Spatial and temporal variations of geochemical processes and toxicity of water, sediments, and suspended solids in Sibuti River Estuary, NW Borneo.

A comprehensive geochemical study was conducted in the Sibuti River estuary by considering water, suspended solids (SS), and sediment samples from 36 stations during southwest monsoon (SWM) and northeast monsoon (NEM). In this study, the distribution of in situ parameters, major ions, nutrients, trace metals, and isotopes (δD, δ18O) were analyzed in water samples, whereas sediments and SS were studied for trace metals. The distribution revealed that suspended solids were the major carrier of Cd, Zn, and Mn, whereas sediments worked as a major source of Co, Cr, Ba, Se, Cu, and Pb. Na-Cl water type and ion exchange dominated the lower part of the estuary during both seasons. However, the mixed mechanism of Ca-Cl, Ca-Mg-Cl, and higher weathering indicated reverse ion exchange in the intermediate and upper parts of the estuary. Isotopic signatures of δD and δ18O in estuarine water indicate that the precipitation over the Limbang area dominates during SWM, whereas higher evaporation was confirmed during NEM. The factor analysis revealed that seawater influence in the estuary majority controlled the water chemistry irrespective of seasons. Major ions were mainly regulated by the tidal influence during the low flow time of the river (SWM), whereas the mixing mechanism of weathering and seawater controlled the concentrations during NEM. Nutrients such as NO3, SO42-, NH3, and NH4+ mainly originated from the agricultural fields and nitrification along with ammonification were responsible for the recycling of such nutrients. Trace metals except Cd were found to be geogenic in nature and originating mainly from the oxidation of pyrites present in the sandstone and mudstones of the Sibuti Formation. Redox condition was catalyzed by microorganisms near the river mouth, whereas Al-oxyhydroxides and Fe-oxyhydroxides complexes in the intermediate and upper part under oxygenated conditions controlled the absorption of metals. Overall, the estuary was found to be absorptive in nature due to ideal pH conditions and was confirmed by the saturation index (SI) of minerals.

Spatiotemporal distribution of microplastics in Miri coastal area, NW Borneo: inference from a periodical observation.

The current study aims to investigate the spatiotemporal distribution of microplastics (MPs) in the Miri coast, targeting their occurrences, characterisation, and potential sources. For a periodical study, coastal sediments were collected from three different time intervals (monsoon, post-monsoon, and post-COVID) and subjected to stereomicroscope, ATR-FTIR, and SEM-EDX analyses. These results show a significant increase of MPs in post-COVID samples by approximately 218% and 148% comparatively with monsoon and post-monsoon samples, respectively. The highest concentration of MPs was detected near the river mouths and industrial areas where the waste discharge rate and anthropogenic activities dominate. Fibre-type MPs are the most abundant, with an average of nearly 64%, followed by fragments, films, microbeads, and foams. The most dominant polymer types were polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyester (PET). Overall, the current study shows a better understanding of MPs occurrence and potential sources in the Miri coastal area.

Delineation of highland saline groundwater sources in Ba'kelalan region of NE Borneo to improve the salt-making production using geochemical and geophysical approaches.

The extraction of mountain salt from the saline waters is the basic livelihood of the Ba'kelalan communities of Sarawak. The current integrated approach is the first attempt to study the sources and geochemical processes of the saline groundwaters in this mountain region. Hence, in this study, saline groundwater samples from five existing wells in different seasons were analysed for hydrochemical parameters and multi-isotope composition (δ18O, δD, δ34S, δ11B and δ37Cl). The significant increase in TDS, EC and salinity was due to seasonal variation and fluctuation in water level based on hourly, daily and monthly observations. The geochemical ratios and the statistical techniques revealed that the salinity was due to the dissolution of marine evaporites as a dominant process, coupled with other factors such as water-rock interaction, ion exchange and sulphate reduction. From the isotopic signatures, it was inferred that the origin of saline groundwater was from the intense dissolution of marine evaporites such as halite dissolution and oxidation of -sulphide (pyrite). 2D electrical resistivity and seismic refraction methods were used to identify the lithological variations, depth of potential sources of saline groundwater, and the subsurface structures. It was inferred the probability of a conductive zone at a depth of 1-14 m, from which the saline groundwater plume migrates towards the perched aquifer. The presence of subsurface faults facilitated the movement of hypersaline groundwater from the saturated zone to the surface. The outcome of the study will support the dependent community to enhance their commercial salt production.

Evaluation of metals and trace elements in sediments of Kanyakumari beach (southernmost India) and their possible impact on coastal aquifers.

Beach sediments of Kanyakumari at the southernmost India were evaluated for metals and trace elements and to assess their possible impact on coastal ecosystems. Positive correlations (except for Cd and Sr) between them indicated metamorphic lithologies and heavy mineral deposits as possible sources. Significant-extremely high enrichment and very high contamination of Th, Zr, Mo, Ti and U reflected the presence of different heavy minerals. The geo-accumulation index, however, mirrored their variable abundances at different sites. Association of Cd with P suggested the influence of anthropogenic solid waste from fishing industry. It might have caused >41-fold enrichment of Cd and the Fe- Mn-oxides possibly acted as scavengers for 13-fold enrichment of As compared to UCC. Concentrations of Zn and Cr between ERL and ERM in 13% and 93% of the samples, and Ni > ERM in 87% of sediments suggest their bioavailability to seawater with a potential risk for coastal aquifers.

Investigation of toxic elements in Carassius gibelio and Sinanodonta woodiana and its health risk to humans.

Increasing toxic metal content in aquatic products has become a universal burden due to the risks to aquatic organisms and human health associated with the consumption of these products. In this study, toxic metal distribution and accumulation in the organs of fish and bivalve species of economic and culinary importance from the lower reaches of the Yangtze River are examined, and the corresponding health risks are also investigated. In general, the viscera and gill show higher concentration of metals than other tissues. The order of the accumulation sequence of metals in muscle tissue of fish and bivalve is Zn > Cu > Mn > Cr > As > Hg > Pb > Cd and Mn > Zn > Cu > As > Cr > Pb > Cd > Hg respectively. Maximum accumulation of Mn (507.50 µg g-1) and Pb (0.51 µg g-1) in the gill tissues indicates the major uptake of these metals from the water column. According to the Hazard Index (HI) calculations (based on USEPA), the analyzed metals will not cause any harmful health effects to individuals for both normal and habitual fish consumers, except for Hg and As in habitual consumers, if these species are consumed at a larger amount. Compared to the Chinese Food Health Criterion and other international standards (WHO/FAO), metal concentrations in the edible muscle tissues of the studied species are lesser than the acceptable levels and found to be fit for human consumption.