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Forty-eight sediment samples collected in the Upper Gulf of Thailand (UGOT) and its nearby rivers including the Mae Klong, Tha Chin, Chao Phraya, and Bang Pakong were analyzed for grain size, heavy metals (Cu, Pb, Zn, Cr, and Cd), and clay minerals. The results reveal that fine-grained sediments with Mz < 30 μm concentrate in the northern coastal area and coarse-grained fractions increase in a seaward direction. The grain size of the sediments mainly controls heavy metal concentrations. The concentrations of Cu, Pb, Zn, and Cr are higher in the northern part of UGOT, with ranges above 20, 23, 45, and 50 mg kg −1 , than in other sampling areas. Meanwhile, Cd content is greater than 120 μg kg −1 in sediments near the Bang Pakong River mouth and area between the Tha Chin and Mae Klong rivers mouth. The concentrations of heavy metals are higher than background data, and statistical analysis of geo-accumulation index indicates that the study area is either unpolluted to moderately polluted or moderately polluted by heavy metals. Our results also verify that illite is the dominant clay mineral, followed by kaolinite, chlorite, and smectite in terms of semi-quantitative content. Smectite/kaolinite can be used as an indicator to trace the riverine sediment in the study area, which present a counterclockwise dispersion pattern of sediment from the Chao Phraya River. [ABSTRACT FROM AUTHOR]

Abstract: In order to elucidate the sources of metals in urbanized areas, heavy metal contents and Pb isotope ratios were determined in the Chao Phraya River sediments. The sediment samples were leached using 1% HNO3 and metal concentrations (Cd, Cu, Cr, Pb, and Zn) and Pb isotopic ratios (208Pb/206Pb and 207Pb/206Pb) in the solutions were analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The highest ranking of potential pollutant evaluations of Cd, Cu, Cr, Pb, and Zn contents was found from samples that were located near to the center of Bangkok. Pb isotope ratios (208Pb/206Pb: 2.075–2.113 and 207Pb/206Pb: 0.834–0.868) in the Chao Phraya River sediments near to the center of Bangkok agreed well to those in the Bangkok road side dust and pond sediments suggesting that river sediments may be contributed from road-side dust and pond sediments. Moreover, Pb isotope ratios confirmed that the polluted sediments were contributed as Pb products of fly ashes (municipal waste combustors) in Bangkok (208Pb/206Pb: 2.100–2.120 and 207Pb/206Pb: 0.867–0.870). [Copyright &y& Elsevier]

• Over 50-years of discharge and sediment data were assessed for 211 stations in the CPR. • For the first time, sub-basin scale sediment yields (42 stations) are reported. • Spatial distribution of sediment yield is analyzed using lithology, climate and human impacts. • Sediment yields were high, but the majority were trapped in dams and floodplains. • This study will be an important reference for future researches in the CPR. In this paper, we provide a holistic view of the hydro-sedimentological regimes of the Chao Phraya River (CPR) Basin, the fifth largest basin in Southeast Asia. Our analysis of daily discharge and sediment data from 42 major gauge stations showed high seasonal variation in the suspended sediment discharge (Qs), with the maximum discharge occurring in October on an inter-annual average. At Nakhon Sawan, the river discharges 304x104 tons of sediment every year, 60% of which is transported in the peak flooding months (September to November). The peak sediment discharge in October is dramatically attenuated at a station 150 km downstream from Nakhon Sawan, mainly due to discharge diversion to irrigation canals, distributaries, and branches, as well as seasonal flooding over the Central Plain. Sediment yield (SY) calculated at major stations showed spatial variability across the basin, generally decreasing in a downstream direction (i.e. as drainage area increases) (R2 = 0.55). Some stations in the upper basin's watersheds showed SY as high as >700 tons/km2/yr, which is comparable to upstream catchments of other large rivers with high sediment production. Two significant sediment sinks were identified in this study: the Bhumibol and Sirikit dams (each on Ping and Nan Rivers) – which trap ~236 × 104 tons of sediment each year (~90% trapping rate) – as well as the floodplain of the CPR which stores 176 × 104 tons annually along the 150 km downstream reach from Nakhon Sawan (~60% of Qs at Nakhon Sawan). By extrapolating the floodplain sediment budget, we estimate that around 300 × 104 tons/yr of suspended sediment can be stored downstream of Nakhon Sawan (to the Gulf); comparable to the total annual storage of the two mega dams upstream. Although these dams have been previously reported to cause substantial sediment starvation in the CPR Delta, this study is the first to recognize the important role of lowland storage on the CPR's basin's sediment discharge to the Gulf of Thailand, and how it contributes a similar degree of threat to the shrinking delta. [ABSTRACT FROM AUTHOR]

Microplastics have received special attention due to their potential risks to environments. However, data on microplastics in estuaries of the Southeast Asian region is still insufficient. This study investigated the abundance and characteristics of microplastics in the sediment and surface water of the Chao Phraya River Estuary, Thailand. Concentrations of heavy metals extracted from microplastics were also reported. The abundance of microplastics in surface water and sediment was 48 ± 8 items/m3 and 39 ± 14 items/kg, respectively. Microplastics with small sizes of 0.05–0.3 mm were predominant in all collected samples. Polypropylene and polyethylene particles were the most abundant in the surface water and sediment, respectively. Toxic metals (Cr, Cu, Ni, Pb, Cd, and Zn) were found in microplastics from surface water samples. Since Chao Phraya River Estuary is an important aquaculture zone in Thailand, the presence of microplastics in this area may severely impact on aquaculture and human health. Unlabelled Image • MPs were detected in all water and sediment samples collected from CPRE. • The highest abundance of MPs was found at bank 2 of the estuary with 63 items/m3. • The variability of MPs on the Chao Phraya Estuary cross-section is not significant. • Small MPs (0.5–0.3 mm) with fragment shapes and types of PP, PE were predominant. • Ni, Cd, Pb, Cu, Zn, and Cr were detected in MPs collected from the surface water. [ABSTRACT FROM AUTHOR]

While a large number of studies on microplastics (MPs) in the western hemisphere have been performed, few studies are available in the eastern hemisphere, especially in Southeast Asia. In this study, the abundance of MPs in water and sediment samples from the Chao Phraya River at the Tha Pra Chan area, Thailand, was investigated. Water samples were collected by a manta trawl, and sediment samples were collected by a Van Veen grab sampler. The average number and concentration of MPs in water samples were 80 ± 65 items/m³ and 53.3 ± 58.4 mg/m³, respectively. The average number and concentration of MPs in sediment samples were 91 ± 13 items/kg and 4.9 ± 3.4 mg/kg, respectively. The main morphologies of MPs were fragments and fibers, mostly white. Polypropylene (PP) was the dominant polymer type found in both water and sediment. Moreover, the content of heavy metals (Cr, Cu, Ni, and Pb) on MPs was extracted by aqua regia solution and analyzed by ICP-OES. Results show high concentrations of Pb and Cu adsorbed on MPs in the study area. In brief, this study suggests that there are high levels of MPs in the water and sediments of the Chao Phraya River at the Tha Pra Chan area. Image 1 • MPs were found in water and sediment of Chao Phraya River at Tha Pra Chan. • MPs in water were detected at 80 ± 65 items/m³ and 53.3 ± 58.4 mg/m³. • MPs in sediment were detected at 91 ± 13 items/kg and 4.9 ± 3.4 mg/kg. • Most MPs were PP, PE and PS with the dominant size of 0.05–0.5 mm. • Heavy metals were found with high concentration of Pb and Cu adsorbed on MPs. [ABSTRACT FROM AUTHOR]