Assessment of metal concentrations and variability using censored data analysis in Hu'u rivers, Sumbawa, Indonesia

Abstract

Water quality monitoring is essential for managing watersheds, but values below detection limits are often mishandled, which can hinder interpretation and lead to these measurements to be ignored or discarded. This study aimed to analyze metal concentrations and their variability in freshwater rivers, focusing on datasets with a high proportion of censored values, where many measurements fell below detection limits. The study was conducted in Hu’u, Sumbawa, Indonesia, from 2019 to 2023. Thirteen selected dissolved metals were analyzed: As, Ba, B, Cd, Cr(VI), Co, Cu, Fe, Pb, Mn, Hg, Se, and Zn. Significant differences between watersheds were observed for six metals, including As, Ba, B, Fe, Mn, and Zn (p < 0.05), while no significant seasonal effects were detected for any parameter. The findings indicate that the watersheds are likely impacted by nearby agricultural and domestic activities, as evidenced by higher metal concentrations near settlements and cornfields. Conversely, more remote watersheds with limited agricultural exposure exhibited lower concentrations. This study practically enhances the representation of censored data concentrations with multiple detection limits, not only through the visualization of censored values but also by illustrating data variability.