57% of the administered dose being eliminated in the urine 48 h after treatment and 40% in the faeces. No significant sex difference was observed. The amount of radioactivity excreted via expired gases was 0.005% of the administered dose and less than 1.5% of the dose remained in the animals 8 days after treatment. The mean percentage recovery of administered dose was 104% for male rats and 97% for female rats. Urinary and faecal metabolites from these rats, and from rats dosed similarly with [cyclopropyl^?14C]-WL 41706 were studied. The rapid metabolism of WL 41706 is due to efficient cleavage of the ester bond by rats in vivo to afford 2,2,3,3-tetramethylcyclopropanecarboxylic acid (partly as glucuronide) and the 3-phenoxybenzyl moiety. Before this cleavage occurs, however, about half of the intake suffers aryl hydroxylation giving the α-cyano-3-(4-hydroxyphenoxy)benzyl ester, part of which is excreted in the bile as a conjugate(s) and part of which is cleaved and eliminated as the O-sulphate of 3-(4-hydroxyphenoxy)benzoic acid and the glucuronide of 2,2,3,3-tetramethylcyclopropanecarboxylic acid. A minor amount of hydroxylation occurs at a trans-methyl group on the cyclopropane acid moiety. The metabolism of WL 41706 by rat liver occurs mainly in the microsomes and mainly via oxidative processes.     

The bioaccumulation and biotransformation of cis,trans-cypermethrin in the rat

The disposition of the pyrethroid insecticide cypermethrin, (RS)-a-cyano-3-phenoxybenzyl (1RS)-cis, trans-3-(2,2-dichlorovinly)-2, 2-dimethylcyclopropane-carboxylate, has been studied in male and female rats following a single toxic oral dose (200mg kg⁻¹) of two radiolabelled forms ([¹⁴C-benzyl] and [¹⁴C-cyclopropyl]) of the insecticide. The bioaccumulation and elimination of ¹⁴C-benzyl-labelled cypermethrin, following repeated administration at a sub-toxic dose (2mg kg⁻¹), has also been studied in male and female rats. Although, at the toxic dose, radioactivity from the two radiolabelled forms was rapidly eliminated in urine and faeces, the increased excretion in the faeces, over that for low doses, was evidence that absorption was incomplete. The major pathways of metabolism involved cleavage of the ester bond, with subsequent hydroxylation and glucuronidation of the cyclopropyl acid moieties, together with hydroxylation and sulphation of the 3-phenoxybenzyl moiety. The absence of sex- or dose-dependent changes was reflected by the constant proportions of these metabolites found in the urine. Constant levels of radioactivity in tissues were achieved rapidly, generally within the first week of repeated administration. Elimination was rapid on the cessation of dosing, although less rapid from the fat and skin. The material in the fat was mainly the cis-isomers of cypermethrin, which were eliminated with a mean half-life of 18.2 days, compared with 3.4 days for the trans-isomers.     

Metabolism and fate of triazophos in rats

The excretion patterns and tissue residues were determined after single and repeated oral dosing of rats with triazophos-¹⁴C Within 4 days after a single oral dose 76.3 % of the ¹⁴C was excreted in the urine and 21.0% in the faeces. After daily application for 12 days 69.5–83.4% of the label was eliminated in urine and 30.9–18.1 % in the faeces. Following prolonged application, however, elimination is distinctly slower. Distribution of radioactive residues in organs and tissue in both test series showed no appreciable or critical concentrations of radioactivity, with the exception of the gastrointestinal tract (contents and walls). Unchanged triazophos and l-phenyl-1,2,4-triazol-3-ol-3-¹⁴C were excreted in the faeces. Renewed release of other metabolites into the gastrointestinal tract apparently does not take place. The following metabolites are detected in the urine: urea-¹⁴C (approx. 85% of the radioactivity excreted with the urine); and three compounds as conjugates with glucuronic acid, i.e. 1-phenyl-l,2,4-triazol-3-ol-3-¹⁴C (approx. 3%), l-phenylsemicarbazide-3-¹⁴C (approx. 5%), and semicarbazide-¹⁴C (approx. 5%). Two further metabolites, so far unidentified, occurred in small quantities.     

