Distribution and Identification of Heavy Metals in Medicinal Herbs Along a River Channel Using LIBS Spectroscopy

Abstract

This study presents an ecotoxicological assessment of two medicinal plants (Hypericum aciculare and Achyrocline alata) collected in the upper micro-watershed of the Las Gradas River, located in Chugur, Cajamarca, using Laser-Induced Breakdown Spectroscopy (LIBS). Plant samples were oven-dried at 70°C, ground, and sieved to produce pellets. These were then analyzed with a LIBS system covering a spectral range from 181 to 1100 nm. The study aimed to identify exogenous contamination using elemental profiles reported by NIST and AndesLIBS software. Mercury (Hg) and lead (Pb) were the target elements. The spectral data were processed using supervised Principal Component Analysis (PCA) for decomposition into principal components. All statistics were performed in R. The results demonstrate that LIBS is a rapid and effective technique for analyzing organic substances, revealing characteristic emission peaks in experimental assays. Furthermore, semi-quantitative analysis confirmed the presence of two heavy metals, mercury (Hg) and lead (Pb). Their distribution varied among sampling sites, possibly due to anthropogenic activities. PCA enabled quick discrimination among samples using fused LIBS data, highlighting this method's potential for future studies. LIBS is a reliable, rapid technique for detecting heavy metal contamination in underexplored species, such as medicinal herbs.