Prediction of As, Cd, Cr, Hg, Ni, and Se Concentrations in Organic Amendments Using Portable X-ray Fluorescence and Multivariate Modeling

Abstract

Portable X-ray fluorescence (pXRF) has been a widely used technique in various applications. However, its use for the analysis of organic amendments (composts, sewage sludges, organic fertilizers) is scarce. In these matrices, concentrations of some elements are below their detection limit. The objective of this work was to find multiple linear regression equations that were able to predict the aqua-regia-soluble concentrations of the elements As, Cd, Cr, Hg, Ni, and Se using the pXRF readings of other measurable elements as predictor variables. For this, a set of 30 samples of organic amendments (composts, sewage sludges, and organic fertilizers) from the Manure and Refuse Sample Exchange Programme of the Wageningen Evaluating Programs for Analytical Laboratories (MARSEP-WEPAL) was used. Several amendment type-dependent single or multiple linear functions were found based on 1, 2, or 3 predictors. The predictor readings corresponded to the concentration of elements of geogenic (Fe, Si, Ti, Cl, Zr Al, Ca, S, Mn, and Ba), anthropogenic (Zn and Pb), and agricultural (P and K) origin. The regression coefficients of these functions were r = 0.90–0.99; therefore, they allowed for the quantitative determination of the target elements. These results will allow for fast and reliable analysis of organic amendments using pXRF that is valid for quality control in treatment plants.

Portable X-ray Fluorescence Analysis of Organic Amendments: A Review

“…The basic search in SCOPUS provided 23 records of which only 13 papers [28][29][30][31][32][33][34][35][36][37][38][39][40] deals with organic amendments. The other papers focused on soils or archaeological studies and were discarded.…”

“…López et al [33] showed that it was also possible to determine the organic matter content of organic amendment samples from linear regression equations that use the undetermined content data (the difference to 100% of all the elements actually measured) with corrections from elements such as silicon, calcium, or iron. The same authors [36] found multiple linear regression equations that can predict aqua regia-soluble concentrations of the elements As, Cd, Cr, Hg, Ni, and Se using pXRF readings of other measurable elements as predictor variables. These target elements were below the LODs of the pXRF instrument used.…”

“…The most common is to place the dry and finely ground sample in XRF sample cups (Figure 2a,b), which are covered with a sufficiently thin protective plastic film (Figure 2c). The most used films are 4 µm prolene [34,35,37,39] and 4 µm polypropylene [33,36,40,43], although some researchers made the measurements directly in plastic (unspecified) bags [28,31,32] (Figure 2d). The thin film between the sample and the X-ray detector can attenuate or scatter fluorescence signals.…”

Impact of Biochar Amendment on Soil Properties and Organic Matter Composition in Trace Element-Contaminated Soil

“…The reference material SRM 2709 San Joaquin Soil [ 45 ], recommended for baseline trace element concentrations, produced by the National Institute of Standards and Technology (NIST, Spain), was used to assess the accuracy of the pXRF instrument. The measured value for each target analyte should be within ±20% relative difference (RD) of the true value in order to consider the verification check as acceptable [ 46 ].…”

Analysis of Quality of Backyard Compost and Its Potential Utilization as a Circular Bio-Waste Source

“…However, in most cases at a household level and small farms, the analysis of the maturity and readiness of the final product is performed by empirical tests based on the compost maker's senses and experience, or lack thereof. Physical characteristics such as texture, smell, or color are the major indicators, rather than laboratory tests, rendering it a challenge to have consistent and accurate results at all times [69]. Consequently, if the compost does not achieve optimal levels of maturity and stability, it could slow down the plant growth process and therefore be considered of inferior quality compared with store-bought compost [70].…”