In a study according to US EPA guidelines, [carbinol-14C]fenarimol (>99% radiochemical purity) dissolved in dilute CaCl2 solution was added to four different soils in triplicate and equilibrated for 22 h at 25°C (Saunders and Powers, 1987). After centrifugation, supernatant (22 ml) was removed and desorption measured by equilibrating the soil with fresh dilute CaCl2 solution for 22
h. This step was then repeated. The radioactivity present in the solutions was quantified by LSC. A further experiment showed that there was no adsorption to the glass centrifuge tubes. The results shown in Table 6 differ slightly from those given in the study which were calculated without converting the organic matter content to the organic carbon content. The slopes of the desorption isotherms were found to be less than those of the adsorption isotherms.
Table 6. Freundlich adsorption constants for fenarimol in four soils.
|
Soils |
Adsorption |
Desorption Kd |
||
|
Kd |
Slope 1/n |
Koc |
||
|
Neuces (sand) |
1.5 |
0.901 |
500 |
1.4-2.6 |
|
Fox (sandy loam) |
5.1 |
0.858 |
634 |
5.1-11.5 |
|
Crosby (loam) |
8.1 |
0.873 |
810 |
8.2-17.3 |
|
Brookston (clay loam) |
11.9 |
0.861 |
992 |
12.7-28.7 |
Air-dried, sieved soils (Marion sand, synthetic sandy loam, Hancock loam, Hancock clay loam) were packed into 30 cm columns. [Pyrimidine-14C]fenarimol (radiochemical purity 98%) was added (326 mg, equivalent to 1 kg/ha) to triplicate columns of each soil in a minimal amount of benzene which was allowed to evaporate overnight (Sullivan and Saunders, 1976). The columns were leached with water (2 litres, 64 cm) for 2-4 days. After extraction, the radioactivity in the soil and water was determined by LSC.
Depending on the soil, the first 250-400 ml water added was required to bring the soil to water capacity before leaching began. Recovery of the applied radioactivity was only 67-83%. In the four soils 0-0.4% of the recovered radioactivity was found in the leachate whilst 91-100% remained in the top 10 cm of the soil. By comparison, atrazine leached in the same soils showed 3.4-43% in the leachate and an even spread of the compound throughout the soil.
Columbus sandy loam soil (stored air-dried and water added one month before incubation to re-establish biological activity) maintained at 75% of 1/3 bar moisture content was incubated at 23-24°C in the dark for 30 days with a mixture of [carbinol-14C]fenarimol (radiochemical purity 96%), [4-chlorophenyl-14C]fenarimol (radiochemical purity >99%) and [2-chlorophenyl-14C]fenarimol (radiochemical purity >99%) (Saunders et al., 1983).
Dry soil (Marion sand, Columbus sandy loam, Greenfield loam or Greenfield clay loam) was packed to a height of 25 cm in glass columns (1 cm diameter) and 5 cm of the aged soil containing fenarimol was added. The columns were leached with water (40 ml, 51 cm) and the radioactivity in the soil and leachate determined by LSC.
After ageing the soil was found to contain 93% of the AR and after leaching recoveries of 14C were 79.7-93.7% of the AR; some losses were considered to be due to volatilization during soil drying processes. Radioactivity in the leachate was 0.24-0.32% of the AR and almost all the radioactivity in the soil was in the top 12 cm. KD values based on the distance moved by the 14C were reported to be 2.7-7.3.
[Carbinol-14C]fenarimol (radiochemical purity not stated) was photochemically degraded by exposure to natural sunlight for 50 h (Vonk and Hoven, 1981). This was then dissolved in methanol and found to contain 80 % of the AR of which 57.5% (46% of the AR) was fenarimol. Solutions of the degraded fenarimol were mixed with Droevendaal sand and Lelystad loam (10 g) at concentrations stated to be equivalent to 0.4 and 1.6 kg/ha. Columns 4.3 cm diameter were packed to a depth of 25 cm with air-dried, sieved soils and saturated with 25 mM CaSO4 solution. The treated soil was added to the columns which were then leached with 25 mM CaSO4 (30 cm) for 3 days. The levels of radioactivity in the leachates and soils were determined by LSC and its nature investigated by TLC.
