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Land use effects on sorption of pesticides and their metabolites in sandy soils. I. Fenamiphos and two metabolites, fenamiphos sulfoxide and fenamiphos sulfone, and fenarimol and azinphos methyl.

Introduction

In Australia and elsewhere there is growing concern about contamination of groundwater by pesticides, especially from intensive agricultural systems (Gerritse et al. 1991; Vighi and Funari 1995; Kookana et al. 1998). Several rural and urban communities in Australia rely heavily on groundwater for drinking water. For example, the shallow, unconfined, groundwater aquifer under the Gnangara Mound, Western Australia, provides nearly half of the drinking water for metropolitan Perth (Davidson 1995). Land use on the Mound has changed considerably over time. Native banksia (predominantly Banksia attenuata and B. menziessii) woodland that used to cover many areas has been cleared and replaced with commercial pine plantations (Pinus pinaster Ait.) and agricultural crops. The major agricultural activity in the Gnangara Mound area is intensive horticulture, notably the production of vegetables, floriculture, and fruit and nursery crops. Because of its close proximity to metropolitan markets, the Mound is also an important area for market gardening, an industry that extracts all its irrigation requirements from groundwater wells (Davidson 1995). Intensive agriculture relies heavily on the use of pesticides for the control of weeds, pests, and diseases. Trace concentrations of pesticide residues have been detected in groundwaters of several Australian regions (Bauld 1996; Kookana et al. 1998).

Sorption of pesticides is one of the major processes influencing their movement through soil. Fenamiphos (ethyl 3-methyl-4-(methylthio)phenyl isopropylphosporamidate, Nemacur) is a broad spectrum, non-volatile nematicide that can rapidly oxidise to fenamiphos sulfoxide (f. sulfoxide), which then slowly transforms to fenamiphos sulfone (f. sulfone). Both metabolites have nematicidal activity (Waggoner and Khasawinah 1974). As the oxidation products are more polar than the parent compound, they are likely to be more mobile in soil (Bilkert and Rao 1985; Ou and Rao 1986). The sorption mad degradation behaviour of fenamiphos has been studied in both American (Bilkert and Rao 1985; Loffredo et al. 1991) and Australian soils (Singh et al. 1989; Kookana et al. 1998), but there is little information on the sorption behaviour of the metabolites. The only study available is by Lee et al. (1986), who measured sorption of the 3 compounds by 1 soil. Fenarimol (2,4'-dichloro-[alpha]-(pyrimidin-5-yl)benzhydryl alcohol) is a systemic fungicide and azinphos methyl (S-(3,4-dihydro-4-oxobenzo[d]-[1,2,3]-triazin-3-ylmethyl) O,O-dimethyl phosphorodithioate) is a non-systemic insecticide used to control chewing and sucking insects. There is little published information about the sorption behaviour of either chemical. All 3 pesticides are used in the agricultural practices on the Gnangara Mound.

There are only limited data available about the behaviour of fenamiphos, f. sulfone, f. sulfoxide, fenarimol, and azinphos methyl in soils worldwide and no information about the effect of land use on sorption behaviour. The purpose of this study was to investigate the sorption of fenamiphos, f. sulfone, f. sulfoxide, fenarimol, and azinphos methyl by sandy soils representing different classifications and land uses in the Swan Coastal Plain area, and relate sorption behaviour to soil properties. This study would also provide sorption data for these compounds specific to Australian soils.

Materials and methods

Pesticides

Analytical grade chemicals (fenamiphos 94.6%, f. sulfone 98%, f. sulfoxide 98%, fenarimol 99.5%, and azinphos methyl 91.5%) were obtained from Chem Service Pennsylvania, USA. Some chemical characteristics are given in Table 1. There is limited chemical information about the fenamiphos metabolites. The degradation of fenamiphos to f. sulfoxide, and then to f. sulfone, has been described by Ou and Rao (1986).

Soil properties

Nineteen surface (0-15 cm) and 18 subsurface (40-50 cm) sandy soils were sampled from the Gnangara Mound area of the Swan Coastal Plain, Western Australia. The soils represented surface and subsurface soils (not different horizons) in 2 of the 3 major dune systems (Bassendean and Spearwood) on the northern Swan Coastal Plain (Fig. 1). The Bassendean Dunes comprise 3 soil types (Gavin, Jaudakot, and Joel), and the Spearwood Dunes comprise 5 soil types (Beonaddy, Karrakata yellow, Karrakata grey, Limestone, and Spearwood) (McArthur and Bettenay 1960). The soils also represented areas that were under 2 different land uses, intensive horticulture and native vegetation. The soils under market gardens had been cropped for over 20 years, and cultivated annually for each new crop.

