ANNUAL REPORT COMPREHENSIVE RESEARCH ON RICE

January 1, 2014 – December 31, 2014 PROJECT TITLE: The Environmental Fate of Pesticides Important to Rice Culture PROJECT LEADER: Ronald S. Tjeerdema, Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, University of California, One Shields Avenue, Davis, CA 95616-8588 PRINCIPAL UC INVESTIGATOR: Ronald S. Tjeerdema, Department of Environmental Toxicology, College of Agricultural and Environmental Sciences, UCD COOPERATORS: Jim Hill, Albert Fischer, Rebecca Mulligan, Caitlin Rering, Katryn Williams (all UCD), David Ball (CSU Chico) LEVEL OF 2014 FUNDING: $66,198 OBJECTIVES AND EXPERIMENTS CONDUCTED BY LOCATION TO ACCOMPLISH OBJECTIVES: Objective I. To investigate the factors governing pesticide dissipation in California rice fields. Emphasis for 2014 will be on characterizing the hydrolytic and photochemical degradation of the insecticide Belay (clothianidin) under rice field conditions. Objective II. To investigate the factors governing pesticide dissipation in California rice fields. Emphasis for 2014 will be on characterizing the hydrolytic and photochemical degradation of the herbicide League (imazosulfuron) under rice field conditions. Objective III. To investigate the factors governing pesticide dissipation in California rice fields. Emphasis for 2014 will be to characterize hydrolysis of the herbicide Butte (benzobicyclon), which forms the active herbicidal product, then its volatilization under rice field conditions. SUMMARY OF 2013 RESEARCH (MAJOR ACCOMPLISHMENTS) BY OBJECTIVE:

Objective I – Photochemical Degradation of Belay (Clothianidin)

Figure 1: Structure of Belay, a neonicotinoid insecticide.

Introduction Belay (Figure 1), a synthetic neonicotinoid insecticide, acts as an agonist at post-synaptic nicotinic acetylcholine receptors within the central nervous system of a variety of insects including Hemiptera, Thysanoptera, Coleoptera, Lepidoptera and Diptera.1-3 Laboratory studies have demonstrated neonicotinoids (in general) and Belay (in particular) are highly toxic towards pollinators and some investigators and regulators are concerned that neonicotinoid exposure in field conditions may be a compounding factor in colony collapse disorder.4, 5 Overall, its use in agricultural areas of California is low, with less than 7,000 pounds of active ingredient applied in 2012.6 However, its use increased significantly since 2011 as a number of products containing the active ingredient were recently registered for cotton, cucumber, grapes and tomatoes.6 It was recently registered for pre-flood (to field soil) and post-flood (to field water) aerial application to protect California rice fields against the rice seed midge, Cricotopus sylvestris, and rice water weevil, Lissorhoptrus oryzophilus. Belay (pKa 11.0) is a neutral species within environmentally-relevant pH ranges, has a low vapor pressure (3.8 x 10-11 Pa at 20oC), a low octanol-water partitioning coefficient (0.7 at 20oC) and is moderately soluble (327 mg L-1 at 20oC) – based on these properties and reports generated by the registrant, volatilization from the water is not likely to occur and soil sorption may allow for decreased risk of offsite transport.7-9 However, the physical properties of a compounded are not sufficient to predict the fate of a pesticide in an environment as chemically complex as a flooded rice field. In order understand the fate, and therefore to characterize potential exposure routes for non-target organisms, partitioning and aqueous photolytic degradation parameters were tested accounting for site-specific environmental conditions and management factors. 10, 11 Summary of Abiotic Partitioning Results (2013) Belay was confirmed to be non-volatile (from water) via the gas-purge method, as no loss from the aqueous phase was observed at 22oC and 37oC; an upper limit KH value was calculated at 2.9×10-11 Pa m3 mol-1 (20oC). Soil-water partitioning was determined by the batch equilibrium method using four soils collected from rice fields in the Sacramento Valley, and sorption affinity (Kd), sorbent capacity, desorption and organic carbon-normalized distribution (Koc) were determined. Values for pH, cation-exchange capacity, and organic matter content ranged between 4.5 to 6.6, 5.9 to 37.9, and 1.25 to 1.97%, respectively. Log Koc values (22oC and 37oC) ranged between 2.6 to 2.7, while sorption capacity was low at 22oC and further decreased at 37oC. Hysteresis was observed in soils at both temperatures, suggesting that bound residues do not readily desorb. These data suggest that soil sorption is primarily controlled by soil organic matter content and that mineral phase properties are less important. The sorption capacity of the soils for Belay is low and will decrease as temperature increases – potentially due to increased water solubility. Sorbed Belay residues are not easily desorbed from the studied rice field soils. Overall, Belay has the potential to be mobile in soil and may pose a risk to both ground and surface waters.7 Further investigation should focus on biological and

Table 1. Properties of natural water samples.

photochemical degradation, processes known to be important in rice fields, and the potential for offsite transport in field trail water12-14. Photolysis-Materials and Methods Chemicals. Belay analytical standard (99.9% purity), 4-nitroanisole (PNA; 97% purity), and pyridine (PYR; Chromosolv® Plus, ≥99.9% purity) were purchased from Sigma-Aldrich (St. Louis, MO, USA). All HPLC grade solvents (acetonitrile, methanol, and Chromosolv® HPLC water), formic acid (puriss. p.a., ~98%), and high purity water (≤ 0.10 mg/L total organic carbon) were purchased from Sigma-Aldrich. Stock solutions of 100 ug mL-1 Belay were prepared in water with 1% acetonitrile and stored in amber borosilicate glass bottles at 4oC. Preliminary experiments demonstrated acetonitrile did not act as a photosensitizer when used as a co-solvent. Natural Water Samples. Photolysis was evaluated in natural water samples collected in the Sacramento Valley in July 2014. Rice field water samples were collected from flooded fields in Davis and Woodland (Yolo County, Ca.) and from the Sacramento River (Elkhorn Launch, Sacramento, Ca.). Surface water samples were collected in amber glass bottles (4 L) and packed on ice during transit. In order to inhibit microbial activity, waters were autoclaved at 120oC for 1h. Waters were stored in the dark at 4oC. Physical-chemical characteristics including pH, turbidity, bicarbonate and carbonate concentrations, and total organic carbon content of the waters were determined by the UCD Analytical Laboratory (Table 1); the analytical methods can be found via the website (http://anlab.ucdavis.edu/). Photolysis. Photochemical degradation experiments were conducted in a bench-top photo-reactor equipped with four (8W) broad UV (300 ± 50 nm) spectrum lights (Southern New England, Branford, CT) mounted 250 mm directly above the reaction surface. The reactor was wrapped in reflective paneling to prevent light contamination equipped with a 6 in. fan to maintain reactor temperature at 25 ± 2oC. Surface irradiance was measured for each reaction position (average 1020 ± 70 μW cm-2) using a portable UVX radiometer (UVP; Upland, CA); average values were comparable to light intensities in rice fields during the growing season (< 1,350 μW cm-2 at 310 nm). 15 Capped (Teflon-lined) borosilicate type-200 reaction vials (60mL; Wheaton Science, Millville, NJ) filtered light below the solar cutoff of 290 nm. The initial concentration of Belay in each experiment was 1.1 ug mL-1 prepared in appropriate matrix (natural water or de-ionized water). At given time points, an aliquot of 1mL was removed from each photolysis cell (n=5) and dark control (n=3) and passed through a 13-mm Acrodisc syringe tip filter with a 0.2-μm Hydrophilic polyvinylidene fluoride syringe (PVDF; Pall, Port Washington, NY) and 900 μL of filtrate sample was mixed with 100 μL methanol with 0.1% formic acid. Controls were light protected (wrapped in foil) were run for each experiment

