Laser Induced Breakdown Spectroscopy applied to the determination of selected nutrient elements and heavy metals in composts used as soil amendment

Laser-Induced Breakdown Spectroscopy (LIBS) is a fast and reliable technique suitable for the simultaneous qualitative and quantitative analysis of major and trace elements in samples of various nature and origin. In last decades, the use of compost as an organic amendment has become a very common, cheap and sustainable agricultural practice to provide soil with organic matter and nutrients, although the content of heavy metals in compost may often represent a risk for its agronomic use. In the present work, the detection and concentration of selected macro- and micronutrients and heavy metals, including Al, Ca, Cr, Cu, Fe, K, Mg, Mn, Na, Pb, Sr, and Zn, in two commercial composts of different origin have been measured comparatively by LIBS and conventional Induced Coupled Plasma - Optical Emission Spectroscopy (ICP-OES) techniques. In general LIBS data are in good agreement with the corresponding ICP-OES data. The best correlation of LIBS values with ICP-OES values are obtained at the laser wavelength of 532 nm for Al, Ca, K, Mg, Mn and Na, and at the wavelength of 355 nm for Cr, Cu, Fe, Pb, Sr and Zn. In conclusion, our results confirm the feasibility of LIBS for the quantitative analysis of several elements in composts with several advantages including no need of (or minimal) sample preparation, rapidity and relatively low costs, showing promising for further applications. However, a number of instrumental and substrate factors still need to be optimized to obtain a better performance for accuracy and precision of LIBS analysis for each element.