Oxytelus acriculiclypeatus, a New Species of Oxytelus Gravenhorst, 1802 (Coleoptera: Staphylinidae: Oxytelinae) from Borneo.

A new species, Oxytelus acriculiclypeatus sp. nov., is described from Malaysia (Borneo: Sabah). The species is similar to O. megaceros Fauvel, 1895, but can be separated based on four male features: a more pointed tip on the anterior margin of the clypeus, a wider central plate on the posterior margin of sternite VIII with a carina that spans the entire width of the posterior margin of medial plate, two sharper and thinner projections on the apical orifice, and the apico-medial hook with a smaller apical tip but without the connecting scape. As a result, a total of 31 confirmed species have been recorded in Southeast Asia hitherto.

New species of Echinobothrium van Beneden, 1849 (Cestoda: Diphyllidea) from Indo-Pacific maskrays (Neotrygon Castelnau) off Australia and Borneo.

Four new diphyllidean species of the genus Echinobothrium van Beneden, 1849 are described from Indo-Pacific maskrays (Neotrygon Castelnau, Dasyatidae). Echinobothrium giraffaeous sp. n. from Neotrygon leylandi (Last) off northern Australia, Echinobothrium ivanovae sp. n. from Neotrygon orientalis Last, White et Serét off Borneo, and Echinobothrium bethae sp. n. from Neotrygon varidens (Garman) off Borneo are distinguished from all but one of the 33 valid species of the genus by the possession of the outermost A hooks with an extended base into which the bases of the three outermost B hooks are inserted. Echinobothrium rhynchobati (Khalil et Abdul-Salam, 1989) is the only known species with this unique feature, but its rostellum has a system of interlocking knobs and sockets that articulate bases of the A and B type hooks with one another, which is not present in any of the newly described species. Echinobothrium tyleri sp. n. from Neotrygon australiae Last, White et Serét off northern Australia is distinguished from all known species of Echinobothrium by its unique rostellar hook formula {2-3 18/17 2-3}. With the present addition of four new species, the central Indo-Pacific realm becomes the major hotspot for Echinobothrium, from which 13 species have been reported.

At the Heart of the Community: Implementation of Echocardiographic Screening for Rheumatic Heart Disease in Primary Care Facilities of Northern Borneo Island.

BACKGROUND: Rheumatic heart disease (RHD) is a potentially life-threatening condition that causes long-standing public health concerns. Echocardiography is a reliable diagnostic and screening technique for many cardiovascular conditions, including RHD. It is commonly used in tertiary care facilities worldwide but less so in the community setting. The primary aim of this study was to introduce and elaborate on the echocardiographic screening for RHD that was implemented by a Malaysian primary care clinic in Penampang district, Sabah. We also set out to present the uptake of the service in its initial years of establishment, as well as the challenges faced. METHODS: In the first part of this study, document reviews were conducted to compile relevant information about the conceptualization and implementation of this service. Following that, we also obtained secondary data on the echocardiographic screening service from its first implementation in April 2020 until May 2021 to examine the uptake and the patient profile. RESULTS: From April 2020 to May 2021, a total of 189 echocardiographic screening was conducted by primary care doctors using handheld ultrasound. Of the 189 children screened, 19 (10.1%) were found to have cardiac anomalies and were referred for a formal echocardiogram. Upon follow-up, 8 were detected with mild mitral regurgitation and referred to the nearest tertiary hospital for further management. CONCLUSION: Based on our review, the echocardiographic screening for RHD among children conducted by the Penampang Health Clinic was deemed successful. Echocardiogram service provided by primary care centers located in suburban and rural areas is highly beneficial for patients with poor access to specialized health care services because they stay far away from tertiary care facilities. Tapping into family medicine physicians located closer to communities to conduct echocardiographic screening and review the results can improve the detection of cardiac anomalies requiring further investigation. With the success of this project, echocardiographic services in the primary healthcare setting can be expanded by garnering the necessary collaborative efforts and consistent support from various stakeholders.

Evaluation of the microplastics in bivalves and water column at Pantai Teluk Likas, North Borneo, Malaysia.

