Microplastic contamination in biota and the surrounding environment in the Bang Pu mangrove forests, Samut Prakan Province, Thailand

The widespread presence of tiny plastic particles, known as microplastics (MPs), has been reported for years. The mangrove ecosystem, considered the potential receptacle of MPs between terrestrial and marine ecosystems, received less attention than other ecosystems. The MPs investigation in mangrove forests is mainly conducted in sediment, followed by water and biota. This study examines the MPs contamination in biota and their adjacent environment in the Bang Pu mangrove forests (BPMFs), Samut Prakan province, Thailand. BPMFs are known as one of the crucial remnant mangrove and mudflat habitats along the Inner Gulf of Thailand. BPMFs is nearby the Chao Phraya River Estuary (CPRE). BPMFs have been invaded by enormous waste from both marine- and land-based sources for years. So far, no studies have investigated MPs contamination in mangrove animals or surrounding environments, such as surface water and sediment, in BPMFs. Thai vinegar crab (Episesarma mederi) is one of the most common mangrove crabs in BPMFs. Thai vinegar crab is a bioindicator in the mangrove forest as they maintain nutrient cycling in the food chain. Their feeding behavior and burrowing construction lead to the exposure of ubiquitous MPs in their surrounding environment. Thai vinegar crab prefers leaves of mangrove trees, such as grey mangrove (Avicennia marina (Forssk.) Vierh.), one of the most widespread plants in the mangrove forests. Giant mudskipper (Periophthalmodon schlosseri) is the most common mudskippers in BPMFs. This carnivore mudskipper is a predator for mangrove crabs in BPMFs. Three species for the producer to the second consumer were selected to examine MPs contamination. Their habitats also play a vital role in MPs exposure to the surrounding environment. In this study, mangrove biota and their surrounding environment (surface water and sediment) from BPMFs were collected. MPs contamination in Thai vinegar crabs (TVCs), giant mudskippers (GMs), and their adjacent environment from the upper and lower BPMFs in the rainy and dry seasons were examined. Due to the limitation of plant digestion, MPs in the leaves of grey mangroves cannot be examined. Fenton’s reagent was used for the digestion of surface water and sediment. Two-step digestion with 10% potassium hydroxide (KOH) and Fenton's reagent was applied to animal samples. Density separation was performed using sodium iodide (NaI) solution. Polymer identification was conducted using Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and micro-Fourier Transform Infrared Spectroscopy (micro-FTIR). MPs were detected in TVCs, GMs, and their adjacent environment. MPs abundance was 7.5 ± 3.8 to 15.9 ± 6.7 items/individual in TVCs and 6.2 ± 5.0 to 10.6 ± 2.6 items/individual in GMs, 24 ± 3 to 37 ± 1 items/L in surface water, and 2 ± 1 to 5 ± 4 items/g wet weight in surface sediment. MPs were also found in the remaining soft tissues of TVCs and fillets of GMs. MPs in size ranges of 0.3 – 0.5 and 0.05 – 0.3 mm were mainly detected in all samples. The main morphology in the rainy season was fiber, while in the dry season differed in each sample. Most MPs were transparent. Polyethylene and polypropylene were observed as the dominant polymer types in all samples. The mean number of MPs in TVCs was higher than in GMs in both sites and seasons. Bioaccumulation in GMs was not detected. The translocation of MPs in the food chain requires further studies. This study indicated the imperiled status of MPs contamination in TVCs and GMs with unhealthy adjacent environments. Moreover, MPs contaminated in edible compartments of both animals, which can alert food safety.