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Purchase of Gas Chromatograph-Mass Spectrometer (GC-MS) for Teaching and Research

Mattice, John
University of Arkansas
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The overall objective is to minimize the amount of pesticides entering the environment in the production of food and fiber by pursuing the following objectives. Identify specific isothiocyanates that are degradation products of glucosinolates produced by brassicaceae plants. The isothiocyanates can help control weeds, soil-borne pathogens, nematodes, and insects. Identify compound(s) exuded by roots of certain non-commercially useful rice plants that inhibit growth of certain weeds. This has been a topic of interest in rice allelopathy since R.H. Dilday first observed the effect on ducksalad (Heteranthera limosa [Sw.} Willd.) in 1985. Many phytotoxic compounds have been extracted from rice tissue or isolated from root exudates or decomposing rice tissue, but the toxicity is not necessarily at concentrations that would be produced by living rice plants, therefore the effect is not truly allelopathy.

Our objective is to determine if some of these compounds are truly allelochemicals in that they produce an effect at levels produced by growing rice plants at typical planting density. Determine if environmental problems are developing due to rice pesticides in water in the rice growing area of Arkansas while the problems are small and more easily remedied. Determine if charred material added to rainwater gardens will increase their efficacy in removing pesticides and oils in runoff water from urban lawns and parking lots.

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Non-Technical Summary: Main objectives are to minimize use of pesticides and to ensure that they are not creating environmental problems when used in production of food and fiber. Some species in the mustard family produce compounds whose decomposition products inhibit growth of weeds and nematodes in tomatoes and peppers. The GCMS will help identify the compounds that are produced by the mustard plants and also help identify the degradation products that act as the pesticide. Some varieties of non-commercially useful rice exude compounds through their roots that inhibit the growth of certain weeds. The instrument will again be used to help identify the causative compounds. The ultimate goal is to help breeders incorporate the trait into commercially useful rice. We are using a GCMS to analyze for some rice pesticides in small rivers whose watersheds are primarily in rice producing areas. The objective is to discover any developing environmental problems due to pesticides in the water while the problem is still small and more easily solved. The instrument will also be used to help determine if adding small amounts of charred material to rainwater gardens will enhance their ability to remove pesticides and oils from runoff water from lawns and parking lots. In each case, the benefit will be to allow us to quantify some compounds in the presence of other compounds, minimize chances of having false positive detections, and help us to identify unknown compounds. Students in both an undergradauate course and a graduate course will get hands on experience with the instrument.

Approach: Isothiocyanates will be extracted from soil samples used to grow the brassicaceae crops. The extracts will be analyzed to identify the isothiocyanates that are present. This will be done by comparison of the mass spectra to those in a computer library. Rice allelopathy: Grow allelopathic rice in water for two weeks and grow an equal number of non-allelopathic rice as a control. Extract the water with organic solvent and wash the roots with organic solvent. Identify compounds that are present in allelopathic samples and not in non-allelopthic samples or are present in both, but in significantly larger amounts in the allelopathic samples. After obtaining standards, quantify the amounts and rates at which they are produced by rice plants. Perform bioassays on target plants at concentrations that would be produced by rice plants to see if there is a comparable effect. Repeat the experiment growing rice in soil for both the same and longer times instead of in water. Water monitoring: Collect samples from four sites each on four small rivers in rice growing country every two weeks from mid April through the first part of August and analyze them for pesticides used in rice production. Look for increasing concentrations, higher frequency of detections, increasing detections of multiple compounds per sample, increasing detections of the same compound on consecutive sampling dates as indicators of potentially a developing problem. Char-amended rainwater gardens: Apply simulated runoff from lawns and parking lots with selected lawn care pesticides and model compounds for oils from parking lots to soil columns. One set of columns will be soil only and one set will contain a small amount of char in the upper several cm. Analyze leachate for the compounds to determine if the char helps remove the compounds.

Funding Source
Nat'l. Inst. of Food and Agriculture
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Chemical Contaminants
Natural Toxins