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70 SNELSON Brooks provided two further extensive reviews of cyclodiene metabolism including an extensive discussion of the pathways of enzymatic degradation [25, 2 6 ]. A further extensive review was provided by Korte [27]. The bulk of the studies had been conducted with the aid of isotope techniques.

Plimmer in an extensive review of the photochemistry of organochlorine

insecticides deals at length with the cyclodiene group and concludes:

"for the organic chemist, the organochlorine insecticides demonstrate a most interesting series of photochemical transformations. Study of their photo-products, however, presents more than an interesting academic exercise. The majority of the organochlorine insecticides are regarded as ' p e r s i s t e n t ', i. e., they are metabolised rather slowly by common organisms. Therefore, we might expect photolysis to play ultimately a s i g n i f i c a n t role in their breakdown. Some of these photolysis products have already been recognised in samples of crops and s o i l s. In view of their potential t o x i c i t y, i t is important that we continue analytical study and i d e n t i f i c a t i o n of new photoproducts, to ensure that we recognise any hazard they might present" [28].

Walker et a l. [29], in an extensive radiotracer-aided study of the comparative metabolism of d i e l d r i n analogues by vertebrates, using eight species of animals and b i r d s, showed that two d i s t i n c t mechanisms are involved in the i n i t i a l degradation in these species: oxidation and hydration. In vivo experiments produced information on the rates and pathways of metabolic excretion.

Klein [ 3 0 ], reviewing the metabolism of pesticides in higher p l a n t s, pointed out that many of this group of pesticides are translocated from s o i l to the a e r i a l parts of plants and are converted to the corresponding epoxide. The presence of.photo-derivatives is noted.

Klein [31] in a review of experimental work carried out between 1969 and 1972 on the fate of cyclodiene residues in s o i l and crop plants paid special attention to hydrophilic conversion products. The quantitative d i s t r i b u t i o n o f residues in various parts of crop plants and d i f f e r e n t soil depths is tabulated.

Klein et a l., reviewing a comprehensive series of isotopic tracer-aided studies of the behaviour of cyclodiene residues in model ecosystems, pointed to the formation of polar metabolites. The degradation of these compounds by green algae was studied as was the a b i o t i c transformation by ultra-violet radiation. The fate of d i e l d r i n in s o i l / p l a n t / f o o d / a n i m a l systems is discussed as a model [32].

FENBUTATIN-OXIDE Fenbutatin-oxide is used as a s p e c i f i c miticide against a wide range of phytophagous mites. I t is recommended especially for the control of the mobile stages on a wide variety of crops, including pome and stone f r u i t s, c i t r u s f r u i t s, grapes, berry f r u i t s, vegetables and ornamentals.

It is interesting to see how isotopic techniques have contributed to the understanding of the e f f e c t and fate of such an organo-metallic compound.

Fenbutatin-oxide is slowly lost after application to crops. The degradation to inorganic tin occurs through successive loss of the phenyldimethylethyl IAEA-SM-263/30 groups. The principal organo tin degradation product found on crops i s, 1, 1, 3, 3, te trakis (B,B-d ime thylphene thyl)-1,3-d ihydroxyd istannoxane, re fer red to subsequently as SD 31723 [33].

In studies of the fate of fenbutatin-oxide on leaves and fruit of apples [ 3 3 ], small apple trees were treated one to three times with 1 1 9 S n - l a b e l l e d fenbutatin-oxide. Recoveries of the H 9 S n 2 to 33 days after the last application were 84-96% of the amount a p p l i e d. V i r t u a l l y a l l the radioactivity in the fruit was found to be on the outer surface of the skin.

Substantial amounts of the radioactivity were removed by rinsing with organic solvents, or simply by wiping the fruit-skin with paper t i s s u e s. It was shown that less than 5% of the total radioactivity present in the fruit originated from the principal break-down of product (SN 31723) and less than 0. 7 % from other organo-tin metabolites. Inorganic tin accounted for nearly 10% of the total H 9 S n on the apples [ 3 3 ].

