Brief Summary of Minutes of Annual Meeting

Objective 1: Identify, develop, and/or validate trace residue analytical methods, immunological procedures, and biomarkers

Washington, Hebert: A major impediment in conducting quantitative biomonitoring within epidemiology studies is the lack of rapid, sensitive, field deployable technologies that measure chemical exposure biomarkers using minimally invasive biological fluids (i.e. saliva, drop of blood or urine). Due to the complexity of occupational exposures and biological systems, measurement of a single biomarker may not an adequate quantitative assessment of exposure. Hence, this project will undertake development, validation, and refinement of a novel multiplex sensor platform capable of quantifying multiple biomarkers associated with pesticide exposures, utilizing saliva, blood, and urine as relevant biological fluids. Validation of this multiplex sensor project will initially focus on chlorpyrifos, diazinon, carbaryl and atrazine and their associated metabolites that are well investigated to be readily excreted in saliva and correlate with blood concentration. A major initial aim will be to compare the responsiveness of the multiplex biosensor system in concert with chromatographic analytical methods in relevant biological matrixes. Results from these validation studies will establish the feasibility and capability to measure very low exposures approaching the current occupational exposures for each analyte.

Objective 2: Characterize abiotic and biotic reaction mechanisms, transformation rates, and fate in agricultural and natural ecosystems

Louisiana, Armbrust: The fungicide 2,6-dichloro-4-nitroaniline (DCNA) is applied to crops grown in areas near both freshwater and saltwater bodies and it can enter the surface waters where it is susceptible to photolysis. The salinity of seawater can influence both the overall rate of degradation of chemicals and impact the distribution and types of photoproducts generated during the photodegradation process. The photodegradation of DCNA was measured in distilled water, artificial seawater, estuarine water, and phosphate buffer to determine the degree of differences in the degradation rate in various matrices. The brominated analogue 2,6-dibromo-4-nitroaniline (DBNA) was measured identically to determine the impacts of other halogens on the degradation process. Solutions of DCNA and DBNA at a concentration of 1 ppm were prepared and irradiated for 24 hours in an Atlas SUNTEST XXL+ photochamber that mimics the wavelength distribution and intensity of sunlight. Dark controls were run simultaneously. Samples were withdrawn at 0, 2, 4, 6, 12, and 24 hours and analyzed for residual DCNA or DBNA using an Agilent 1260 Infinity High Performance Liquid Chromatograph. The formation of ions such as nitrate, nitrite, bromide, and chloride were measured using a Thermo Dionex ICS-5000+ Ion Chromatograph. The half-life of DCNA in distilled water was calculated to be 7.62 ± 0.094 hours and 7.37 ± 0.279 hours in artificial seawater; statistically there was no significant difference in the degradation rate through the first half-life. Analysis of the quick formation of nitrite and chloride ions, and later formation of nitrate ions, suggests photonucleophilic substitution processes are occurring as the compound is degrading, followed by further degradation of nitrite to nitrate likely also due to photolysis processes. Small aliphatic acids, maleic and fumaric acid, were detected after 12 hours of irradiation by HPLC indicating degradation of the aromatic ring structure. Differences in formation rate and decline for intermediate photoproducts were observed in seawater and distilled water suggesting salinity affects the rate of formation of this photoproduct.

Maryland, Hapeman: Riparian buffers are known to mitigate hydrologic losses of nutrients and other contaminants as they exit agricultural fields. The vegetation of riparian buffers can also trap atmospheric contaminants, which can subsequently be delivered via rain to the riparian buffer floor. Stemflow is rain contacting the tree canopy traveling down smaller to larger branches and down the tree trunk, whereas throughfall is rain that may or may not contact leaves and branches and falls to the floor. These processes, however, are poorly understood especially for pesticide residues. Therefore, we conducted a four-year study examining stemflow and throughfall within and precipitation outside a riparian buffer which was adjacent to a corn field. Stemflow concentrations were larger than throughfall concentrations and were larger for metolachlor than atrazine. Larger depositional fluxes were measured when leaves were more fully emerged and when temperatures and humidity were elevated. Enhanced herbicide loading to the riparian buffer stream was found to be linked to tree canopy deposition and subsequent washoff during rain events. These results indicate that during low overland-flow precipitation events, the tree canopy can be a dominant pesticide source to surface waters.

