Accumulation In Sediments Research Articles

Radioactivity and Heavy Metal Accumulation in Surface Sediment from the West Aegean Coast

ABSTRACT Sediment quality can be assessed by analyzing radionuclides and heavy metals from pollution sources. These substances also provide insight into sediment structure and marine pollution. The aim of this study was to evaluate the risk of radiation and heavy metal accumulation in İzmir Bay by taking into account both lithologic and anthropogenic factors. Sediment samples were collected from İzmir Bay on a seasonal basis. Gamma-ray spectrometry techniques were used to determine radionuclides in the sediment using a NaI (Tl) scintillation gamma spectrometer. X-ray fluorescence spectrometry (XRF) was employed to measure heavy metal concentrations in the samples. Mean concentrations of 232Th (43.6 Bq/kg), 226Ra (35.3 Bq/kg), 40K (699.2 Bq/kg), and heavy metals Fe (13408.3 ppm), Al (16891.6 ppm), Mn (517.3 ppm), Zn (59.8 ppm), Cr (96 ppm), Ni (31.6 ppm), and Pb (31.8 ppm) were determined in the surface sediment. The elevated levels of both radionuclides and heavy metals were attributed to industrial accumulation and sedimentation patterns in the bay. The study highlights the importance of considering both geological structures and environmental risks in assessing sediment quality.

Isotopic signatures unveil the lead sources and migration in surface mangrove sediments

Mangrove sediments act as both sinks and secondary sources for lead (Pb), yet the sources, migration, and transformations of Pb in mangrove environments are poorly understood. In this study, Pb concentration in three mangrove sediments adjacent to different land-use types was evaluated. The Pb sources were quantitatively identified using Pb isotopes. Our data indicated minor Pb contamination in the mangrove sediments, possibly due to the relative lack of developed industry in this region. The Pb isotopic ratios suggested, on average, natural sources, coal combustion, agricultural activities, and traffic-related emissions respectively contributed approximately 61.4 %, 18.8 %, 14.0 %, and 5.8 % of the Pb accumulation in the mangrove sediments, suggesting that coal combustion and agriculture were important anthropogenic Pb sources. Significant relationships were observed between the 206Pb/207Pb ratios and total organic content (TOC) in mangrove sediments, which implied contrasting Pb cycling in two mangrove environments. We further suggested that organic matter and sulfur content significantly reduced Pb mobility and bioavailability in mangrove sediments. Our study provides isotopic method to investigate the Pb sources and migration in the mangrove environment.

Characterization of pollutants and identification of microbial communities in the filter media of green infrastructures

Green infrastructure (GI) technologies use natural mechanisms and processes associated with microorganisms, plants, and filter media to facilitate mass circulation and energy flow in the ecosystem. Despite the numerous studies focused on the functions and pollutant treatment performance of nature-based stormwater treatment technologies, studies concerning the effects of filter media characteristics on the diversity and abundance of microorganisms in green stormwater infrastructures are still lacking. In this study, the physico-chemical characteristics of filter media and accumulated sediments in an infiltration trench (IT) and bioretention facility (BI) were investigated. Moreover, the composition and distribution of different microbial communities in GIs designed for stormwater treatment were identified. As compared with BI, higher pollutant concentrations were noted on the filter media and sediments accumulated in IT due to the higher degree of anthropogenic activities in IT's catchment area. Inorganic filter media (i.e., gravel) tend to have greater pollutant trapping efficiency due to the accumulation of sediments in the macropores. On the other hand, organic filter materials (i.e., woodchips) may serve as carbon sources for fueling microbial processes and promote better moisture retention in the facility. Proteobacteria, which constituted 38.6% to 43.0% of the total bacterial population in IT and 37.9% to 41.4% of the total bacterial population in BI, was found to be the most dominant type of bacteria in the facilities. In terms of microbial diversity, BI exhibited a higher diversity index, which is most likely due to the presence of vegetative components forming a symbiotic relationship with microbial colonies. Generally, inorganic filter media are mainly used for improving the GI technologies' drainage and infiltration functions, whereas organic filter media provide suitable growth environments for different bacterial communities involved in important biogeochemical cycles.

