Browsing by Author "Berens, Matthew"

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    Assessing the Degradation of Munitions Compounds by Compound Specific Isotope Analysis in Natural and Engineered Environments (2021-11-19)
    (2021) Berens, Matthew; University of Minnesota Duluth. Department of Chemistry and Biochemistry
    Iron-bearing minerals are important reductants in the contaminated subsurface, but their availability for the reduction of anthropogenic pollutants is often limited by competition with other electron acceptors including microorganisms and poor accessibility to Fe(II) in complex hydrogeologic settings. The supply of external electron donors through in situ chemical reduction (ISCR) has been proposed as one remediation approach, but the quantification of pollutant transformation is complicated by the perturbations introduced to the subsurface by ISCR. Here, we evaluate the application of compound specific isotope analysis (CSIA) for monitoring the reduction of 2,4-dinitroanisole (DNAN), a component of insensitive munitions formulations, by mineral-bound Fe(II) generated through ISCR of subsurface material from two field sites. Electron balances from laboratory experiments in batch and column reactors showed that 3.6% to 11% of the total Fe in the sediments was available for the reduction of DNAN and its partially reduced intermediates after dithionite treatment. The extent of DNAN reduction was successfully quantified from its N isotope fractionation measured in the column effluent based on the derivation of a N isotope enrichment factor, ?N, derived from a comprehensive series of isotope fractionation experiments with numerous Fe(II)-bearing minerals as well as dithionite-reduced subsurface materials. Our observations illustrate the utility of CSIA as a robust approach to evaluate the success of in situ remediation through abiotic contaminant reduction.
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    Exploring the Reactions and Presence of Munitions Compounds and Insecticides in Aquatic Systems
    (2020-09) Berens, Matthew
    Organic chemicals are ubiquitous in the environment and are responsible for the widespread pollution of many natural and engineered ecosystems including surface and groundwater, soils and sediments, and municipal water systems. In the environment, these chemicals are toxic to many species of plants, animals, and humans. There is still much to be understood, however, about the occurrence and fate of chemical pollutants and what approaches can be taken to mitigate their environmental impacts. In this dissertation, two classes of chemical pollutants, nitroaromatic compounds (NACs) and neonicotinoid insecticides, were investigated to address these knowledge gaps. An analytical technique was developed to better quantify the extent of degradation of the novel munitions compound, 2,4-dinitroanisole (DNAN), by naturally occurring iron oxide minerals across a wide range of environmental conditions. This research incorporated the use of compound specific isotope analysis (CSIA) and revealed that stable isotope ratios of nitrogen and carbon during DNAN reduction are not affected by the type of iron oxide mineral, the presence of natural organic matter, and repeated exposures to a pollutant. Across all experiments, N-isotope enrichment factors (εN), ranged from -11.1 ± 4.3‰ to -21.5 ± 2.6‰ with an overall average of -14.9 ± 1.3‰. These values resulted in N and C apparent kinetic isotope effects (AKIEs) of 15N-AKIE = 1.0317 ± 0.0064 and 13C = 1.0008 ± 0.0005 that are typical for abiotic nitro-group reduction of NACs by iron-bearing minerals (15N-AKIE = 1.030–1.045 and 13C ~ 1.000). The results of CSIA were then used to generate a model to estimate the extent of DNAN degradation from measured N-isotope ratios. The model produced accurate predictions with an average error in predicted vs. actual values of 0.091 ± 0.063 as c/c0. Neonicotinoid concentrations were measured in water samples collected from lakes, rivers, streams, groundwater wells, and treated wastewater effluents throughout the state of Minnesota. These results showed that neonicotinoid concentrations were predominantly affected by the type of land use and the time of year for which they were applied. Neonicotinoid concentrations were the highest in agricultural watersheds (median = 12 ng/L) followed by urban (2.9 ng/L) and undeveloped watersheds (1.9 ng/L). Clothianidin was the most frequently detected neonicotinoid in agricultural areas, and imidacloprid was most frequently detected in urban waters. In addition, concentrations were typically greatest at the beginning of the year and decreased thereafter. The potential impacts of neonicotinoids on several planktonic assemblages were assessed, but no significant correlations were observed between neonicotinoid concentrations and plankton population sizes. The overall results of this dissertation showed that while there are many factors that drive environmental pollution, measurements, and predictions of the extent of contamination will continue to improve.