Investigating the relationship between heavy metals concentration and soil fractions in Benoa Bay, Indonesia

Abstract

Heavy metal contamination in coastal environments is a persistent concern due to the ability of soils to act as longterm sinks for pollutants such as lead (Pb), cadmium (Cd), copper (Cu), and chromium (Cr). This study aims to investigate the relationship between heavy metal concentrations and soil particle size distribution in Benoa Bay, a semi-enclosed tropical bay in southern Bali, Indonesia. A total of nine surface soil samples were collected from different environmental settings, including areas near landfills, ports, mangroves, and open coasts. Soil fractions were analyzed using dry sieving and the pipette method, while metal concentrations were measured using flame Atomic Absorption Spectrophotometry (AAS) following wet acid digestion. Pearson correlation analysis was used to examine the statistical relationships between soil particle size and heavy metal content. The results showed that cadmium levels exceeded the ANZECC/ARMCANZ soil guideline (1.5 mg/kg) at several locations (S3, S5, and S9), indicating ecological risk. Strong positive correlations were found between heavy metals and fine soil fractions (fine clay: r = 0.92 for Cd; medium silt: r = 0.98 for Cr), while coarse fractions like gravel showed strong negative correlations (e.g., r = –0.92 for Cr). This study is limited to surface soils (0–30 cm) and does not address vertical distribution or seasonal variations. However, it provides important baseline data for environmental monitoring and pollution management. The findings have practical value in identifying contamination hotspots, informing landfill leachate control, and guiding soil remediation planning. This research also offers a deeper understanding of how soil texture influences metal retention, which is critical for developing effective coastal management strategies. This study is original in its integrated approach to combining granulometric and geochemical analysis in a tropical bay setting and highlights the significance of particle size in controlling heavy metal mobility and accumulation.