[FIGURE 1 OMITTED]

Soils were air-dried, ground, and passed through <2-mm sieve prior to any analysis. Selected properties of the soils, determined using previously published methods (Salama et al. 2001), are given in Table 2.

Briefly, the range of OC in the surface soils was 0.74-2.94% for those under native vegetation and 0.57-2.16% for those under market gardens. Generally, the OC content was smaller in the subsurface soils and ranged from 0.18 to 0.89% for those under native vegetation and from 0.09 to 3.08% for those under market gardens. Generally, the soils under native vegetation were slightly more acidic than those under market gardens. The [pH.sub.w], range in the surface soils was 4.53-6.08 under native vegetation and 4.43-7.87 under market gardens. In the subsurface soils the [pH.sub.w] ranged from 4.51 to 6.14 under native vegetation and from 4.39 to 7.94 under market gardens.

Sorption studies

Sorption coefficients for all pesticides and the 2 fenamiphos metabolites were determined by a batch method. For both multipoint and singlepoint sorption measurements, soil (5 g) was weighed into polypropylene centrifuge tubes to which 10 mL of 0.005 M [Ca([NO.sub.3]).sub.2] solution, spiked with a known concentration of the chemical, was added. Multipoint measurements were made in duplicate and the singlepoint measurements in triplicate. The soil suspensions were shaken for 4 h on an end-over-end shaker and then centrifuged at 1100G for 5 min. The supernatants were decanted, filtered through 0.45-[micro]m Acrodisk filters, and stored at 4[degrees]C prior to analysis by high performance liquid chromatography (HPLC). The amount sorbed was calculated from the difference between the initial and final concentrations in solution. Pesticide sorption onto walls and loss during filtering were checked by running blanks (spiked solution with no soil) in every batch. For singlepoint measurements the sorption coefficient ([K.sub.d]) was calculated from the ratio of the concentration sorbed on to the soil ([micro]g/g) to the solution concentration ([micro]g/mL) after equilibration. Multipoint sorption data were fitted to linear and Freundlich sorption models.

A subset of soils (9 for fenamiphos and 6 for fenarimol) was chosen for determining multipoint isotherms. For the multipoint studies the following concentrations were used: 2.5, 5.0, 7.5, and 10.0 mg/L. These concentrations were chosen to cover a range of application rates used in the area (up to 9.6 kg a.i./ha). Stock solutions were prepared in methanol. Spiking solutions were diluted volumetrically from stock solutions using 0.005 M [Ca(NO.sub.3]).sub.2] solution to give 1% methanolic solutions. Although cosolvents can affect sorption behaviour, a previous study indicated that 1% methanol had no significant effect (Kookana et al. 1990). Because the multipoint sorption isotherms were not always linear, it was decided to use 2 mg/L for the singlepoint studies. Isotherms that are linear at low solute concentrations can become non-linear when the concentration is increased.

Pesticide analysis

The concentrations of pesticides in the equilibrium solutions were determined using a Varian HPLC instrument equipped with a Star 9012 ternary gradient pump, a Polychrom 9065 diode array detector (PDA), and a Star 9100 autosampler with an electric sample valve. Data were collected and processed using the commercially available Star HPLC software.

The following conditions were used for fenamiphos, f. sulfoxide and f. sulfone: SGE SS Wakosil [C.sub.18] column (25 cm by 4.6 mm I.D.; 4-[micro]m particle size); isocratic elution with mobile phase 50:50 [H.sub.2]O:C[H.sub.3]CN; a flow rate of 1 mL/min; PDA detector at a wavelength of 224 nm for f. sulfoxide and f. sulfone and 248 nm for fenamiphos; and retention times of: f. sulfoxide 4.5 min, f. sulfone 7.4 min, and fenamiphos 15 min.

