The comparative plastisphere microbial community profile at Kung Wiman beach unveils potential plastic-specific degrading microorganisms.

Background: Plastic waste is a global environmental issue that impacts the well-being of humans, animals, plants, and microorganisms. Microplastic contamination has been previously reported at Kung Wiman Beach, located in Chanthaburi province along with the Eastern Gulf of Thailand. Our research aimed to study the microbial population of the sand and plastisphere and isolate microorganisms with potential plastic degradation activity. Methods: Plastic and sand samples were collected from Kung Wiman Beach for microbial isolation on agar plates. The plastic samples were identified by Fourier-transform infrared spectroscopy. Plastic degradation properties were evaluated by observing the halo zone on mineral salts medium (MSM) supplemented with emulsified plastics, including polystyrene (PS), polylactic acid (PLA), polyvinyl chloride (PVC), and bis (2-hydroxyethyl) terephthalate (BHET). Bacteria and fungi were identified by analyzing nucleotide sequence analysis of the 16S rRNA and internal transcribed spacer (ITS) regions, respectively. 16S and ITS microbiomes analysis was conducted on the total DNA extracted from each sample to assess the microbial communities. Results: Of 16 plastic samples, five were identified as polypropylene (PP), four as polystyrene (PS), four as polyethylene terephthalate (PET), two as high-density polyethylene (HDPE), and one sample remained unidentified. Only 27 bacterial and 38 fungal isolates were found to have the ability to degrade PLA or BHET on MSM agar. However, none showed degradation capabilities for PS or PVC on MSM agar. Notably, Planococcus sp. PP5 showed the highest hydrolysis capacity of 1.64 ± 0.12. The 16S rRNA analysis revealed 13 bacterial genera, with seven showing plastic degradation abilities: Salipiger, Planococcus, Psychrobacter, Shewanella, Jonesia, Bacillus, and Kocuria. This study reports, for the first time of the BHET-degrading properties of the genera Planococcus and Jonesia. Additionally, The ITS analysis identified nine fungal genera, five of which demonstrated plastic degradation abilities: Aspergillus, Penicillium, Peacilomyces, Absidia, and Cochliobolus. Microbial community composition analysis and linear discriminant analysis effect size revealed certain dominant microbial groups in the plastic and sand samples that were absent under culture-dependent conditions. Furthermore, 16S and ITS amplicon microbiome analysis revealed microbial groups were significantly different in the plastic and sand samples collected. Conclusions: We reported on the microbial communities found on the plastisphere at Kung Wiman Beach and isolated and identified microbes with the capacity to degrade PLA and BHET.

Equilibrium partitioning approach for metal toxicity assessment in tropical estuarine sediment of Bandon Bay, Thailand.

An equilibrium partitioning approach (EqPA) was employed to evaluate the metal toxicity and define sediment quality guidelines (SQGs) for arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn), and mercury (Hg) in the cockle cultivated areas located in Bandon Bay, Thailand. An assessment of metal toxicity using the [∑SEM]-[AVS] and [∑SEM]-[AVS]/foc models indicated no adverse effect on benthic organisms. The normalized total metal concentrations in this area were below the established SQG values for As, Cd, Cu, Ni, Pb, Zn, and Hg, namely respectively 21.3, 0.8, 84.6, 36.0, 34.6, 440.9 mg/kg dry weight, and 49.3 µg/kg dry weight on sand and calcium carbonate free with 1 % total organic carbon basis, suggesting low metal toxicity. This study provides locality adapted SQG values for supporting sediment quality management specifically in Bandon Bay, potentially serving as a model for other coastal areas.

Weekly variations of nutrients and their associations with phytoplankton blooms in the urban coastal waters of Andaman Sea coast: A case study in Patong Bay, Phuket, Thailand.

Nutrient inputs to coastal waters are among the main contributors to phytoplankton blooms that can damage coastal ecosystems. To understand the main causal factors and timing of phytoplankton blooms in Patong Bay, where phytoplankton blooms have frequent occurred for the last decade, variations in phytoplankton abundance and the dissolved inorganic nutrients (nitrogen (DIN), phosphorus (DIP), and dissolved silica (DSi)) were monitored weekly from December 2021 to December 2022. The results revealed that ratios of DIP and DSi to DIN in seawater had increased rapidly in approximately 1-7 days prior to the blooms of Chaetoceros and Eunotogramma. This suggests that the diatom blooms in this area are significantly controlled by an excess of DIP and DSi, in otherwise appropriate environmental conditions. Our findings provide a thorough understanding of the role of excess nutrients on phytoplankton blooms in urban coastal waters, supporting informed coastal management actions.