Table 2. Product ion, dwell time, fragmentor voltage, collision energy, and collision cell voltage for Belay and TZMU.

to show that: 1) Belay was stable to hydrolysis and did not sorb to the surface of the borosilicate tubes or PVDF filter (≤ 2.6% and 3% loss for Belay and TZMU, respectively), and 2) no interfering compounds were detected in water samples. The concentration of Belay and its degradation products were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Photolysis data were fit to log-transformed and photodegradation rate constants were calculated based on pseudo-first order kinetics using Equation 1:

(1) where k is the pseudo-first order rate constant, Co is the initial concentration (ug mL-1) of Belay, Ct is the concentration (ug mL-1 ) at time t (min)16. The half-life DT50 was calculated from the absolute value of the pseudo-first order rate constant k using Equation 2:

(2) Sample Analysis. Photolysis samples were analyzed using an Agilent 1220 HPLC with an 1220 series autosampler coupled to a model 6420 triple quadrupole mass spectrometer (Santa Clara, CA) equipped with an atmospheric pressure chemical ionization source (APCI) and controlled by Mass Hunter (version B.06.00). The chromatographic column used was a 5 μm particle size, 3.2 x 100 mm ID Ultra PFP analytical column (Restek; Bellefonte, PA) with gradient elution at a flow rate of 0.5 mL min-1 at 37 oC with a 10 μL injection volume. The solvent gradient profile was as follows: Solvent A, water (0.1% formic acid); solvent B, methanol (0.1% formic acid); 0 minutes, 90% A: 10% B; 3.5-6 minutes, 10% A: 90% B; 6.1-10 minutes, 90% A, 10% B. Quantification was performed in positive ion mode, multiple reaction monitoring (MRM) with the protonated molecular ions (M-H)+ of 250 m/z and 206 m/z as the precursor ions for Belay and TZMU, respectively. The product ion, dwell time, fragmentor voltage, collision energy, and collision cell voltage for both compounds are summarized in Table 2. Other MS parameters were as follows: gas temperature, 325oC; APCI heater temperature, 350oC, curtain gas flow, 4 l min-1; nebulizer, 20 psi; capillary voltage, 4500 V. External matrix matched calibration curves were constructed for both compounds and were linear from 0.007 to 2 ug mL-1 with a regression coefficient of R2= 0.999 and residuals <10%. Actinometer samples were analyzed using an Agilent 1100 HPLC with an Agilent 1100 autosampler coupled to a DAD and controlled by an Agilent Chem Station Interface. A

Figure 2: First-order rate plots for the degradation of Belay: deionized water,

Sacramento River water, Davis field water, Conway Ranch field water. Luna C18 column (5 μm particle size, 4.6 x 150mm i.d.; Phenomenex, Torrance, CA) with isocratic mobile phase consisting of 80% acetonitrile and 20% water at a flow rate of 1 mL min-1 with a 10-μL injection volume. PNA was detected at 314 nm. First-order rate constants for actinometer solutions were calculated as a function of decrease in PNA absorbance. Preliminary experiments demonstrated calibration curves constructed for PNA were linear from 1μM to 1mM with a regression coefficient of R2= 0.999. Quantum Yield. The reaction quantum yield ϕC of Belay or Belay was estimated using a PNA-PYR actinometer system. 17, 18 Briefly, the reaction quantum yield of PNA actinometer ϕPNA is calculated based on the molar concentration of PYR according to Equation 3. 17, 18

(3) Preliminary experiments demonstrated that a PYR concentration of 0.009 M (ϕPNA = 0.0042) allowed for reasonable agreement between the rate of degradation of PNA (0.012 min-1) and Belay (0.017 min-1) in de-ionized water. The absorbance of Belay in deionized water and Davis rice field water was measured between 250 and 400 nm using a UV spectrophotometer and a 10-mm quartz cuvette. The molar absorptivity ε (M-1 cm-1) was calculated for each wavelength (at intervals between 250 < λ< 400 nm) according to the Beer-Lambert law:

Figure 3: Molar absorptivity (ε) versus wavelength of Belay in

deionized water and Davis field water.

(4) where A is the absorbance (Au) at wavelength λ (nm), l is the cell path length (cm), and c is the molar concentration of the compound. The reaction quantum yield of Belay was calculated as described using Equation 5:

(5) where ϕC and ϕPNA are the reaction quantum yield for Belay and PNA, respectively, kC and kPNA are the photolysis rate constants for Belay and PNA, respectively, ελ(C) and ελ(PNA) are the molar absorptivities of Belay and PNA at wavelength λ, and Iλ is the incident filtered photon irradiance (mol cm-2 min-1).19 Data Analysis. Data were analyzed using JMP software package version 10.0 (SAS Institute Inc., Cary, NC). The pseudo-first order rate constants k, standard errors, and coefficient of determination R2 were obtained from a linear regression analysis of the semi-log transformed photolysis data. Standard errors were used to distinguish

Table 3: Rate constants (k), half-life values (DT50), and correlation coefficients (R2) for pseudo first-order photodegradation of Belay.

differences between pseudo-first order rate constants. Discrete differences among natural and high purity water samples were determined by calculating the p-values associated with one-way ANOVA test and post hoc comparison (Tukey HSD test, α = 0.05). Significance was determined at alpha=0.05 confidence. Results and Discussion Photodegradation. The log-transformed photodegradation data for Belay in natural and high purity water samples are shown in Figure 2. In all cases, degradation plots are linear (0.946< R2 <0.996) indicating that the photodegradation of Belay follows pseudo-first-order kinetics; corresponding photolysis rate constants k, standard errors, and DT50 values are listed in Table 3. Belay loss in dark control was ≤4.8%, and corrections for dark reactions were not performed. The rate of direct photodegradation of a pesticide in water is dependent upon light intensity, the compounds molar absorptivity ελ, and the reaction quantum yield. 16, 18 In order to compare the light absorption capacity between pure and Davis field water, molar absorptivity values were calculated for Belay for wavelengths at intervals between 250 < λ< 400 nm using Equation 4, and are presented in Figure 3. Calculated ε values for wavelengths at intervals between 290 < λ< 400 nm ranged between 14,560 to 4,810 M-1 cm-1 and 5,870 to 105 M-1 cm-1 for deionized and Davis field water, respectively. This indicates that even under conditions of lower light attenuation (e.g. higher turbidity), Belay is capable of strong absorbance of environmentally relevant long (UV-A; 320 to 400 nm) and short (UV-B; 290 to 320 nm) UV waves. The photodegradation rate and corresponding DT50 of Belay in deionized water (direct photolysis) occurred rapidly (0.0167± 0.0004 min-1, DT50 = 42 min); after 2.7 hours of light exposure, less than 7% of the initial concentration of Belay remained. Analysis of variance demonstrated significant differences between degradation rates and DT50 values in pure water, Sacramento River water (0.0146± 0.0005 min-1, DT50 = 46.5 min), and rice field waters. Photolysis rates and DT50 values in field water samples were significantly