Fenarimol was determined using the following conditions: [C.sub.18] column (25 cm by 4.6 mm I.D.; 4-[micro]m particle size); isocratic elution with mobile phase 30:25:45 [H.sub.2]O:C[H.sub.3]CN:C[H.sub.3]OH; a flow rate of 0.8 mL/min; PDA detector at a wavelength of 220 nm for fenarimol; and a retention time of 10.2 min for fenarimol. Azinphos methyl was determined using the following conditions: Waters radial pak liquid chromatography [C.sub.18] column (10 cm by 5 mm I.D., 4-[micro]m particle size); gradient elution with a mobile phase of 90:10 [H.sub.2]O:C[H.sub.3]CN for the first 2 min which then changed to 50:50 [H.sub.2]O:C[H.sub.3]CN over the following 5 min. This composition was maintained for the next 8 min. The flow rate was 1 mL/min, the UV-Vis detector wavelength was 220 nm, and the retention time for azinphos methyl was 10.4 min.

Statistical analysis

Sorption coefficients ([K.sub.d] values) were determined from the singlepoint measurement (batch equilibrium with 1 concentration). The [K.sub.d] values front the singlepoint studies were then compared with [K.sub.d] and [K.sub.f] values from regressions using a range of spiking concentrations (multipoint studies). The multipoint data were also fitted to the Freundlich model, S = [K.sub.f] [C.sup.n], where [K.sub.f] is the Freundlich coefficient, which is the same as [K.sub.d] when n is 1; S is sorbed concentration; and C is solution concentration. The relationships between [K.sub.d] values (determined by singlepoint studies) and pH, organic carbon (%OC) and silt + clay (<0.063 mm) content were determined by regression analysis. Statistical analyses were conducted on log-transformed data to stabilise the variance. An analysis of variance (ANOVA) was performed to determine the effect of land use on the sorption coefficients for each chemical. The surface and subsurface data were treated separately for the ANOVA because the [K.sub.d] values for each chemical were not comparable between the 2 soil depths. A paired t-test was performed to compare the [K.sub.d] values from the surface and subsurface group for each chemical.

Results and discussion

Multipoint sorption isotherms for fenamiphos and fenarimol were measured on a subset of soils (Table 3). Generally, for fenarimol and fenamiphos the Freundlich model provided a better fit for the data. However, for the purpose of assessing the effect of land use on sorption behaviour, the use of a singlepoint sorption coefficient ([K.sub.d]) measured at a low concentration, was considered a good approximation of the sorptive behaviour for most soils. Although 5-g soil samples were used in the sorption tests, a large variability between replicates was observed in some cases. This might due to the sandy nature of the soils, and the presence of discrete particles of organic matter.

Effect of land use on sorption of pesticides

Although the [K.sub.d] values of all 5 compounds in surface soils showed a trend of being larger under native vegetation (banksia bush) than under market gardens, the differences between land uses were significant (P < 0.05) only for the azinphos methyl data. In the subsurface soils, [K.sub.d] values for fenamiphos, f. sulfoxide, f. sulfone, and fenarimol were significantly (P < 0.01) greater under native vegetation than under market gardens (Figs 2 and 3). Sorption values for fenamiphos, f. sulfoxide, f. sulfone, and azinphos methyl showed a greater range in surface soils under native vegetation than under market gardens. For example, [K.sub.d] values for fenamiphos in surface soils varied almost 11-fold (4.6-53.7 L/kg) under native vegetation, compared with a 4-fold range (2-8 L/kg), for the market garden, surface soils (Table 4). A similar wide range was measured for [K.sub.d] values for f. sulfone and f. sulfoxide. This same trend was evident in the subsurface soils for fenamiphos and f. sulfoxide, and to a lesser extent for f. sulfone (Table 4). Sorption values for fenarimol in surface soils, however, showed a similar range (approx. 5-fold) under both land uses. The [K.sub.d] values for all 5 compounds were significantly (P < 0.001) greater in surface than in subsurface soils.

[FIGURES 2-3 OMITTED]

Clearing natural vegetation for cropping commonly leads to a decline in the original OC content of soil (Jenkinson 1990). The OC content of the surface soils was around 1% for the market garden soils (except for soil 35 which was 2.16%) and ranged from approximately 1 to 3% for the banksia soils. In the subsurface soils, the OC content decreased sharply to approximately 0.25-1.0% for both market garden and banksia soils. Soil 36, with an organic carbon content of 3.08%, was an exception to this generality (Table 2). The surface soils under native vegetation tended to be more acidic ([pH.w] ~ 5) than those under market garden ([pH.sub.w] ~ 7). The pH of subsurface soils was approximately 0.5-1 unit smaller than that of the surface soils. Because all the compounds used in this study are non-ionic, sorption is expected to be independent of pH.

