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

Abstract

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.