Microplastics (MPs) are a pervasive pollutant in the marine environment. Pantai Teluk Likas in Sabah, Malaysia is one of the most visited beaches where tourism, recreational, and fisheries activities are high in this area. Hence, the area suffers from severe pollution, particularly from plastics. This study aims to quantify the microplastic composition in terms of color, shapes, and polymer types in marine bivalves (Anadara granosa, Glauconome virens, and Meretrix lyrata) and water column samples from Pantai Teluk Likas. All samples were digested using sodium hydroxide (NaOH) and incubated in the oven for at least 48 h. Serial filtration was done for each sample before they were observed under the dissecting microscope. The microplastics were identified and counted based on their physical attributes which were colors and shapes. The functional group of the polymers was determined using FTIR spectroscopy. Microplastics were found present in all samples collected. G. virens had the highest abundance of microplastics at 113.6 ± 6.5 particles/g followed by M. lyrata at 78.4 ± 3.7 particles/g. On the contrary, A. granosa had the least microplastics with an abundance of 24.4 ± 0.6 particles/g. Meanwhile, 110.0 ± 36.2 particles/L of microplastics were found in water column samples from Pantai Teluk Likas. Based on the analysis, fibers were the most common shape in bivalves, while fibers and films were common in the water column. In terms of colors, black, blue, and red were a few of the most abundant colors observed in both samples. The most common polymer detected in all bivalve species and water column samples is polycarbonate (PC), followed by polymethyl methacrylate (PMMA). Future study that focuses on the correlation between microplastic abundance in the marine biota and the water column is recommended to better understand microplastic availability and exposure.

Projected development in Borneo and Sumatra will greatly reduce connectivity for an apex carnivore.

The islands of Borneo and Sumatra are strongholds for biodiversity and home for many endemic species. They also have experienced amongst the highest deforestation rates globally. Both islands are undergoing massive, rapid infrastructure development, leading to further deforestation and habitat fragmentation. Here, we identify priority areas for continued functional forest connectivity across Borneo and Sumatra, using spatial models of clouded leopard (Neofelis diardi, a forest indicator species) movement, and impacts thereto from existing and future infrastructure development. We specifically measure and map the anticipated impacts on forest functional connectivity of three major infrastructure development projects (Pan Borneo Highway, Trans-Sumatran Toll Road, and the new Indonesian capital city of Nusantara). We found that core clouded leopard habitats are already highly fragmented in Sumatra, constituting only ∼13 % of the island, with potential dispersal corridors still linking some habitat fragments. In Borneo, clouded leopard core habitats cover 34 % of the island, with one large central core area and several much smaller satellite cores, which are largely unprotected (15 % protected, compared to 42 % in Sumatra). The largest negative effect on habitat connectivity was predicted for Nusantara (66 % of the total connectivity loss predicted for all three infrastructure projects), reverberating across the entirety of Borneo with the strongest effects in East Kalimantan. The Pan Borneo Highway accounted for 28 % of the total connectivity loss, affecting every province in Borneo and Brunei, with 6 % of this decrease located within protected areas. The Trans-Sumatran Toll Road had the smallest negative effect on connectivity (6 %) but only when excluding the already built segments, which, when included, produce a total negative impact similar to that of the Pan Borneo Highway.

New species of the elusive crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) from Sabah, Borneo.

Only one species of Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) was previously known to occur in Borneo: Pendleburyella eirmosa Tan, Muhammad & Wahab, 2023 from Brunei Darussalam. Here, two additional new species of crickets from the genus Pendleburyella are described from the highlands of Sabah, Borneo: Pendleburyella eremita sp. nov. from Bukit Hampuan and Pendleburyella nimba sp. nov. from Mount Trus Madi. In total, six species of Pendleburyella are currently known, three from Borneo and three from Malay Peninsula. It is likely that many more species are awaiting discovery owing to its cryptic morphology and elusive nature.

Links between socio-demographic characteristics and body mass index to colorectal cancer in North Borneo, Malaysia: A case-control study.

