D. Sarah Garland

Natural organic matter and DBP formation potential in Alaskan water supplies

Disinfection by-products (DBP) are formed when natural organic matter (NOM) in water reacts with a disinfectant, usually chlorine. DBPs are a health risk element and regulated under the Safe Drinking Water Act. A study was conducted to evaluate the characteristics of NOM that contribute to DBPs in 17 different drinking water systems in Alaska. In order to determine the nature of the organic matter contributing to DBPs, DBP formation potential was compared with standard water quality parameters such as UV-254, color and dissolved organic carbon (DOC), as well as pyrolysis-gas chromatography/mass spectrometry (GC/MS). Results showed strong correlations between UV-254 and DBP formation potential for all waters studied. DOC, on the other hand, was less strongly correlated to DBP formation potential. Unlike previous studies, the total trihalomethane and haloacetic acid formation potentials were equal on a mass concentration basis for the waters studied. Pyrolysis-GC/MS indicated that NOM contributing to DBPs were primarily phenolic compounds. This finding was consistent with previous studies; however, unlike other studies, no correlation was found between aliphatic compounds in the raw waters and DBP formation potential.

Heterogeneity of natural organic matter from the Chena River, Alaska.

Water samples were collected in July 2001 from the Chena River in central Alaska. The natural organic matter (NOM) was size fractionated into particulate (POM,>0.45 microm), colloidal (COM,1kDa-0.45 microm) and dissolved (DOM,<1k Da) organic matter fractions, using filtration and ultrafiltration. The size-fractionated organic matter was then analyzed for organic carbon (OC) and nitrogen (N), isotopic (delta13C and delta15N) and molecular composition, using continuous flow isotope ratio mass spectrometry and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Results of phase partitioning showed that, on average, about 6% of OC and 16% of N occurred in the form of POM while 66% of OC and 57% of N occurred in the form of COM, and 28% of the OC and 27% of the N were in the DOM form. Organic matter in the river water was found to be highly heterogeneous in terms of chemical composition and isotopic signatures. The C/N ratio was as low as 16+/-1 in the POM (n=2) to as high as 48+/-1 in the COM (n=3) and 38+/-4 in the DOM (n=3), suggesting a diagenetically younger POM. Values of delta13C increased with decreasing size, varying from -29.59+/-0.45% in the POM to -27.47+/-0.06% in the COM to -16.93+/-0.08% in the DOM. In contrast, values of delta15N decreased with decreasing size, from 2.64% in POM to 1.64% in COM to 1.33% in DOM. These results, together with radiocarbon measurements, suggest a preferential decomposition of lighter C isotope (12C) and heavier N isotopic (15N) from POM to COM to DOM. Results of py-GC/MS showed that the percentage of polysaccharides decreased with decreasing size, further supporting a degradation pathway of NOM from POM to COM and DOM in Chena River waters. More studies are needed to examine the seasonal and spatial variations of size-fractionated organic matter.

Pyrolysis-GC/MS fingerprinting of environmental samples

Abstract This paper describes four recent applications of analytical pyrolysis in environmental science and engineering. In all applications, samples were analyzed in order to provide information about the origin of organic matter or changes to an organic matrix. In the first application, pyrolysis-gas chromatography/mass spectrometry (GC/MS) and pyrolysis-GC/flame ionization detection (FID) were used to help classify the origin of natural organic matter (NOM) buried in the Antarctic. In the second application, pyrolysis-GC/MS was used to compare the recalcitrance of NOM to biological degradation. In the third application, pyrolysis-GC/FID was used to quantitatively differentiate between lipogenic NOM and petroleum contamination in highly organic soil. In the fourth application, pyrolysis-GC/MS was used to fingerprint organic matter in water samples to help describe the relationship between surface water, groundwater and springs in a complex watershed. In all applications the benefits of analytical pyrolysis are still being discovered.