Similar experiments were carried out on oranges [34]. Leaves were treated with formulated 119gn-labelled fenbutatin-oxide at a concentration of 40 mg/L and analysed at intervals up to nine months after treatment. Forty days after the treatment, 65% of the applied radioactivity was s t i l l present in the leaves, of which 71% was unchanged fenbutatin-oxide. At the end of the 9-month period the total radioactivity present had declined to about 11% of that a p p l i e d, and of this amount 60% was s t i l l present as fenbutatin-oxide;

SD 31723 accounted for about 3% w h i l s t inorganic tin made up the remainder [34].

An experiment was carried out in which three lactating Guernsey cows were fed on a d i e t containing H ^ s n - l a b e l l e d fenbutatin-oxide [ 3 5 ]. The quantity given was equivalent to 34 ppm fenbutatin-oxide in the whole ration which was given twice d a i l y during a 21-day period. Milk samples were taken from each animal at each milking, and the total radioactivity determined in each sample.

No radioactivity above back-ground level was found, indicating that total residues in milk were equivalent to less than 0. 0 1 mg/kg fenbutatin-oxide.

The animals were slaughtered 12 hours after the final feeding and the radioactivity was determined in samples of f a t, muscle, b r a i n, kidney and liver. No residues were detected in b r a i n, muscle, fat or liver at a limit of determination equivalent to 0. 0 2 mg/kg fenbutatin-oxide. Similar results were obtained with the kidney sample from two of the animals, but the third was found to contain radioactivity equivalent to 0. 0 3 mg/kg fenbutatin-oxide, i. e.

just above the limits of determination in these tissues.

Thin layers of H 9 s n fenbutatin-oxide on a glass surface, when exposed to s u n l i g h t, slowly decomposed to the derivative SD 31723 and to more polar compounds such as inorganic tin s a l t s. After 230 hours of exposure, 81% of the i n i t i a l H 9 s n deposit was extractable by organic solvents and 6% by In this sample 76% of the organo-soluable 1 1 9 S n consisted aqueous solvents.

of unchanged fenbutatin-oxide and 2 1. 3 % of the degradation product SD 31723 [36].

–  –  –

active sites on the soil so that more molecules can be degraded i n i t i a l l y.

The subsequent decrease in rate as compared with live s o i l s indicates that microbial degradation, which occurred in the l a t t e r, became the main factor in degradation. No accumulation of degradation products could be measured [37].

In another experiment in which 10 mg/kg H 9 s n - l a b e l l e d fenbutatin-oxide was mixed into the same sandy loam, the residue degradation was studied under aerobic and anaerobic conditions. One set of s o i l samples was kept under aerobic conditions at ambient temperatures in a glasshouse; another set was kept under nitrogen after an i n i t i a l 30 days aerobic period. The amount of solvent-extractable r a d i o a c t i v i t y, which was nearly a l l

-fenbutatin-oxide, decreased slowly during the 180 days of the experiment. No s i g n i f i c a n t d i f f e r e n c e s could be found between the rates of degradation under aerobic and anaerobic conditions [38].


Imazalil is a systemic fungicide from the group of N-substituted imidazoles.

Members of this chemical class a f f e c t the c e l l u l a r permiability barrier of the yeasts. The fungi-toxic action of imazalil on Pénicillium may also involve the i n h i b i t i o n of the c e l l membrane functions. Uptake and membrane e f f e c t s noted in several studies suggest that imazalil inhibits ergosterol biopynthesis in fungal s o i l s.

It is interesting to note how the use of nuclear techniques have contributed to the understanding of the mode of a c t i o n, e f f e c t and fate of this fungicide which is used as a cereal seed treatment, as a foliar spray and as a post-harvest treatment of c i t r u s, bananas and pome f r u i t.

Imazalil is rapidly absorped, d i s t r i b u t e d, metabolised and excreted by r a t s.

Groups of rats were given a single 20 mg/kg oral dose of Зн-labelled imazalil sulphate. Almost 90% of the administered radioactivity was excreted within 96 hours, with approximately equal quantities detected in the urine and faeces. Tissue residues ranged from 5. 4 to 6. 1 % of the administered radioactivity 48 hours after dosing and from 1. 8 to 3. 5 % 96 hours after dosing. The highest levels of radioactivity were found in the l i v e r, lung and kidneys. Analysis of the urine from dosed animals indicated that 4% of the tritium was v o l a t i l e by l y o p h i l i z a t i o n. Thus, tritium exchange apparently occurred to a minor extent [ 3 9 ].