INTRODUCTION: The fourth leading cause of cancer-related mortality and morbidity worldwide is colorectal cancer (CRC). Numerous reasons have contributed to the massive rise in CRC cases, for which Asian nations differ significantly in terms of risk incidence rates. The objectives of this study were to, first, identify the socio-demographic characteristics of those of North Borneo ethnicity and body mass index (BMI) and, second, determine the association of these factors with CRC. This research will contribute to preventing this form of cancer. MATERIALS AND METHODS: This study is an analysis of a matched case-control study with a ratio of 1:2. The case group contained 206 respondents, and the control group contained 412. All CRC cases were confirmed with the histological results. The control group was matched for links between age, sex and ethnicity with CRC. The Statistical Package for Social Sciences Statistics (SPSS) IBM version 28.0 was used to conduct descriptive analysis using chi-squared testing and simple logistic regression. The statistical significance was P < 0.05. RESULT: Overall, 618 respondents took part in this survey, of which 256 (41.4%) were female and 362 (58.6%) were male. The maximum age was 76, with a mean age ± SD of 53.17 ± 11.4. Those of Bajau ethnicity comprised 24.6% (152) of the population, followed by Dusun with 22.8% (141), Kadazan with 17.6% (109%), other North Borneo ethnic groups with 15.5% (96), Bugis with 9.7% (60), Brunei with 4.4% (27) and other predominant races with 5.3% (33). Regression analyses revealed that the incidence of CRC in North Borneo, Malaysia, was substantially correlated with income, occupation, other linked diseases and BMI. CONCLUSION: Various risk factors are linked to CRC, based on the findings related to socio-demographic characteristics and BMI. Therefore, to lower the nationwide prevalence of CRC, national public health campaigns should include collaboration with the regional authorities to highlight the incidence and risk factors of CRC based on ethnicity.

Disentangling the intersection of inequities with health and malaria exposure: key lessons from rural communities in Northern Borneo.

BACKGROUND: The increasing incidence of Plasmodium knowlesi malaria poses a significant challenge to efforts to eliminate malaria from Malaysia. Macaque reservoirs, outdoors-biting mosquitoes, human activities, and agricultural work are key factors associated with the transmission of this zoonotic pathogen. However, gaps in knowledge regarding reasons that drive malaria persistence in rural Kudat, Sabah, Northern Borneo remain. This study was conducted to address this knowledge gap, to better understand the complexities of these entangled problems, and to initiate discussion regarding new countermeasures to address them. This study aims to highlight rural community members' perspectives regarding inequities to health relating to P. knowlesi malaria exposure. METHODS: From January to October 2022, a study using qualitative methods was conducted in four rural villages in Kudat district of Sabah, Malaysia. A total of nine in-depth interviews were conducted with community and faith leaders, after the completion of twelve focus group discussions with 26 photovoice participants. The interviews were conducted using the Sabah Malay dialect, audio-recorded, transcribed, and translated into English. The research team led the discussion and analysis, which was approved by participants through member checking at the community level. RESULTS: Participants identified disparity in health as a key issue affecting their health and livelihoods. Injustice in the social environment was also identified as a significant challenge, including the importance of listening to the voices of affected communities in disentangling the social and economic phenomena that can impact malaria control. Specific concerns included inadequate access to health-related resources and degradation of the environment. Participants recommended improving access to water and other necessities, increasing the availability of malaria control commodities in healthcare facilities, and developing sustainable programs to reduce socioeconomic disparities. CONCLUSION: Inequities to health emerged as a key concern for malaria control in rural Kudat, Sabah. A locally targeted malaria programme cantered on improving the social and economic disparities associated with health outcomes, could be a potential strategy for malaria prevention in such areas. Community-level perspectives gathered from this study can be used as a foundation for future discussions and dialogues among policymakers and community members for achieving greater transparency, improving social equity, and interoperability in addressing P. knowlesi malaria control.

Deep ancestry of Bornean hunter-gatherers supports long-term local ancestry dynamics.

Borneo was a crossroad of ancient dispersals, with some of the earliest Southeast Asian human remains and rock art. The island is home to traditionally hunter-gatherer Punan communities, whose origins, whether of subsistence reversion or long-term foraging, are unclear. The connection between its past and present-day agriculturalist inhabitants, who currently speak Austronesian languages and have composite and complex genetic ancestry, is equally opaque. Here, we analyze the genetic ancestry of the northeastern Bornean Punan Batu (who still practice some mobile hunting and gathering), Tubu, and Aput. We find deep ancestry connections, with a shared Asian signal outgrouping modern and ancient Austronesian-ancestry proxies, suggesting a time depth of more than 7,500 years. They also largely lack the mainland Southeast Asian signals of agricultural Borneans, who are themselves genetically heterogeneous. Our results support long-term inhabitation of Borneo by some Punan ancestors and reveal unexpected complexity in the origins and dispersal of Austronesian-expansion-related ancestry.