Early diagenesis and benthic fluxes of redox-sensitive metals in eastern China shelf sediments

Thirteen Short sediment cores (30-50 cm) were collected from Bohai Sea, Yellow Sea and Changjiang Estuary in China, and the early diagenesis of several redox sensitive metals (Fe, Mn, Mo, U and V, referring to as RSMs) in sediment were studied. The recycling process of Mo and Mn was closely correlated with each other, generating benthic fluxes diffusing upward from sediment to overlying water column, and the flux rates are related to the organic carbon oxidation rates. The recycling of U and V were more tightly coupled with Fe oxides, generating benthic fluxes going downward into the sediment in most cores. Significant authigenic accumulation of U, in contrary to little to no accumulation of Mo and V, were found in the study region, even in Changjiang Estuary where hypoxic condition was often found during summer. Benthic diffusive fluxes were compared with authigenic mass accumulate rates (MAR), which indicated that, besides the benthic diffusion process, there are other processes controlling the authigenic accumulation of the RSMs. The close relationships between authigenic accumulation of RSMs with OCburial and OCburial with Sburial, indicating the authigenic accumulation of RSMs is a consequence of redox environment in shelf sediment, which directly influencing the organic carbon degradation process. Compared with other continental margin, moderate enrichment of U was found in China continental sediment. The authigenic U accumulation in BS and NYS sediments accounted for 20 - 68% of the Yellow River input, whilst in SYS sediments accounted for ~ 64% of the Yellow River and Changjiang River input, which acting as important U sinks that cannot be ignored.

Cyanobacterial organic matter (COM) positive feedback aggravates lake eutrophication by changing the phosphorus release characteristics of sediments

Phosphorus is a key nutrient that causes eutrophication in lakes. Our investigation of 11 eutrophic lakes found that the concentrations of soluble reactive phosphorus (SRP) in the water column and EPC0 in sediments decreased with aggravated eutrophication. There was a significant negative correlation between the SRP concentrations and eutrophication parameters such as chlorophyll a (Chl-a), total phosphorus (TP) and algal biomass (P < 0.001). In addition, SRP concentrations were significantly affected by EPC0 (P < 0.001), while EPC0 was significantly affected by the content of cyanobacterial organic matter (COM) in sediments (P < 0.001). Based on these findings, we hypothesized that COM can alter the phosphorus release characteristics of sediments, including the phosphorus adsorption parameters of sediment (PAPS) and the phosphorus release rate of sediment (PRRS), thereby stabilizing SRP concentrations at lower levels and rapidly replenishing them when depleted by phytoplankton, which in turn benefits cyanobacteria due to their low SRP adaptation strategies. Simulation experiments were conducted to confirm this hypothesis by adding higher plant OM and COM to sediments. The results showed that all types of OM could significantly increase the maximum phosphorus adsorption capacity (Qmax), but only COM could reduce sediment EPC0 and promote PRRS (P < 0.001). Changes in these parameters (i.e., Qmax, EPC0, and PRRS) resulted in a larger SRP adsorption quantity and faster SRP release rate at low SRP concentrations. This promotes the competitive edge of cyanobacteria due to they have a higher affinity for phosphorus than other algae. As an important component of cyanobacteria, EPS can change the phosphorus release characteristics (i.e., PAPS and PRRS) by reducing sediment particle size and increasing sediment surface functional groups. This study revealed the positive feedback effect of COM accumulation in sediments on lake eutrophication from the perspective of phosphorus release characteristics of sediments, which provides a basic reference for the risk assessment of lake eutrophication.

