Thomas L. Potter

Occurrence of alachlor environmental degradation products in groundwater.

Groundwater samples collected beneath a Massachusetts corn field were analyzed by gas chromatography/mass spectrometry. In addition to alachlor, 20 compounds were detected whose El and CIMS data indicated that they were derived from alachlor, presumably via environmental degradation. Structural assignments were confirmed for six of these compounds by analysis of standards. They were among 10 alachlor-related compounds that were synthesized by use of either the parent compound or 2,6-diethylaniline as starting material. To our knowledge, none of the confirmed compounds have previously been reported in groundwater samples. The concentration range of the degradation products ranged from 4 to 570 ng L -1 . In all samples, the total concentration of the degradation products exceeded the parent compound concentration by at least 2-fold.

Fungicide dissipation and impact on metolachlor aerobic soil degradation and soil microbial dynamics.

Pesticides are typically applied as mixtures and or sequentially to soil and plants during crop production. A common scenario is herbicide application at planting followed by sequential fungicide applications post-emergence. Fungicides depending on their spectrum of activity may alter and impact soil microbial communities. Thus there is a potential to impact soil processes responsible for herbicide degradation. This may change herbicide efficacy and 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 (alpha-[2-(4-chlorophenyl)ethyl]-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), flutriafol (alpha-(2-fluorophenyl)-alpha-(4-fluorophenyl)-1H-1,2,4-triazole-1-ethanol), and cyproconazole (alpha-(4-chlorophenyl)-alpha-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol) on the dissipation kinetics of the herbicide, metolachlor (2-chloro-N-(6-ethyl-o-tolyl)-N-[(1RS)-2-methoxy-1-methylethyl]acetamide), and on the soil microbial community. This was done through laboratory incubation of field treated soil. Chlorothalonil significantly reduced metolachlor soil dissipation as compared to the non-treated control or soil treated with the other fungicides. Metolachlor DT(50) was 99 days for chlorothalonil-treated soil and 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 DT(50) 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.

SURFACE RUNOFF AND LATERAL SUBSURFACE FLOW AS A RESPONSE TO CONSERVATION TILLAGE AND SOIL-WATER CONDITIONS

Conservation tillage has significant potential as a water management tool for cotton production on sandy, drought-prone soils. Plant residue remaining at the soil surface from prior crops serves as a vapor barrier against water loss, reduces raindrop impact energy, slows surface runoff, and often increases infiltration. By increasing infiltration, the potential for greater plant-available water can be enhanced and irrigation requirements reduced. Five years of data were collected to quantify the hydrologic differences between strip till and conventional till production systems. Surface runoff and lateral subsurface flow were measured on six 0.2 ha plots in South Georgia in order to quantify the water-related effects of conservation tillage. Significant differences in surface and subsurface water losses were observed between the conventional and strip tilled plots. Surface runoff from the conventionally tilled plots exceeded that from the strip tilled plots, while subsurface losses were reversed. Surface runoff losses from the conventionally tilled plots exceeded those from the strip tilled plots by 81% (129 mm/year). Shallow lateral subsurface losses from the strip tilled plots exceeded those from the conventionally tilled plots by 73% (69 mm/year). Overall, a net annual gain of 60 mm of water was observed for the strip tilled plots.

Herbicide incorporation by irrigation and tillage impact on runoff loss.