Metabolite profiling of Borneo's Gonystylus bancanus through comprehensive extraction from various polarity of solvents.

Gonystylus bancanus wood or ramin wood has been generally known as a source of agarwood (gaharu) bouya, a kind of agarwood inferior type, or under the exported trading name of aetoxylon oil. The massive exploitation of ramin wood is causing this plant's extinction and putting it on Appendix II CITES and IUCN Red List of Threatened Species. To date, no scientific publication concerns the chemical exploration of G. bancanus wood and preserving this germplasm through its metabolite profiling. Therefore, research focused on chemical components profiling of G. bancanus is promised. This research is aimed to explore metabolomics and analyze the influence of solvent polarities on the partitioning of metabolites in G. bancanus wood. A range of solvents in different polarities was applied to provide comprehensive extraction of metabolites in G. bancanus wood. Moreover, a hydrodistillation was also carried out to extract the volatile compounds despite the non-volatile ones. LCMS and GCMS analyses were performed to identify volatile and non-volatile components in the extracts and essential oil. Multivariate data analysis was processed using Principal Component Analysis (PCA) and agglomerative hierarchical clustering. 142 metabolites were identified by LCMS analysis, while 89 metabolites were identified by GCMS analysis. Terpenoids, flavonoids, phenyl propanoids, and saccharides are some major compound classes available from LCMS data. Oxygenated sesquiterpenes, especially 10-epi-γ-eudesmol, and ß-eudesmol, are the major volatile components identified from GCMS analysis. PCA of LCMS analysis demonstrated that PC1 discriminated two clusters: essential oil, dichloromethane, and n-hexane extracts were in the positive quadrant, while methanol and ethyl acetate extracts were in the negative quadrant. Three-dimensional analysis of GCMS data revealed that n-hexane extract was in the superior quadrant, and its composition can be significantly distinguished from other extracts and essential oil. G. bancanus wood comprises valuable metabolites, i.e., terpenoids, which benefit the essential oil industry. Comprehensive extraction by performing solvents in different polarities on G. bancanus wood could allow exploration of fully extracted metabolites, supported by the exhibition of identified metabolites from LCMS and GCMS analysis.

Detection of novel coronaviruses from dusky fruit bat (Penthetor lucasi) in Sarawak, Malaysian Borneo.

BACKGROUND: Sarawak has one of the highest diversity of fruit bats species (family Pteropodidae) in Malaysia, with 19 species described. Most coronavirus (CoV) studies have mainly focused on insectivorous bats, resulting in a lack of information on CoVs present in frugivorous bats. In addition, bat CoV surveillance activities are lacking in Malaysia. OBJECTIVES: Our study focuses on determining the presence of bat CoVs in dusky fruit bat (Penthetor lucasi). METHODS: Guano samples belonging to P. lucasi were collected from Wind Cave Nature Reserve. The samples were screened for the presence of CoVs using validated hemi-nested consensus RNA-dependent RNA polymerase consensus primers. RESULTS: The bat CoV positivity rate was 38.5% (n = 15/39), with the viruses belonging to two subgenera: Alphacoronavirus (α-CoV) and Betacoronavirus (ß-CoV). Phylogenetic analysis revealed that CoVs from 14 samples of P. lucasi belong to the genus α-CoV and may represent previously described genetic lineages in insectivorous bats in Wind Cave. However, only one sample of P. lucasi was detected with ß-CoV which is closely related to subgenus Nobecovirus, which is commonly seen in frugivorous bats. CONCLUSIONS: This study provides the first available data on CoVs circulating in P. lucasi.

The Garlic Tree of Borneo, Scorodocarpus borneensis (Baill.) Becc. (Olacaceae): Potential Utilization in Pharmaceutical, Nutraceutical, and Functional Cosmetic Industries.