Nevada, Miller: Biofuel crops can potentially be grown on arid lands that do not compete with other food and feed crops. Grindelia squarrosa, commonly known as gumweed, is a flowering plant species common to Nevada that is found in many areas of the inter-mountain west, particularly along roadsides where increased precipitation is available from runoff. A preliminary analysis of numerous desert plants by Lemaire in 1982 (unpublished) singled out gumweed as a strong candidate for crude oil production. High oil yield per acre, along with minimal watering requirements, makes gumweed a strong crop for biodiesel production in the western United States. Processed gumweed has provided an average of 12-23 % crude oil by dry weight, depending on the plant stand collected and the method of sample drying. While the majority of hydrocarbons present in the extracts are at the heavy end of diesel fuel, a derivatized B20 blended biodiesel was shown to meet ASTM standards for flash point, kinematic viscosity, and sulfur content. Gumweed biodiesel blends offer a useful source of additional fuel that can be produced from crops grown in arid environments with minimal irrigation needs, while reducing the competition between food and biofuel crops. No additional engine modifications are needed for the use of B5 or B20 biofuels. Additionally, we have investigated the direct conversion of biocrude into a potentially usable jet/diesel fuel via pyrolysis. Heating the biocrude to 400 ^oC produced a decarboxyated mixture of compounds. The two major compounds were tri- and tetramethlyltetralin. Tetralins are compounds similar to naphthalene that contain one of the rings saturated and the other aromatic. Further investigation of this process is warranted, since the yield of the distillate from the biocrude is approximately 45% (by weight). Additional characterization of this product is required to fully characterize the distillate.

Oregon, Jenkins: For more than 20 years pesticides have consistently been detected in the Zollner Creek watershed, Willamette Basin, OR, more frequently, and at higher levels, than in other surface waters of the Pacific Northwest. To address this concern the watershed scale ecohydrologic model – Soil and Water Assessment Tool (SWAT) – was used to better understand pesticide loading pathways that may direct the development of mitigation strategies. Using a mechanistic approach to refining ecohydrology, SWAT deterministic parameterization scenarios of increasing local knowledge were evaluated in relation to USGS observed average daily stream flow near the outlet of the watershed. Uncertainty of selected model inputs was further investigated using a probabilistic approach; statistics used to evaluate model performance – PBIAS, NSE, RSR, R² – were improved and deemed acceptable for the evaluation of pesticide fate. To evaluate model performance in estimating pesticide fate, probabilistic methods were used to evaluate the spatial and temporal distribution of atrazine applications and resulting surface water concentration profiles. Model estimates – mean atrazine surface water concentration and 95% confidence interval as a result of the spatial and temporal probability distributions of atrazine applications – for 2010 and 2011 are compared to USGS and Oregon DEQ atrazine grab sample surface water concentrations. Ninety-two percent of grab samples were within a factor of 4 of SWAT mean estimates of atrazine concentrations. This modeling approach shows promise in estimating pesticide surface water concentration exceedance probabilities for alternate cropping practices, mitigation measures, and pest management strategies.  

Objective 3: Determine adverse impacts from agrochemical exposure to cells, organisms, and ecosystems

Montana, Peterson: The insecticides currently used for management of adult mosquitoes are broad-spectrum and highly toxic to most bees, but toxicity is not the same thing as risk. Moreover, risk information is not available for real-world exposures of bee pollinator species to insecticides used for mosquitoes. Therefore, we are conducting insecticide susceptibility research on the honey bee (Apis mellifera) and the alfalfa leafcutting bee (Megachile rotundata), an important non-honey bee pollinator in the western U.S. that can also serve as a surrogate for other solitary bees. This two-year research study encompasses three primary objectives that are providing knowledge about the risks to bees from exposure to insecticides. The objectives are to determine: (1) LD50 values (the dose that causes 50% mortality) for alfalfa leafcutting bees when exposed to three pyrethroid insecticides; (2) the effects on foraging alfalfa leafcutting bees and honey bees the day after field applications of pyrethroids; and (3) the effects on populations of alfalfa leafcutting bees after field applications of permethrin directly on nest boxes. Data from 2015 are presented here for objectives 1 and 2. Preliminary LD50 values were estimated for permethrin, etofenprox, and deltamethrin. LD50 values for female alfalfa leafcutting bees were 0.04 µg/bee for etofenprox (slope, 4.093; heterogeneity, 1.12), 0.048 µg/bee for permethrin (slope, 6.266; heterogeneity, 1.33), and 0.0032 µg/bee for deltamethrin (slope, 6.893; heterogeneity, 1.22). These LD50 values are approximately twice the values for honey bee, indicating that alfalfa leafcutting bees are about twice as tolerant. Preliminary results indicate that there were no statistically significant effects on mortality of alfalfa leafcutting bees and honey bees after permethrin and etofenprox were sprayed at maximum label rates directly over alfalfa fields. Control mortality and treatment mortality were very low and not statistically different (p-value range = 0.28 – 0.99).

