Fate of the organophosphorus pesticide profenofos in cotton fiber.

Pesticides carried by cotton fiber are potential risk for production workers and consumers. Dissipation behaviour of a commonly used cotton pesticide profenofos in cotton fiber during growing period and scouring treatment was investigated. The results showed that profenofos in the fiber from the pre-opened and post-opened bolls both decreased to undetectable amounts 21 days after pesticide application. However, a minority of profenofos was converted to a strongly irritant compound, 4-bromo-2-chlorophenol and retained a non-negligible amount in cotton fiber even after 28 days. Profenofos and its degradation product could be completely removed during the conventional cotton scouring process. The degradation half-time of profenofos in scouring bath was only 3.0 min, and the degradation product was also 4-bromo-2-chlorophenol. Cotton products made of profenofos-carrying fiber are safe; however, the scouring waste should be detoxicated before discharge due to the accumulation of 4-bromo-2-chlorophenol in the scouring bath. These results could be useful for evaluating the risk of cotton fiber from the profenofos applied fields.

Determining high-quality critical body residues for multiple species and chemicals by applying improved experimental design and data interpretation concepts.

Ecotoxicological effect data are generally expressed as effective concentrations in the external exposure medium and do thus not account for differences in chemical uptake, bioavailability, and metabolism, which can introduce substantial data variation. The Critical Body Residue (CBR) concept provides clear advantages, because it links effects directly to the internal exposure. Using CBRs instead of external concentrations should therefore reduce variability. For compounds that act via narcosis even a constant CBR has been proposed. Despite the expected uniformity, CBR values for these compounds still show large variability, possibly due to biased and inconsistent experimental testing. In the present study we tested whether variation in CBR data can be substantially reduced when using an improved experimental design and avoiding confounding factors. The aim was to develop and apply a well-defined test protocol for accurately and precisely measuring CBR data, involving improved (passive) dosing, sampling, and processing of organisms. The chemicals 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 2,3,4-trichloroaniline, 2,3,5,6-tetrachloroaniline, 4-chloro-3-methylphenol, pentylbenzene, pyrene, and bromophos-methyl were tested on Lumbriculus variegatus (California blackworm), Hyalella azteca (scud), and Poecilia reticulata (guppy), which yielded a high-quality database of 348 individual CBR values. Medians of CBR values ranged from 2.1 to 16.1 mmol/kg wet weight (ww) within all combinations of chemicals and species, except for the insecticide bromophos-methyl, for which the median was 1.3 mmol/kg ww. The new database thus covers about one log unit, which is considerably less than in existing databases. Medians differed maximally by a factor of 8.4 between the 7 chemicals but within one species, and by a factor of 2.6 between the three species but for individual chemicals. Accounting for the chemicals' internal distribution to different partitioning domains and relating effects to estimated concentrations in the target compartment (i.e., membrane lipids) was expected to but did not decrease the overall variability, likely because the surrogate partition coefficients for membrane lipid, storage lipid, protein, and carbohydrate that were used as input parameters did not sufficiently represent the actual partitioning processes. The results of this study demonstrate that a well-designed test setup can produce CBR data that are highly uniform beyond chemical and biological diversity.

Residues of ¹4C-ethion along the extraction and refining process of maize oil, and the bioavailability of bound residues in the cake for experimental animals.

Maize seeds obtained from ¹4C-ethion treated plants contained about 0.01 % of the originally applied radioactivity 1 month following the last pesticide application. Hexane and methanol extracts of the seeds accounted for 35 % and 22.5 % of the radioactive residues, respectively, with 40 % remaining in the seed cake. Commercial processing procedures resulted in a gradual decrease in the total amount of ¹4C-residues in oils with aged residues. The refined oil contained ¹4C-residues that amounted to about 30 % of the amount that was originally present. The major residues in processed oil are ethion monooxon, O,O-diethyl phosphorothioate and O,O-diethyl S-hydroxymethyl phosphorodithioate, in addition to one unknown compound. After feeding rats with the cake containing ethion bound residues, a substantial amount (71 %) of ¹4C-residues was eliminated in the urine, while about 12 % was excreted in the feces. About 5 % of the radioactive residues were distributed among various organs. The bound residue was quite readily bioavailable to the rats.

Environmental behavior of profenofos under paddy field conditions.