Plots of [K.sub.d] values v. %OC for all 5 compounds (Figs 4 and 5) showed that at a given %OC the soils under banksia bush generally had a greater sorption capacity than the soils under market gardens. This effect became more pronounced with increasing organic carbon content, suggesting that the nature and composition of organic matter in uncultivated soils (i.e. under native vegetation) is different from that in cultivated soils. To reduce the variability in sorption coefficients among soils, the values were normalised with respect to OC (i.e. [K.sub.oc] = [K.sub.d]/%OC). Expressing the sorption as [K.sub.oc] did not decrease the variability. However, Ahmad et al. (2001) has recently reported that the aromatic fraction of soil organic matter was a better predictor of pesticide sorption than total OC. Their work also suggests that total OC is not a sufficiently specific indicator of the complex interactions between pesticides and organic matter.

[FIGURES 4-5 OMITTED]

Sorption behaviour of many pesticides is determined by various soil factors, but the best correlation is usually observed with soil organic matter (Osgerby 1970; Brouwer et al. 1990; Kookana et al. 1998). The relationship between [K.sub.d] or [K.sub.oc] values and soil parameters that may influence sorption behaviour, namely organic matter, silt + clay content, and pH, was determined. There was generally only a weak relationship between [K.sub.d] values for fenamiphos, f. sulfone, and f. sulfoxide and %OC, pH, or %silt + clay. The exception to this was the sorption affinity of market garden soils for fenamiphos where a strong positive relationship with %OC ([r.sup.2] = 0.76, ***) was observed (Fig. 4a). Singh et al. (1989) also observed a similar general trend. Generally the relationship between [K.sub.d] and pH was also weak for fenamiphos, f. sulfoxide and f. sulfone, but where this relationship was significant (P < 0.05) the [K.sub.d] values decreased with increasing pH (data not shown). Singh et al. (1989) also measured decreasing sorption of fenamiphos as the pH of the soil solution increased. Solution pH would not be expected to influence fenamiphos sorption, as this compound is non-ionic. However, pH can affect the charge characteristics of OC, which in turn can affect sorption behaviour.

There was a positive relationship between the [K.sub.d] values and %OC for azinphos methyl for soils under both native vegetation and market gardens and for fenarimol for soils under native vegetation (Fig. 5a and b respectively). The strongest relationships were obtained for both azinphos methyl and fenarimol with the soils under native vegetation ([r.sup.2] = 0.71 *** and 0.73***, respectively). The weak relationship between [K.sub.d] and [K.sub.oc] values and %silt + clay (data not shown) may have been due to the limited range of silt + clay content of the soils. All the soils in this study had a low clay content (<1%). Other studies have showed that clay content and type only become a significant factor determining the sorption behaviour of pesticides when the %OC content of the soils is <1% (Roy and Krapac 1994). In summary, %OC was the main factor affecting the sorption of azinphos metbyl by soils under both land uses, of fenarimol for banksia soils, and of fenamiphos for market garden soils. However, to distinguish differences in sorption behaviour between the 2 land uses the chemical nature of the organic matter needs to be characterised using techniques, such as solid-state [sup.13]C-NMR spectroscopy (Ahmad et al. 2001).

[FIGURE 5 OMITTED]

Comparison of sorption behaviour of parent compound with metabolites

Generally, the [K.sub.d] values for fenamiphos were significantly (P < 0.001) larger than those for the 2 metabolites, f. sulfoxide and f. sulfone. This applied to both surface and subsurface soils whether they were under native vegetation (banksia bush) or market garden (Fig. 2). The exceptions were Soils 10, 14, 8, and 16 for which the [K.sub.d] values were low (<1.5 L/kg), and not significantly different for each compound. All 4 were subsurface soils under market garden, except for Soil 10 which was covered with native vegetation. The sorption coefficients decreased in the order fenamiphos >> f. sulfone [greater than or equal to] f. sulfoxide. The [K.sub.d] values for fenamiphos were generally 1 order of magnitude larger than those for its metabolites. Similarly, Lee et al. (1986) observed the sorption of fenamiphos on a silty clay loam to be about 4 times larger than that of its 2 metabolites. As in this study, f. sulfoxide was less sorbed than fenamiphos or f. sulfone, in keeping with the larger polarity of f. sulfoxide. Our findings agree with those obtained by Bilkert and Rao (1985) and Loffredo et al. (1991) from leaching studies, which indicated that f. sulfoxide and f. sulfone were more mobile, and hence more easily leached than the parent compound. Like fenamiphos, aldicarb (2-methyl-2-(methythio) propionaldehyde, O-(methylcarbamoyl)oxime) degrades into aldicarb sulfoxide and aldicarb sulfone. Sorption of aldicarb and its 2 metabolites followed the same order as fenamiphos and its metabolites (Lemley et al. 1988).

