Mangroves are areas that connect the land and sea, and are important to the ecosystem. They are important places for food sources and the habitat of aquatic fauna in the tidal areas. However, the existence of plastic debris poses a risk to the aquatic environment. This study aimed to investigate the accumulation of microplastics (MPs) in sediment cores from two mangrove areas. The first mangrove area is in the outer section of the Songkhla lagoon (SK), while the second is in the coastal area of Pattani province (PN). Sediment core sampling was performed from SK = 8 stations and PN = 5 stations. Surface enrichment of MP was observed, especially in sediments of 0–4 cm. MPs were found throughout the depth in both areas, while fewer MPs were found in deeper sediment core layers (p < 0.05) at some stations inside the mangrove zone. Simple linear regression of the observed MPs and distance in the horizontal were found to be significant at SK within the mangrove zone with r² = 0.79 (p < 0.05). MP fibers were the most commonly found MP type in both areas and were less than 1 mm. Blue and black MPs were the most abundant colors found in both areas. The six polymer types reported in this study comprised polyethylene, rayon, rubber, styrene, Poly (vinyl acetate), and paint. The findings of the present study suggest that long-term monitoring of marine debris along coastlines is necessary to help improve national policies and measures related to marine plastic debris.

The present study determined the metal levels in surface sediment and in soft tissue of the Strombus canarium at Libong Island, Thailand, and estimated the possible risk from consuming the shellfish. The mean concentrations of the metals Fe, Cu, Co, Pb, Mn, and Ni in sediment were 2711.94 ± 1424.83, 0.47 ± 0.37, 0.11 ± 0.09, 1.32 ± 1.48, 40.41 ± 16.12, and 2.75 ± 4.04 µg/g, respectively, and are below the sediment quality guidelines. The enrichment factor (EF) and geoaccumulation index (Igeo) showed that the sediment conditions ranged from “no pollution” to “moderate contamination”. The mean concentrations in Strombus canarium had rank order Fe > Mn > Cu > Ni > Co > Pb. The bioaccumulation (BSAF) suggests that the Strombus canarium accumulated Cu and Co the most. The estimated daily intakes of these metals through shellfish consumption were below the oral reference dose (Rfd) and the calculated target hazard quotients (THQ) were less than 1. The results from this study inform about the background levels of metals in the sediment and in Strombus canarium species at Libong Island. In addition, these data might help ensure that the consumption of shellfish in this area remains safe.