Sources of contamination in sediments of retention tanks and the influence of precipitation type on the size of pollution load

Densification of cities and urban population contributes to increased runoff and suspended solids and alteration of the urban water cycle. Nowadays, Blue-Green Infrastructure is promoted to increase a city’s resilience to floods; however, stormwater drainage systems, supported with retention tanks are still important in protecting urban areas against floods. Sediment accumulation in stormwater infrastructure relates to an issue of pollutants such as heavy metals, nutrients etc. Research on the origin of the pollutants associated with the suspension and ultimately sediment accumulated in sewage can bring new insights about processes in urban catchment areas. This is the first study, which is focused on the analysis of stable carbon and nitrogen isotopes in bottom sediments collected from municipal retention tanks to verify the origin of the deposited pollutants immediately after pluvial floods. The research was additionally extended with water quality analyzes immediately after three types of weather: a dry period, typical precipitation (< 30 mm) and torrential rainfalls (2 events with daily precipitation over 30 mm which caused pluvial flooding of the city area). Analyses of sediments indicated that the main source of carbon and nitrogen in the bottom of the retention tanks had been brought with stormwater runoff from the city area. Organic nitrogen fertilizers appeared to be the main source of nitrogen, while the sources of organic carbon were mixed: C3 land plants, wood, and oil. Additionally, it was found that torrential rainfall caused a 23-fold increase of N-NO3 concentration, a sevenfold increase of P-PO4 concentration, and an over fivefold increase of concentration of organic matter, in comparison to typical precipitation.

А conceptual model for the formation of oil and gas accumulation zone within the Paleozoic basement of the southeastern West Siberian basin

In modern conditions of high demand for oil reserves in the Russian Federation, the most important region for its production remains the West Siberian oil and gas basin with target objects in well studied and developed Jurassic and Cretaceous sediments. The high degree of depletion of oil reserves at traditional sites and low exploration of complex and unconventional oil accumulations contribute to intensification of prospecting activities in Achimov, Bazhenov and Tyumen deposits, as well as those in deeper and less studied Lower Jurassic, Triassic and Paleozoic deposits located in the basement of sedimentary cover. The issue of oil and gas content of the pre-Jurassic complex of the West Siberian oil and gas basin has been debated for many years by experts, who highly appreciate the potential of identifying new large-scale oil and gas accumulations in such sediments. A series of recent discoveries in the Tomsk region (Urman-Archinsk group) confirms the importance of selecting such an exploration area. A review of existing ideas about the prospects of oil and gas content in the Paleozoic basement of the southeastern part of the West Siberian basin, along with an analysis of the identified conditions of hydrocarbon accumulation formation, allowed to propose a conceptual model that can be used as a basis for prediction when searching for accumulations in the pre-Jurassic complex.

Controls on continental shelf width: A machine learning approach

The continental shelf edge marks the transition between shallow- and deep-water environments, and records the cumulative influence of subaerial and submarine processes. The width of the shelf therefore dictates where, and how efficiently, particulates are transferred into the deep-ocean. Previous studies have shown that shelf width is heavily influenced by eustasy and tectonics through geological time, however the dominant subaerial and submarine controls on shelf width during the present-day highstand remains unquantified on a continental scale. Using 15 climatic, hydrographic, oceanographic and tectonic variables, coupled with machine learning algorithms, we assess the dominant predictors of shelf width along 51,000 km of the continental margin of the Americas. Results show that the thickness of sediment accumulated on the shelf and the seismicity of the nearest onshore catchment best predict shelf width, with thinner sediment accumulations and more seismically-active catchments resulting in narrower shelves. Tectonics is therefore a first order predictor of shelf width, with the narrowest shelves associated with tectonically-active, steep and low-accommodation margins. These findings support the view that tectonics is the dominant control on shelf width variation across the Earth's surface in the present-day, and indicate that tectonics will modify the width of the shelf during all sea-level stands.