Conclusions

This study showed a wide range of sorption coefficients for azinphos methyl, fenarimol, fenamiphos, f. sulfone and f. sulfoxide in 34 sandy soils from the Gnangara Mound region, WA. Generally, a greater range of [K.sub.d] values for all compounds was obtained in soils under native vegetation than in soils under market garden. However, for surface soils the [K.sub.d] values were significantly (P < 0.05) larger under native vegetation than market gardens only for azinphos methyl. For a given %OC content, sorption coefficients were up to 5 times greater for soils under native vegetation than for market garden soils. All things being equal, this observation may be due to differences in organic matter composition among the soils. The importance of the chemical compositions of organic matter to pesticide sorption by soils needs to be assessed.

Sorption coefficients of all 5 compounds were generally weakly correlated with %silt + clay and pH. However, there was a strong relationship between [K.sub.d] and %OC for fenamiphos ([r.sup.2] = 0.76***) and azinphos methyl ([r.sup.2] = 0.56**) in soils under market gardens. There was also a strong relationship between [K.sub.d] and %OC for azinphos methyl ([r.sup.2] = 0.71***) and fenarimol ([r.sup.2] = 0.73***) in soils under native vegetation. Even when sorption coefficients were normalised on the basis of mass OC (i.e. [K.sub.oc]), an order of magnitude difference was measured. Thus, [K.sub.oc] does not adequately describe the complex interactions between pesticides and organic matter.

Although sorption coefficients for azinphos methyl and fenarimol did not show a consistent trend, they were nearly always greater than the [K.sub.d] values for fenamiphos, f. sulfone and f. sulfoxide. Generally the [K.sub.d] values for fenamiphos were significantly (P < 0.001) larger than those for its 2 metabolites. Sorption coefficients (K.sub.d]) were determined to decrease in the order: fenamiphos [much greater than] f. sulfone [greater than or equal to] f. sulfoxide. This would indicate that the 2 metabolites of fenamiphos, f. sulfone and f. sulfoxide, are more likely than the other 3 pesticides studied to move through the soil, and hence pose a greater threat to groundwater contamination, than the parent compound. Current Australian drinking water guidelines specify limits for fenarimol (30 [micro]g/L), azinphos methyl (3 [micro]g/L), and fenamiphos (300 ng/L), but not for the 2 metabolites of fenamiphos (DeHayr et al. 1999). This study indicates that metabolites as well as parent compounds need to be considered when setting drinking water guidelines, particularly in regions where groundwater is to be used as potable water.
Table 1. Selected characteristics of fenamiphos, f. sulfoxide, f.
sulfone, azinphos methyl and fenarimol

Chemical Solubility in water at Vapour pressure at
 20[degrees]C (mg/L) (A) 20[degrees]C (mPa) (A)

Fenamiphos 700 0.133
F. sulfoxide 400 --
F. sulfone 400 --
Azinphos methyl 28 0.18
Fenarimol 13.7 0.065

(A) Tomlin 1994.

Table 2. Selected physico-chemical properties of the soils studied

Land use: V, native vegetation (banksia bush); MG, market gardens

No. Soil Classification (A) Sampling Land use Organic
 depth carbon
 (cm) (%)

