1611-t.pdf

Scientific Registration Number : 1611Symposium n° : 7Presentation : poster Solute transport in South Australian Riverland red
calcareous earth soils
Transport de solutés dans des sols rouges calcaires du
Riverland (Australie du Sud)
ALLINSON2 Graeme, UEOKA1 Mayumi, GRAYMORE2 Michelle, GIBSON2
David, KELSALL2 Yasmin, and STAGNITTI Frank 2
1. Department of Environmental Science and Management, University of Adelaide, 2. School of Aquatic Science and Natural Resources Management Deakin University, Introduction
Australiaís grape and wine industries are significant contributors to both the domestic and export economies. The Australian viticultural industry comprises over5,000 idependent grapegrowers and more than 800 wineries spread across all States andTerritories (GWRDC, 1996). The physical and chemical heterogeneity of the Australianenvironment makes the accurate prediction of the fate of agrochemicals very difficult.
Despite these difficulties, the fact that some chemicals can be transported long distancesby soil water and may be detected far from the application site makes the prediction oftheir environment fate through experimentally validated models of utmost importance.
The growing season in the South Australian Riverland is hot (mean January temperature 23 - 24.9 oC), with very low humidity and scant rainfall. are very important
viticulturally. Water stress is common during the summer, although vineyards obviate
this by irrigating with water extracted from the River Murray (Northcote, 1995).
Atrazine (Figure 1, I) is no longer licensed for use in Australian vineyards but, being
chemically quite stable in soils and its transport properties well studied, provides an
excellent model for the fungicides dithianon and vinclozolin. Dithianon (III) is primarily
used in vitculture for the control of downy mildew caused by Plasmopara viticolla,
while vinclozolin (II) is used to control Botrytis bunch rot caused by Botrytis cinerea
(Tomlin, 1994).
Figure 1. Chemical structures of atrazine (I), dithianon (II), and vinclozolin (III).
MATERIALS
All HPLC and SPE chemicals were of HPLC grade. Distilled water was purified with an ion exchange- activated carbon filter system (MilliQ, Millipore Corp.). Dithianonformulation (DelanÆ WP, 75% a.i.) was kindly provided by Nuriootpa Research Station,Department of Primary Industries, South Australia; vinclozolin formulation (RonilanÆ500FL, 50% a.i.) was purchased from BASF. Dithianon standard (95%, Riedel-de HaenAG., Germany), vinclozolin standard (99%, Chem Service, West Chester, PA, USA);atrazine formulation (Nu-Zinole AA, 400 g/kg a.i.) was purchesed from Nufarm. Vic.
Australia. Atrazine standard (99.5 %, Chem Service, West Chester, PA, USA).
Fungicide extraction from leachate and soil was by soild phase extraction using Sep- Pak C18 solid phase extraction cartridges (adsorbent 500 mg; hold-up volume 0.8 mL;Waters Australian Pty. Ltd.). Solute elution using demountable vacuum manifold with 12screw type vacuum bleed connections for SPE columns coupled to water aspiratorpump; sample loaded through Visiprep Large Volume Samplers (Sigma-Aldrich Pty.
Ltd., Sydney, Australia).
The cores were drip irrigated by means of a Model CPP 30 Peristaltic Pump (ChemLab, England), and Flow Measured Pump tubes (i.d. 0.38 mm, A.I., Queensland,Australia). Soil pH was measured using a Hannah Instruments Model HI 8519 pH meter.
Dithianon and vinclozolin concentrations were determined using HPLC : Waters Model 501 HPLC pump equipped with a 20 µL sample loop injector, Nova-Pak® Phenyl60Å 4µm 150 x 3.9 mm i.d., stainless steel column (Millipore Corporation, MA, USA),and Waters Model 481 UV detector set at 254nm for dithianon, 210nm for vinclozolin.
Quantitation was by peak area integration. Operating conditions: isocratic mobile phaseacetonitrile + water (50 + 50 by volume); flow rate 1.0 mL min-1; temperature 22 ± 3 oC.
Atrazine concentrations were also determined using HPLC : Waters Model 501 HPLC pump equipped with a 20 µL sample loop injector, Hypersil ODS 5 mm 150 x 4.6mm i.d column (Shandon HPLC), and Waters Model 481 UV detector set at 220 nm.
Quantitation was by peak area integration. Operating conditions: isocratic mobile phaseacetonitrile + water (40 + 60 by volume); flow rate 1.2 mL min-1; temperature 22 ± 3 oC.
