Metabolism and environmental fate

Environmental fate in soil and water/sediment systems

The characteristics of the soils in some of the studies reviewed are given below (Table 1). Table 1. Characteristics of soils in the studies reviewed.

Ref.	Soil description1	% oc	pH	% sand	% silt	% clay	Pre-study microbial activity (mg C/g soil)
Rainey, 1990	Greenfield (sandy loam)	1.5	7.1	66	21	13
Althaus & Beaty, 1982	Coarse (sandy loam)	0.9	6.0	54	32	14
Althaus & Beaty, 1982	Medium (silty loam)	1.3	6.1	28	57	15
Althaus & Beaty, 1982	Fine (clay loam)	1.9	6.3	20	50	30
Perkins, 1993	Ismaning (clay loam)	4.9	7.3	1	90	9	950
Perkins, 1993	Rohr (clay loam)	2.8	7.1	36	42	22	32
Perkins, 1993	Alsfeld (silt loam)2	1.5	6.5	42	32	26
Perkins, 1993	Grebin (sandy silt loam)	1.2	5.6	47	36	17	25
Saunders & Powers, 1987	Neuces (sand)	0.3	7.7	89	6	5
Saunders & Powers, 1987	Fox (sandy loam)	0.8	5.7	66	22	12
Saunders & Powers, 1987	Crosby (loam)	1.0	6.5	28	48	24
Saunders & Powers, 1987	Brookston (clay loam)	1.2	6.9	24	44	32
Smith & Saunders, 1982	Hancock (silt loam)	1.6	6.2	24	60	16
Sullivan & Saunders, 1976	Marion (sand)	0.6	8.1	91	5	4
Sullivan & Saunders, 1976	Synthetic (sandy loam)	2.0	5.6	69	21	10
Sullivan & Saunders, 1976	Hancock (loam)	1.2	7.7	40	34	26
Sullivan & Saunders, 1976	Hancock (clay loam)	0.8	5.6	36	36	28
Vonk & Hoven, 1981	Droevendaal (sand)3	2.5	5.0	86	6	4
Vonk & Hoven, 1981	Lelystad (loam)3	1.7	7.5	32	36	21

¹ UK or USA classification of sand, silt and Clay used unless otherwise stated
² Sand >20-2000 mm, silt 2-20 mm, clay <2mm
³ Sand 50-2000 mm, silt 2-50mm, clay <2mm

Degradation in soil - laboratory studies. In a study according to the German BBA guidelines (Jackson and Lewis, 1994) [carbinol-¹⁴C]fenarimol (radiochemical purity 97.3%) was incubated with Marcham clay loam, Faringdon clay, Marcham sandy loam and Speyer 2.2 loamy sand at concentrations of 0.05 and 0.25 mg/kg, equivalent to 0.1 and 0.5 kg/ha, at 40% maximum water holding capacity and 20°C. Ethanolamine traps were used to collect gaseous compounds.

Single (duplicate for Speyer 2.2) samples were taken at six representative times up to 180 days after application at the low rate and at four times at the high rate. The soils were Soxhlet-extracted with 2-butanol/water and analysed by TLC. The extraction of fenarimol by this method was initially >95% and during the course of the experiment mass balances were generally 95-105%. Results are shown in Table 2.

Table 2. Degradation of fenarimol in soil; laboratory study.

Soil	Half-life of fenarimol, days
	Low application rate	High application rate
Marcham clay loam	473	917
Marcham sandy loam	436	889
Faringdon clay	542	1204
Speyer 2.2 loamy sand	1360	1833

The radioactivity in the ethanolamine trap accounted for <5% of the applied ¹⁴C and was assumed by the authors to be ¹⁴CO₂. Unextractable residues in the soil rose to 3.3-17.2% of the applied radioactivity (AR) at 180 days. Two unidentified products were extracted from the soil, each accounting for <3% of the AR at any time.

