Historical trend of heavy metals in mangrove sediment from Nusa Lembongan, Bali using ²¹⁰Pb-geochronology

Abstract

Mangrove sediment is a natural filter for retaining pollutants before entering the coastal area and ocean. This study collected sediment cores from a Marine Protected Area (MPA) in Nusa Lembongan, Bali, to establish 210Pb geochronology and heavy metals records. Alpha spectrometry and Instrumental Neutron Activation Analysis (INAA) were used to determine 210Pb and heavy metals (Co, Cr, Fe, Hf, Sb, Sc, Se, and Zn), respectively. The Contamination Factor (CF), Enrichment Factor (EF), and Geo-accumulation Index (I_geo) were assessed. The result shows that 210Pb provided records of sediment accumulation spanning approximately 100 years. The vertical profiles of all heavy metals from the 1910s to the 1930s were slightly constant. From the 1930s to the 1990s, the profiles of Co, Cr, Hf, Sb, Sc, and Zn slightly increased; meanwhile, Fe and Se were slightly constant. From the 1990s to 2017, all heavy metals decreased gradually. Based on the CF, heavy metals Cr, Hf, Sb, Sc, and Zn were categorized as moderate contamination, and Co, Fe, and Se were low contamination. The average EFs of all heavy metals suggested their origin was derived from crustal material. In the I_geo index, only Sb was classified as moderate pollution, while the other heavy metals were not pollutants.