Abstract
The determination of heavy metals in soils and organic amendments, such as compost, manure, biofertilizer, and sludge, generally involves the digestion of samples with aqua regia, and the determination of those in the solution using various techniques. Portable X-ray fluorescence (PXRF) has many advantages in relation to traditional analytical techniques. However, PXRF determines the total elemental content and, until now, its use for the analysis of organic amendments has been limited. The objective of this work is the calibration of a PXRF instrument to determine the aqua regia-soluble elemental contents directly in solid samples of organic amendments. Our proposal will avoid the digestion step and the use of other laboratory techniques. Using a training set of samples, calibration functions were obtained that allow the determination of the aqua regia-soluble contents from the PXRF readings of total contents. The calibration functions (obtained by multiple linear regression) allowed the quantitative determination of the aqua regia-soluble contents of Fe, K, P, S, Zn, Cu, Pb, Sr, Cr, and Mn, as well as the organic matter content and a semi-quantitative assessment of Al, Ca, V, Ba, Ni, and As contents. The readings of Si, Fe, Al, Ca, K, or S were used as correction factors, indicating that the calibrations functions found are truly based on the chemical composition of the sample matrix. This study will allow a fast, cheap, and reliable field analysis of organic amendments and of other biomass-based materials.
Highlights
Urban agriculture is a growing activity in many cities on a worldwide scale [1,2]
The range of values for several elements extended over one order of magnitude, which indicated a high variability among the different materials analyzed
The results of this study have shown that in samples of organic amendments, it is possible to determine the contents of aqua regia-soluble elements from the measurements made with a portable XRF analyzer
Summary
Urban agriculture is practised in both developed and developing economies, it can serve different purposes in different places, such as recreation or food security [3]. Under both approaches, there is a revitalised interest in research concerning urban agriculture from a variety of perspectives, including landscaping and urban planning [4], social and economic aspects [5], health and the environment [6], as well as technical subjects [7]. There are many well-documented benefits of urban agriculture: subsistence survival, food sovereignty and security, reduced food transportation distance, carbon sequestration, a potentially reduced urban heat island effect, improved physical and mental health, improved aesthetics, community building, employment. Public Health 2019, 16, 4317; doi:10.3390/ijerph16224317 www.mdpi.com/journal/ijerph
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