longer than in de-ionized and Sacramento River water samples. In contrast, no significant difference was observed between the rates and DT50 values for Conway Ranch (0.0148± 0.0007 min-1, DT50 = 46.8 min) and Davis (0.0127± 0.004 min-1, DT50 = 54.6 min) field water. The decrease in light absorption and observed increase in degradation DT50 values for field waters suggest reduced susceptibility to photolysis in rice fields. Reaction Quantum Yield (ϕ). Measured ε values and UV intensity data were used to calculate ϕC values of 0.01 and 0.005 for Belay in deionized and Davis field water, respectively, using Equation 5. These values are consistent with reported ϕ values for Belay measured in pure water and ranged between 0.02 and 0.01 in a photo reactor and natural sunlight, respectively. 20 Calculated ϕC values suggest that approximately 1% and 0.5% of the light energy absorbed results in photochemical transformation in pure and field water, respectively. The lower absorptivity and decreased efficiency of photo-transformation observed in Davis field water suggest that the rate of photodegradation of Belay is primarily controlled by turbidity and light attenuation. Degradation Products. Degradation products in aqueous photolysis samples were determined using LC-MS/MS analysis. Only one product, TZMU, was observed and accounted for ≤17% in deionized water and ≤ 8% in natural water. The conversion of Belay to TZMU can be attributed to the photo-oxidation of the nitroguanidine moiety and is consistent with reports generated by the registrant. 8, 9 Furthermore, the methyl urea moiety of TZMU is structurally analogous to the major degradation product of Imidacloprid (1-(6-chloro-3-pyridylmethyl)-imidazolidin-2-one)), which is formed following the loss nitro group. 21 We purpose that the formation of TZMU under conditions of direct photolysis likely occurs in three steps: 1) direct absorption of light by the NO2 group, 2) photo-reduction of the excited nitro group to a nitroso derivative, 3) oxidative loss of the nitroso derivative to yield TZMU.16, 21-23 Conclusions Belay undergoes rapid photolytic degradation under simulated California summertime field light conditions. Observed degradation rates were faster in pure and Sacramento River (surface) water than in rice field water. Likewise, lower absorptivity and decreased quantum yields observed in field water, suggesting that the rate of photodegradation of Belay is primarily controlled by turbidity and light attenuation. Given its moderate solubility (327 mg L-1) and relatively low affinity for rice field soils (Log Koc 2.6), photodegradation is expected to dominate the dissipation when applied to a flooded field. In order to fully characterize its persistence and potential for offsite transport in field tail water, further investigation should focus on biological degradation of residues in field soils. Objective II – Photochemical fate of Imazosulfuron (League) Introduction

League (Fig. 4), a sulfonylurea herbicide, was registered for pre- and post-emergent use on rice in 20101. Sulfonylurea herbicides are valued for their high broad-spectrum

Figure 4. Structure of League.

phytotoxicity, low mammalian toxicity and good crop selectivity2. Although League has not yet been widely adopted by California rice growers 3, it is expected to be mobile in the rice field environment, due to its high water solubility (308 mg L-1, pH 7.0, 25°C), low vapor pressure (4.5 x 10-5 mPa, 25°C)4 and low affinity for soils (Kd: 0.96-13.8 mL g-

1)5; off-site transport will be influenced by aqueous degradation rates and cultivar practices. Some California rice growers drain their fields following germination to help establish rice seedlings and the degree to which aqueous degradation processes (e.g. photolysis and hydrolysis) have removed League from discharged tailwater will determine the risk posed by its use. In the US and Japan, League and other sulfonylurea herbicides have been detected in both ground and surface waters near agricultural areas6. During the growing season, California rice fields experience both temperature fluxes between 18-36°C7 and high intensity UV radiation (<1400 W m-2)8. Soils have poor internal drainage due to a high clay content9. Fields are often re-flooded post-harvest to aid in straw decomposition and provide habitat for wildlife. However, prolonged periods of flooding and high temperatures promote the evapoconcentration of salts in irrigation water. Such salinization is a global land degradation issue that is particularly pervasive in arid or semi-arid regions with high agricultural use10. A survey of fields California Central Valley of California found aqueous salt concentrations ranging from ~0.1-3.5 dS m-1 and reduced crop yields in fields exceeding 1.9 dS m-1 11. Strategies adopted by rice growers to protect surface waters from pesticide loading (e.g. recirculation between basins and longer flooding periods) are contributing significantly to soil salinization. Previous studies of League indicate that it is photolabile. Morrica et al. 12 report a photolysis half-life of 480 min in DI water, however the intensity of the radiation (≦290 nm) was not reported, precluding extrapolation to environmental rates. Tagaki et al.13 calculated a half-life of 8.5 days when field water amended with League was irradiated with natural light. However, this investigation both lacked replication and failed to report radiation intensity. Therefore, the goal of the present investigation was to determine the photolysis rate of League under simulated California rice field conditions and characterize the influence of several environmental factors on degradation, including natural organic matter (NOM), temperature, and high salinity conditions. To the best of our knowledge, no previous studies have addressed the influence of such factors. Materials and Methods Chemicals. League analytical standard (1-(2-chloroimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl) urea) was purchased from Santa Cruz Biotechnologies,

Inc. (Santa Cruz, CA). ADPM (2-amino-4,6-dimethoxypyrimidine), IPSN (2-chloroimidazo [1,2-α] pyridine-3-sulfonamide) and UDPM (2-ureido-2,6-dimethoxypyrimidine) were synthesized, purified and characterized by our collaborator, Dr. David Ball (Chico State University, Chico, CA). Acetic acid, NaCl, CaCl2, MgSO4 and Na2SO4 were purchased from Fisher Scientific (Hampton, NH). Standard solutions were prepared in acetonitrile and stored at -20°C and all solvents were HPLC grade. Water Collection and Characterization. Rice field water was collected three days prior to the start of the experiment from the Yolo Bypass Wildlife Area, Yolo County, California (38.55853°N, 121.62859°W), which is densely populated with rice fields. Field water was stored in glass bottles with minimal headspace at 4°C. Onsite measurements included pH, electrical conductivity (EC) and temperature. Temperature and pH (21.6°C and 7.72, respectively) were measured with an Oakton pHTestr® 30 and EC (1.08 dS m-1) was measured with an Oakton ECTestr™11 Plus (Oakton Instruments, Vernon Hills, IL). Further water characterization was performed by the Division of Agriculture and Natural Resources (ANR) Analytical Laboratory at the University of California, Davis, and included, briefly: elemental analysis by inductively coupled plasma-atomic emission spectrometry14, turbidity by nephelometric analysis15, and alkalinity by titration16. Water and glassware were autoclaved (121°C, 15 psi, 30 min) prior to use. Photolytic Experiments. Three exposure solutions were prepared from the collected field water as follows: 1) unadjusted field water; 2) filtered field water (0.22 µm, EMD Millipore Darmstadt, Germany); and 3) field water adjusted to ca. 3 dS m-1 with known quantities of NaCl, CaCl2, MgSO4 and Na2SO4 in molar ratios reflective of a salinization-impacted field, per the instructions detailed in Grattan et al.17. In addition to these three solutions, HPLC water (adjusted to pH 7.7 with NaOH) was used as a control. All prepared solutions (5.5 L each) were fortified with ca. 200 µg L-1 (0.48 µM) League (three orders of magnitude below solubility; approximate US field application rate assuming 10 cm flood depth) and allowed to equilibrate while stirring for one hour. To individual vials (60 mL borosilicate type-200 vials for photoexposed samples, capable of filtering UV <290 nm; and 50 mL amber serum bottles sealed with bromobutyl stoppers for dark controls; Wheaton Science, Millville, NJ), 50 mL was delivered. Photovials were placed in exposure chambers, outfitted with ten (8 W) broad UV (300±50 nm) spectrum lights (Southern New England Ultraviolet Company, Branford, CT) mounted 25 cm above the samples. Exposures were carried out at 25.0 and 35.0°C (±1.5 °C). Irradiation in the chambers was measured using a portable radiometer (Ultra Violet Products, Upland, CA) and measured between 7.08-9.50 W m-2, comparable to sunlight intensity on California rice fields during the summer growing season. In comparison, readings taken midday in June on the roof of Meyer hall at the University of California, Davis campus were 12.7-14.3 W m-2. Dark controls of each solution, used to monitor dark degradation processes and sorption to glassware, were wrapped in aluminum foil and enclosed in separate temperature-controlled chambers. All photoexposed solutions and controls were collected in triplicate at each time interval (0, 6.5, 12.75, 19.25, 30.25, 42.5, 54.25, 65.75 and 78.75 h), briefly vortexed and then centrifuged (3500g for 30 min). The supernatant was collected and stored at -20°C prior to analysis. Our previous studies indicate all analytes are stable under these conditions for at least one month (data not shown).

