Heavy metal accumulations in tropical seaweed and seagrass species as the basis of an ecological risk assessment.

Human activities often cause heavy metal pollution in coastal ecosystems. This study investigates the potential of seaweeds and seagrasses to act as bioindicators of heavy metal contamination and coastal ecosystem status. The investigation was based on the calculation of ecological indexes, including the geoaccumulation index (Igeo), enrichment factor (EF), metal pollution index (MPI), and bioconcentration factor (BCF). Surface sediment, and macrophyte samples were collected from three different disturbed locations along the coast of the Andaman Sea. Based on the Igeo, EF and MPI, coastal sediment from Libong Island showed moderate contamination by most heavy metals while coastal sediment from Lidee Island and Tangkhen Bay showed low to moderate contamination. In all the studied areas, the most present heavy metals were As and Cd, possibly from herbicides, pesticides, and sewage released from the mainland. Our results revealed that the bioaccumulation of heavy metals varied within seagrass and seaweed species, and in different areas. Even where seagrasses and seaweeds were found in the same area, they presented different levels of accumulation based on the BCF value. This study found that the seagrass Thalassia hemprichii and the seaweed Padina sp. could act as promising bioindicators of heavy metal contamination in the studied areas. Future research should focus on investigating the effects of heavy metal contamination on their morphology and physiology under laboratory conditions.