Emerging Contaminants: Artificial Sweetener Sample Preservation and Palladium Nanoparticle Transport in Porous Media

Emerging contaminants are an increasing concern for regulatory bodies: artificial sweeteners and nanoparticles (NPs) included. Artificial sweeteners are found in domestic waste waters and can be used as tracers of anthropogenic impacts in groundwater and surface water. Collection procedures for aqueous samples for the analysis of artificial sweetener compounds are not delineated in standard published methods. Identifying the acceptable limits for sample collection and storage is important to provide guidelines for studies which will provide cost and time savings for industry and government agencies. Nanoparticles are used in consumer products at an increasing rate. These particles are introduced into the environment through the breakdown of these products or from accidental spills or release during manufacturing or shipping. The effects that NPs have on the environment are unknown both in terms of human and ecological health and their ultimate fate. This thesis describes two experiments on the shared topic of emerging contaminants, (1) a set of batch experiments to determine the effects of sample collection materials and storage conditions on groundwater samples for artificial sweetener analysis and, (2) column experiments to understand the transport of NPs through different porous media using a non-destructive imaging technique. Laboratory batch experiments were conducted to determine appropriate storage methods and sampling materials to be used for groundwater samples for the analysis of artificial sweeteners. The storage methods investigated included: acidification, isolation from light, reduction of temperature, and elimination of headspace. Data were combined to evaluate the frequency distributions of concentrations at each sampling time to delineate the number of samples with analyses that fell outside of the range of 60 – 120 % of the input concentration, a range recommended to be acceptable for interpretation of data in many environmental fate studies. Over the course of the experiment, the measured concentrations for the majority of samples fell within the acceptable range for sample preservation. The only samples with concentrations that fell outside of this range were those that were both acidified and stored at room temperature, irrespective of headspace or exposure to light. The sampling materials investigated included: three types of plastic tubing; polytetrafluoroethylene (Teflon™), styrene-ethylene-butylene co-polymer (MasterFlex™) and polypropylene (PharMed BPT™) tubing, three types of metals; aluminum, steel and stainless steel, and two types of solid plastics; polyamide (Nylon) and polyvinyl chloride. Sampling materials were submerged in simulated groundwater (SGW) to maximize contact of the sampling materials with the water samples. Artificial sweetener concentrations in aqueous samples remained constant over time in all sampling material trials, except with steel, when compared to a control test. The artificial sweetener concentration in groundwater samples in contact with steel decreased by more than 70% for each compound after 289 days (9.5 months). SEM images of the steel surfaces after 90 days (3 months) showed the presence of substantial quantities of iron oxyhydroxide precipitates and TEM images of the solution showed the presence of iron oxyhydroxide particles in suspension. These results suggest that aqueous samples for artificial sweetener analysis can be stored for up to 241 days (8 months), unless they are both acidified and stored at 25 oC, and that artificial sweeteners are stable in the presence of all of the sampling materials tested with the exception of steel. Laboratory column experiments were conducted and the transport of palladium (Pd) NPs was investigated with traditional effluent analysis and novel synchrotron x-ray computerized micro tomography (SXCMT), a non-destructive imaging technique. Five columns were packed with standard Ottawa sand, 98% Ottawa sand with 2% attapulgite clay, and, Borden sand to understand the effect of different porous media on NP transport. The column experiments were conducted with SGW or ultrapure water (UPW). Breakthrough-curve and mass-balance data from direct analysis of Pd in effluent samples suggest that NPs are more retarded in Borden sand than in Ottawa sand. The SXCMT data used to calculate the Pd concentration in individual pores, derived from three-dimensional images of the column suggest that the Pd NP can be transported in porous media and can be quantified by the SXCMT technique

Microbiological and geochemical characterization of As-bearing tailings and underlying sediments

Over the past 100 years, extensive oxidation of As-bearing sulfide-rich tailings from the abandoned Long Lake Gold Mine (Canada) has resulted in the formation of acid mine drainage (pH 2.0-3.9) containing high concentrations of dissolved As (∼400 mg L ), SO , Fe and other metals. Dissolved As is predominantly present as As(III), with increased As(V) near the tailings surface. Pore-gas O is depleted to < 1 vol% in the upper 30-80 cm of the tailings profile. The primary sulfides, pyrite and arsenopyrite, are highly oxidized in the upper portions of the tailings. Elevated proportions of sulfide-oxidizing prokaryotes are present in this zone (mean 32.3% of total reads). The tailings are underlain by sediments rich in organic C. Enrichment in δ S-SO in pore-water samples in the organic C-rich zone is consistent with dissimilatory sulfate reduction. Synchrotron-based spectroscopy indicates an abundance of ferric arsenate phases near the impoundment surface and the presence of secondary arsenic sulfides in the organic-C beneath the tailings. The persistence of elevated As concentrations beneath the tailings indicates precipitation of secondary As sulfides is not sufficient to completely remove dissolved As. The oxidation of sulfides and release of As is expected to continue for decades. The findings will inform future remediation efforts and provide a foundation for the long-term monitoring of the effectiveness of the remediation program. [Abstract copyright: Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.

A cross scale investigation of galena oxidation and controls on mobilization of lead in mine waste rock.

Abstract Galena and Pb-bearing secondary phases are the main sources of Pb in the terrestrial environment. Oxidative dissolution of galena releases aqueous Pb and SO4 to the surficial environment and commonly causes the formation of anglesite (in acidic environments) or cerussite (in alkaline environments). However, conditions prevalent in weathering environments are diverse and different reaction mechanisms reflect this variability at various scales. Here we applied complementary techniques across a range of scales, from nanometers to 10 s of meters, to study the oxidation of galena and accumulation of secondary phases that influence the release and mobilization of Pb within a sulfide-bearing waste-rock pile. Within the neutral-pH pore-water environment, the oxidation of galena releases Pb ions resulting in the formation of secondary Pb-bearing carbonate precipitates. Cerussite is the dominant phase and shannonite is a possible minor phase. Dissolved Cu from the pore water reacts at the surface of galena, forming covellite at the interface. Nanometer scale characterization suggests that secondary covellite is intergrown with secondary Pb-bearing carbonates at the interface. A small amount of the S derived from galena is sequestered with the secondary covellite, but the majority of the S is oxidized to sulfate and released to the pore water