Assessment of heavy metal contamination in river stream sediment in urban area: a case study of Yogyakarta City, Indonesia.

Heavy metals (Pb, Cu, Cd, and Zn) in river sediments from the Winongo, Code, and Gajahwong rivers in Yogyakarta City were investigated. Fifteen samples were collected from each river, systematically from upstream to downstream. Background sediment samples were collected from the furthest upstream point to reflect natural sediment conditions. Inductively coupled plasma-atomic emission spectrometry (ICP-AES) was performed to measure the Fe, Pb, Cu, Cd, and Zn concentrations in the samples. We created distribution graphs to analyze the spatial patterns from upstream to downstream of these metals. Sequential extraction analysis was performed to investigate heavy metals mobility. Several indices were calculated to evaluate heavy metals assessment in the study area, including the enrichment factor (EF), geoaccumulation index (I), risk assessment code (RAC), and pollution load index (PLI). A statistical analysis of variance (ANOVA) was conducted to compare the metal content among the three rivers. Our results revealed that Pb, Cu, Cd, and Zn levels in the sediment samples were generally higher than background values, indicating enrichment in the study area. The distribution patterns revealed an increase in metal content in the middle section of the study area, a densely populated residential and traffic zone with significant human activity, followed by a decrease downstream. The mobility of heavy metals showed that the mobile fraction was dominant in the river stream sediment in the study area, indicating an anthropogenic origin of heavy metals. The RAC calculation shows that the mean RAC value of Pb has a high risk, followed by Cu, Cd, and Zn with medium risk and low risk, respectively. The analysis of the PLI indicated that the primary contributors to sediment contamination in the river sediments in the study area were Pb and Cd, reflected for PLI values exceeding than 1. The EF calculations indicated moderate enrichment for Pb and low enrichment for the other metals, attributing these findings to human activities. The I values suggested moderate pollution for Pb and no pollution for the other metals, particularly Zn. The statistical ANOVA revealed no significant differences in the metal content among the three rivers which most likely resulted from the similar heavy metal origin in the study area.