Chloride ion was determined using an ion selective electrode. Working standards were prepared containing 3,000, 300, 30, 3 mg/L chloride ion by dilution of a 30,000mg/L stock standard. Aliquots of sample (25 mL) were transferred to clean beakers andan aliquot of the ionic strength adjuster (ISA; 5mL; ISA = 40g ammonia nitrate(NH4NO3) and 2mL nitric acid (HNO3) diluted with deionised water to 100mL) wasadded to each solution. The chloride ion selective electrode and double junctionreference electrodes were immersed in the solutions. The mV reading was recorded when stable (3-5 minutes). Leachate concentrations were determined by externalstandard method.
Nitrate ion was determined using flow injection analysis (FIA). Chemicals : carrier : ammonium chloride (NH4Cl; 8.0g) (AJAX Chemicals) and disodium EDTA (1.0g) indeionised water (800mL). Concentrated ammonia solution was added (AJAX Chemicals)to bring the carrier solution to a pH of 8.2-8.5. This latter solution was then diluted to1L; Sulfanilamide : sulfanilamide (10.0g BDH Laboratory Supplies) was added to 10%HCl solution (AJAX Chemicals), diluted to 1L; N-(1-naphyl) ethylendiamicdilydrochlordie (NED) : 0.1% (w/v) NED of (Merck) was added to 10% HCl solution(AJAX Chemicals), diluted to 1L. The colorimeter (ChemLab Continous FlowColorimeter, 15mm flowcell, Filter λ = 550nm) was turned on for approximately 10minutes to allow time to warm up. The samples were filtered to remove particulatematter which would otherwise block the cadmium column of the FIA. All 3 reagenttubes were removed from the deionised water reservoir and placed into the appropriatereagent bottles. The reagents were pumped through the system, with the cadmiumcolumn isolated from the flow line initially to prevent ingress of air bubbles to thecolumn. After this initial flushing period, the cadmium column was reconnected into thesystem and reagent flow recommenced. The samples were analysed by making triplicateinjections of each. The leachate nitrate determinations were by the external standardmethod.
GENERAL METHODS
Leaching Experiments.
The small, undisturbed soil cores were extracted in December 1996 from a vineyardapproximately 10 km south-west of Overland Corner in South Australia. This vineyardhad never applied atrazine, dithianon or vinclozolin to its grapes or vines. The vineyard islocated on a gentle south-facing incline (north-south slope, approximately 10 %)overlooking the Murray River valley. The vineyard soil, a highly alkaline reddish brownsand loam of variable depth (1 - 4 m) and moderate organic carbon content (1 - 2 %), istypical of the soils of the mallee highlands near the River Murray used for viticulture(Northcote, 1995). The cores were extracted from between the rows of vines near thelower edge of the vineyard.
The cores were transported back to Warrnambool and placed in a controlled environment laboratory (20 ± 2 oC). The cores were fitted onto single-wick lysimetersconsisting of a 12.5 cm diameter glass fibre filter paper pressed onto a 40 cm glass fibrewick, the top 15 cm of which was spread out evenly underneath the filter paper. Thecores were irrigated at 5-10 mL h-1 for several weeks. Water leaching from the coreswas collected every two days, and the volume and pH determined. Thereafter, nitrate,chloride, atrazine, dithianon and vinclozolin were applied to the cores over the centre ofthe irrigation area. The cores were irrigated further at the same rate for a several moreweeks. The leachate was collected every 24 hours for up to 2 months. At the end of thistime, a 2.5 cm diameter column of soil was taken through the full depth of the cores atthe centre of the irrigation area. Where possible, this column was extracted from the corewhole and then divided into 2 cm lengths for core pesticide residue profiling.
RESULTS AND DISCUSSION
A nitrate breakthrough curve was determined (Figure 2). Nitrate was initially present in the core leachate at ~ 23 mg/L. These concentrations reduced over the initial flushing time to around7.00 mg/L. After nitrate application on day 14, it took some 7 days for the nitrate breakthroughto occur in OC1 (peak concentration 37mg/L, 5 days for the concentration to be reduced to22mg/L), and some 9 days for the nitrate breakthrough to occur in OC2 (peak concentration36.6mg/L).
A chloride breakthrough curve was also established (Figure 3). Prior to the application of the chloride, chloride was present in the core leachates at concentrations of 49.5 mg/L and56.7mg/L respectively. These concentrations were reduced prior to chloride application toaround 12.5mg/L. After chloride application on day 14, it took some 5 days for chloridebreakthrough to occur in OC1 (peak leachate concentration 651mg/L, 7 days for chlorideconcentration to be reduced to370mg/L), but some 12 days for chloride breakthrough in OC2(peak concentration 669mg/L.
Analysis of leachate prior to fungicide application showed a number of small peaks due to unknown organic compounds, none of which interfered with the determination ofatrazine, vinclozolin or dithianon.