In a further study according to USA EPA guidelines (Rainey, 1990) [carbinol-¹⁴C]fenarimol (radiochemical purity 97.6%) was evenly mixed with Greenfield sandy loam at 75% 33 kPa moisture content to produce a final concentration of 5 mg/kg (equivalent to 9.75 kg/ha). Soil was placed in a closed flow-through system with KOH and charcoal traps to collect volatile products and incubated in the dark at 24°C for one year. After ten representative intervals aliquots of soil (15 g) were removed, extracted with methanol/water under reflux (and later samples also with butanol/water under reflux) and the extracts analysed by TLC.

The mass balance for the radioactivity in combusted soil did not change over the year and was all accounted for in the various fractions after extraction. After one year the total radioactivity collected from the KOH trap had reached 0.6% of the AR and the unextractable residues in the soil had risen steadily to 9.4%. A single product, identified by MS as a-(2-chlorophenyl)-a -(4- chlorophenyl)-1,2-dihydro-2-oxo-5-pyrimidinemethanol, reached a maximum level of 4.1% after 6 months. Fenarimol levels were reported to have decreased to 79% after one year and a half-life of 840 days was calculated.

Althaus and Beaty (1982) added [carbinol-¹⁴C]fenarimol (radiochemical purity 98.9%) to coarse, medium and fine soils to produce a final concentration of 5 mg/kg (equivalent to 9.75 kg/ha). The soils were adjusted to 75% of 33 kPa moisture content and kept in the dark at 20-25°C for one year. Samples were removed at ten intervals, Soxhlet-extracted with 2-butanol/water and analysed by TLC. Anaerobic degradation was investigated in a further set of soils which were prepared in the same manner but flooded with water after four weeks of aerobic degradation and incubated for a further 4-8 weeks.

In the aerobic experiment the total radioactivity recovered throughout the study was 88-113% of the AR. Over the one-year period the unextractable radioactivity rose to 3.9-5.8% of the AR. Fenarimol accounted for 78-83% of the extractable radioactivity in the one-year samples and the remaining extractable radioactivity was not attributable to any individual compounds.

In the anaerobic system 94-96% of the total radioactivity remained as fenarimol after 8 weeks incubation and only 4% of the radioactivity was in the water phase.

In a study by Althaus and Bewley (1978b) [carbinol-¹⁴C]fenarimol (radiochemical purity >99%) was mixed with Crosby silt loam soil (3 kg, properties not given) to obtain a concentration of 1 mg/kg (equivalent to 1.95 kg/ha). The soil was then flooded with water and the atmosphere purged with nitrogen. The incubation temperature was not stated but after one year 98% of the AR was in the soil and 91% was extracted from soil/water samples as fenarimol.

Degradation in soil - field studies. An EC formulation of fenarimol was sprayed at 0.27 kg ai/ha on to bare soil at four German field sites (Ismaning, Rohr, Alsfeld and Grebin) in May 1990 (Perkins, 1993). Cores were taken at each site at 0, 14, 60, 120 and 210 days (100 cm depth) and at 12, 16 and 20-24 months (30 cm depth). The 100 cm cores were sectioned into depths of 0-10, 10-20, 20-40, 40-60 and 60-100 cm except in the Grebin trial where the samples from 0 to 60 days were inadvertently bulked. The 30 cores were divided into 0-10, 10-20 and 20-30 cm sections.

Each sub-section of the soil cores was mixed and sieved. Sub-samples were extracted with methanol/water, cleaned up and analysed by GLC. The LOD of the method was 0.05 mg/kg and the mean recovery was 94%.

0-10 and 10-20 cm soil cores were combined before analysis and no deeper samples were analysed. In the early Grebin cores the totals found in the 100 cm cores was assumed to be in the 0-20 cm range and concentrations were calculated accordingly. At Grebin and Alsfeld very high concentrations of fenarimol found at day 0 (three to four times those predicted from the application rate) resulted in short calculated half-life (DT50) values. The results are plotted in Figure 1 and the calculated DT50 and DT90 values are given in Table 3.