Analysis. Analysis was performed using an Agilent 1200 Series high-pressure liquid chromatograph coupled to a 6420 triple quadrupole mass spectrometer (LC/MS/MS) run in positive ion ESI multiple reaction monitoring mode (MRM). The column (25°C) was an Agilent Eclipse XDB-C18 (150 x 4.6 mm i.d., 5 µm particle size) with a 25 µL injection volume. A gradient mobile phase consisting of water (0.25% formic acid, solvent A) and acetonitrile (0.25% formic acid, solvent B) was used; the initial flow rate of 0.25 mL min-1 from 0‒18.6 min was subsequently increased to 1 mL min-1 to rapidly equilibrate the column. The gradient was as follows: 0‒4 min, B was ramped up from 30‒90%; 4-18.6 min, 10% A, 90%B; 18.6‒21 min B was ramped down to initial 30%; 21‒24.5 min 70% A, 30%B. Only eluent from 7‒17 min was directed to the MS and data were quantified by comparison against a first order external calibration curve generated in Masshunter Workstation Software version B.06.00 (Santa Clara, CA). Mass transitions used for quantitation were: m/z 413→153, m/z 156→100, m/z 232→153 and m/z 199→182, for IMZ, ADPM, IPSN and UDPM, respectively. For each analyte, two additional qualitative transitions were monitored for identity confirmation. Declustering potentials and collision energies were optimized for each analyte and the quantification limit (5 µg L-1 for all compounds) was determined by multiplying three times the standard deviation of replicate injections of low level standards. Data Analysis. League photodegradation was fitted to a pseudo-first-order model. The rate constants (k, h-1) and the half-lives (t1/2) were determined according to equations 1 and 2, respectively: Ct =C0e-kt (1) t1/2 = (ln 2) / k (2) C0 is initial concentration (µg L-1) of League, Ct is concentration (µg L-1) at time t (h). Statistical analysis was performed using JMP® 11.0 (SAS Institute, Cary, NC) and differences between treatments were determined using an ANCOVA test for equality of slopes at 95% confidence. Results and Discussion Table 4. Pseudo-first order reaction rate constants (k, hour-1) for IMZ degradation in solution. conditions HPLC H2O filtered field

H2O field H2O high salinity field

H2O 25°C, Light 0.0455±0.0028 0.0409±0.0024 0.0437±0.0028 0.0373±0.0034

35°C, Light 0.0568±0.0066 0.0474±0.0066 0.0432±0.0031 0.0423±0.0068

25°C, Dark 0.0002±0.0004* 0.0004±0.0005* -6.97E-5±0.0004* -4.67E-5±0.0004*

35°C, Dark 0.0010±0.0006 0.0007±0.0041 0.0009±0.0005 0.0007±0.0005

* Not significantly different from 0 at α = 0.05.

League Photolysis. Pseudo first-order reaction rate constants (k) and 95% confidence intervals of League are reported in Table 4. Tests for slope = 0 found no significant loss of IMZ in dark control solutions incubated at 25°C (α = 0.05; P < 0.3748, 0.2294, 0.7612 and 0.8163 for HPLC control, filtered field water, intact field water and high salinity field water, respectively). At 35°C, slopes of dark solutions were significantly different than 0 (P < 0.0053, 0.0048, 0.0014 and 0.0086 for HPLC control, filtered field water, intact field water and high salinity field water, respectively), demonstrating loss from solution. Morrica et al. 18 reported a very slow hydrolysis rate at neutral and basic pH (t1/2~578 days, pH 5.9) and a strong temperature dependence (3‒5 fold increase in reaction rate with each 10°C increase in temperature); our findings are in agreement with these results. As seen in Figure 5, irradiated samples had slopes indicative of a first-order kinetic reaction and were significantly different than 0 (P > 0.001 for all cases). Photolytic half-lives ranged from 12.2-18.6 h under California conditions. Tagaki et al.13 investigated League’s photoreactivity in a Japanese rice field, which received a reported 5 h of sunlight each day. Cloud cover and solar radiation intensity were not described, making

Figure 5. Degradation profiles for League at 25°C in light (○) and dark (●) and at 35°C in light ( ) and dark (▲) in A) HPLC water, B) filtered field water, C) intact field water, D) high salinity field water. Points represent mean ± standard deviation.

Figure 6. Photo-induced degradation products of IMZ. Percent recovery of applied IMZ on a molar basis of ADPM (○), UDPM (▲) and IMZ (●). Data points are mean values ± standard deviation. direct comparisons difficult. However, they reported an aqueous photolysis half-life of 8.5 days (~ 43 h, if five hours of sun each day), confirming that League is susceptible to photodegradation. Identification and Quantification of Degradation Products. Figure 6 shows the formation of products in HPLC water irradiated at 25°C, which was similar to all irradiated solutions. Previous reports12, 18 have identified ADPM, IPSN and UDPM as major photolytic products of League and all three were detected at similar levels in irradiated solutions. IPSN remained below quantification limits (LOQ: 5 µg L-1) throughout the study, while ADPM and UDPM seemed to reach steady-state concentrations (~5% and 8-15% recovery of applied IMZ for ADPM and UDPM, respectively). Both ADPM and IPSN are chromophores themselves, with appreciable absorption <290 nm12, so their accumulation under irradiation was not expected. Product formation was not observed in the dark controls. Comparison of Slopes. ANCOVA tests for homogeneity of slopes are reported in Table 5. No significant diffe0rence in slopes of dark controls was found (P < 0.9545 or greater). Among irradiated samples, photolytic rates in HPLC water were significantly faster than those in all field water treatments (P < 0.001 in all cases), while field water rates were statistically identical to one another (kHPLC > kintact = kfilter = ksalt; P > 0.5575‒0.9997). This suggests that direct photolysis is the primary degradation route for IMZ in simulated

Table 5. ANCOVA tests for slope homogeneity. Levels not connected by the same letter are statistically different (reject H0: the slopes are equal). Significance level α = 0.05. conditions HPLC H2O filtered field