 1 Typic Durothod 0-15 V 2.90
 3 Xeric Quartzipsamment 0-15 V 1.02
 5 Typic Durothod 0-15 V 2.94
 9 Typic Psammaquent 0-15 V 2.88
 17 Petrocalcic Xerochrept 0-15 V 2.50
 19 Xeric Quartzipsamment 0-15 V 0.75
 21 Xeric Quartzipsamment 0-15 V 1.02
 29 Typic Durothod 0-15 V 1.14
 39 Xeric Quartzipsamment 0-10 V 0.86
 2 Typic Durothod 40-50 V 0.89
 4 Xeric Quartzipsamment 40-50 V 0.14
 6 Typic Durothod 40-50 V 0.56
 10 Typic Psammaquent 40-50 V 0.18
 18 Petrocalcic Xerochrept 40-50 V 0.25
 20 Xeric Quartzipsamment 40-50 V 0.28
 22 Xeric Quartzipsamment 40-50 V 0.34
 30 Typic Durothod 40-50 V 0.84
 7 Typic Durothod 0-15 MG 1.05
 13 Xeric Quartzipsamment 0-15 MG 0.57
 15 Petrocalcic Xerochrept 0-15 MG 0.78
 23 Petrocalcic Xerochrept 0-15 MG 0.85
 25 Xeric Quartzipsamment 0-15 MG 0.82
 27 Xeric Quartzipsamment 0-15 MG 0.78
 31 Xeric Quartzipsamment 0-15 MG 1.13
 35 Typic Psammaquent 0-15 MG 2.16
 37 Xeric Quartzipsamment 0-15 MG 1.05
 42 Xeric Quartzipsamment 0-10 MG 0.58
 8 Typic Durothod 40-50 MG 0.09
 14 Xeric Quartzipsamment 40-50 MG 0.10
 16 Petrocalcic Xerochrept 40-50 MG 2.16
 24 Petrocalcic Xerochrept 40-50 MG 0.24
 26 Xeric Quartzipsamment 40-50 MG 0.49
 28 Xeric Quartzipsamment 40-50 MG 0.29
 32 Xeric Quartzipsamment 40-50 MG 0.31
 36 Typic Psammaquent 40-50 MG 3.08
 38 Xeric Quartzipsamment 40-50 MG 0.48
 43 Xeric Quartzipsamment 40-50 MG 0.16

No. Soil Classification (A) Silt+clay (B) Sand (C)
 (%) (%)

 1 Typic Durothod 1.62 98.91
 3 Xeric Quartzipsamment 0.74 99.21
 5 Typic Durothod 0.87 98.65
 9 Typic Psammaquent 1.13 98.78
 17 Petrocalcic Xerochrept 1.34 98.52
 19 Xeric Quartzipsamment 1.26 98.77
 21 Xeric Quartzipsamment 0.1 99.12
 29 Typic Durothod 1.02 99.13
 39 Xeric Quartzipsamment 1 99.04
 2 Typic Durothod 1.36 98.57
 4 Xeric Quartzipsamment 0.25 99.42
 6 Typic Durothod 0.59 99.35
 10 Typic Psammaquent 1.59 98.35
 18 Petrocalcic Xerochrept 0.61 99.57
 20 Xeric Quartzipsamment 1.16 98.97
 22 Xeric Quartzipsamment 0.93 99.25
 30 Typic Durothod 1 99.20
 7 Typic Durothod 1.04 98.96
 13 Xeric Quartzipsamment 1.03 98.98
 15 Petrocalcic Xerochrept 1.42 98.59
 23 Petrocalcic Xerochrept 2.72 97.34
 25 Xeric Quartzipsamment 3.78 96.42
 27 Xeric Quartzipsamment 3.17 97.29
 31 Xeric Quartzipsamment 1.78 98.39
 35 Typic Psammaquent 3.01 97.14
 37 Xeric Quartzipsamment 1.52 98.55
 42 Xeric Quartzipsamment 1.58 98.72
 8 Typic Durothod 0.68 99.38
 14 Xeric Quartzipsamment 1.04 98.98
 16 Petrocalcic Xerochrept 0.82 99.22
 24 Petrocalcic Xerochrept 1.07 98.43
 26 Xeric Quartzipsamment 2.33 97.88
 28 Xeric Quartzipsamment 2.61 97.62
 32 Xeric Quartzipsamment 1.8 98.37
 36 Typic Psammaquent 1.96 97.96
 38 Xeric Quartzipsamment 1.05 98.95
 43 Xeric Quartzipsamment 1.43 98.41

No. Soil Classification (A) [pH.sub.W] (D)