The metabolism of the herbicide flamprop-methyl in rats and some comparative data for dogs,mice and rabbits

[¹⁴C]Flamprop-methyl administered orally to rats (3-4 mg kg^?1 body weight) was excreted mostly via the faeces (78.7 and 61.6% in males and females, respectively). Elimination was rapid and 90% of the dose of ¹⁴C was excreted in faeces and urine 0-48 h after dosing. The distribution of ¹⁴C between faeces and urine was different in males and females. No expired [¹⁴C]carbon dioxide was detected and less than 2% of the dose remained in the animals 4 days after dosing. The predominant metabolic pathway was hydrolysis of the ester bond to afford the carboxylic acid which was excreted unchanged and as its glucuronide conjugate. Aromatic hydroxylation occurred at the para- and meta-positions of the N-benzoyl ring. N-(3)-Chloro- 4-fluorophenyl-N-(3,4-dihydroxybenzoyl)-DL -alaninate was also formed. This hydroxylated form of flamprop-methyl was partially O-methylated at the 3-hydroxy group. Flamprop-methyl was also metabolised and eliminated rapidly by dogs, mice and rabbits. The last of these three species afforded very little aromatic hydroxylation and also differed from the others in that the metabolites were eliminated mostly in the urine. Aromatic hydroxylation lay in the order: male rat = female rat > dog= mouse>rabbit (female).     

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.     

Field experiments on the effects of a new pyrethroid insecticide WL-85871 on bees foraging artificial aphid honeydew on winter wheat

Two large and two small plots of winter wheat were enclosed beneath large mesh-covered tunnels. A small beehive was placed in each tunnel and sucrose solution was sprayed on to all of the wheat in order to simulate aphid honeydew. WL-85871 (a 1:1 mixture of two stereoisomers of cypermethrin) as ‘Fastac’ at three dose rates, dimethoate, pirimicarb or water were applied to the larger plots of wheat when the bees were actively foraging the sugar deposits. No increase in bee mortality, compared with that in the pre-treatment period, was observed after the applications of WL-85871 or pirimicarb. By contrast, large numbers of dead bees were found following the applications of dimethoate. Foraging activity in the plots, treated with all dose rates of WL-85871 or with pirimicarb, declined sharply after treatment and remained at a reduced level. With dimethoate no foraging activity occurred after application in either the treated or untreated plots. Only very low concentrations of WL-85871 were detected in post-treament samples of honey, wax, and live or dead bees. It was concluded that the application of WL-85871, to wheat already treated with artificial honeydew, resulted in no adverse effects on the honey-bee colonies.     

The fate of the rodenticide flocoumafen in the rat: Retention and elimination of a single oral dose

A single oral dose of 0.14 mg kg^?1 of [¹⁴C] flocoumafen to rat, which gave a transient, non-lethal, effect, was rapidly absorbed, radioactivity appearing in the blood maximally at 4 h and falling to half maximum value by 8 h. The maximum effect on prothrombin time was at 24 h and the value returned to normal by 48 h. Elimination of radioactivity was very slow, with less than 0.5% of the dose in the urine up to 7 days after dosing, and 23-26% in the faeces (more than half of which appeared in the first 24 h). Most of the administered radioactivity (74-76%) was retained 7 days after dosing. Approximately half of the dose was in the liver; it was eliminated with a halflife of 220 days. At 48 h after dosing, most of the hepatic radioactivity comprised unchanged flocoumafen. Treatments of flocoumafen-dosed rats with warfarin or with cytochrome P450-inducing doses of phenobarbitone were without effect on the hepatic residue of flocoumafen.     

The metabolism in the rat of the herbicidally active isomer (R)- flamprop-methyl in comparison with the racemic form

A single dose (4 mg kg^?1) of ¹⁴ C-labelled (R)-flamprop-methyl to rat was rapidly metabolised and 90% of the dose was eliminated in urine and faeces within 48 h. Four days after dosing, tissue residues were 0–1 μg equivalents g^?1 tissue or much less, with the exception of kidney (0–22 μg g^?1). There was a statistically significant sex difference in the routes of elimination; this may be attributed to differences in the biliary elimination of the major metabolite, flamprop acid, or its glucuronide conjugate. The fate of racemic flamprop-methyl was very similar to that of the (R)-isomer. The major metabolic routes were hydrolysis of the esters to the corresponding acids, hydroxylation of the benzoyl aromatic rings and conjugation. The flamprop acid derived from the (R)-flamprop-methyl was found to be partially converted to the (S)-form (R:S ratio, 87:13). This reaction is discussed in the context of other such biological racemisations recently reported.     