Atrazine was detected in the leachate of cores OC3 (subsoil) and OC4 (topsoil) suggesting a degree of mobility in these sandy loam soils. The cores showed anasymmetrical breakthrough curve (Figure 4) with a rapid increase in the mass of atrazineleached followed by a reasonably slow decline. A much lower mass of atrazine leachedthrough the topsoil (OC4) compared to the subsoil (OC3), presumably due to the higherlevel of organic matter, lower pH and higher adsorption capacity of the topsoil.
No dithianon was detected in OC5 leachate. Dithianon was found at low levels only in the top 2 cm of the soil near the application area, suggesting that this compound isrelatively immobile in alkaline soils and also relative unstable under alkaline conditions.
These observation agrees with the reported dithianon half-life, t1/2 , at 22oC and similarpHs ie. pH 7, t1/2 15.7 h., pH9, 0.15 h. (FAO/WHO, 1992).
No vinclozolin was detected in OC6 leachate. Vinclozolin was found at low levels throughout the core profile suggesting that vinclozolin is both somewhat mobile in thesesoils, but also degraded rapidly in non-sterile alkaline soils. Vinclozolin is known to beunstable under alkaline conditions at 22oC: pH 7, t1/2 19.7 h., pH9, 0.15 (FAO/WHO,1992), and our observations agree with those reported by Walker who stated that over90% of applied vinclozolin dose was lost after 40 days when applied to a sand loam soilpreviously untreated with this fungicide (Walker, 1987; Walker et al., 1986).
CONCLUSION
In these studies we determined that nitrate, chloride and atrazine were mobile in the red calcareous earth soils of the South Australian Riverland. Dithianon was immobile andunstable in these alkaline conditions. Vinclozolin, although was somewhat mobile asevidenced by its detection throughout the soil profiles, was also unstable under alkalineconditions. These results suggest that the red calcareous earth soils of the SouthAustralian Riverland are unlikely to be prone to leaching of viticulturally deriveddithianon or vinclozolin, nor, as a result of their chemical instability, is it likely that either fungicide would pose any significant threat to groundwater supplies in the area.
However, the soils may be prone to nutrient leaching and use of triazine herbicidesshould be undertaken with care.
ACKNOWLEDGEMENTS
This research was in part funded through the Australian Research Councilís Large Grant Scheme (Grant No. A89701825). The authors would also like to thank CarolynShaw and Steven Shaw for access to the site.
REFERENCES
AWRI, 1996. Agrochemicals registered for use in Australian viticulture : a grid of registered agrochemicals and their MRLs in grapes for Australian wine export destinations, compiled bySas, A.N., and Daniel, C.G., The Australian Wine Research Institute, Adelaide. South Bergstrom, L.F., and Jarvis, N.J., 1993. Leaching of Dichlorprop, Bentazon and 36Cl in Undisturbed Field Lysimeters of Different Agricultural Soils, Weed Science, 41, 251-261.
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Stagnitti, F.; Parlange, J.-Y.; Steenhuis, T. S.; Boll, J.; Pivertz, B.; Barry, D.A., 1995. Transport of Moisture and Solutes in the Unsaturated Zone By Preferential Flow. In EnvironmentalHydrology; V. P. Singh, Ed.; Kluwer Academic Publishers, Vol. 15; pp 193 - 224.
Steenhuis, T.S., Nijssen, B.M, Stagnitti, F., and Parlange, J.-Y., 1991. Preferential Solute Movement in Structured Soils: Theory and Application, Inst. of Engs, Aust., Nat. Conf. Pub.
No. 91/19, Vol 3, 925-930.
Steenhuis, T.S., Boll, J., Jolles, E., and Selker, J.S., 1995. Field evaluation of wick and gravity pan samplers. In Vadose Zone Characterization and Monitoring, ed. L. Everett, S. Cullenand L. Wilson, Lewis Publishers, Ann Arbor, MI., pp 629 - 638.
Tomlin, C., 1994. The Pesticides Manual Incorporating The Agrochemicals Handbook, Tenth Ed., ed. C. Tomlin, Crop Protection Publications. 1341 pp.
Walker, A., Brown, P.A., and Entwistle, A.R., 1986. Enhanced degradation of iprodione and vinclozolin in soil, Pestic. Sci., 17, 183-193.
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Keywords :red calcareous earth soil, South Australia, nutrient transport, pesticidemobility, fungicides, nitrate, chloride, atrazine, dithianon, vinclozolinMots clés : sols rouges calcaires, Australie, nutriments, transport, pesticides, fongicides,nitrate, chlorure, atrazine, dithianon, vinclozoline

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