Fingerprinting soil organic matter in the arctic to help predict CO2 flux

Abstract In the past 30 years, the arctic climate has warmed appreciably and there is evidence for a significant polar amplification of global warming in the future. A warming and drying of northern soils could result in an increase in organic matter decomposition and positive feedback to future climate warming. Northern ecosystems have accumulated 25–33% of the worlds soil carbon, much of which is preserved as poorly decomposed plant remains. The soil organic matter (SOM) decomposition rate, however, depends on many variables such as temperature, nutrient availability, pH, oxidation/reduction potential, and chemical composition of the SOM. This paper addresses the effect of SOM composition on CO2 respiration in arctic soil. In order to isolate the effect of SOM composition on respiration rate, 19 soils from the circumpolar arctic were incubated in a 25 °C, nutrient-rich, pH neutral, constantly mixed environment. The SOM composition was studied using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS), an analytical technique that produces a “fingerprint” of SOM. Correlations were made between SOM composition and CO2 respiration rate for the 19 soils. From these data, a model was built to predict respiration rates in soil subjected to similar incubation conditions using py-GC/MS fingerprints. Results go on to compare model predictions of measured respiration in laboratory incubations of 15 soils from four different locations in the Northern and Western Alaska Transects. Predictions for cumulative respiration over a 70-day laboratory respiration test were within 20% of measured values.

Use of dissolved organic matter to support hydrologic investigations in a permafrost-dominated watershed

Abstract Pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) is an analytical tool used to produce a “fingerprint” of dissolved organic matter (DOM) in water. Py-GC/MS fingerprinting was used in this research to lend insight into the complex subsurface hydrology of a permafrost-dominated watershed near Fairbanks, AK. Fingerprinting analysis was conducted on groundwater, artesian spring, and stream samples from two watersheds and used to characterize relationships between the individual samples and between the watersheds. Fingerprinting analyses supported the hypothesis that spring water emerging on opposite sides of a hydraulic divide was of the same origin. Results also supported the hypothesis that individual water samples and their probable origin could be distinguished from one another based on their DOM fingerprint alone. This type of analysis could be used for flow path characterization in other complex watersheds or for characterizing important properties of DOM, such as its potential to mobilize contaminants.

Analytical methods for petroleum in cold region soils

Introduction In order to demonstrate the effectiveness of a bioremediation project, one must have an accurate measure of the contaminants, both at the start of the project and throughout the treatment process. The measurement of the contaminants throughout the process is important to demonstrate that the treatment is successful and to identify advances or set-backs quickly and effectively. Proving the disappearance of hydrocarbons is important to the success of a bioremediation project. An accurate measurement of hydrocarbons and their biodegradation products is needed to confirm that petroleum was actually consumed by bacteria (discussed in Chapter 7, Section 7.3). One method of confirming biodegradation of petroleum is the coupled measurement of biodegradation rates by proxy methods and the disappearance of the contaminant. Biodegradation rates do not, in and of themselves, prove the decomposition of contaminants. Measurement of biodegradation rates, however, can be an easy way to demonstrate that the potential exists for contaminant removal. While measures of biodegradation rates are often used to estimate time to closure for a site, or proof of technology, biodegradation rates can be unreliable. Common measures of aerobic biodegradation are loss of contaminants, oxygen (O 2 ) consumption, and carbon dioxide (CO 2 ) evolution. Unfortunately, the CO 2 can result from non-biological sources (see Chapter 7, Section 7.2.2.2 for additional discussion). Particularly in low pH groundwater, pH adjustment made during bioremediation could result in CO 2 off-gassing from groundwater. Oxygen depletion in the subsurface is also not proof of biodegradation.

Bioremediation of Petroleum Hydrocarbons in Cold Regions: Analytical methods for petroleum in cold region soils

Introduction In order to demonstrate the effectiveness of a bioremediation project, one must have an accurate measure of the contaminants, both at the start of the project and throughout the treatment process. The measurement of the contaminants throughout the process is important to demonstrate that the treatment is successful and to identify advances or set-backs quickly and effectively. Proving the disappearance of hydrocarbons is important to the success of a bioremediation project. An accurate measurement of hydrocarbons and their biodegradation products is needed to confirm that petroleum was actually consumed by bacteria (discussed in Chapter 7, Section 7.3). One method of confirming biodegradation of petroleum is the coupled measurement of biodegradation rates by proxy methods and the disappearance of the contaminant. Biodegradation rates do not, in and of themselves, prove the decomposition of contaminants. Measurement of biodegradation rates, however, can be an easy way to demonstrate that the potential exists for contaminant removal. While measures of biodegradation rates are often used to estimate time to closure for a site, or proof of technology, biodegradation rates can be unreliable. Common measures of aerobic biodegradation are loss of contaminants, oxygen (O 2 ) consumption, and carbon dioxide (CO 2 ) evolution. Unfortunately, the CO 2 can result from non-biological sources (see Chapter 7, Section 7.2.2.2 for additional discussion). Particularly in low pH groundwater, pH adjustment made during bioremediation could result in CO 2 off-gassing from groundwater. Oxygen depletion in the subsurface is also not proof of biodegradation.