The metabolism of the pyrethroid insecticide cypermethrin in rats; excreted metabolites

The metabolism of the pyrethroid insecticide cypermethrin has been studied in rats using three forms of ¹⁴C-labelling (benzyl-, cyclopropyl- and cyano-) and separate cis- and trans- isomers. The proportion of the dose absorbed from the intestines (50–70% at 2–3 mg kg^?1) is rapidly metabolised and eliminated. The major reaction is cleavage of the ester bond to afford the constituent cis- and trans- acids which are conjugated with glucuronic acid and eliminated in the urine. The 3-phenoxybenzyl portion of the molecule is probably released as the α-hydroxynitrile, which is converted via the aldehyde into 3-phenoxybenzoic acid. This compound is then largely hydroxylated and eliminated as a sulphate conjugate. The cyanide ion is metabolised via predictable routes, for instance, as thiocyanate. Cypermethrin is hydroxylated to some extent before hydrolysis. Most of this hydroxylation occurs at the methyl group trans to the cyclopropane carboxyl group, and at the 4-position of the phenoxy group. cis- Cypermethrin is slightly more stable than the trans-isomer.     

The effects of a new pyrethroid insecticide WL-85871 on foraging honey bees (Apis mellifera L.)

Emulsifiable concentrate formulations of WL-85871 (‘Fastac’) at 10 and 20 g a.i. ha⁻¹, parathion-methyl (MEP) at 500 g a.i. ha⁻¹, and phosalone at 1200 g a.i. ha⁻¹ were individually applied to flowering mustard during June and July 1982. The applications were made by tractor-mounted boom-and-nozzle equipment to small plots in Normandy, France. Before each application, bee hives were placed adjacent to the mustard plots and fitted with either a pollen trap or a dead-bee trap. The application of both dose rates of WL-85871 and phosalone resulted in no increase in bee mortalities and no discernible effect on pollen collection or long-term hive development. In contrast, the application of MEP resulted in substantial bee mortalities, reduced pollen collection and adversely affected hive development. Both dose rates of WL-85871 caused a sharp decline in foraging activity immediately after application, followed by a return to normal activity within a few hours. A prolonged gradual reduction in foraging activity occurred throughout the afternoon period after the phosalone application; with MEP, foraging activity fell rapidly to a very low level and remained so for the rest of that day and the following day. It was concluded that the ground application of WL-85871 at 10 and 20 g a.i. ha⁻¹ had no direct effect on honey bee survival and no observable effect on hive development.     

The dietary toxicity of flocoumafen to hens: Elimination and accumulation following repeated oral administration

In a dietary toxicity study, laying hens received a diet containing the rodenticide flocoumafen at concentrations of 1.5, 5, 10 and 50 mg kg^?1 for five consecutive days. The LC₅₀ at termination following a 28-day observation period was 16.4 mg kg^?1. Livers of birds which received doses of flocoumafen between 5 and 50 mg kg^?1 had concentrations of flocoumafen (1.5 nmol g^?1) that were independent of dose. The data indicate the presence in hen liver of a saturable high-affinity flocoumafen binding site with similar characteristics and capacity to that of the quail and rat. Residues of flocoumafen in samples of breast and leg muscle were low in all exposure groups. Higher, dose-related residues were found in samples of abdominal fat and skin-associated fat and there was a clear demonstration of the transfer of dose-related residues into eggs. In a separate study in which hens were dosed with [¹⁴C]flocoumafen for five consecutive days at a daily rate of 1 and 4 mg kg^?1 body weight, the majority (68 %) of the daily radioactive dose was eliminated over the following 24 hours via excreta. Residues in liver at death or when killed accounted for < 1 % of the cumulative administered radioactivity. Residues in eggs were located primarily in the yolk with maximum concentrations 1.0 mg kg^?1 or 0.18% of the low dose; 2.1 mg kg^?1 or 0.06% of the high dose as [¹⁴C]flocoumafen equivalents were observed at 10 days after start of dosing. Some 40 % of the total activity in the yolk was unchanged flocoumafen.     