Heavy metal bioaccumulation and risk assessment in fishery resources from the Gulf of Thailand.

The muscle tissues of 19 fish species, two crab species, and one shrimp species collected from the Gulf of Thailand (GoT) were analyzed to determine the levels of heavy metals, including Cu, Zn, Fe, Mn, Ni, Pb, Cd, and Hg. The results revealed that the mean concentrations of the heavy metals, in descending order, were Zn > Cu > Fe > Cd > Hg > Mn > Pb > Ni. Among the examined metals, zinc was found to be the most prevalent in fish tissues. Based on the risk assessment indices, the estimated average daily doses (ADD) of the heavy metals were found to be below the provisional tolerable daily intake (PTDI) recommended by the joint Committee of the Food and Agriculture Organization (FAO) and the World Health Organization (WHO) on food contaminants. The results of the target cancer risk analysis revealed no related cancer risk from the consumption of the fishes considered for the study. However, the target hazard quotient (THQ) values exceeded the threshold of 1 (THQ > 1) specifically for mercury in Gymnothorax spp. and Terapon spp. Furthermore, the calculated hazard index (HI) values for fish muscles were all below 1, indicating that there is no significant health risk for humans at the current consumption rates, except in Terapon species for both normal and habitual consumers. Notably, habitual consumers of Gymnothorax species showed the highest HI value (>1), suggesting potential long-term effects on human health when consuming larger quantities of these fishes.

Riverine and submarine groundwater nutrients fuel high primary production in a tropical bay.

River discharge has long been recognized as a major source of nutrients supporting high primary production (PP) in Bandon Bay, while submarine groundwater discharge (SGD) and atmospheric deposition have largely been overlooked. In this study, we evaluated contributions of nutrients via river, SGD and atmospheric deposition, and their roles on PP in the bay. Contribution of nutrients from the three sources during different time of the year was estimated. Nutrients supply from Tapi-Phumduang River accounted for two-fold the amount from SGD while very little supply was from atmospheric deposition. Significant seasonal difference in silicate and dissolved inorganic nitrogen were observed in river water. Dissolved phosphorous in river water was mainly (80 % to 90 %) of DOP in both seasons. For the bay water, DIP in wet season was two-fold higher than in dry season while dissolved organic phosphorus (DOP) was only one half of those measured in dry season. In SGD, dissolved nitrogen was mostly inorganic (with 99 % as NH4+), while dissolved phosphorous was predominantly (DOP). In general, Tapi River is the most important source of nitrogen (NO3-, NO2-, and DON), contributing >70 % of all considered sources, especially in wet season, while SGD is a major source for DSi, NH4+ and phosphorus, contributing 50 % to 90 % of all considered sources. To this end, Tapi River and SGD deliver a large quantity of nutrients and support high PP in the bay (337 to 553 mg-C m-2 day-1).

Preindustrial levels and temporal enrichment trends of mercury in sediment cores from the Gulf of Thailand.

Four sediment cores in the middle of Gulf of Thailand (GOT) and one core close to Bang Pakong River mouth were examined for total mercury (T-Hg) using direct thermal decomposition coupled with the atomic absorption spectrometry (DTD-AAS) method and acid digestion (acid-CVAAS) method, and sediment chronologies using 210Pb dating. T-Hg in the river mouth core ranged 44.49-52.76 µg/kg and higher than the cores from the middle of GOT (18.26-36.68 µg/kg). The age span obtained from the cores dated back to the 1940s with the sediment accumulation rates of 0.15-0.76 cm/year. The preindustrial levels of T-Hg showed an initial slow increase followed by a rapid elevation since the 1960s which marked the start of the industrialized period in the country. To this end, we posit that T-Hg in the GOT sediment can be attributed to not only land-based sources but also offshore activities including petroleum exploration and frequent accidental oil spills.