H2O field H2O high salinity field

H2O 25°C, Light A B B B

35°C, Light A B B B

25°C, Dark C C C C

35°C, Dark C C C C

sunlight, with minimal input from indirect processes. Differences in rates between HPLC and field water could be attributed to greater light absorption in colored field water or quenching with non-target organic species. Significant differences in rates caused by turbidity between filtered (3.1 nephelometric turbidity units; NTU) vs. unfiltered field water (104.3 NTU) were not observed, possibly due to settling of NOM during exposure. NOM may play either a synergistic or antagonistic role in IMZ photolysis. In sunlight, NOM forms reactive oxygen species (ROS; e.g. hydroxyl radical, singlet oxygen or superoxide anion) and other reactive intermediates such as 3NOM, which may contribute to photolytic degradation19. NOM can also retard photolytic rates via light attenuation and quenching of ROS and 3NOM. Turbidity effects may have been masked due to the relatively small size of the vials, which provided a shorter path length for light to travel, minimizing attenuation. Excess salts may also either accelerate or retard photodegradation of organic pollutants20. Though photolytic rates in simulated hypersaline field water were slightly slower relative to intact field water exposures, suggesting quenching of excited states, this effect was not significant. The effect of temperature (25°C vs. 35°C) on rate was not determined to be significant, again suggesting direct processes dominate. Conclusions League degraded relatively rapidly under simulated California growing conditions, yielding half-lives of 12-18 h under constant irradiation. Hydrolysis was not observed at 25°C, and was very slow at 35°C (DT50 >710 h). League’s photolytic and hydrolytic degradation products were observed but did not accumulate, due to their own susceptibility to photoreaction. Photolysis proceeded fastest in pure laboratory water, suggesting that light attenuation in field water (due to turbidity and colored organic material) is not compensated by the contribution of indirect photoreactions. Field relevant differences in salinity and temperature did not influence photolytic rates significantly. Future studies will examine the contribution of microbial degradation to League’s fate.

Objective III. Hydrolysis of Butte (Benzobicyclon) Introduction Resistance of several weeds to current herbicides remains a prevalent issue impacting California rice production. Herbicides with alternative modes of action, such as Butte (benzobicyclon), are currently being sought to combat recalcitrant weeds such as Schoenoplectus mucronatus, Cyperus difformis, Heteranthera limosa, and Echinochloa oryzoides (Fischer, 2012). Butte, a pro-herbicide, may undergo hydrolysis to form benzobicyclon hydrolysate (BH), the active herbicide, in both the environment and in plants (Figure 7). BH inhibits the enzyme hydroxyphenylpyruvate dioxygenase (HPPD), subsequently halting the production of a carotenoid precursor within the plant. The loss of carotenoids results in the degradation of chlorophyll and ultimately plant death. Volatilization of Butte was initially of interest due to its low water solubility (0.052 mg/L at 20oC) (Tomlin, 2012). No experimentally derived air-water partitioning coefficients (H) are currently available for Butte. The US Environmental Protection Agency’s estimation software EPI Suite™ estimates an H value of 1.16E-7 Pa*m3mol-1 at 25oC (US EPA, 2014). Air-water partition experiments conducted in 2013 suggest volatilization does not play a significant role in its dissipation under field conditions as loss via volatilization could only account for a low fraction of Butte within the experimental setup. More than 90% of Butte was lost over the course of the experiment due an unknown process, which was hypothesized to be loss due to hydrolysis of Butte to BH. H values were calculated theoretically as 4.06E-3 Pa*m3mol-1 and 2.03E-2 Pa*m3mol-1 for Butte at 25oC and 37oC, respectively. Loss of Butte via hydrolytic degradation appears to be significant contributor to its dissipation. As of this writing, the rate of hydrolysis from Butte to BH has not been reported in the literature. Therefore, characterization of the hydrolysis rates and half-lives of Butte is crucial to better understand its fate under field conditions.

Figure 7. Structures of Butte (L) and BH (R)

Materials and Methods Chemicals. Butte analytical standard (100% purity) was purchased from Wako Chemicals USA (Richmond, VA, USA). BH (97% purity) was custom synthesized by GTM China Co. LTD (Changzhou, Jiangsu, China). NMR and MS spectra confirmed the BH standard. All solvents were HPLC grade and purchased from Sigma Aldrich (St. Louis, Missouri, USA). Sodium hydroxide, potassium biphthalate, potassium phosphate, boric acid, and potassium chloride were purchased from Fisher Scientific (Pittsburgh, PA, USA). Stock solutions of Butte (20 mg/L) were prepared in acetonitrile and stored at -20oC in amber bottles. Stock was diluted into each aqueous treatment (as described below) and equilibrated to reach the final concentrations. Aqueous treatments. Three aqueous treatments were used: buffered water, unbuffered water and field water. Treatments (except for field water) were constituted in HPLC grade water. Both buffered and unbuffered water treatments were prepared at pH 4, 7, and 9 (± 0.03). The pH of the field water was measured to be 8.80. Buffered water treatments were prepared as described by the US Environmental Protection Agency (OECD 111, 2004). The pH 4 buffer treatment was made by diluting 0.04 mL 0.001N sodium hydroxide and 0.5 mL 0.01M potassium biphthlalate to 1 L. The pH 7 buffer treatment was prepared by diluting 0.5 mL of 0.01M potassium phosphate and 2.91mL 0.001N sodium hydroxide to 1 L. The pH 9 buffer treatment was made by diluting 2.13 mL 0.001N sodium hydroxide and 0.5 mL 0.01M boric acid in 0.01M potassium chloride to 1L. The pH of all buffer solutions were checked using an Oakton® Waterproof pHTestr 30 and adjusted as necessary with 2.5N hydrochloric acid or 0.1N sodium hydroxide. The pH values of all unbuffered solutions were also checked and adjusted as necessary. Buffer concentrations were lowered by an order of 107 from those reported in OECD 111 as suggested by the method to reflect the concentration of Butte. Field water collection. Water was collected from a rice field in Davis one month prior to the experiment and immediately sterilized using an autoclave at 121oC and 15 psi for 30 minutes before storage at 4oC. The ANR Analytical Laboratory at UC Davis determined various properties of the field water, results shown in Table 6. Hydrolysis. The hydrolysis of Butte was measured using the experimental method proposed by the US EPA (US EPA, 1998). Aqueous treatments, filtered to 0.2 μm for sterilization, were equilibrated with Butte (spiked at 0.025 mg mL-1, with acetonitrile comprising less than 0.15% of the overall solution) for 15 min before 15 mL aliquots were transferred to 15 mL amber vials. Vials were capped and placed in a Precision ™ Reciprocal Shaking Bath (Thermo Scientific) set at 25 ± 0.1oC and 40 rpm. All glassware

Table 6. Selected properties of collected field water

Sample pH EC (dS m-1)

HCO3 (meq/L)

CO3 (meq/L)

TOC (mg/L)

Turbidity (NTU)

DOC (mg/L)