Excretion and residues of the herbicides benzoylprop-ethyl flamprop-isopropyl and flamprop-methyl in cows,pigs and hens

Two wild oat herbicides, benzoylprop-ethyl and flamprop-methyl were administered to lactating cows at low dose levels (0.3–3.0 mg/kg in total diet) and the excretion of total metabolites in milk, urine and faeces was measured. Total residues in tissues were also determined. Similarly a third and related herbicide flamprop-isopropyl was fed to cows, pigs and hens (at 0.5 mg/kg in total diet) and the residues were determined in excreta and tissues, including eggs. The amounts of the compounds fed were equivalent to approximately 10–300 times the total residue found in cereal treated in the field. Residues in milk in most cases were well below 0.001 mg/kg; in muscle samples <0.003 mg/kg; and in eggs, 0.0008 mg/kg, decreasing by 50% in approximately 3 days to 0.0001 mg/kg 4 days after the termination of treatment. Elimination of the herbicides from the animals was rapid in every case and this, together with the low residue levels, was attributed to very efficient metabolic de-esterification to the parent carboxylic acid metabolites (benzoylprop and flamprop). These metabolites possess physical properties ideally suited for excretion via the kidneys and bile into urine and faeces and, conversely, unsuited for transport into milk and eggs.     

Toxico‐kinetics,recovery efficiency and microsomal changes following administration of deltamethrin to black Bengal goats

A study of the toxico‐kinetics, recovery percentage from different substrates, cytotoxicity and role of cytochrome P₄₅₀ and b₅ of liver microsome in the metabolism of deltamethrin were carried out in female black Bengal goat. The ALD₅₀ value of deltamethrin in goat by intravenous route lies between 0.2 and 0.6 mg kg^?1. Intravenous disposition kinetics using a dose of 0.2 mg kg^?1 showed that the maximum blood concentration of deltamethrin was recorded at 0.5 min, followed by rapid decline, and a minimum concentration was detected at 6 min after administration. The following values were obtained : Vd_area 0.148 (± 0.02) litre kg^?1; t_1/2 (α) 0.22 (± 0.02) min; t_1/2 (β) 2.17 (± 0.37) min; K_el 1.05 (± 0.24) min^?1; AUC 4.30(± 0.45) µg min ml^?1; Cl_B 0.05 (± 0.006) litre kg^?1 min^?1; T～B 1.93 (± 0.58); fc 0.40(± 0.05). After 10 min, liver retained the maximum residue, and heart, adrenal gland, kidney, spleen, fat and brain also held the insecticide; liver, fat, heart and spleen retained residue after 30 min, and bone, liver and fat retained residue after 60 min of intravenous administration. Oral absorption of deltamethrin was poor and inconsistent, and approximately 65% of administered dose was recovered from faeces and gastrointestinal contents. The excretion of deltamethrin through urine was meagre, and only 0.01 and 0.013% of the administered dose was recovered after 3 and 5 days of oral administration respectively. All the tissues retained the residue after 3 days; while fat, rumen, reticulum, omasum, abomasum, large and small intestine and bone retained the residue after 5 days of oral administration; and the percentage recoveries were 1.73 and 0.027 respectively. Deltamethrin reduced the level of cytochrome P₄₅₀ content of liver microsomal pellet of goat after 5 days of oral administration. Histopathological examination of liver, kidney, heart, spleen brain and lung sections of treated goats did not reveal any pathological changes. © 2001 Society of Chemical Industry     

The metabolism of cis-2,5-dimethylpyrrolidine-1-carboxanilide in rodents

The metabolism of cis-2,5-dimethylpyrrolidine-1-carboxanilide was studied in rats, rabbits, guinea-pigs and mice. The major metabolite in all species was cis-4′-hydroxy-2,5-dimethylpyrrolidine-1-carboxanilide, both free and as glucuronide and sulphate conjugates. About 95% of the compound was absorbed from the gut; over a 3-day period, about 50% of the administered dose was excreted in urine and about 27% in faeces.     

Deposition of spray liquid on the soil below cereal crops after applications during the growing season

The aim of this study was to investigate how big a proportion of the spray liquid applied in a typical application was deposited on the soil surface below the crop. From an agronomical point of view this part of the spray is an undesirable loss of foliar acting pesticides during application and it also constitutes a primary source of leaching and surface run‐off. The investigation was carried out during 1998–2001 in winter wheat and in spring barley. Applications were carried out at approximate intervals of 10 days during the whole growing season in the two cereal crops. The results showed that a high proportion of the spray liquid reaches the soil below the crop during applications at early growth stages corresponding to the growth stages where weed control on farms is carried out. At later growth stages soil deposition declined and reached values below 5% of the applied dose in winter wheat after inflorescence emergence (50–59 BBCH). The spring barley crops remained more open and minimum soil deposit values were approximately 15% of the applied dose at growth stages (50–59 BBCH). During ripening soil deposition values increased again as crop cover decreased.     

