# Portable X-ray Fluorescence Analysis of Organic Amendments: A Review
### Legislative Framework  
This section summarizes the current regulations in the European Union regarding organic amendments, organic fertilizers, growing media, and sewage sludge. The limit values for potentially toxic elements (PTEs) (Table 1) have been taken from these regulations and will be compared in the results section with the LOQ.  
It is necessary to indicate here that XRF is not considered in European legislation as an accepted procedure for the analytical characterization of organic amendments and fertilizers. It is also an unknown procedure for use in compost and other organic amendments in scientific and technical publications, with a few exceptions that will be cited in this review. An example is a recent report by [PERSON] et al. [16] which indicated that heavy metal contents in the compost can be determined on a dried and ground sample after the destruction of the sample in strong acids, e.g., _aqua regia_. This report, while mentioning spectroscopic methods as indicated before, only considers near-infrared spectroscopy (NIRS) and Fourier-transform infrared spectroscopy (FTIRS).  
\begin{table}
\begin{tabular}{c c l} \hline \hline  & **Limit** & **Product** \\ \hline As & 40 & Organic fertilizer, organo-mineral fertilizer, organic soil improve, growing media, & [23] \\  & & plant biostimulant \\ \hline  & 1.5 & Organic fertilizer \\  & 3 & Organo-mineral fertilizer (P\({}_{2}\)O\({}_{5}\) \(<\) 5\%) & [23] \\  & 2 & Organic soil improve & [23] \\  & 1.5 & Growing media & [23] \\  & 1.5 & Plant biostimulant \\  & 1 & Ecolabel for soil improves, mulch and organic constituents of growing media & [24] \\  & 3 & Ecolabel for growing media, including mineral growing media & [24] \\  & 20–40 & Sewage sludge & [25] \\ \hline Cr & 100 & Ecolabel for soil improvers, mulch and organic constituents of growing media & [24] \\  & 150 & Ecolabel for growing media, including mineral growing media & [24] \\ \hline  & 300 & Organic fertilizer, organic soil improver & [23] \\  & 600 & Organo-mineral fertilizer, plant biostimulant & [23] \\  & 200 & Growing media & [23] \\  & 100 & Ecolabel for soil improvers, mulch and organic constituents of growing media, and growing media, including mineral growing media & [24] \\  & 1000–1750 & Sewage sludge & [25] \\ \hline  & 1 & Organic fertilizer, organo-mineral fertilizer, organic soil improver, growing medium, & [23] \\ Hg & & Ecolabel for soil improvers, mulch and organic constituents of growing media, and growing media, including mineral growing media & [24] \\  & 16–25 & Sewage sludge & [25] \\ \hline  & 50 & Organic fertilizer, organo-mineral fertilizer, organic soil improver, growing medium, & [23] \\ Ni & 90 & Ecolabel for soil improvers, mulch and organic constituents of growing media, and growing media, including mineral growing media & [24] \\  & 300–400 & Sewage sludge & [25] \\ \hline  & 120 & Organic fertilizer, organo-mineral fertilizer, organic soil improver, growing medium, & [23] \\ Pb & 100 & Ecolabel for soil improves, mulch and organic constituents of growing media & [24] \\  & 150 & Ecolabel for growing media, including mineral growing media & [24] \\  & 750–1200 & Sewage sludge & [25] \\ \hline  & 800 & Organic fertilizer, organic soil improver & [23] \\  & 1500 & Organo-mineral fertilizer, plant biostimulant & [23] \\ Zn & 500 & Growing media & [23] \\  & 300 & Ecolabel for soil improvers, mulch and organic constituents of growing media, and growing media, including mineral growing media & [24] \\  & 2500–4000 & Sewage sludge & [25] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Maximum allowable concentrations (mg kg\({}^{-1}\)) of potentially toxic elements in organic amendments in the European regulations.