2005 Progress Report: Using Carbohydrates as Molecular Markers to Determine the Contribution of Agricultural Soil to Ambient Fine and Course PMEPA Grant Number: R832164
Title: Using Carbohydrates as Molecular Markers to Determine the Contribution of Agricultural Soil to Ambient Fine and Course PM
Investigators: Fraser, Matthew P.
Institution: Rice University
Current Institution: Arizona State University - Main Campus
EPA Project Officer: Chung, Serena
Project Period: December 1, 2004 through November 30, 2007 (Extended to November 30, 2010)
Project Period Covered by this Report: December 1, 2004 through November 30, 2005
Project Amount: $441,299
RFA: Source Apportionment of Particulate Matter (2004) RFA Text | Recipients Lists
Research Category: Particulate Matter , Air Quality and Air Toxics , Air
The overall goal of this proposed research project is to fully develop, employ, and verify a technique to quantify the contribution of agricultural soils entrained in the atmosphere to ambient fine and coarse particulate matter (PM). This project will test the hypothesis that the carbohydrate species present in agricultural soils are chemically distinct from organic components in native soils as a result of soil improvements designed to raise the organic content and productivity of agricultural soil. This project will focus on comparison of the concentrations of marker species in agricultural soils to unimproved soils, and attempt to separate agricultural emissions from other fugitive dust sources (such as windblown dusts, unpaved road dusts, or construction dusts).
Year 1 of this project focused on refining extraction and quantification methods to measure carbohydrate compounds, developing isotopically labelled extraction standards, conducting preliminary extraction of local soil samples, and studying the stability of the proposed molecular markers in laboratory studies.
Four different extraction methods were compared to evaluate the most effective extraction technique to recover the highly polar monosaccharide. The four techniques used to determine the extraction efficiency of sugars spanned from extraction procedures designed to extract highly polar sugars (hot water extraction), to moderately polar solvents suited for single stage extraction of nonpolar and polar species (1:1 methanol:dichloromethane and 1:1 acetonitrile:dichloromethane) to extraction suites developed to sequentially recover nonpolar and polar compounds (hexane followed by 2:1 benzene:isopropanol). For this last method, because hexane is not expected to recovery the polar sugars, only the benzene:isopropanol solvent was used. For this study, 20 mg of dry, sieved agricultural soil collected outside Giddings, TX, was extracted by each method. For recovery of sugars, the hot water extraction technique developed for quantification of sugars from soils was defined as 100 percent recovery, and three specific sugar species were targeted for quantification: sucrose, mycose, and glucose. All sugars were quantified by gas chromatography/mass spectrometry as their trimethylsilylester derivatives. The average recovery for the three sugar species was determined (±10%) to be: 90-94 percent (methanol:dicholormethane); 80-87 percent acetonitrile:dichloromethane, and 74-78 percent benzene:isopropanol. Based on these results, we will use the methanol:dichlo
A preliminary study also was conducted on the presence of sugars in agricultural soil and surrounding native soil. The purpose of this investigation was to determine if monosaccharide could be used to separate the contribution of agricultural soils from native soils in suspended fine and coarse PM. The soil samples were collected from a sorghum field outside Giddings, TX, surrounding unimproved lands to represent native soils, and the vicinity of local roadways (to represent road dusts). Samples were sieved to remove material larger than 0.125 mm and dried at 40°C. The results of this study were mixed: most sugars were enriched in agricultural soils but not to the level required to assume the markers to be unique to agricultural soils. The one sugar that is most promising as a unique marker for agricultural soils was sorbitol. Sorbitol was quantified to be between 0.4 and 1.4 μg g-1 soil for agricultural soils but less than 0.2 μg g-1 for the native soils and road dust samples. Because 0.2 μg g-1 is the determined minimum quantification level, however, this result might be related to method detection limits and is not the most promising conclusion.
The stability of a molecular maker is key to use in tracking emissions from sources to receptor locations: without atmospheric stability, there is no guarantee that preferential loss of the marker species will bias source receptor calculations. For that reason, the stability of sugar species when exposed to representative atmospheric conditions was studied in the laboratory. Solutions of deuterated sugars were prepared to represent the possible conditions in atmospheric liquid water droplets, which include acidic conditions (pH = 2) in the presence of high concentrations of ammonium sulfate and sulfuric acid. Ambient air was bubbled through the solutions for a period of 7 days, and the solutions were exposed to direct sunlight. The results for stability of glucose and mycose are shown in Figures 1 and 2. Both sugars show no degradation over a period of seven days in the laboratory.
Figure 1. Stability Test for Glucose
Figure 2. Stability Test for Mycose
The next step in the research is field sampling: collecting ambient PM samples in regions affected by agricultural emissions and local soil samples. This will allow the direct comparison of sugar content in soils and ambient PM samples. Soil samples will be resuspended and sampled using traditional PM2.5 and PM10 sampling methods to generate a source sample appropriate to compare to ambient PM2.5 and PM10 samples. Until now, soil samples have been sieved only to remove very large material (> 0.125 mm) and resuspension will more accurately represent the chemical composition of soil components that augment local PM2.5 and PM10 concentrations. The resuspension chamber has already been built and tested as part of a separate parallel project.