Baseline analysis of uranium and heavy metals in soil and air PM collected along US-Highway 89 in Northern Arizona, by using ICP-MS and SEM / EDS-analysis.

摘要

Heavy and transition metals and toxic uranium waste coming from uranium milling facilities in the form of uranium oxide (U3O8) are both a concern in large parts of Northern Arizona, in particular around abandoned uranium mines.12 It was therefore hypothesized that significant levels of U238 at multiple locations along US-Highway 89 could be found, thus strengthening the arguments against initiation of anticipated uranium hauling along the road.42 Not only uranium but the presence of waste rock is also a concern as it can contain radionuclides and heavy metals such as Ni, Cu, As, Mb, Se, Pb, and Cd which can be acid generating depending on the rock's mineral composition. Acid generation from rocks can result in contamination of nearby surface and ground water. Consequently, the purpose of the research was to perform bulk and surficial analyses on soil and air particulate collected along US-Highway 89N for baseline data collection and verifying the existence and levels of U238 and trace metals found. Soil was collected in two rounds for a total of 175 samples whereas air was collected on teflon filters during three different rounds using the MOUDI and SuperSASS passive air samplers. Soil samples were analyzed for levels of U238 (in ppm) using ICP-MS instrumentation and a set of calibration standards whereas the presence of trace metals was analyzed using EDS-analysis. The fine air-PM (PM2.5) collected on teflon filters was analyzed using in-situ LA-ICP-MS analysis in addition to EDS-analysis. The ICP-MS analysis of soil showed that U238 levels of soil collected from both rounds were all below normal background levels (< 3 microg / g of soil) with concentrations being higher for soil collected from the second round. The EDS-analysis of soil from both rounds showed significant weight percentages of Fe, Al, Si, and Ca whereas significant weight percentages of As and W were found in soil from the second round, suggesting they are a result of nearby road traffic. During analysis of fine air-PM, significant weight percentages of Fe and Pb were found, therefore making these two metals the most present ones in the ambient air.