The environmental behavior of 40% profenofos EC under paddy field conditions was studied. After application of 40% profenofos EC at 900 g a.i./ha level, the initial deposits of profenofos on rice plant, soil and water were found to be 32.700, 0.224 and 3.854 mg/kg respectively. Half-lives (t(1/2)) of profenofos on those substrates were observed to be 5.47, 3.75 and 3.42 days respectively. The residue levels of profenofos on rice straw, soil and rice grain were significantly affected by the dosage and frequency applied. The obtained results might help to recommend the suitable dose and calculate the safety period of profenofos application.

Assessment of long-term subacute exposure to dimethoate by hair analysis of dialkyl phosphates DMP and DMTP in exposed rabbits: The effects of dose, dose duration and hair colour.

Hair analysis for dialkyl phosphates' (DAPs) residues could provide a measure of chronic exposure to organophosphate pesticides (OPs). The aim of this study was to determine whether these metabolites can be internally incorporated into the hair of rabbits exposed to dimethoate and also to investigate the influence of dose and dose duration of this OP, as well as the effect of hair colour on the concentrations of its DAPs in hair. Two-coloured rabbits were daily exposed to dimethoate (0, 12 or 24mgkg(-1) body weight) via their drinking water. Hair samples of both colours were obtained 4 and 6 months after the beginning of exposure from the back of all treated rabbits, and each hair colour sample was analyzed for dimethyl phosphate (DMP) and dimethyl thiophosphate (DMTP) by gas chromatography-mass spectrometry (GC-MS). Analysis revealed the incorporation of these metabolites into the rabbit hair in a dose-dependent manner. The mean concentrations found ranged from 0.18 to 0.77ngmg(-1) for DMP and from 0.43 to 1.53ngmg(-1) for DMTP. Mixed results for the significance of the relationship between dose duration and the levels of the two DAPs in hair are observed. Hair pigmentation does not appear to affect the concentration values of DMTP, whereas it seems to be a critical factor in the incorporation of DMP into hair. These data confirm the ability of hair testing to assess chronic OP exposure by the detection of DAPs.

Oligonucleotide therapy.

Rapid progress in oligonucleotide therapeutics has continued over the past year as major programs established in the past four years have grown and begun to be productive. Important advances were reported in the medicinal chemistry of oligonucleotides and in understanding their pharmacodynamic properties. Significant progress was made in understanding the pharmacokinetic and toxicologic properties of first generation analogs, particularly phosphorothioates and one oligonucleotide, ISIS 2105, entered clinical trials. Additionally, combinatorial approaches designed to identify oligonucleotides that may bind to a variety of targets were reported.

Transition metal chemistry of main group hydrazides, Part 14: Evaluation of new Tc-99m chelates of thiol functionalized phosphorus hydrazides.

Ligands containing a combination of amine or amide nitrogens and thiol functionalities have been found to form stable chelates with Tc-99m, presumably in oxidation state +5. Two new thio-phosphorus monohydrazides [(MeO)2P(S)NMeNHCH2C6H4SH], SL1 and [(MeO)2P(S)NMeNHC(O)C6H4SH], SL2 were synthesized and their complexation properties with Re(V) and Tc-99m have been studied. Neutral-lipophilic Tc-99m chelates with both SL1 and SL2 were formed in high yields (95-97%) as a single species ascertained by electrophoresis and reversed-phase HPLC. Biodistribution studies show good in vivo stability and primary clearance of both 99mTc chelates is via the hepatobiliary pathway. Re(V) complexes with SL1 and SL2 were also synthesized using the ReOCl3(PPh3)2 precursor to obtain the product ReOCl(L)(PPh3), where L = SL1 or SL2. H+ was lost from the N-atom and the thiol group in these Re chelates. Even though the Tc-99m chelates of SL1 and SL2 formed at tracer levels are not identical to the Re-chelates (different synthons were used), the Re data suggests complexation of Tc-99m by these hydrazido-thiol ligands will be similar to N,S ligand systems previously used. The good in vitro and in vivo stability and high yields of the Tc-99m complexes of SL1 and SL2 indicate the potential hydrazido-thiols hold for use as a basis in formulating new Tc-99m radiopharmaceuticals, particularly when thiol moieties are used in conjunction with multi-functional phosphorous hydrazide compounds.

Degradation of nerve gases by CLECS and cells: kinetics of heterogenous systems.