 1 Typic Durothod 4.64
 3 Xeric Quartzipsamment 5.00
 5 Typic Durothod 4.92
 9 Typic Psammaquent 5.96
 17 Petrocalcic Xerochrept 6.08
 19 Xeric Quartzipsamment 5.52
 21 Xeric Quartzipsamment 4.83
 29 Typic Durothod 4.53
 39 Xeric Quartzipsamment 4.87
 2 Typic Durothod 4.51
 4 Xeric Quartzipsamment 5.12
 6 Typic Durothod 4.93
 10 Typic Psammaquent 5.50
 18 Petrocalcic Xerochrept 6.14
 20 Xeric Quartzipsamment 5.62
 22 Xeric Quartzipsamment 4.64
 30 Typic Durothod 4.65
 7 Typic Durothod 4.43
 13 Xeric Quartzipsamment 6.24
 15 Petrocalcic Xerochrept 5.61
 23 Petrocalcic Xerochrept 7.19
 25 Xeric Quartzipsamment 7.02
 27 Xeric Quartzipsamment 7.05
 31 Xeric Quartzipsamment 7.00
 35 Typic Psammaquent 7.16
 37 Xeric Quartzipsamment 7.87
 42 Xeric Quartzipsamment 6.58
 8 Typic Durothod 4.39
 14 Xeric Quartzipsamment 6.38
 16 Petrocalcic Xerochrept 6.18
 24 Petrocalcic Xerochrept 7.28
 26 Xeric Quartzipsamment 6.74
 28 Xeric Quartzipsamment 7.15
 32 Xeric Quartzipsamment 7.14
 36 Typic Psammaquent 7.94
 38 Xeric Quartzipsamment 7.81
 43 Xeric Quartzipsamment 5.83

(A) Soil Survey Staff 1994.

(B) <0.063 mm.

(C) 2.0-0.063 mm.

(D) Soil: water (1:5).

Table 3. K values from a subset of soils as determined from multipoint
sorption isotherms

The multipoint data were fitted to both a linear regression model (S =
[K.sub.d] C) and a Freundlich model (S = [K.sub.f][C.sup.n]) where S is
concentration sorbed, and C is concentration remaining in solution

Soil No. Multipoint sorption isotherm

 Linear Freundlich model

 [K.sub.d] (A) [R.sup.2] [K.sub.f] (B)

 Fenarimol

 1 76.72 0.77 62.04
 5 33.23 0.64 23.30
 13 1.90 0.61 5.42
 31 12.18 0.91 11.24
 36 27.70 0.93 17.61
 43 3.64 0.56 4.30

 Fenamiphos

 1 49.75 0.85 44.61
 5 17.31 0.48 17.76
 9 9.07 0.95 9.54
 13 1.09 0.44 2.11
 15 2.62 0.80 3.40
 20 1.33 0.44 2.53
 31 3.28 0.93 2.45
 33 9.97 0.86 10.59
 36 12.6 0.82 12.84

Soil No. Multipoint sorption isotherm

 Freundlich model

 n [R.sup.2]

 Fenarimol

 1 0.89 0.82
 5 0.68 0.96
 13 0.42 0.72
 31 0.89 0.97
 36 0.63 0.99
 43 0.43 0.75

 Fenamiphos

 1 0.94 0.84
 5 0.84 0.78
 9 0.84 0.98
 13 0.58 0.84
 15 0.78 0.89
 20 0.56 0.73
 31 1.30 0.96
 33 0.72 0.95
 36 1.08 0.85

(A) units L/kg.

(B) units [[micro]g.sup.(1-n)[mL.sup.n]/g.

Table 4. Sorption coefficients ([K.sub.d]) and [K.sub.oc] for
fenarimol, azinphos methyl, fenamiphos, f. sulfoxide and f. sulfone for
all soils as determined from single point measurements

 Fenarimol Azinphos methyl

Soil [K.sub.d] [K.sub.oc] [K.sub.d] [K.sub.oc]

 Native vegetation, surface (0-15 cm) soils

 1 50.34 1735 47.81 4781
 3 24.95 2446 39.40 1313
 5 49.33 1677 48.06 961
 9 50.08 1738 32.51 361
17 50.94 2037 48.02 282
19 44.49 5932 24.07 126
21 50.05 4907 46.99 223
29 50.82 4457 48.13 165

 Native vegetation, surface (40-50 cm) soils

 2 49.72 5586 47.90 2395
 4 2.56 1828 0.70 17
 6 17.47 3119 24.90 415
10 1.89 1047 0.00 0
18 3.84 1536 1.31 7
20 10.83 3867 5.57 27
22 18.39 5408 4.56 20
30 42.93 5110 48.06 160

