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Runoff and recycled water management: Continue to address research and extension needs related to improving runoff management by: (1) gathering comprehensive runoff-related information from the following sectors: a) growers, b) regulatory agencies, and c) university research and extension. Quantify the relative impacts of nursery runoff on surface water resources through detailed on-site investigations. Characterize critical control points within production systems and their influence on the presence and fate of pests, pesticides, and other agrichemicals (mineral salts) in production runoff, irrigation reservoirs, and other water sources. Develop chemical, physical, and biologically-based water treatment technologies to mitigate adverse effects of pesticides, salts, and pests in recycled irrigation water. Develop BMP guidelines for water recycling programs to minimize potential for negative effects on plant health by pests, pesticides, and mineral salts in recycled irrigation water.
1) Determine how plant induced changes in the rhizo-sphere affect pharmaceutical and personal care products (PPCP) sorption to growth media and availability to plants:Soil sorption tests will be correlated with plant uptake experiments where changes in rhizosphere pH will be evaluated. Both controlled growth media and field soils will be tested. The controlled growth media experiment will allow us to investigate the relationships between sorption, plant uptake, and plant induced changes in the rhizosphere without the complicating factors introduced by field soils such as microbial interactions and spatial variation. The soil tests will demonstrate how our methods of studying rhizosphere pH can be applied to investigating PPCP uptake in realistic situations.The initial sorption test to growth media will include the 4 compounds - two bases, one acid, and one neutral PPCP. All have previously been found to be taken up by plants and have been detected in reclaimed wastewater (RWW). Sorption tests will be conducted in polypropylene centrifuge tubes with pH adjusted growth matrix and Hoagland's solution. Compounds will be spiked in at 100 ug/L. Tubes will equilibrate in a shaker box for 24 hours then be centrifuged at high speed and filtered (0.22 um). The amount of compound remaining in the dissolved phase will be measured using liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS). Initially, pHs 4-8 will be tested, as the starting rhizosphere pH values will be within that range.Rhizosphere experiments: Plants will initially be grown hydroponically in a container designed to shape the roots into a flat mat on top of a layer of 30 um mesh which will allow water, nutrients, contaminants, and root hairs through, but not full roots. After 3 weeks, the mesh set up will be transferred from hydroponic solution to a thin layer of growth media (3 g dry weight) connected to nutrient solution by a filter paper wick. The nutrient solution will contain the four PPCP compounds. Exposure time will be eight days, after which the soil will be considered as the rhizosphere. Control set ups with no plants will be subjected to the same conditions so that the effects of the plant on the soil can be deduced. At the end of the experiment, total mass of roots and above-ground tissue will be measured to account for the varying test conditions effects on plant growth. Wheat plants will be used for all plant uptake experiments in this section. It grows well in the set up we plan to use and can cause large changes in the rhizosphere pH, so it is ideal for our study.Analytical Methods: At the end of the exposure, above and below ground tisues and growth media will be harvested. Growth media will be centrifuged and the supernatant will be used to determine the rhizosphere pH. The supernatant will then be combined with methanol (50:50 ratio) and filtered using a 0.2 um PTFE filter, and PPCP levels will be measured used LC-MS/MS, as in the sorption experiments. Aboveand below ground tissues will be separated, rinsed with purified water, freeze-dried, and ground using a mortar and pestle. Powdered samples will then be extracted using accelerated solvent extraction (ASE). Extracts will be dried down to 2 mL or less and filtered using a 0.2 um PTFE filter, then analyzed using LC-MS/MS.Data Analysis: Plant uptake is expected to correlate with the fraction of the compound in the dissolved phase at the pH of the rhizosphere. Data from the sorption experiment at the appropriate pH will be plotted against concentration in the above ground and below ground plant tissue. Additionally, plant concentration will be plotted against dissolved fraction at the initial soil pH and R2 values will be compared between the correlations. If necessary, additional sorption experiments will be completed so that they cover the necessary range of pHs.2) Measure PPCP accumulation in bulk plant tissue and relate to observed uptake pathways:A. thaliana will be grown hydroponically in nutrient solution. Plants will be sprouted in agar-filled pipette tips and transferred to the nutrient solution when they have approximately 6 leaves. After 5-6 weeks, plants will be harvested. Both leaves and roots will be analyzed for amount of uptake using the ASE and LC-MS/MS methods described above. We will look for a correlation between the uptake pathways (elucidated in separate experiments performed in our group) and the distribution of compound between the leaves and roots.