Mapping Heavy Metal Enrichment in Surface Sediments of Catchments Areas of Davao City and Samal Island (IGaCoS): Basis for Resource Management

Heavy metals enter riverine and estuarine environments through both natural processes and human activities, with sediments acting as primary sinks where these contaminants accumulate over time. Their presence at varying depths raises concerns about pollution sources, concentration levels, and spatial patterns. This study presents a spatial assessment of selected heavy metals (Cd, Cu, Fe, Pb, Mn, As, Hg, Cr, and Zn) in surface and bottom sediments collected from five sampling sites across the ecological catchments of Davao City and the Island Garden City of Samal (IGaCoS), covering approximately 354 km2. Metal concentrations were analyzed using Flame Atomic Absorption Spectrometry (FAAS). Results indicate higher levels of As (0.103 mg/kg), Cu (195.11 mg/kg), Cr (69.92 mg/kg), Pb (27.59 mg/kg), Zn (170.0 mg/kg), and Mn (373.78 mg/kg) in industrial zones of Davao City compared to residential, riverine, and recreational areas. Spatial distribution patterns suggest that human activities are the dominant source of metal enrichment in these environments. The findings provide baseline data that can support water resource management planning and help address potential ecological risks within the Davao-IGaCoS catchment system.