Runoff from farm fields is a common source of herbicide residues in surface waters. Incorporation by irrigation has the potential to reduce herbicide runoff risks. To assess impacts, rainfall was simulated on plots located in a peanut (Arachis hypogaea L.) field in Georgias Atlantic Coastal Plain region after pre-emergence application of metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(1S)-2-methoxy-1-methylethyl]-acetamide) and pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine). Runoff, sediment, and herbicide loss as function of strip tillage (ST) versus conventional tillage (CT) were compared with and without irrigation (12.5 mm) after application of an herbicide tank mixture. For the CT system, metolachlor runoff was reduced 2x and pendimethalin 1.2x when compared with the non-irrigated treatment. The difference in irrigated and non-irrigated metolachlor means was significant (P = 0.05). Irrigation reduced metolachlor runoff by 1.3x in the ST system, but there was a 1.4x increase for pendimethalin. Overall results indicated that irrigation incorporation reduces herbicide runoff with the greatest impact when CT is practiced and products like metolachlor, which have relatively low K(oc) and high water solubility, are used. The lower ST system response was likely due to a combination of spray interception and retention by the ST system cover crop mulch and higher ST soil organic carbon content and less total runoff. During the study, the measured K(oc) of both herbicides on runoff sediment was found to vary with tillage and irrigation after herbicide application. Generally, K(oc) was higher for ST sediment and when irrigation incorporation was used with the CT system. These results have significant implications for simulation model parametization.

Streptomyces costaricanus sp. nov., Isolated from Nematode-Suppressive Soil

A new bacterial strain, strain CR-43T (T = type strain), which was isolated from tropical soil and was previously shown to have antinematodal and antibiotic properties, is described. The name Streptomyces costaricanus is proposed for this organism. The generic placement of strain CR-43T was based on its typical morphology, its production of LL-diaminopimelic acid, and its fatty acid composition. To clarify the taxonomic position of strain CR-43T, it was compared with the type strains of similar Streptomyces species. The results of a number of biochemical tests and a profile analysis of the hydrolyzable fatty acids indicated that CR-43T differs from previously described species. Strain CR-43 (= ATCC 55274 = NRRL B-16897) is the type strain of S. costaricanus sp. nov.

Tillage, cover-crop residue management, and irrigation incorporation impact on fomesafen runoff.

Intensive glyphosate use has contributed to the evolution and occurrence of glyphosate-resistant weeds that threaten production of many crops. Sustained use of this highly valued herbicide requires rotation and/or substitution of herbicides with different modes of action. Cotton growers have shown considerable interest in the protoporphyrinogen oxidase inhibitor, fomesafen. Following registration for cotton in 2008, use has increased rapidly. Environmental fate data in major use areas are needed to appropriately evaluate risks. Field-based rainfall simulation was used to evaluate fomesafen runoff potential with and without irrigation incorporation in a conventional tillage system (CT) and when conservation tillage (CsT) was practiced with and without cover crop residue rolling. Without irrigation incorporation, relatively high runoff, about 5% of applied, was measured from the CT system, indicating that this compound may present a runoff risk. Runoff was reduced by >50% when the herbicide was irrigation incorporated after application or when used with a CsT system. Data indicate that these practices should be implemented whenever possible to reduce fomesafen runoff risk. Results also raised concerns about leaching and potential groundwater contamination and crop injury due to rapid washoff from cover crop residues in CsT systems. Further work is needed to address these concerns.

Reduction in metolachlor and degradate concentrations in shallow groundwater through cover crop use.

Pesticide use during crop production has the potential to adversely impact groundwater quality. In southern Florida, climatic and hydrogeologic conditions and agronomic practices indicate that contamination risks are high. In the current study, dissipation of the widely used herbicide, metolachlor, and levels of the compound and selected degradates in shallow groundwater beneath six 0.15-ha plots in sweet corn (Zea mays) production were evaluated over a two-year period. During fallow periods (May to October), plots were either left bare or cover cropped with sunn hemp (Crotalaria juncea L.). Metolachlor was broadcast applied at label recommended rates prior to planting sweet corn each year. Groundwater monitoring wells hydraulically upgradient and downgradient, and within each plot were sampled biweekly. Results showed that metolachlor dissipation was rapid, as evidenced by the detection of relatively high levels of the metolachlor ethane sulfonic degradate (MESA) in groundwater beneath plots and a rapid metolachlor DT(50) (9-14 days) in a companion laboratory soil incubation. Other degradates detected included hydroxymetolachlor in soil and in groundwater metolachlor oxanilic acid (MOA) and a product tentatively identified as 2-chloro-N-(2-acetyl-6-methylphenyl-N-(2-methoxy-1-methylethyl) acetamide, a photo-oxidation product. Metolachlor and MESA levels, up to 16 and 2.4 times higher in groundwater beneath the noncover cropped plots when compared to those of the cover cropped plots, indicate that cover cropping results in more rapid dissipation and/or reduced leaching. The study demonstrated that integration of cover crops into agronomic systems in the region may yield water quality benefits by reducing herbicide inputs to groundwater.