Montana, Sterling: Smooth brome (Bromus inermis Leyss.) is a cool-season, perennial grass that spreads by rhizomes and was introduced in the 1880s as a livestock forage and for erosion control; it grows across North America in proximity to wheat-growing regions, and is considered weedy in some habitats. The major wheat pest, wheat stem sawfly (Cephus cinctus Norton) causes $350 million of annual damage in wheat fields throughout the Northern Great Plains. Insecticides are not effective in this pest system, but smooth brome may be an alternate host and serve as a perimeter trap; however, no empirical data exist to demonstrate its effectiveness. We used a combination of laboratory analysis and field sampling to evaluate smooth brome’s role as an alternate host. In the lab, we identified and quantified attractive volatile compounds from wheat and smooth brome using GC-MS. In the field, we sampled smooth brome adjacent to wheat fields and monitored the number of eggs, larvae, and parasitoids in each species through the growing season. Smooth brome produced the same attractive green leaf volatile compounds as wheat, but at 4- to 8-fold higher concentrations. In the field, a greater proportion of smooth brome stems were infested with wheat stem sawfly eggs than wheat stems in adjacent fields. Among infested stems, smooth brome had more eggs per stem than wheat. These results suggest a proof of concept that smooth brome chemistry plays a role in its efficacy as a trap for wheat stem sawfly management.

Washington, Felsot: A comparative assessment of apiaries in urban, rural and agricultural areas was undertaken in 2013 and 2014 to examine potential honey bee colony exposure to neonicotinoid insecticides from pollen foraging.   Apiaries ranged in size from one to hundreds of honey bee colonies, and included those operated by commercial, sideline (semi-commercial) and hobbyist beekeepers. Residues in/on wax and beebread (stored pollen in the hive) were evaluated for the nitro-substituted neonicotinoid insecticides imidacloprid and its olefin metabolite and the active ingredients clothianidin, thiamethoxam, and dinotefuran.  Beebread and comb wax collected from hives in agricultural landscapes were more likely to have detectable residues of thiamethoxam and clothianidin than that collected from hives in rural or urban areas (~50% of samples vs <10%).  The maximum neonicotinoid residue detected in either wax or beebread was 3.9 ppb imidacloprid.  A probabilistic risk assessment was conducted on the residues recovered from beebread in apiaries located in agricultural, urban, and rural landscapes.  The calculated risk quotient based on a dietary no observable adverse effect concentration (NOAEC) suggested low potential for negative effects on bee behavior or colony health.

Objective 4: Develop technologies that mitigate adverse human and environmental impacts

Hawaii, Li: Polycyclic aromatic hydrocarbons (PAHs), a class of priority hazardous substances, are persistent, ubiquitous and carcinogenic. Bioremediation is an economical technology to degrade PAHs. Understanding mechanisms of PAH toxicity and bioavailability to bacteria allows optimization of factors for bioremediation efficiency. Burkholderia sp. C3 degrades PAHs including dibenzothiophene (DBT) that is typically used as a model PAH for bioremediation studies. Chemical biodegradation, bacterial growth and toxicity studies showed that glycerol, a biodiesel production byproduct, enhanced DBT biodegradation kinetics by 18-fold in C3. Surface tension measurement, metabolite analysis and gene cloning identified secretion of rhamnolipids, glycolipid biosurfactants, by C3. Rhamnolipid fortification experiments further confirmed the relevance of rhamnolipids to the enhanced DBT biodegradation. The use of β-oxidation and rhamnolipid synthesis inhibitors reduced C3 growth and DBT biodegradation rate. It is concluded that that glycerol supports C3 growth and co-metabolism of DBT via a rhamnolipid mediated mechanism. This study provided insights into mechanisms of glycerol induced co-metabolism of DBT in Burkholderia sp. C3, which will allow to design effective bioremediation strategies to remove PAHs from contaminated sites.