The total recovery of the radioactivity applied to the columns was 88-100%. In the sand soil 1.7% was detected in the leachate whilst 80-92% remained in the top 5 cm of the columns and in the loam soil the corresponding figures were 5.5% and 89% (both soils). At the higher application rate slightly more radioactivity (4.5-9%) was found in the leachate and the major component was o-chlorobenzoic acid (34-50% of the radioactivity present). The remainder of the radioactivity was associated with a complex mixture of very polar compounds.
Photolysis in soil. [14C]carbinol-, [14C]p-chlorophenyl- or [14C]o-chlorophenyl-labelled fenarimol, or a mixture of the three, (radioactive purities >99%) were deposited in baking dishes by evaporation of a dichloromethane solution and exposed to natural sunlight in Indiana, USA, between December and February (the maximum temperature during this period was 18°C). After 100 days the dishes were thoroughly washed with methanol, and the extract purified by column chromatography and analysed by TLC (Althaus, 1984).
At the conclusion of the photolysis period 72-85% of the AR remained, suggesting that 15-28% had been lost by volatilization. Fenarimol accounted for 33-38% of the AR. Many products were observed but none individually accounted for >6%. The major product (3.1-5.7% of the AR) was o-chlorobenzoic acid and only one additional compound was seen by labelling in the phenyl rings (<1% of the AR).
In a further briefly summarized study (Althaus and Donoho, 1977) the examination of mixtures irradiated with natural or artificial light in which 40-50% of the [14C]fenarimol had been degraded indicated the formation of more than 50 photodegradation products, but the most abundant products detected were less than 3% of the AR.
Comparisons of the TLC profiles and autoradiograms of the photolysis mixture and soil extracts indicated that the photodecomposition products were present in the soil, but the most abundant degradation product in soil accounted for less than 2% of the AR. The main compound in the soil extract, confirmed as fenarimol, accounted for 92% of the radioactivity.
Fenarimol formulated as either an EC or WP was added dropwise to 0.4 mm layers of silt loam soil in petri dishes (Smith & Saunders, 1982a). Samples were exposed to natural sunlight in
Indiana, USA, for periods up to 32 h. Soil was extracted by boiling with methanol/water and, after clean-up, analysed by GLC. There was no degradation of fenarimol after 32 h.
Photolysis in water. [Carbinol-14C]fenarimol (radiochemical purity >99%) was dissolved in distilled water, sealed in ampoules and irradiated at 28°C under artificial light for 4 h (Smith and Saunders, 1982b). Analysis by GLC showed fenarimol to have decreased to 52% of its initial concentration and the tentatively identified 2'-chloro-2-(5-pyrimidinyl)-4-chlorobenzophenone to have increased to 17%. TLC and LSC showed ten other photodegradation products but none individually accounted for >3.3% of the AR.
A further study in which aqueous photolysis half-lives of fenarimol were calculated (Saunders, 1991) was submitted but not reviewed.
Stability of pesticide residues in stored analytical samples
Samples of two varieties of hops were fortified at 1 mg/kg and stored below -16°C for nearly two years. Samples were taken at intervals and analysed by GLC with an ECD. The procedural recoveries were in the range 73-96%. Residues of fenarimol (uncorrected for recovery) ranged from 0.66 to 0.91 mg/kg during the storage period as shown in Table 7.
Table 7. Concentrations of fenarimol in fortified hops (Target and Golding varieties) following storage at <-16°C.
|
Storage time, days |
Residue, mg/kg |
|
|
Target |
Golding |
|
|
0 |
0.79 |
0.76 |
|
161 |
0.78 |
0.86 |
|
276 |
0.66 |
0.84 |
|
371 |
0.75 |
0.70 |
|
463 |
0.83 |
0.91 |
|
666 |
0.72 |
0.66 |
|
706 |
- |
0.83 |