Pressurized liquid extraction of soil microbial phospholipid and neutral lipid fatty acids.

Soil microbial lipid biomarkers are indicators of viable microbial biomass and community structure. Pressurized liquid extraction (PLE) of soil phospholipid fatty acids (PLFA) and neutral lipid fatty acids (NLFA) was compared to a conventional extraction method in four soils with differing physical and chemical properties. PLE efficiency was greater than that of the conventional method for about half of the saturated PLFA and for selected other Gram-positive (i16:0) and Gram-negative bacteria (18:1omega7c) PLFA, fungal PLFA (18:2omega6,9c), and eukaryotic NLFA from a coarse-textured soil. Lipids extracted by the two methods did not indicate a significant difference in microbial community structure data. Principle component analysis revealed that PLFA clustered by location, with data indicating that the group of microbes contributing the greatest weight differed among soils. Overall, the PLE method proved to be more efficient at extracting soilborne microbial lipids while not altering microbial community information. These advantages indicate the PLE method is robust and well-suited to soil microbial ecology research.

Endosulfan wet deposition in Southern Florida (USA).

The atmosphere is an important transport route for semi-volatile pesticides like endosulfan. Deposition, which depends on physical-chemical properties, use patterns, and climatic conditions, can occur at local, regional, and global scales. Adverse human and ecological impact may result. We measured endosulfan wet deposition in precipitation over a 4-year period within an area of high agricultural use in Southern Florida (USA) and in nearby Biscayne and Everglades National Parks. Endosulfans two isomers and degradate, endosulfan sulfate, were detected at high frequency with the order of detection and concentration being β-endosulfan>α-endosulfan>endosulfan sulfate. Within the agricultural area, detection frequency (55 to 98%) mean concentrations (5 to 87 ng L(-1)) and total daily deposition (200 ng m(-2) day(-1)) exceeded values at other sites by 5 to 30-fold. Strong seasonal trends were also observed with values at all monitored sites significantly higher during peak endosulfan use periods when vegetable crops were produced. Relatively high deposition in the crop production area and observations that concentrations exceeded aquatic life toxicity thresholds at all sites indicated that endosulfan volatilization and wet deposition are of ecotoxicological concern to the region. This study emphasizes the need to include localized volatilization and deposition of endosulfan and other semi-volatile pesticides in risk assessments in Southern Florida and other areas with similar climatic and crop production profiles.

Atrazine fate and transport within the coastal zone in southeastern Puerto Rico

Agrichemical transport to coastal waters may have adverse ecological impact. This work examined atrazine fate and transport in a field adjacent to Puerto Ricos Jobos Bay National Estuarine Research Reserve. The herbicides use was linked to residue detection in shallow groundwater and movement toward the estuary; however, data indicated that transport via this pathway was small. In contrast, surface runoff as tropical storm systems moved through the area appeared to have high potential for atrazine transport. In this case, transport to the estuary was limited by runoff event timing relative to atrazine application and very rapid atrazine dissipation (DT(50)=1-3 days) in field soil. Soil incubation studies showed that accelerated degradation conditions had developed in the field due to repeated atrazine treatment. To improve weed management, atrazine replacement with other herbicide(s) is recommended. Use of products that have greater soil persistence may increase runoff risk.