Metrological Aspects of Platinum Group Elements Atmospheric Deposition in Roadside Tree Leaves: Uncertainties and Environmental Data Interpretation

Atmospheric pollution is one of the main concerns in modern society and it poses a direct impact on the environment and public health. Therefore, an enormous number of environmental samples are collected and analyzed around the world on a daily basis. In order to obtain reliable and comparable results, it is paramount to establish a well-defined protocol for environmental sampling and analysis considering the more relevant variations associated with these activities and the processes that affect the distribution of the analytes in the environment. The present case study proposes a protocol to determine the amounts of the platinum group elements (PGEs: palladium, platinum, rhodium) due to atmospheric deposition in Tibouchina granulosa leaves that takes into account the estimation of measurement uncertainties including the sampling component. The samples were collected at a standardized height, in the second node of the branches, with approximately 2 months of environmental exposure. The particulate matter was extracted from the leaf surface by acid leaching using an ultrasonic bath followed by aqua regia digestion. Platinum (Pt), palladium (Pd), and rhodium (Rh) were separated from impurities by cation chromatography and analyzed by ICP-MS. The measurement uncertainties found were in the range of 24 to 33% while the analytical uncertainty lied between 4.5 and 7.3%. The results were expressed regarding metrological aspects, with the expanded uncertainty, within a 95% confidence level, to allow for a more robust interpretation of their relevance in the environmental and regulatory context.