Figure 1. Concentrations of fenarimol in four German field soils.

The DT50 and DT90 values estimated from Figure 1 are shown in Table 3.

Table 3. DT50 and DT90 values for four German soils.

Soil	DT50, days	DT90, days
Ismaning	123	>610
Rohr	95	>610
Alsfeld	14	550
Grebin	21	120

In a further study according to BBA guidelines (Butcher and Rawle, 1994) an EC formulation of fenarimol was sprayed at 270 g ai/ha on to bare soil at two German field sites (Herford and Gornitz) in May 1992. Cores (20 cm long) were taken at each site and at day 0 they were sectioned into 0-10 and 10-20 cm and analysed separately. At days 14, 31-32, 90-92, 214, 361-365, 488-389 and 609 they were analysed as 0-20 cm.

The initial concentrations in the 10-20 cm sections were below the LOD at Gornitz and 0.006 mg/kg at Herford; the concentrations in the 0-10 cm sections were incorrectly calculated and should have been half those reported. The DT50 and DT90 values are given in Table 4 below.

Table 4. DT50 and DT90 values for two German soils.

Soil	DT50, days	DT90, days
Herford	66	489
Gornitz	150	>609

Crosby silt loam soil (properties not given) was used to fill steel cylinders to a height of 10 cm. [Carbinol-¹⁴C]fenarimol (radiochemical purity >99%) was added to the surface at a nominal rate of 1.2 kg/ha and the cylinders were placed in the ground and subjected to normal weather conditions (not detailed) at Greenfield, Indiana, USA (Althaus and Bewley, 1978a). One cylinder was removed and the soil mixed at each sampling point at intervals during 511 days.

In another experiment at the same site (Althaus and Bewley, 1978b) was incorporated into the top 7.6 cm of a Crosby silt loam field plot at application rates of 1.1 and 5.6 kg/ha. Soil cores (depth at least 15 cm) were taken at each sampling point at intervals for 129 weeks.

In both experiments soil was Soxhlet-extracted with methanol and sometimes also butanol/water and analysed by TLC. In the experiment in which fenarimol was applied to the surface the half-life was 112 days and after 511 days 35% of the AR was extractable as fenarimol, 13% was unextractable, and unidentified extractable radioactivity accounted for 9% of the AR with no discrete region >5%. The rest of the radioactivity was reported as being dissipated but was not otherwise accounted for. Where fenarimol was incorporated into the soil no radioactivity was lost from the 0-15 cm core, but at times after 27 weeks 7-28% of the AR was found in the 7.6-15 cm section. No difference in the rate of degradation was observed between the two application rates. After 189 days extractable residues other than fenarimol individually accounted for <5% of the AR and after 903 days 65% of the AR was still fenarimol.

A long-term field dissipation study was carried out at locations in California, Florida, Indiana, and Maryland, using a WP formulation of fenarimol (Day, 1982). The soils were described as loam, sand, clay loam and silt loam although no detailed soil analysis was reported.

Two studies were conducted at each location. In the first, bare soil plots were divided to receive applications of fenarimol at 3.4 or 6.7 kg ai/ha in either the first year only, the first two years only, or for three years. In the second, bare soil plots were treated six to eight times with fenarimol at 0.56 kg ai/ha at biweekly intervals.

Soil samples were taken according to a defined schedule from all plots, in a few cases for as long as four years after application. Dissipation constants and DT50 values averaged from both investigations are shown in Table 5.

Table 5. Dissipation constant and DT50 values at four locations in the USA.

State	Average dissipation constant per day	DT50, days
California	0.00106	651
Florida	0.00722	98
Indiana	0.00217	322
Maryland	0.00167	413

The rate of dissipation was reported to be correlated with the moisture history of the area. Shorter half-lives were observed where the rainfall or supplemental irrigation was heavier.