A barn owl feeding study with [14c]flocoumafen-dosed mice: Validation of a non-invasive method of monitoring exposure of barn owls to anticoagulant rodenticides in their prey

A study was carried out to assess the feasibility of monitoring the exposure of barn owls (Tyto alba) to an anticoagulant rodenticide, flocoumafen, by analysis of residues in regurgitated pellets following consumption of flocoumafen-contaminated mice. Mice were fed on a diet containing [¹⁴C]flocoumafen, equivalent to 12 mg kg^?1, and killed 24 h later. A single [¹⁴C]flocoumafen-contaminated mouse was fed to each of four captive barn owls, equivalent to 0·11-0·23 mg kg^?1 per bird, followed on seven successive days by control diet (i.e. undosed mice). The [¹⁴C]flocoumafen dose was eliminated by the owls over the eight-day period in pellets (44%, range 35–55%) and faeces (18%, range 11–21%), with the highest residues being observed in samples from the first 24-h period. Further detailed analysis of the pellets confirmed that flocoumafen residues in the first-day pellets represented 15% (range 8–26%) of the original flocoumafen residues ingested by the barn owls. Calculations based on these data and typical flocoumafen residues in live captured rodents (following baiting) confirm that pellet residue analysis is a sensitive and appropriate method for the non-invasive monitoring of exposure of barn owls to flocoumafen. There were no symptoms of anticoagulant poisoning in any of the birds; two of the birds were successfully paired the next season and produced fledgelings.     

The metabolic fate of tridemorph in rats

A single oral dose of [¹⁴C]tridemorph was partly, but rapidly absorbed by rats. Most of the radioactivity was excreted with a half-life of about 15 h. During 5 days, 42.6% was excreted in the urine, 46.7% in the faeces, 1.5% in the expired air and 3.4 % was still retained. 24 % was excreted in the 48 h bile. Sequential wholebody autoradiography indicated that much of the radioactivity was confined to the gastrointestinal tract, liver and kidneys. There was no unexpected uptake of radioactivity. Urinary metabolites were more polar than tridemorph and were also detected in the bile and faeces. The major metabolite in 24 h urine, accounting for 22.3% of the dose appeared to be a side-chain hydroxylated derivative. Cleavage of the morpholine ring was limited to about 1.5 % of the dose.     

Some effects of paraquat on crop establishment in killed swards

The establishment of crops direct-drilled after various times into swards treated with paraquat (1,1′-dimethyl-4,4′-bipyridylium- 2/A) was examined. Best results with Brassica napus and B. oleracea were obtained with 1–1 kg/ha applied 7 days before drilling and 2–3 kg/ha applied 14 days before. Although delaying drilling from 7 to 14 days after application reduced the phytotoxicity, the higher dose was needed when drilling was delayed, to reduce competition from the sward regrowth. In the glasshouse, mulches of paraquat-treated herbage affected seedling growth and development of Brassica napus, Hordeum vulgare and Lolium perenne; B. napus was the most susceptible. Quelques effets du paraquat sur des cultures implantées aprés destruction d'herbages L'implantation de cultures en semis direct, apres divers intervalles de temps, dans des herbages trait6s au paraquat (l,r-diméthyl-4-4′-bipyridylium-2/4) a été examinée. Avec Brassica napus et B. oleracea, les meilleurs résultats ont été obtenus par des applications de 1,1 kg/ha et de 2,3 kg/ha, respectivement 7 jours avant et 14 jours avant le semis. Bien que le fait de porter de 7 à 14 jours le délai entre le traitement été le semis ait réduit la phytotoxicité, la dose la plus forte a été nécessaire lorsque le semis a été retardé, pour réduire la competition due à la repousse de la prairie. En serre, des paillis d'herbages traités au paraquat ont affecté la croissance et le développement de Brassica napus, Hordeum vulgare et Lolium perenne; B. napus s'est montré le plus sensible. Einige Effekte von Paraquat auf die Entwicklung von Kulturpflanzen in abgetöteten Pflanzendecken Es wurde die Entwicklung von Kulturen untersucht, die in unterschiedlichen Zeitabständen direkt in mit Paraquat (l,l'-Dimethyl-4,4′-bipyridylium-2/4) behandelte Pflanzendecken gesät wurden. Die besten Ergebnisse mit Brassica napus und B. oleracea wurden erzielt, wenn 1.1 kg/ha 7 Tage und 2 3 kg/ha 14 Tage vor der Saat gespritzt wurden.     