Scorodocarpus borneensis (Baill.) Becc. is attracting increased attention as a potential commercial medicinal plant product in Southeast Asia. This review summarizes the current knowledge on the taxonomy, habitat, distribution, medicinal uses, natural products, pharmacology, toxicology, and potential utilization of S. borneesis in the pharmaceutical/nutraceutical/functional cosmetic industries. All data in this review were compiled from Google Scholar, PubMed, Science Direct, Web of Science, ChemSpider, PubChem, and a library search from 1866 to 2022. A total of 33 natural products have been identified, of which 11 were organosulfur compounds. The main organosulfur compound in the seeds is bis-(methylthiomethyl)disulfide, which inhibited the growth of a broad spectrum of bacteria and fungi, T-lymphoblastic leukemia cells, as well as platelet aggregation. Organic extracts evoked anti-microbial, cytotoxic, anti-free radical, and termiticidal effects. S. borneensis and its natural products have important and potentially patentable pharmacological properties. In particular, the seeds have the potential to be used as a source of food preservatives, antiseptics, or termiticides. However, there is a need to establish acute and chronic toxicity, to examine in vivo pharmacological effects and to perform clinical studies.

Rock art and frontier conflict in Southeast Asia: Insights from direct radiocarbon ages for the large human figures of Gua Sireh, Sarawak.

Gua Sireh, located in western Sarawak (Malaysian Borneo), is known for its rock art. The cave houses hundreds of charcoal drawings depicting people, often with headdresses, knives and other accoutrements. Here, we present direct radiocarbon dates and pigment characterizations from charcoal drawings of two large (>75 cm), unique Gua Sireh human figures (anthropomorphs). To our knowledge, these are the first chronometric ages generated for Malaysian rock art, providing insights into the social contexts of art production, as well as the opportunities and challenges of dating rock art associated with the Malay/Austronesian diasporas in Southeast Asia more generally. Previous archaeological excavations revealed that people occupied Gua Sireh from around 20,000 years ago to as recently as AD 1900. The site is within Bidayuh territory, and these local Indigenous peoples recall the cave's use as a refuge during territorial violence in the early 1800s. The age of the drawings, dated between 280 and 120 cal BP (AD 1670 to 1830), corresponds with a period of increasing conflict when the Malay elites controlling the region exacted heavy tolls on the local hill tribes. We discuss rock art production at Gua Sireh in this context of frontier conflict and Bidayuh resistance.

Serological evaluation of risk factors for exposure to malaria in a pre-elimination setting in Malaysian Borneo.

Malaysia has reported no indigenous cases of P. falciparum and P. vivax for over 3 years. When transmission reaches such low levels, it is important to understand the individuals and locations where exposure risks are high, as they may be at greater risk in the case of a resurgence of transmission. Serology is a useful tool in low transmission settings, providing insight into exposure over longer durations than PCR or RDT. We ran blood samples from a 2015 population-based survey in northern Sabah, Malaysian Borneo on a multiplex bead assay. Using supervised machine learning methods, we characterised recent and historic exposure to Plasmodium falciparum and P. vivax and found recent exposure to P. falciparum to be very low, with exposure to both species increasing with age. We performed a risk-factor assessment on environmental, behavioural, demographic and household factors, and identified forest activity and longer travel times to healthcare as common risk-factors for exposure to P. falciparum and P. vivax. In addition, we used remote-sensing derived data and geostatistical models to assess environmental and spatial associations with exposure. We created predictive maps of exposure to recent P. falciparum in the study area and showed 3 clear foci of exposure. This study provides useful insight into the environmental, spatial and demographic risk factors for P. falciparum and P. vivax at a period of low transmission in Malaysian Borneo. The findings would be valuable in the case of resurgence of human malarias in the region.

A new species of the rare monotypic genus Cyrtinoclerus Chapin from Borneo, with notes on Meprinogenus Kolibác (Coleoptera: Thanerocleridae).