We have reported the enzymatic hydrolysis of phosphoro- and phosphonofluoridates and phosphoro- and phosphonothiolates and -thionates by an organophosphorus hydrolase (OPH) from Pseudomonas diminuta. In screening for other microbial sources of nerve gas hydrolyzing enzymes, it would be convenient, indeed essential, to be able to determine such hydrolyses on intact cells. As a preliminary step to such screening we have measured the hydrolysis of O,O-diisopropyl S-(2-diisopropylaminoethyl) phosphorothiolate (Tetriso) and O,O-diethyl S-(2-ethylthioethyl) phosphorothiolate (Demeton-S; formerly Isosystox) by intact cells and sonicates. The purified OPH has also been cross-linked to itself (CLEC = cross-linked enzyme crystals) and this has also been tested for its ability to hydrolyze Tetriso and Demeton-S. The testing of such heterogenous systems by a spectrophotometric assay (Ellman) has required novel modifications. Our findings are that both Tetriso and Demeton-S are subject to intact-cell assay, that both are readily hydrolyzed by the CLEC-ed OPH without marked change in kinetics, but that at any given substrate concentration Tetriso is hydrolyzed much more rapidly. However, since Demeton-S is commercially available, this appears to be the substrate most suitable for screening for our final goal in a search for sources of enzymes to detoxify O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothiolate (VX).

Dimethylphosphorus metabolites in serum and urine of persons poisoned by malathion or thiometon.

The urinary excretion rates of dimethyl-phosphate, -phosphorothioate and -phosphorodithioate were studied in six persons of whom four had ingested a concentrated solution of malathion and two of thiometon. The concentration decrease of single and total dimethylphosphorus metabolites was biphased, with a fast initial rate and a slow later rate. The excretion rate of total metabolites in the faster phase depended on the initial concentration in urine. At concentrations higher than 100 nmol/mg creatinine, the excretion half-times ranged from 7.5 to 15.4 h and at concentrations between 52 and 95 nmol/mg creatinine from 34.7 to 55.4 h. Non-metabolized malathion was detected only in one urine sample collected from one person immediately after hospitalization. Two persons poisoned with malathion were taken blood serum samples for the analysis of the parent pesticide and its metabolites on a daily basis after hospitalization. The parent pesticide was detectable in the serum only one day after the poisoning. The concentration of total malathion dimethylphosphorus metabolites in serum decreased very quickly within 1.5 days after hospitalization. The total metabolite elimination half-times were 4.1 and 4.7 h in the initial phase, and 53.3 and 69.3 days in the later slower elimination phase. There was no correlation between maximum concentrations of total metabolites measured in serum and/or urine on the day of admission to hospital and the initial depression of serum cholinesterase (BChE, EC 3.1.1.8) and erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7).

Profenofos residues in wild fish from cotton-growing areas of New South Wales, Australia.

The organophosphorus (OP) pesticide profenofos (O-4-bromo-2-chlorophenyl O-ethyl S-propyl phosphorothioate) is used heavily in cotton-growing areas of eastern Australia toward the end of the growing season. European carp (Cyprinus carpio), bony bream (Nematalosa erebi), and mosquitofish (Gambusia holbrooki) were collected from the cotton-growing areas around Wee Waa, New South Wales, to determine the relationship between profenofos residues and acetyl-cholinesterase (AChE) activity in wild fish. Profenofos concentrations in water, sediment, and fish tissue reflected its general level of use; levels in March 1994 were significantly higher than in 1993 and generally decreased in May, 6 wk after cessation of spraying. Residues in carp and bony bream generally correlated with concentrations in water and sediment, although residues in fish tend to persist longer at some sites. Acetylcholinesterase inhibition was a useful indicator of profenofos exposure within a season, particularly if linked with residue measurements. Bony bream and gravid female mosquitofish recovered AChE levels more slowly than carp or nongravid mosquitofish. Recovery in creeks was generally more rapid than in lagoons.

Pharmacokinetic mechanisms associated with synergism by DEF of cypermethrin toxicity in larval and adult Helicoverpa zea, Spodoptera frugiperda, and Agrotis ipsilon (Lepidoptera: Noctuidae).

Penetration, metabolism, and excretion of radiocarbon were observed after topical treatment of Helicoverpa zea (Boddie), Spodoptera frugiperda (J. E. Smith), and Agrotis ipsilon (Hufnagle) larvae and adults with cypermethrin-14C. These pharmacokinetic events usually were higher with trans-cypermethrin-14C than with cis-cypermethrin-14C. They also were generally higher with H. zea and S. frugiperda than with A. ipsilon, and they were higher in larvae than in adults. No marked sex differences in the degradation of trans-cypermethrin were apparent. Pretreatment of H. zea, S. frugiperda, and A. ipsilon larvae and adults with S,S,S-tri-n-butyl phosphorotrithioate (DEF) 30 min before application of cypermethrin resulted in a perturbation of trans-cypermethrin pharmacokinetics manifested primarily by a lower rate of pyrethroid metabolism as compared with that in the absence of DEF. Appreciably higher internal levels of the toxic parent pyrethroid were often observed in the presence of DEF than in the absence of DEF in most cases. Suppression of cypermethrin penetration and elimination also was usually detected. Inhibition by DEF of the enzymatic degradation of cypermethrin may account for the synergy observed between these two compounds.