Studies involving a single 20 mg/kg oral dosing of rats with 3fî_]_abelled imazalil sulphate indicate that extensive metabolism of imazalil occurs in the rats. In one study [39] two major metabolites were identified in the urine.

In this study 10% of the radioactivity in the urine and 3% of the radioactivity in the faeces was i d e n t i f i e d as unchanged in imazalil.

Barley seeds were treated with a dose of ^H—^^g^alil corresponding to 10 g / 1 0 0 kg seed. After germination on water agar for nine days, 42% of the radioactivity was found in the agar and 37% in the seed coats. Only 10% of the total radioactivity was present in the roots and 2% in the leaves of the seedlings [ 4 0 ].

–  –  –

three weeks the green parts of the plants contained only 6% of the radioactivity which had originally adhered to the seeds [40].

The metabolic fate of imazalil on banana plants was studied in a complex series of experiments in which small banana plants was sprayed with a solution of 3 H-imazalil sulphate labelled especially on the asymmetric carbon.

The leaves contained 95-100% of the total radioactivity recovered in the plants treated one to nine times. The radioactivity was practically a l l concentrated on the upper surface of the leaf tested with autoradiography.

Transport of the radioactivity to the roots or the rhizome was minimal.

Analysis of various plant extracts on radio-HPLC revealed that the main part of the radio-activity originated from imazalil and its metabolite alpha-(2,4-dichlorophenyl)-lH-imidazole-l-ethanol (R 1 4 8 2 1 ). The results indicated that imazalil was degraded slowly as a function of time and that R 14821 was the main degradation product which was found in alkaline extracts. The remaining part of the radio-activity might be explained by the presence of a large number of minor metabolites [41].

Fourteen weeks after treatment of oranges with a solution containing 1000 mg/kg imazalil labelled with tritium at the 2-ethyl functional group, approximately 50% of the radioactivity remaining was found in the peel in an organo-soluable form: 30% was bound to the insoluable residue of the p e e l.

In the flesh of the fruit 18% of the remaining radio-activity was present as the metabolite R 14821.

The polar, hydrophilic fraction containing nearly 50% of the radioactivity was present in the methanol extract of the peel but did not contain tritiated water or other v o l a t i l e radio-activity. Since concentrations of radioactivity were i d e n t i f i e d before and after lyophilisation of this fraction, i t seems that no label loss is to be expected during metabolism [ 4 2 ].

The distribution of imazalil in/on oranges was determined at intervals after treatment at 1000 mg/kg [43]. It was shown that the degradation of imazalil on oranges is slow; the half-life is expected to be 12 to 20 weeks; and only small amounts of the imazilil are present in the fruit flesh and part of this may result from contamination during the peeling.

Kraght [44] carried out a study under conditions closer to commercial practice when the distribution of radioactivity in the fruit and the presence of metabolites were studied during and after a storage period of 12 weeks. Most of the radioactivity (89%) remained as unchanged i m a z a l i l, in contrast to the previous studies where considerable degradation was reported. This was due to the extreme storage conditions used in the t r i a l s reported above where high temperatures and high light intensity prevailed. No tritium exchange was detected, thus confirming the s u i t a b i l i t y of the tritium labelling for the purpose of the study. Over 99% of the radioactivity in the H-imazalil-treated oranges was solvent-extractable. After 12 weeks of storage approximately 10% of the original radioactivity appeared in the form of an unknown water-soluble compound [ 4 4 ].

–  –  –

LINDANE It i s interesting to note how isotope-tracers studies have helped to illucidate the understanding of the d i s t r i b u t i o n, persistence and metabolism of lindane in p l a n t s, animals and processed foods. Saha [46) summarised the results of several biodégradation studies of l^C—lindane in plants and animals. These r e s u l t s, together with those from previous s t u d i e s, indicate a common biodégradation pattern for lindane in p l a n t s, insects and animals, as chlorobenzene and chlorophenolic metabolites are formed in a l l cases. Various isomers of di-, tri-, and tetrachlorobenzene and chlorophenols;

pentachlorobenzene and pentachlorophenol have been found in plants, insects and animals. The gamma isomer of pentachlorocyclohexane has been found in plants and insects but not in mammals.

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