Heavy Metal Contamination (Cu and Pb) in Rhizophora apiculata Ecosystems: A Comparative Study between Two Coastal Areas in North Sumatra

Abstract

Mangrove ecosystems are increasingly threatened by heavy metal contamination resulting from rapid industrial and urban development. This study evaluated and compared the concentrations of Copper (Cu) and Lead (Pb) in water, sediment, and different tissues of Rhizophora apiculata collected from Sicanang Island, Belawan, an industrial coastal area, and Sembilan Island, Langkat, a conservation area in North Sumatra. Heavy metal concentrations were determined using Atomic Absorption Spectrophotometry (AAS) to assess their distribution and accumulation within the mangrove ecosystem. The results showed that Pb concentrations in seawater at both sites ranged from 0.25 to 0.26 mg/L, greatly exceeding the Indonesian marine water quality standard of 0.008 mg/L. Overall, metal accumulation was higher in Belawan than in Langkat, reflecting the influence of industrial activities and port operations. Among the plant tissues, fibrous roots accumulated the highest Cu concentration (1.33 mg/kg), followed by stilt roots and stem bark, indicating that R. apiculata effectively retains heavy metals within its root system and limits their translocation to aboveground tissues. These findings demonstrate the serious level of heavy metal pollution in Belawan and confirm the potential of R. apiculata as a reliable bioindicator and a promising species for phytoremediation in contaminated tropical mangrove ecosystems.