[Pharmacokinetics and stability in the blood in vivo of phosphodiester and modified oligonucleotide derivatives]. / Issledovanie farmakokinetiki i stabil'nosti v krovi in vivo fosfodiéfirnykh i modifitsirovannykh proizvodnykh oligonukleotidov.

In vivo stability and distribution of deoxyribooligonucleotides and 3'-end modified oligodeoxyribooligonucleotides were studied in blood serum and cells. Substitution of two 3'-end internucleotide phosphodiester bonds increased the stability of modified oligonucleotides. Modified oligonucleotides were shown to be stable in blood serum for up to 24 hours. Leukocytes did not bind oligonucleotides significantly, whereas erythrocytes accumulate mono-, di-, three-, tetranucleotides appeared in the blood stream as degradation products of the parent oligonucleotide.

Residues of profenofos in spring onion.

Profenofos is one of the commonly used insecticides in the control of Trips tabaci on spring onion in Iran. Residues of profenofos in spring onion were determined in two different fields under the same conditions. In the first field, onion plants were sprayed with profenofos (40EC) at the rate of 1000 g/ha. Spraying was repeated 2 weeks later. In the second field one spraying was preformed at the same rate. Spring onionwere sampled at different time intervals and analyzed for profenofos residues using a GC equipped with NPD detector. In the first field's samples, the residues were 0.097 and 0.025 mg/kg at 2 and 6 days after spraying, respectively. The residues declined to 0.002 mg/kg on the day twelve. Two days after the second spraying the residues was 0.27 mg/kg, which reduced to 0.032 on the day sixth. However the residues were not detectable 32 days after the second spraying. In the second field, residue levels were 0.193 and 0.043 mg/kg at 2 and 6 days after spraying. Residues, which found after 32 days, were less than 0.001 mg/kg. The rate of residue decay in the first field was higher than the second field.

Transcriptional responses in Atlantic salmon (Salmo salar) exposed to deltamethrin, alone or in combination with azamethiphos.

Recently, Atlantic salmon (Salmo salar) fish farmers have applied a combination of deltamethrin and azamethiphos in high-concentration and short-duration immersion treatment to improve protection against sea-lice (Lepeophtheirus sp.). In this work we aimed to study the effects of deltamethrin, alone or in combination with azamethiphos, on the transcription of stress and detoxification marker genes. Atlantic salmon kept at 12°C (one group was also kept at 4-5°C) were treated with deltamethrin alone or in combination with azamethiphos for a total of 40min, and gill and liver tissue harvested for transcriptional analysis 2 and 24h post treatment. No lethality was observed during the experiment. The result showed that deltamethrin, alone or in combination with azamethiphos, affected the transcriptional levels of several oxidative stress markers, including MnSOD (SOD2) and HSP70 (HSPA8) in the liver, and GPX1, CAT, MnSOD, HSP70 and GSTP1 in the gills. Significant responses for CASP3B, BCLX, IGFBP1B and ATP1A1 (Na-K-ATPase a1b) by some of the treatments suggest that the pharmaceutical drugs may affect apoptosis, growth and ion regulation mechanisms. In fish kept at 4-5°C, different effects were observed, suggesting a temperature-dependent response. In conclusion, the observed responses indicate that short-term exposure to deltamethrin has a profound effect on transcription of the evaluated markers in gills and liver of fish. Co-treatment with azamethiphos appears to have small mitigating effects on the transcriptional response caused by deltamethrin exposure alone.

Metabolism of profenofos to 4-bromo-2-chlorophenol, a specific and sensitive exposure biomarker.