Bacterial community shifts in a di-(2-ethylhexyl) phthalate-degrading enriched consortium and the isolation and characterization of degraders predicted through network analyses.

Di-(2-ethylhexyl) phthalate (DEHP) is an extensively used and toxic phthalate plasticizer that is widely reported in marine environments. Degradation of DEHP by bacteria from several environments have been studied, but little is known about marine sediment bacteria that can degrade DEHP and other phthalate plasticizers. Therefore, in this study, we enriched a bacterial consortium C10 that can degrade four phthalate plasticizers of varying alkyl chain lengths (DEHP, dibutyl phthalate, diethyl phthalate, and dimethyl phthalate) from marine sediment. The major bacterial genera in C10 during degradation of the phthalate plasticizers were Glutamicibacter, Ochrobactrum, Pseudomonas, Bacillus, Stenotrophomonas, and Methylophaga. Growth of C10 on DEHP intermediates (mono-ethylhexyl phthalate, 2-ethylhexanol, phthalic acid, and protocatechuic acid) was studied and these intermediates enhanced the Brevibacterium, Ochrobactrum, Achromobacter, Bacillus, Sporosarcina, and Microbacterium populations. Using a network-based approach, we predicted that Bacillus, Stenotrophomonas, and Microbacterium interacted cooperatively and were the main degraders of phthalate plasticizers. Through selective isolation techniques, we obtained twenty isolates belonging to Bacillus, Microbacterium, Sporosarcina, Micrococcus, Ochrobactrum, Stenotrophomonas, Alcaligenes, and Cytobacillus. The best DEHP-degraders were Stenotrophomonas acidaminiphila OR13, Microbacterium esteraromaticum OR16, Sporosarcina sp. OR19, and Cytobacillus firmus OR20 (83.68%, 59.1%, 43.4%, and 40.6% degradation of 100 mg/L DEHP in 8 d), which agrees with the prediction of key degraders. This is the first report of DEHP degradation by all four bacteria and, thus, our findings reveal as yet unknown PAE-degradation capabilities of marine sediment bacteria. This study provides insights into how bacterial communities adapt to degrade or resist the toxicities of different PAEs and demonstrates a simple approach for the prediction and isolation of potential pollutant degraders from complex and dynamic bacterial communities.

Mercury content and consumption risk of 8 species threadfin bream (Nemipterus spp.) caught along the Gulf of Thailand.

Total mercury (T-Hg) was examined in 8 threadfin bream species (Nemipterus spp.) caught in the Gulf of Thailand (GoT). The T-Hg contents ranged from 11.3 to 374 µg kg-1 wet weight, with the lowest in Nemipterus peronii and the highest in Nemipterus nemurus and Nemipterus tambuloides. Accumulation of T-Hg in fish tissue was found to be related to fish size, trophic levels, feeding habits and habitat. Threadfin bream caught in the upper GoT exhibited significantly (p < 0.05) lower T-Hg than those in the middle and lower parts of GoT, which possibly due to local mercury sources e.g., internal anthropogenic activities in the GoT and external from terrestrial input via river discharge. The estimated daily intakes were ranged from 0.03 to 0.07 µg kg-1 bodyweight day-1. All threadfin breams in the GoT have HQ <1. To prevent the associated potential risk, the maximum safe daily consumption is recommended at 95.3 g day-1.

Feeding Habits and the Occurrence of Anthropogenic Debris in the Stomach Content of Marine Fish from Pattani Bay, Gulf of Thailand.

This study assessed the feeding habits and ingestion of anthropogenic debris in 34 marine fish species from the southern Gulf of Thailand. A total of 5478 fish samples of 12 families were categorised into seven groups: planktivore, Lucifer feeder, fish feeder, Acetes feeder, shrimp feeder, piscivore, and zoobenthivore fish. A total of 2477 anthropogenic debris items were extracted from 12 fish species by visual inspection. Their ingestion of anthropogenic debris was influenced by season (p < 0.0001), with the highest ingestion during the northeast monsoon season. Furthermore, planktivorous fish displayed more ingested anthropogenic debris than the other investigated species (p = 0.022). Blue-coloured anthropogenic debris was commonly detected in the stomachs of fish and significantly differed between species (p > 0.001). Water depth and season significantly influenced the availability of food types (AF) for fish (p < 0.001). These findings provide evidence of the ingestion of anthropogenic debris by fish inhabiting a natural bay and signal the future anthropogenic pollution of marine fish.