Field water 8.66 1.13 5.9 1 15.2 27.3 12.4

used for experimental preparation was sterilized via autoclave at 121oC and 15 psi for 30 min. Samples were stored in the dark to prevent photodegradation and were removed over the course of 168 h in triplicate for extraction and analysis. Extraction and Analysis. Samples were solvent-exchanged into acetonitrile under acidic conditions using Agilent Bond Elut® C18 solid-phase extraction (SPE) cartridges. Samples were stored at -20oC for one week before analysis. An Agilent 1100 Series HPLC with an 1100 series autosampler coupled to an Agilent 6420 triple quardrupole mass spectrometer fitted with an electrospray ionization source (ESI) was used in conjunction with Agilent MassHunter Qualitative Analysis Software version B.06 for sample analysis. The instrument was equipped with a Titan phenyl column (50 mm x 2.1 mm ID, 5 μm particle size) with a Thermo Scientific Hypersil phenyl guard cartridge (10 mm x 2.1 mm ID, 5 μm particle size). Mobile phases (0.25% formic acid, A; and 0.25% formic acid in acetonitrile, B) were used with a gradient. The flow rate was kept at 0.4 mL min-1 throughout the run. Percent acetonitrile was kept constant at 20% until 1 min, then ramped to 95% from 1-8 min, held for 2 min, then ramped back to 20% from 10 – 11 min. The total run time was 11 min, followed by a 5-min equilibration period. The column was kept at 25oC and the injection volume was 15 μL. MRM positive ion mode was used to detect the [M+H]+ precursor ions (447 m/z and 355 m/z for Butte and BH, respectively). All samples were analyzed in duplicate. A seven-point external calibration curve was constructed from the peak areas of triplicate injections of Butte and BH mixed standards prepared in acetonitrile. Field water standards were prepared in matrix-matched acetonitrile eluted through SPE cartridges that had previously extracted blank field water. Calibration curves were weighted accordingly (with either a weight of 1/x or no weight), with a range (linear) from 0.01 μg/mL to 1 μg/mL, regression coefficients (R2) greater than 0.99 and residuals less than 10%. Calculations. Responses for duplicate injections were averaged for each sample then converted to aqueous concentrations (in μg mL-1). Sample concentrations were averaged for the initial time point and used as a collective initial concentration (C0) for each treatment. As hydrolysis is considered a pseudo-first-order reaction, a pseudo-first-order reaction model was applied to the hydrolysis of Butte.

d[Ct]/dt = -kH[Ct]

where kH is the hydrolysis constant at fixed pH and temperature (in hour-1). Rearrangement gives:

ln [Ct] = (-kHt) + ln [C0] Values of kH were obtained from the slopes of the data plotted as ln(Ct/C0) versus time (in hours). Half-lives were calculated from kH values as:

t1/ 2 =ln(2)kH

where t1/2 is the half-life (in hours). Statistical Analysis. JMP® Pro 11 software (SAS Institute Inc., Cary, NC) was used for statistical analysis of experimental data. An ANCOVA for testing the homogeneity of slopes was used to compare treatments at α = 0.05. Preliminary Results and Discussion Hydrolysis. Butte dissipation was found to correspond with increasing BH concentration in all treatments (Figure 8). Over the course of 168 h virtually greater than 99% loss of Butte was observed, with loss of Butte peak detection occurring after 72 h. BH concentrations appeared to remain approximately stable during the course of the experiment. Data graphed as ln(Ct/C0) versus time are shown in Figure 9 (for all treatments). Values of kH, calculated from the slopes of the data, are given in Table 7 along with the corresponding half-lives. Field water produced the most rapid degradation of Butte, with a half-life of 12.3 hours while HPLC water treatment half-lives (buffered and unbuffered) ranged from 15.19 h to 18.06 h. Overall, Butte was confirmed to degrade rapidly under aqueous conditions to form BH at 25oC, regardless of pH. Shorter Butte half-lives for field water and pH 9 treatments compared to those for pH 4 treatments suggest the hydrolysis reaction may be base-catalyzed.

Figure 8. Example time course for hydrolysis of Butte in buffered pH 9 solution

Figure 9. Butte hydrolysis in HPLC water (buffered and unbuffered) and field water

Table 7. Preliminary hydrolysis rate constants and half-lives of Butte at 25oC

Water pH Rate of hydrolysis (hr -1) Half-life (hr)

HPLC

4 0.0404 ± 0.0015 17.17 ± 0.64

7 0.0384 ± 0.0025 18.06 ± 1.08

9 0.0456 ± 0.0022 15.19 ± 0.68

Buffer

4 0.0412 ± 0.0028 16.84 ± 1.09

7 0.0430 ± 0.0018 16.12 ± 0.65

9 0.0422 ± 0.0013 16.44 ± 0.52

Field 8.8 0.0564 ± 0.0026 12.30 ± 0.55

Statistical Analysis. Data were analyzed statistically with an ANCOVA testing for the homogeneity of slopes at α = 0.05 with a Tukey HSD effects test. The hydrolysis rate for Butte in field water was determined to be significantly different from every other treatment. HPLC and buffer treatment hydrolysis rates at pH 4 and 9 were found to be statistically similar, respectively, while the HPLC and buffer treatment hydrolysis rates at pH 7 differed significantly. Hydrolysis rates for all treatments except for field water, HPLC water at pH 7, and buffered water at pH 4 were found to be statistically similar.

Conclusions Preliminary studies suggest that Butte rapidly degrades under aqueous conditions, regardless of pH. Hydrolysis appears to a significant, if not dominant, dissipation processes of Butte, which will be confirmed with a more thorough study. With evidence for rapid conversion from Butte to BH, especially in field water, future studies will investigate the dissipation processes of BH. Little information is currently available for BH, the active herbicide, which increases the importance of discovering more about the prominent partitioning and transformation behavior of BH under California rice field conditions. References Objective 1 1. P. Jeschke. Clothianidin (TI-435) the third member of the chloronicotinyl insecticide

family. . Planzenshutz-Nachricten Bayer (2003). 2. M. Tomizawa and J.E. Casida, Neonicotinoid Insecticide Toxicology: Mechanisms

of Selective Action. Annu Rev Pharmacol Toxicol; 45(247-268 DOI Electronic Resource Number (2005).

3. H. Umene, M. Konobe, A. Akayama, T. Yokota and K. Mizuta. Discovery and developement of a novel insecticide clothianidin. Sumitomo Kagaku (2006).

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5. T. Blacquiere, G. Smagghe, C.A.M van Gestel and V. Mommaerts, Neonicotinoids in bees: a review on concentrations, side-effects and risk assesment. Ecotoxicology; 21(973-992 DOI Electronic Resource Number (2012).

6. California Department of Pesticide Regulation. Summary of Pesticide Use Report Data 2011, Indexed by Commodity. California Environmental Protection Agency, Sacramento, CA, pp. 86. (2013).

7. USEPA. -Registration Review: Problem Formulation for the Environmental Fate and Ecological Risk, Endangered Species, and Drinking Water Exposure Assesment of Clohtianidin: Washington, D.C. 20460.

8. USEPA. - Environmental Fate and Effects Division. (2010). Clothianidin Registration of Prosper T400 Seed Treatment on Mustard Seed (Oi seed and Condiment) and Poncho/Votivo Seed Treatment on Cotton. Environmental Risk Assessment. Memorandum from Joseph DeCant and Michael Barret to Kable Davis, Risk Management Reviwer. : Washington, D.C. 20460.

9. H.-P. Stupp and U. Fahl. Environmental fate of clothianidin (TI-435; Poncho). In Pflanzenschutz-Nachrichten Bayer, pp. 59-74 (2003).

10. R.D. Wauchope, S. Yeh, J BHJ. Linders, R. Kloskowski, K. Tanaka, B. Rubin, A. Katayama, W.; Klein Kordel, W., Z. Gerstl, M. Lane and J.B. Unsworth, Review. Pesticide soil sorption parameters: theory, measurement, uses, limitations and reliablity. Pest Manag Sci; 58(419-445 DOI Electronic Resource Number (2002).

11. W.A. Jury, D.D. Focht and W.J. Farmer, Evaluation of Pesticide Groundwater Pollution Potential from Standard Indices of Soil-Chemical Adsorption and Biodegradation. J Environ Qual; 16(4): 422-428 DOI Electronic Resource Number (1987).