Profenofos is a direct acting phosphorothioate organophosphorus (OP) pesticide capable of inhibiting ß-esterases such as acetylcholinesterase, butyrylcholinesterase, and carboxylesterase. Profenofos is known to be detoxified to the biologically inactive metabolite, 4-bromo-2-chlorophenol (BCP); however, limited data are available regarding the use of urinary BCP as an exposure biomarker in humans. A pilot study conducted in Egyptian agriculture workers, demonstrated that urinary BCP levels prior to application (3.3-30.0 µg/g creatinine) were elevated to 34.5-3,566 µg/g creatinine during the time workers were applying profenofos to cotton fields. Subsequently, the in vitro enzymatic formation of BCP was examined using pooled human liver microsomes and recombinant human cytochrome P-450s (CYPs) incubated with profenofos. Of the nine human CYPs studied, only CYPs 3A4, 2B6, and 2C19 were able to metabolize profenofos to BCP. Kinetic studies indicated that CYP 2C19 has the lowest Km, 0.516 µM followed by 2B6 (Km=1.02 µM) and 3A4 (Km=18.9µM). The Vmax for BCP formation was 47.9, 25.1, and 19.2 nmol/min/nmol CYP for CYP2B6, 2C19, and 3A4, respectively. Intrinsic clearance (Vmax/Km) values of 48.8, 46.9, and 1.02 ml/min/nmol CYP 2C19, 2B6, and 3A4, respectively, indicate that CYP2C19 and CYP2B6 are primarily responsible for the detoxification of profenofos. These findings support the use of urinary BCP as a biomarker of exposure to profenofos in humans and suggest polymorphisms in CYP 2C19 and CYP 2B6 as potential biomarkers of susceptibility.

The kinetic study of the inhibition of human cholinesterases by demeton-S-methyl shows that cholinesterase-based titration methods are not suitable for this organophosphate.

The organophosphorus insecticide, demeton-S-methyl (DSM), is considered as a good surrogate of the highly toxic nerve agent VX for skin absorption studies due to similar physico-chemical properties and in vitro percutaneous penetration profile. But, when skin distribution was estimated by measuring inhibition of cholinesterase activity, the results were poorly reproducible. The various grades of commercial DSM solutions were suspected to be the origin of the discrepancies. This hypothesis was tested by measuring inhibition of human acetyl- and butyrylcholinesterase by two commercial DSM solutions. The inhibition rate was independent on the enzyme concentration confirming pseudo-first order conditions. But complete inhibition of butyrylcholinesterase activity was achieved only when the DSM concentration was at least 1500-fold higher than the enzyme concentration. Besides, complete inhibition of acetylcholinesterase was never achieved. Mass spectrometry analysis of the inhibited butyrylcholinesterase adducts identified monomethoxyphosphorylated-serine, the aged product of inhibition by DSM or a derivative with a modified leaving group. Neither spontaneous reactivation nor aging of the dimethoxyphosphorylated-serine could account for the inhibition kinetics observed, suggesting an overly complicated kinetic scheme not compatible with the requirement of a titration experiment. In conclusion, cholinesterase-based analytical methods should be avoided for DSM titration in skin penetration studies.

Persistence and nematicidal efficacy of carbosulfan, cadusafos, phorate, and triazophos in soil and uptake by chickpea and tomato crops under tropical conditions.

The productivity of chickpea, Cicer arietinum (L.), and tomato, Solanum lycopersicum (L.), is adversely affected by root-knot nematode, Meloidogyne species. Nematode-resistant chickpea and tomato are lacking except for a few varieties and therefore grower demand is not met. The available nematicides, namely, carbosulfan, cadusafos, phorate, and triazophos, were, therefore evaluated for their efficacy and persistence in soil and crops to devise nematode management decisions. In alluvial soil, cadusafos was the most persistent nematicide followed by phorate, carbosulfan, and triazophos in that order. The percent dissipation of cadusafos was greater (P < 0.05) in chickpea than in tomato plots, which influenced its half-life in soil. Nematicide residues were differentially taken up by chickpea and tomato plant roots with active absorption continuing for up to 45 days. Cadusafos and triazophos were absorbed to greater extent (P < 0.05) in tomato than in chickpea. The translocation of residues to shoot was highest by day 15 for cadusafos and at day 45 for other nematicides, with carbosulfan residues translocated the most. Nematicide residue concentrations in shoots never exceeded those in roots, with residues in both roots and shoots persisting beyond 90 days. Nematicide residues in green seeds of chickpea and tomato fruits were all below the Codex/German MRLs of 0.02, including the Indian tolerances of 0.1 microg/g in fruits and vegetables. Cadusafos was found to be the most effective nematicide followed by triazophos against Meloidogyne incognita and reniform nematode, Rotylenchulus reniformis . Application of cadusafos (Rugby 10 G) or, alternatively, spray application of triazophos (Hostathion 40 EC) in planting furrows, both at 1.0 kg of active ingredient/ha, followed by light irrigation is recommended for the effective control of M. incognita and R. reniformis infestations on chickpea and tomato.