Cyrtinoclerus sabahensis sp. nov. of the less diverse cleroid family Thanerocleridae is described from Borneo. The unique specimen was found in the Malaysian state of Sabah and represents the first collecting record of the genus in one hundred years. The new species is assigned to the hitherto monotypic genus Cyrtinoclerus Chapin, 1924, whose single species is known from a single specimen from Basilan, Philippines, with no subsequently collected specimens known to date. Cyrtinoclerus is distinct in its unique synapomorphies, namely the tarsi with formula 5-5-5 but tarsomeres 4 reduced in size, elytron depressed in basal third with distinct bulge, and seriate punctation of elytra. The genus is re-examined and again classified within Thanerocleridae. A systematic status of Cyrtinoclerus and its relative Meprinogenus Kolibác, 1992, also known only from two just one-hundred-year-old specimens, is discussed and possible synonymy of the latter genus suggested. The family Thanerocleridae now comprises 38 extant species in eleven genera and four extinct Cretaceous genera and species found in Burmese and Charentese ambers. A phylogenetic analysis of all fifteen extinct and extant genera of Thanerocleridae based on 36 morphological characters is presented and updated key to the tribe Thaneroclerini provided.

New curious genus of the subfamily Cladonotinae (Orthoptera: Tetrigidae) from Borneo Island with remarks on the classification of this subfamily.

A new monotypic genus Trusmaditetrix gen. nov. (type species: Trusmaditetrix complanata sp. nov.) is described from Malaysia. New tribe Trusmaditetrigini trib. nov. is established for six genera of Cladonotinae (Trusmaditetrix gen. nov., Devriesetettix Tumbrinck, Eurymorphopus Hancock, Ichikawatettix Tumbrinck, Planotettix Tumbrinck, and Tepperotettix Rehn). A key to genera and an annotated list of the genera and species of the new tribe are also provided. The species Eurymorphopus dubius Günther, 1974 from Mauritius is placed in the genus Morphopoides Rehn, 1930 and a new combination is proposed: M. dubius (Günther, 1974), comb. nov.

Burkholderia Pseudomallei As The Predominant Cause Of Splenic Abscess In Kapit, Sarawak, Malaysian Borneo.

BACKGROUND: Splenic abscess is an uncommon condition, with autopsy studies estimating an incidence rate of 0.14-0.70%. Causative organisms can be extremely diverse. Burkholderia pseudomallei is the most common cause of splenic abscess in melioidosis-endemic areas. METHODS: We reviewed 39 cases of splenic abscesses in a district hospital in Kapit, Sarawak, from January 2017 to December 2018. The demographics, clinical characteristics, underlying diseases, causative organisms, therapeutic methods, and mortality rates were investigated. RESULTS: There were 21 males and 18 females (mean age, 33.7±2.7 years). Almost all patients (97.4%) had a history of pyrexia. Diabetes mellitus was present in 8 patients (20.5%). Splenic abscesses were diagnosed using ultrasonography and were multiple in all 39 cases. Positive blood cultures were obtained in 20 patients (51.3%), and all yielded B. pseudomallei. Melioidosis serology was positive in 9 of 19 patients (47.4%) with negative blood cultures. All patients were treated for melioidosis with antibiotics without the need for surgical intervention. All splenic abscesses resolved after anti-melioidosis treatment was completed. One patient died (2.6%) as a result of B. pseudomallei septicaemia with multiorgan failure. CONCLUSIONS: Ultrasonography is a valuable tool for diagnosing splenic abscesses in resource-limited settings. B. pseudomallei was the most common etiological agent of splenic abscesses in our study.

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.

Geochemical fractionation, mobility of elements and environmental significance of surface sediments in a Tropical River, Borneo.

Miri River is a tropical river in Borneo that drains on flat terrain and urbanised area and debauches into the South China Sea. This paper documents the environmental status of this river, and provides an insight into the provenance using bulk chemistry of the sediments, and brings out the geochemical mobility, bioavailability, and potential toxicity of some critical elements based on BCR sequential extraction. The sediments are intense to moderately weathered and recycled products of Neogene sedimentary rocks. The hydrodynamic characteristics of the river favoured an upstream section dominated by fine sand, while the downstream sediments are medium silt. Based on the bulk geochemistry, the Miri River sediments are moderate to considerably contaminated by Cu, Mo, and As in the upstream and by Sb, As and Cu in the downstream. The potential ecological risk values are low except Cu and a significant biological impact is expected in downstream due to Cu, As, Zn and Cr. The mobility, bioavailability and Risk Assessment Code values for Zn and Mn are higher and thus may pose moderate to very high risk to aquatic organisms. Though a high bulk concentration of Cu is observed, the association of Cu with the bioavailable fraction is low.