The basis of selectivity of 4-(2, 6-dichlorobenzyloxymethyl)-4-ethyl-2, 2-dimethyl-1, 3-dioxolan (WL 29, 226), a new pre-emergence herbicide for use in cereals

A series of pot experiments were undertaken to assess the selectivity of the pre-emergence herbicide 4-(2, 6-dichlorobenzyloxymethyl)-4-ethyl-2, 2, -dimethyl-1, 3-dioxolan (WL 29,226) against a number of annual weeds in wheat. When applied at dose rates of 0.5–2 kg/ha it gave good control of a number of annual monocotyledonous weeds, including Alopecurus myosuroides (blackgrass), without any adverse effects on the crop. WL 29,226 is relatively immobile in soil, remaining at the soil surface and thus favouring uptake via the emerging shoot. Since WL 29,226 is transported predominantly via the xylem, to reach its site of action in the regions of cell division, and hence to be effective, the compound has to penetrate the shoot either at or below the stem apex. The roots are inhibited only when these come into direct contact with the compound. Selectivity of the herbicide is dependent upon the relative anatomical positions of the stem apices of the weeds and the crop with respect to the soil surface. Mesocotyl elongation in many of the weed species was such that the meristematic tissue was raised to the soil surface and into contact with the compound during the emergence of the shoot. In contrast, the stem apex of wheat remained some distance below the soil surface until considerably later, by which time the leaf sheaths offered protection to the meristematic tissue from direct contact with the herbicide. Selectivity is further enhanced in the field as a result of both the depth of planting for wheat and the tendency of many annual weed species to germinate more readily when near the soil surface. Tolerance of the wheat is lost where it germinates in direct contact with the herbicide, due to the lack of any biochemical selectivity. Under field conditions WL 29,226 gives good control of many dicotyledonous species. In pot experiments, however, these exhibit some tolerance to the compound. Radio-tracer studies indicate that the tolerance shown by the shoots of these plants is due to limited transport of the herbicide from the shoot to its site of action at the apex. This suggests that control of broad-leaved weeds occurs predominantly through an inhibition of root growth. However, in species such as sugar-beet, soyabean and cotton a rapid rate of root elongation confers increased tolerance to the compound. Availability of WL 29,226 for uptake by young seedlings is favoured by soil moisture. Low temperatures further improve performance by reducing the rate of shoot emergence and hence prolonging contact with the compound at the most sensitive stage of growth. After emergence uptake of the compound via the shoot becomes a less efficient mode of entry.     

Excretion and residues of the pyrethroid insecticide cypermethrin in lactating cows

Two radiolabelled forms of racemic [¹⁴C]cypermethrin (¹⁴C at the benzylic carbon or at C-1 of the cyclopropane ring) were separately administered twice daily to lactating cows in portions of the feed. The amounts dosed were equivalent to 0.2, 5 and 10 μg of cypermethrin per g of feed. The radioactivity eliminated in the milk indicated that the ingestion and elimination of radioactivity were in balance at about day 4 after the start of dosing. Urine and faeces were equally the major routes of elimination, and only a fraction of a percent of the dose appeared in the milk. The residue in the milk was unchanged cypermethrin and was found at a concentration that was proportional to the dose. At the high cypermethrin intake of 10 μg g^?1 of diet, the residue in the milk was 0.03 μg g^?1. Concentrations of residues in the tissues, measured after 7, 20 or 21 days of treatment, were low and in the order: liver>kidney>renal fat>subcutaneous fat>blood>muscle>brain. The major residue in the liver and kidney of a cow that received 10 μg of cypermethrin per g of diet was N-(3-phenoxybenzoyl)glutamic acid. Other conjugates of 3-phenoxybenzoic acid and of 3-(4-hydroxyphenoxy)benzoic acid (unidentified, with the exception of the glycine conjugate) were also present. The residue in fat (about 0.1 μg g^?1 from an intake of 10 μg g^?1 of feed) consisted mainly of cypermethrin.