Technical note phytoremediation of triazophos by Canna indica Linn. in a hydroponic system.

The phytoremediation of triazophos (O, O-diethyl-O-(1-phenyl-1, 2, 4-triazole-3-base) sulfur phosphate, TAP) by Canna indica Linn. in a hydroponic system was studied. After 21 d of exposure, the removal kinetic constant (K) of TAP was 0.0229-0.0339 d(-1) and the removal percentage of TAP was 41-55% in the plant system and the K and removal percentage of TAP were about 0.002 d(-1) and 1%, respectively, in darkness and disinfected control. However, the K and removal percentage of TAP were 0.006 d(-1) and approximately 11%, respectively, in the treatment with eluate from the media of constructed wetland. The contribution of plant to the remediation of TAP was 74% and C. indica played the most important role in the hydroponic system. Under the stress of TAP and without inorganic phosphorus nutrient, the activity of phosphatase in the plant system increased and phytodegradation was observed. The production and release of phosphatase is seen as the key mechanism for C. indica to degrade TAP. C. indica, which showed the potential of phytoremediation of TAP, and is commonly used in constructed wetland, so the technique of phytoremediation of TAP from contaminated water can be developed with the combination of constructed wetland.

Sublethal effects of profenofos on locomotor behavior and gill architecture of the mosquito fish, Gambusia affinis.

Subacute studies of profenofos on mosquito fish, Gambusia affinis, were carried out for 20 days to assess the locomotor behavior and structural integrity of gill in relation to bioaccumulation and targeted enzyme acetylcholinesterase (AChE; EC 3.1.1.7). The sublethal concentration of 0.13 mg/L (1/5 of LC50) altered locomotor behavior such as distance traveled and swimming speed in exposed fish. This could be due to inhibition in the activity of acetylcholinesterase and deformities in the primary and secondary lamella of gill. The bioaccumulation values indicated that the accumulation of profenofos was highest in viscera followed by head and body. The average bioconcentration factor values are 254.83, 6.18, and 2.52 microg/g for viscera, head, and body. The findings revealed that profenofos is highly toxic even at sublethal concentrations to the mosquito fish, Gambusia affinis.

Metabolic fate of S,S,S-tributyl phosphorotrithioate (DEF) in the lactating goat.

1. Metabolism of [1-14C] DEF (S,S,S-1-14C-tributyl phosphorotrithioate, 1) in the lactating goat has been investigated. A goat was dosed orally by capsule on 3 consecutive days at a rate of 0.82 mg/kg body weight/day based on 25 times the maximum DEF residue anticipated in animal feed. 2. Urine and milk were collected throughout the study. The goat was killed 21 h following the last treatment, and kidney, liver and composite samples of muscle and fat were collected. The radioactive residue levels (following the three doses) were 3.45 ppm in liver, 0.35 ppm in kidney, 0.19 ppm in fat, 0.06 ppm in muscle and 0.12 ppm in milk collected at the final 16 h and prior to killing. 3. Urinary metabolic profile indicated that DEF was efficiently metabolized to many metabolites. Tissue and milk extracts also indicated that DEF was extensively metabolized. 4. DEF comprised 31 and 5% of the total radioactive residue in fat and milk, respectively. The amount of DEF in liver, kidney and muscle represented < 1% of the total radioactive residue. 5. A major metabolite, 3-hydroxybutylmethyl sulphone (HBM sulphone, UP3), was found in tissue, milk and urine. The identification of this metabolite was accomplished by a combination of MS, nmr and comparison with an authentic standard. The glucuronide (UP1) and sulphate (UP2) conjugates of HBM sulphone were found in urine, and the sulphate conjugate was a major metabolite in kidney. 6. The hydrolytic products of DEF, S,S-dibutyl phosphorodithioate (Dibufos, U16) and S-butyl phosphorothiate (Bufos, U8), were identified as minor components in urine, comprising 5 and 4% of the total radioactive residue, respectively. Butyl mercaptan was not found, but mixed disulphides of butyl mercaptan with either glutathione (U10, 3%) or N-acetyl cysteine (U13, 2%) were found. 7. Direct evidence for the incorporation of DEF residue into natural constituents was also established. Fatty acids from milk and fat were isolated and shown to be radioactive.