12. T. W. Jabusch and R.S. Tjeerdema, Photodegradation of Penoxsulam. J Agric Food Chem; 54(5958-5961 DOI Electronic Resource Number (2006).

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15. K.K. Ngim. The Fate and Kinetics of Pesticides in California Flooded Rice Fields. Dissertation, University of California, Davis, Ann Arbor, MI 48106-1346, (1999).

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Objective II

1. Registration of the herbicide, imazosulfuron, on peppers (bell and non-bell), rice, tomatoes and turf grass. United States Environmental Protection Agency: 2010; p. 20. www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0205-0019.

2. (a) Brown, H. M.; Kearney, P. C., Plant Biochemistry, Environmental Properties, and Global Impact of the Sulfonylurea Herbicides. 1991, 443, 32-49; (b) Shimizu, N.; Sakamoto, J.; Kamizono, H.; Ohta, K.; Tashiro, S., Mode of growth inhibitory activity and metabolism of imazosulfuron in excised roots of plants. Journal of Pesticide Science 1996, 21 (3), 287-292.

3. Bergin, R., 2011 Status report pesticide contamination prevention act. Regulation, D. o. P., Ed. California Environmental Protection Agency 2012; p 30.

4. The Pesticide Manual. 11 ed.; British Crop Protection Council: Farhnam, Surrey, U.K, 1997; p 1606.

5. Mikata, K.; Ohta, K.; Tashiro, S., Adsorption and desorption of herbicide imazosulfuron in soils. Journal of Pesticide Science 2000, 25 (3), 212.

6. (a) Battaglin, W. A.; Furlong, E. T.; Burkhardt, M. R.; Peter, C. J., Occurrence of sulfonylurea, sulfonamide, imidazolinone, and other herbicides in rivers, reservoirs and ground water in the Midwestern United States, 1998. The Science of the total environment 2000, 248 (2-3), 123-33; (b) Vu, S. H.; Ishihara, S.; Watanabe, H., Exposure risk assessment and evaluation of the best management practice for controlling pesticide runoff from paddy fields. Part 1: Paddy watershed monitoring. Pest management science 2006, 62 (12), 1193-1206; (c) Degenhardt, D.; Cessna, A. J.; Raina, R.; Pennock, D. J.; Farenhorst, A., Trace level determination of selected sulfonylurea herbicides in wetland sediment by liquid chromatography electrospray tandem mass spectrometry. Journal of environmental science and health. Part. B, Pesticides, food contaminants, and agricultural wastes 2010, 45 (1), 11-24; (d) Struger, J.; Grabuski, J.; Cagampan, S.; Rondeau, M.; Sverko, E.; Marvin, C., Occurrence and distribution of sulfonylurea and related herbicides in central Canadian surface waters 2006-2008. Bulletin of environmental contamination and toxicology 2011, 87 (4), 420-5.

7. Roel, A.; Mutters, R. G.; Eckert, J. W.; Plant, R. E., Effect of Low Water Temperature on Rice Yield in California. Agronomy Journal 2005, 97 (3), 943.

8. Yoshida, S., Fundamentals of rice crop science. The International Rice Research Institute: Los Banos, Laguna, Phillipines, 1981; p. 279. http://books.irri.org/9711040522_content.pdf (accessed November 7, 2014).

9. Williams, J. F.; Mutters, R. G.; Greer, C. A.; Horwath, W. R., Rice nutirent managemnet in California. University of California Agriculture and Natural Resources Publications: Davis, CA, 2010.

10. (a) Cassel, F.; Zoldoske, D., Assessing canal seepage and soil salinity using the electromagnetic remote sensing technology. In Sustainable Irrigation Management, Technologies and Policies, Lorenzini, G.; Brebbia, C. A., Eds. Wit Press: Southampton, 2006; Vol. 96, pp 55-63; (b) Ghassemi, F.; Jakeman, A. J.; Nix, H. A., Salinisation of Land and Water Resources: Human Causes, Extent, Management and Case Studies. NSW University Press: Sydney, Australia, 1995.

11. Scardaci, S. C.; Shannon, M. C.; Grattan, S. R.; Eke, A. U.; Roberts, S. R.; Goldman-Smith, S.; Hill, J. E., Water management practices can affect salinity in rice fields. Calif. Agr. 2002, 56, 184-188.

12. Morrica, P.; Fidente, P.; Seccia, S., Identification of photoproducts from imazosulfuron by HPLC. Biomedical chromatography : BMC 2004, 18 (7), 450-6.

13. Takagi, K.; Fajardo, F. F.; Ishizaka, M.; Phong, T. K.; Watanabe, H.; Boulange, J., Fate and transport of bensulfuron-methyl and imazosulfuron in paddy fields: experiments and model simulation. Paddy and Water Environment 2012, 10 (2), 139-151.

14. Method 200.7, Trace Elements in Water, Solids, and Biosolids by Inductively Coupled Plasma-Atomic Emission Spectrometry.

http://water.epa.gov/scitech/methods/cwa/bioindicators/upload/2008_11_25_methods_method_biological_200_7-bio.pdf.

15. Method 2130 (Turbidity-Nephelometric Method). In Standard Methods for the Examination of Water and Wastewater, 20 ed.; Clesceri, L. S.; Greenberg, A. E.; Eaton, A. D., Eds. American Public Health Association: Washington, D.C., 1998; p 1325.

16. Method 2320 (Alkalinity) In Standard Methods for the Examination of Water and Wastewater, Clesceri, L. S.; Greenberg, A. E.; Eaton, A. D., Eds. American Public Health Association: Washington, D.C., 1998; pp 2-26–2-29.

17. Grattan, S. R.; Zeng, L.; Shannon, M. C.; Roberts, S. R., Rice is more sensitive salinity than originally thought. Calif. Agr. 2002, 56 (6), 189-195.

18. Morrica, P.; Barbato, F.; Dello Iacovo, R.; Seccia, S.; Ungaro, F., Kinetics and mechanism of imazosulfuron hydrolysis. Journal of agricultural and food chemistry 2001.

19. (a) Cooper, W. J.; Zika, R. G.; Petasne, R. G.; Fischer, A. M., Sunlight-induced photochemistry of humic substances in natural-waters - major reactive species. Acs Symposium Series 1989, 219, 333-362; (b) Hoigne, J.; Faust, B. C.; Haag, W. R.; Scully, F. E.; Zepp, R. G., Aquatic humic substances as sources and sinks of photochemically produced transient reactants. Acs Symposium Series 1989, 219, 363-381; (c) Zepp, R. G.; Baughman, G. L.; Schlotzhauer, P. F., Comparison of photochemical behavior of various humic substances in water .1. Sunlight induced reactions of aquatic pollutants photosensitized by humic substances. Chemosphere 1981, 10 (1), 109-117.

20. (a) Conceicao, M.; Mateus, D. A.; da Silva, A. M.; Burrows, H. D., Kinetics of photodegradation of the fungicide fenarimol in natural waters and in various salt solutions: Salinity effects and mechanistic considerations. Water research 2000, 34 (4), 1119-1126; (b) Grebel, J. E.; Pignatello, J. J.; Mitch, W. A., Impact of halide ions on natural organic matter-sensitized photolysis of 17beta-estradiol in saline waters. Environmental science & technology 2012, 46 (13), 7128-34; (c) Prak, D. J. L.; Milewski, E. A.; Jedlicka, E. E.; Kersey, A. J.; O'Sullivan, D. W., Influence of pH, temperature, salinity, and dissolved organic matter on the photolysis of 2,4-dinitrotoluene and 2,6-dinitrotoluene in seawater. Marine Chemistry 2013, 157, 233-241.