Seasonal microplastic variations in estuarine sediments from urban canal on the west coast of Thailand: A case study in Phuket province.

To improve knowledge of the relationships of human activities with microplastic pollution in the urban estuary in Phuket province, which has a densely populated city on the western coast of Thailand, a total of 463 plastic-like items from 24 sediment samples in the dry and the rainy seasons were identified by micro-Fourier transform infrared spectroscopy. The microplastic abundance ranged in 300-900 and 33-400 items/kg dry weight in the dry and the rainy seasons, respectively, indicating that the estuary is moderately contaminated with microplastics. The most abundant polymer types were rayon and polyester with colored fibers, suggesting that the microplastics deposited in this area originate mainly from washing effluents. Additionally, our findings show that the microplastic distribution is significantly governed by hydrodynamic energy in the estuary. This provides basic information for a better understanding of the fate of microplastics within estuary, and for management actions to address microplastics in urban estuary.

Effects of crude oil and aromatic compounds on growth and bioluminescence of Vibrio campbellii FS5.

Fifteen native luminescent bacteria were isolated from the Gulf of Thailand, and their sensitivity for the detection of toxicity of crude oil and its aromatic components was investigated. Of these isolates, Vibrio campbellii strain FS5 was one of the two most highly inhibited bacteria at all crude oil concentrations. This bacterium showed a decrease in luminescence intensity of between 10.7 and 80.2% after a 15-min exposure to 0.0001-10 mg/L of crude oil. The degree of bioluminescence inhibition increased with increasing concentrations of crude oil. The presence of crude oil at all concentrations had negative effects on the log bioluminescence per log number of viable cells after 15- to 105-min exposure. About 10 to 100 times, lower half maximal effective concentration (EC50) values were observed for polycyclic aromatic hydrocarbons (PAHs) than those for benzene, toluene, ethylbenzene, and xylene (BTEX). In the presence of each individual BTEX and PAH, the bioluminescence inhibition increased with increasing exposure time (1-32 h). This indigenous bacterium can be used as a simple and general indicator of oil contamination and its impact on coastal waters as well as for assessing potential toxicity during oil bioremediation.

Abundance, composition, and fate of microplastics in water, sediment, and shellfish in the Tapi-Phumduang River system and Bandon Bay, Thailand.

Microplastic contamination in the environment is a global problem, as evidenced by the increasing amount of research worldwide. To our knowledge, this study is the first to investigate the microplastic distribution in Bandon Bay, one of the most important maricultural areas of Thailand. Water and sediment samples from the Tapi-Phumduang River system (n = 10) and Bandon Bay (n = 5) were collected. Water sampling at the river mouth was carried out during a complete tidal cycle to estimate the microplastic flux to the bay during the wet season. Moreover, two commercial bivalve species grown in the bay, the green mussel (Perna viridis) and lyrate Asiatic hard clam (Meretrix lyrata), were analyzed. More items of microplastics were found in the river system than in the bay. During the tide cycle, one-third of the microplastics entering the bay were washed back upstream during high tide. This backflow consisted mainly of larger microplastics. The average daily load of microplastics to the bay was 22.4 × 109 items day-1. The load during low tide was approximately 4-5 times higher than that during high tide. The overall accumulation of microplastics in the bottom sediments of the river and in the bay was similar (p < 0.05). Green mussels showed significantly higher contamination with microplastics than clams. Notably, the small-sized shellfish contained more particles (items/g) than the large ones (p < 0.05). Fibers were detected in virtually all samples: water (98%), sediment (94%), mussels (100%), and clams (95%). Among these, microfibers (<1 mm) were detected in water (71%), sediment (63%), green mussels (63%), and clams (52%). Blue and white particles were the two most frequently observed colors, while the most dominant polymers were rayon, followed by polypropylene (PP) or polyethylene (PE), polyethylene terephthalate (PET), and nylon. To this end, we posit that river discharge was a significant source of microplastics in Bandon Bay, with minor additional contributions from fishing and mariculture activities within the bay. Ultimately, these microplastics may end up in the sediments and living organisms.