 Market gradens, surface (0-15 cm) soils

 7 38.53 3669 10.06 143
13 12.47 2186 2.93 22
15 38.38 4920 7.74 51
23 12.02 1414 14.44 62
25 21.57 2630 27.91 111
27 7.41 949 3.33 12
31 9.13 807 44.68 144
35 27.25 1261 48.10 137

 Market gradens, surface (40-50 cm) soils

 8 2.10 2329 0.00 0
14 2.18 2175 0.00 0
16 2.13 1328 0.00 0
24 1.54 643 0.08 0
26 20.26 4134 41.66 160
28 2.41 829 0.15 0
32 4.82 1554 5.08 15
36 34.65 1125 48.18 133
38 7.21 1502 7.44 19
43 5.82 3640 1.66 3

 Fenamiphos F. sulfoxide

Soil [K.sub.d] [K.sub.oc] [K.sub.d] [K.sub.oc]

 Native vegetation, surface (0-15 cm) soils

 1 38.68 1333 n.d. n.d.
 3 4.60 450 0.07 6
 5 25.86 879 3.01 102
 9 21.90 760 1.65 57
17 8.86 354 1.25 50
19 7.37 982 0.81 108
21 16.94 1660 1.59 156
29 53.67 4707 5.61 492

 Native vegetation, surface (40-50 cm) soils

 2 22.48 2526 1.01 113
 4 0.35 250 0.00 0
 6 2.74 489 0.20 35
10 0.58 320 0.36 200
18 0.25 100 0.00 0
20 4.06 1451 0.58 208
22 4.74 1394 0.36 104
30 12.82 1526 0.35 41

 Market gradens, surface (0-15 cm) soils

 7 7.61 724 0.83 79
13 2.27 397 0.34 60
15 5.29 678 0.68 87
23 5.01 589 0.86 100
25 2.58 314 0.04 4
27 1.96 251 0.33 42
31 3.47 307 0.08 7
35 8.04 372 0.38 17

 Market gradens, surface (40-50 cm) soils

 8 0.71 783 0.42 467
14 0.59 594 0.25 250
16 0.58 359 0.29 179
24 1.03 431 0.29 118
26 2.70 551 0.00 0
28 1.45 498 0.32 110
32 0.53 170 0.00 0
36 16.06 521 n.d. n.d.
38 1.68 350 0.00 0
43 1.40 874 0.23 140

 F. sulfone

Soil [K.sub.d] [K.sub.oc]

 Native vegetation, surface (0-15 cm) soils

 1 n.d. n.d.
 3 0.48 47
 5 2.82 95
 9 4.04 140
17 0.53 21
19 2.09 278
21 3.83 375
29 6.92 607

 Native vegetation, surface (40-50 cm) soils

 2 1.76 197
 4 0.00 0
 6 0.11 19
10 1.12 619
18 0.00 0
20 1.35 481
22 1.86 546
30 0.66 78

 Market gradens, surface (0-15 cm) soils

 7 2.36 224
13 1.40 245
15 1.80 23
23 2.24 263
25 0.04 4
27 1.39 178
31 0.01 1
35 0.53 24

 Market gradens, surface (40-50 cm) soils

 8 1.12 1247
14 1.20 1197
16 1.19 745
24 1.09 455
26 0.05 9
28 1.26 436
32 0.00 0
36 n.d. n.d.
38 0.00 0
43 1.26 788

n.d., Not determined.


Acknowledgments

The authors gratefully acknowledge the financial assistance of the Australian Centre for International Agricultural Research (ACIAR). This work was conducted under ACIAR project 'Agrochemical Pollution of Water Resources under Tropical Intensive Agricultural Systems'. John Byrne and Andrew Kerekes (CSIRO) are thanked for their technical assistance.

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Manuscript received 1 August 2002, accepted 7 January 2003

D. P. Oliver (A,C), R. S. Kookana (A), R. B. Salama (B)

(A) CSIRO Land and Water, PMB No. 2, Glen Osmond, SA 5064, Australia.

(B) CSIRO Land and Water, PMB PO Wembley, WA 6014, Australia.

(C) Corresponding author; email: Danni.Oliver@csiro.au
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Author:Oliver, D.P.; Kookana, R.S.; Salama, R.B.
Publication:Australian Journal of Soil Research
Geographic Code:8AUST
Date:Sep 1, 2003
Words:6102
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