Fungicide Dissipation and Impact on Metolachlor Aerobic Soil Degradation and Soil Microbial Dynamics☆

Science of the Total Environment 408 (2010) 1393–1402 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Fungicide dissipation and impact on metolachlor aerobic soil degradation and soil microbial dynamics☆ Paul M. White a,b,⁎, Thomas L. Potter a, Albert K. Culbreath c a USDA-ARS Southeast Watershed Research Unit, 2381 Rainwater Road, Tifton, GA 31793, United States b Current address: USDA-ARS Sugarcane Research Unit, 5883 USDA Road, Houma, LA 70360, United States c Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton, Georgia 31793, United States article info abstract Article history: Pesticides are typically applied as mixtures and or sequentially to soil and plants during crop production. A common Received 21 September 2009 scenario is herbicide application at planting followed by sequential fungicide applications post-emergence. Received in revised form 25 October 2009 Fungicides depending on their spectrum of activity may alter and impact soil microbial communities. Thus there is a Accepted 8 November 2009 potential to impact soil processes responsible for herbicide degradation. This may change herbicide efficacy and Available online 16 December 2009 environmental fate characteristics. Our study objective was to determine the effects of 4 peanut fungicides, chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile), tebuconazole (α-[2-(4-chlorophenyl)ethyl]-α- Keywords: fl α fl α fl Metolachlor (1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), utriafol ( -(2- uorophenyl)- -(4- uorophenyl)-1H-1,2,4- Tebuconazole triazole-1-ethanol), and cyproconazole (α-(4-chlorophenyl)-α-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol) Cyproconazole on the dissipation kinetics of the herbicide, metolachlor (2-chloro-N-(6-ethyl-o-tolyl)-N-[(1RS)-2-methoxy-1- Flutriafol methylethyl]acetamide), and on the soil microbial community. This was done through laboratory incubation of field Chlorothalonil treated soil. Chlorothalonil significantly reduced metolachlor soil dissipation as compared to the non-treated Soil microorganisms control or soil treated with the other fungicides. Metolachlor DT50 was 99 days for chlorothalonil-treated soil and PLFA 56, 45, 53, and 46 days for control, tebuconazole, flutriafol, and cyproconazole-treated soils, respectively. Significant reductions in predominant metolachlor metabolites, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOA), produced by oxidation of glutathione-metolachlor conjugates were also observed in chlorothalonil-treated soil. This suggested that the fungicide impacted soil glutathione-S-transferase (GST) activity. Fungicide DT50 was 27–80 days but impacts on the soil microbial community as indicated by lipid biomarker analysis were minimal. Overall study results indicated that chlorothalonil has the potential to substantially increase soil persistence (2-fold) of metolachlor and alter fate and transport processes. GST mediated metabolism is common pesticide detoxification process in soil; thus there are implications for the fate of many active ingredients. Published by Elsevier B.V. 1. Introduction et al., 2005; Jordan et al., 2009). Conclusions from these studies are that there is potential for interaction between herbicides and fungicides on Modern agriculture depends heavily on pesticides to control weed control and those interactions are compound and weed specific. weeds, plant diseases, and insect pests. Products are typically applied Increased soil persistence has also been observed (e.g., Kaufman as mixtures and or sequentially during the growing season. A common et al., 1970; Ferris and Lichtenstein, 1980; Fogg and Boxall, 2003). For scenario is application of one or more herbicides at planting followed example soil DT50 of the herbicide isoproturon increased 4-fold when it by sequential foliar fungicide applications post-emergence. This ap- was applied with the fungicide chlorothalonil (Fogg and Boxall, 2003). It proach is used almost universally by peanut (Arachis hypogaea L.) was suggested that the chlorothalonil impact was due to suppression of farmers in the Southeastern USA. non-target soil organisms by the parent compound and its primary soil Investigations in peanut and in other crops, and with other chemical degradate 4-hydroxy-chlorothalonil; however this was not investigated. combinations, e.g. herbicides and insecticides, have shown that interac- Results of studies examining the impact of chlorothalonil and degradates tions in terms of weed control between chemicals are possible (Lancaster on soil organisms have in some cases demonstrated a suppressive effect while in others there was no impact (Chen et al., 2001; Bending et al., 2007; Zhang et al., 2007). This