Assessing Metal Accumulation in Biological Systems and the Transformations of Trace Organic Contaminants in the Environment Using Mass Spectrometric Methods
Mullin, Elizabeth J.
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Industrialization has had a huge impact on the quality of the environment. Contaminants enter the environment via either natural or anthropogenic sources including wastewater treatment plants (WWTPs), agricultural practices, and mining. The focus of this work is to monitor the fate and transformation of antimicrobials, hormones, and metals from these sources. The first part of this work focuses on measuring the accumulation of manganese (Mn) in rat brain and ear tissue with oral exposure by inductively coupled plasma mass spectrometry (ICP-MS). Mn, iron (Fe), copper (Cu), and zinc (Zn) are essential transition metals for mammals that are required in trace amounts, however chronic exposure to high concentrations can cause severe and irreversible neurotoxicity. Since prolonged exposure to Mn leads to manganism, a disorder exhibiting a diverse array of neurological impairments progressing to a debilitating and irreversible extrapyramidal condition symptomatically similar to Parkinson’s disease, we measured the concentrations of Mn as well as Fe, Zn, and Cu in three regions of the brain (globus pallidus, striatum, and inferior colliculus) and three regions in the cochlea (stria vascularis, basilar membrane, and modiolus) under normal conditions (untreated), or after 30 or 60 days of oral administration of Mn (10 mg/mL ad libitum). Under normal conditions, Mn, Zn and Fe were typically higher in the cochlea than in the three brain regions, whereas Cu was detected at equal to or lower concentrations. Oral treatment with Mn for 30 or 60 days resulted in 20-75 % increases in Mn concentrations in both cochlea and brain samples, but had little effect on Cu and Fe levels. In contrast, Zn levels decreased (20-80 %) with Mn exposure. The results show how prolonged oral Mn-ingestion affects the concentrations of Mn, Cu, Zn, and Fe, in the three regions of the cochlea, the inferior colliculus in the auditory midbrain and the striatum and globus pallidus, two regions implicated in Parkinson’s disorder. The Mn-induced changes in the concentrations of Mn, Cu, Zn, and Fe may provide new insights on the relevance of these metals to the neurotoxicity of Mn, and the transport and accumulation of these metals in cochlea and brain. The second part of this work focuses on the development of a laser ablation ICP-MS (LA-ICP-MS) method to determine the spatial distribution of metals in brain tissue. Mass spectrometry imaging allows for the direct analysis of solid samples and provides more information about elemental distribution than traditional digestion procedures. A LA-ICP-MS method was optimized and validated prior to its application on the analysis of metals in brain tissue samples. The optimized laser parameters were set to ablate the entire 40 μm thick sample while minimizing the amount of slide matrix ablated. Optimized laser parameters for the 213 nm Nd:YAG laser consisted of 40% energy, repetition rate of 2 Hz, spot size of 75 μm square, and a scan speed of 75 μm/sec. These parameters as well as being able to ablate the sample using a raster scan method rather than ablate each spot individually, made analysis time 20 times more efficient. Imaging software was utilized to construct images of rat brain tissue to determine spatial distribution of Mn, Fe, Zn, Cu in untreated and Mn-exposed tissue. Standards prepared by spiking sheep brain with metal salts were used for quantification. Results show that Mn, Fe, and Zn are evenly distributed throughout the tissue samples while Cu is primarily located along the edges of the tissue. (Abstract shortened by ProQuest.)