Objective III 1. Fischer, A. 2012. Comprehensive Rice Research Annual Report: Weed Control in

Rice. Project No. RP-1. CARRB. 2. Koyanagi, H., Nakahara, S., 2009. Discovery and development of a new herbicide,

benzobicyclon. J. Pestic. Sci. 34:113-114. 3. OECD. 2004. Hydrolysis as a function of pH. OECD Guidelines for the testing of

chemicals 111. Organization for Economic Cooperation and Development. 4. Tomlin, C. D. S., Ed. 2012. The Pesticide Manual, 16th ed.; BCPC: Farhnam, Surrey,

U.K; 95-96.

5. US EPA. 1998. Hydrolysis as a function of pH and temperature. Fate, transport, and transformation test guidelines, OPPTS 835.2130. United States Environmental Protection Agency, Washington DC, USA.

6. US EPA. 2014. Estimation Programs Interface Suite™ for Microsoft® Windows, v 4.11. United States Environmental Protection Agency, Washington, DC, USA.

Total Publications Resulting From RRB-Funded Research – To Date In order to disseminate our findings to the broader agricultural community, the publications below have to-date arisen from our Rice Research Board-funded research. 1. Palumbo, A. J., P. L. TenBrook, A. Phipps and R. S. Tjeerdema, 2004. Comparative

toxicity of thiobencarb and deschlorothiobencarb to rice (Oryza sativa). Bull. Environ. Contam. Toxicol. 73, 213–218.

2. Schmelzer, K. R., C. S. Johnson, P. L. TenBrook, M. R. Viant, J. F. Williams and R. S. Tjeerdema, 2005. Influence of organic carbon on the reductive dechlorination of thiobencarb (Bolero) in California rice field soils. Pest Manage. Sci. 61, 68–74.

3. TenBrook, P. L. and R. S. Tjeerdema, 2005. Comparative actions of clomazone on β-carotene and growth in rice and watergrasses (Echinochloa spp.). Pest Manage. Sci. 61, 567–571.

4. Gunasekara, A. S., A. J. Palumbo, P. L. TenBrook and R. S. Tjeerdema, 2005. Influence of phosphate and copper on reductive dechlorination of thiobencarb in California rice field soils. J. Agric. Food. Chem. 53, 10113–10119.

5. Jabusch, T. W. and R. S. Tjeerdema, 2005. Partitioning of penoxsulam: A new sulfonamide herbicide. J. Agric. Food Chem. 53, 7179–7183.

6. Jabusch, T. W. and R. S. Tjeerdema, 2006. Microbial degradation of penoxsulam in flooded rice field soils. J. Agric. Food Chem. 54, 5962–5967.

7. Jabusch, T. W. and R. S. Tjeerdema, 2006. Photochemical degradation of penoxsulam. J. Agric. Food Chem. 54, 5958–5961.

8. TenBrook, P. L. and R. S. Tjeerdema, 2006. Biotransformation of clomazone in rice (Oryza sativa) and early watergrass (Echinochloa oryzoides). Pestic. Biochem. Physiol. 85, 38–45.

9. Gunasekara, A. S., J. Troiano, K. Goh and R. S. Tjeerdema, 2007. Chemistry and fate of simazine. Rev. Environ. Contam. Toxicol. 189, 1–24 (invited).

10. Gunasekara, A. S., K. Goh and R. S. Tjeerdema, 2007. Chemistry and fate of fipronil. J. Pestic. Sci. 32, 189–199 (invited).

11. Jabusch, T. W. and R. S. Tjeerdema, 2008. Chemistry and fate of triazolopyrimidine sulfonamide herbicides. Rev. Environ. Contam. Toxicol. 193, 31–52 (invited).

12. Yasuor, H., P. L. TenBrook, R. S. Tjeerdema and A. J. Fischer, 2008. Responses to clomazone and 5-ketoclomazone by Echinochloa phyllopogon resistant to multiple herbicides in Californian rice fields. Pest Manage. Sci. 64, 1031–1039.

13. Gunasekara, A. S., K. Goh, F. Spurlock, A. L. Rubin and R. S. Tjeerdema, 2008. Environmental fate and toxicology of carbaryl. Rev. Environ. Contam. Toxicol. 196, 95–121 (invited).

14. Gunasekara, A. S., I. D. P. de la Cruz, M. J. Curtis, V. P. Claassen and R. S. Tjeerdema, 2009. The behavior of clomazone in the soil environment. Pest. Manage. Sci. 65, 711–716.

15. Vasquez, M. E., A. S. Gunasekara, T. M. Cahill and R. S. Tjeerdema, 2010. Partitioning of etofenprox under simulated California rice growing conditions. Pest Manage. Sci. 66, 28–34.

16. Tomco, P., D. M. Holstege, W. Zhou and R. S. Tjeerdema, 2010. Microbial degradation of clomazone in California rice fields. J. Agric. Food. Chem. 58, 3674–3680.

17. Yasuor, H., W. Zou, V. V. Tolstikov, R. S. Tjeerdema and A. J. Fischer, 2010. Differential oxidative metabolism and 5-ketoclomazone accumulation are involved in Echinochloa phyllopogon resistance to clomazone. Plant Physiol. 153, 319–326.

18. Vasquez, M. E., D. M. Holstege and R. S. Tjeerdema, 2011. Aerobic versus anaerobic microbial degradation of etofenprox in a California rice field soil. J. Agric. Food Chem. 59, 2486–2492.

19. Vasquez, M. E., T. Cahill and R. S. Tjeerdema, 2011. Soil and glass surface photodegradation of etofenprox under simulated California rice growing conditions. J. Agric. Food Chem. 59, 7874–7881.

20. Tomco, P. and R. S. Tjeerdema, 2012. Photolytic versus microbial degradation of clomazone in a flooded California rice field soil. Pest. Manage. Sci. 68, 1141–1147.

21. Tomco, P., W. Holmes and R. S. Tjeerdema, 2013. Biodegradation of clomazone in a California rice field soil: Carbon allocation and microbial community effects. J. Agric. Food Chem. 61, 2618–2624.

22. Mulligan, R. A., S. J. Parikh and Ronald S. Tjeerdema, 2014. Abiotic partitioning of clothianidin under simulated rice field conditions. Pest. Manage. Sci. (in press).

CONCISE GENERAL SUMMARY OF CURRENT YEAR’S RESULTS: 1. The overall goal of our ongoing research program is to characterize the dissipation of

pesticides under California rice field conditions. There are generally four processes that can contribute to such dissipation that are investigated: volatilization to air, sorption (bonding) to soils, and degradation by either sunlight or soil microbes.

2. For the insecticide Belay, rapid photolytic degradation in field water under simulated California summertime light conditions was observed. Photodegradation is expected to control the dissipation when applied to a flooded field.

3. For the herbicide League, rapid degradation was observed in field water under

simulated California summertime light conditions. Light absorption from colored field water inhibited photolysis rates. Very slow hydrolysis was observed at high temperatures and is not expected to contribute to field dissipation.

4. For the herbicide Butte, preliminary data suggest that the potential to hydrolyze is

significant and is expected to occur rapidly under standard field conditions. The rate of hydrolysis may be affected by both temperature and pH.