is also the case with many other pesticides ☆ Mention of trade names or commercial products is solely for the purpose of including numerous fungicides, insecticides and herbicides. providing specific information and does not imply recommendation or endorsement by Regardless of the mechanism, herbicide soil persistence if the U.S. Department of Agriculture. increased has positive and negative implications. Negative outcomes ⁎ Corresponding author. Current address: USDA-ARS Sugarcane Research Unit, 5883 USDA Road, Houma, LA 70360, United States. Tel.: +1 985 853 3168; fax: +1 985 868 8369. include herbicide injury to agronomic crops and positive outcomes E-mail address: [email protected] (P.M. White). enhance weed control (Nash, 1967). Greater ecologic risk due to off- 0048-9697/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.scitotenv.2009.11.012 1394 P.M. White et al. / Science of the Total Environment 408 (2010) 1393–1402 site transport may be observed since increased soil residence time has recovered by vacuum filtration (Whatman 55-mm GF/F). The pro- the potential to increase runoff and leaching risks. The significance of cedure was repeated 2 times, extracts combined, and concentrated to pesticide interactions on soil persistence, although high, has not been 10 mL under an N2 gas stream. One gram subsamples were fortified with systematically investigated. The few published studies are limited to a 5μg of 2-chlorolepidine (internal standard), and analyzed by HPLC-MS narrow range of active ingredients and soil conditions. with a Thermoquest-Finnegan LCQ DECA ion trap system (Thermo-Fisher The current study focused on collecting soil persistence data which Scientific, San Jose, CA). Metolachlor, chlorothalonil, tebuconazole, can be used to guide weed and disease control management decisions flutriafol, and cyproconazole were analyzed by APCI using a Gemini® and evaluate environmental risk for peanut production on sandy soils C18 HPLC column, 150×4.6 mm, 0.5 μm, 110 Å (Phenomenex, Torrance, in the Southeastern USA. Specifically we examined the impact of four CA) with methanol (A) and 0.1% formic acid (B) gradient elution at fungicides, three triazoles and the chloronitrile, chlorothalonil, when 1mLmin−1. Initial conditions 10% A/90% B were changed to 90% A/10% B used individually on soil microbial dynamics of a Tifton loamy sand over 6 min, held for 5 min, and returned to initial conditions in 1 min. soil and the dissipation kinetics of a widely used herbicide, Positive ions (M+H)+ for metolachlor, cyproconazole, flutriafol, and metolachlor. These products are used on many other crops, thus tebuconazole were detected in the full scan mode (100–450 m/z). For findings are broadly applicable. chlorothalonil the negative ion corresponding to (M−Cl+O)− was monitored. Chlorothalonil is converted to its 4-hydroxy analog under 2. Materials and methods APCI conditions (Chaves et al., 2007). Full scan, positive ion scans were also used to test for metolachlor degradates hydroxymetolachlor, 2.1. Soil collection and incubation deschloroacetyl metolachlor propanol, metolachlor morpholinone, and phenyl alkyl-substituted metolachlor (keto-metolachlor) based on The investigation was conducted in conjunction with field-based previous reports (Sakkas et al., 2004; Hladik et al., 2005), and the peanut fungicide efficacy test conducted at a University of Georgia farm tebuconazole lactone degradate (Potter et al., 2005). Bayer CropScience located in south central Georgia (31° 30′N, 83° 32′W). Metolachlor was donated a reference lactone standard. Retentions times and ionization applied to the field on 21 May 2008 at 1.6 kg ha−1 as Dual Magnum® conditions for the metolachlor degradates were determined on the (Syngenta, Wilmington, DE). Peanut (cultivar Florida-07) was planted mixtures of degradates produced by hydrolysis in base (1 M KOH) or acid on 27 May 2008. After emergence the field was divided into replicate 2 (6 N HCl). Signal response was assumed equivalent to metolachlor. All by 8 m plots and four plots each were randomly selected for treatment analytes and ions monitored are summarized in Table 1. groups. Plots were treated with fungicides on 9 July 2008, 43 days after Two acidic metolachlor degradates, metolachlor ethane sulfonic planting. Timing reflected common practice among the region's peanut (2-[(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl)amino]-2- growers. Soil (Tifton loamy sand; fine-loamy, kaolinitic, thermic, oxoethanesulfonic acid) acid, termed MESA, and metolachlor oxanilic Plinthic Kaniudult) was collected from 0 to 2 cm depth increment acid (2-[(2-ethyl-6-methylphenyl)(2-methoxy-1-methylethyl) from 4 untreated control plots and from plots treated immediately

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