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Heavy metal pollution is a serious environmental problem in freshwaters, potentially impacting public health, water quality and ecosystem integrity worldwide. However, the potential public health risks associated with heavy metal accumulation in water, sediment and commercial fish samples remain unclear. Here we assessed the concentrations and distribution of five heavy metal of public health importance (Iron, Copper, Zinc, Lead and Copper) in water, sediment, and edible organs (muscles, liver, gills, and intestines) of the African sharptooth catfish, Clarias gariepinus obtained from aquaculture ponds. Water, sediment, and fish samples were randomly collected from commercial fishponds across different five locations in Ondo. Metal concentrations in water, sediment and fish samples were analyzed using Atomic Absorption Spectrophotometry (AAS, Model AA-680/ Shimadzu). Mean metal levels observed in water, sediment and fish samples were compared with recommended regulatory guidelines for human consumption. Our results showed mean concentrations for all metals in water exceeded recommended permissible limits in freshwater bodies and aquatic biota, presumably suggesting potential risks for human consumers. Heavy metal levels in sediment samples indicated Fe was maximally accumulated, followed by Zn, Cu, Pb, and Cd. The highest and least accumulations for all the metals were recorded in the gills, and in the liver respectively. Higher concentrations of metals observed in gills corroborate the fact that the gill is a major route for heavy metal accumulation in fish whereas the reduced concentration of metals observed in the liver may be associated with enhanced detoxification mechanism in the liver. These results suggest that fish obtained from these aquaculture ponds may be unsafe for human consumption. Hence, we recommend a periodic assessment of heavy metal levels in commercial fish samples as a major regulatory priority.

Cr(III) and Cr(VI) removal in floating treatment wetlands (FTWs) using Typha domingensis

Floating treatment wetlands (FTWs) are a cost-effective ecological engineering tool for the restoration of polluted water bodies. The aims of this work were to evaluate the removal of Cr(III) and Cr(VI) by FTWs using Typha domingensis, and to assess Cr accumulation and distribution in plant tissues and sediment. Treatments were 5 and 10 mg L−1 of Cr(III), and 5 and 10 mg L−1 of Cr(VI), with and without FTWs, and biological control (BC) with FTW without Cr addition. Both Cr species were efficiently removed from water in all treatments (Cr removal > 80%). Cr concentration in sediments of treatment without FTWs was significantly higher than in sediments of treatments with FTWs, indicating that T. domingensis was directly involved in Cr removal. In sediment, Cr was mainly bound to the organic matter in all treatments with a low risk of future release under FTW conditions. T. domingensis demonstrated tolerance to both Cr species at 5 and 10 mg L−1 with Cr accumulated mainly in the roots in all treatments. The use of FTWs planted with T. domingensis is a suitable tool to remediate water bodies contaminated with Cr.

A new concept to forecast the process of suspended sediment accumulation in the bottom sediment of small reservoirs

The new concept presented for forecasting the rate of accumulation of suspended sediment in reservoir water in the bottom sediment allows reasonable estimates of the siltation process globally, regionally, or locally, to be obtained without the need for costly research. The method draws on three key parameters, i.e., the concentration of suspended sediments (SS), and its organic matter (OMSS) content, as well as the storage capacity (VR) (i.e., the water storage in the reservoir). All of these parameters easy to determine, with information on them, in fact, made widely available by most agencies managing reservoirs in different parts of the world. In practice, the proposed method can represent a missing link in the precise determination of a reservoirs rate of siltation (and hence, losses of storage capacity).

Uranium in Lake Sediments of Humid Zone: A Case Study in the Southeast Fennoscandia (Karelia, Russia)

The article presents data on the analysis of U accumulation in recent sediments of lakes in the territory of the Southeast Fennoscandia. The research was carried out in the study area of the Republic of Karelia. It has been established that the content of U in sediments varies from 0.1 to 42.3 mg/kg (median is 0.91 mg/kg). In general, the studied sediments of the region had low concentrations of U in comparison with the average content of this element in the upper part of the Earth’s crust. In some areas associated with deposits or ore occurrences of U, an increased content of U in lake sediments was revealed. The highest U accumulation level was found in the lake sediments, which are under the influence of the North Onega ore-geochemical region, where V deposits and ore occurrences that contain U, Fe, Mo and Cu are widespread. In the sediments of some studied lakes, Th anomalies were found, which often accompany U in ore geological formations. The analysis of uranium fractions in the sediments of some lakes in Karelia revealed the key role of the mineral (insoluble) phase in the accumulation of U, up to 64–68% of the total U content. The share of the organic fraction in the accumulation of U in the studied sediments of the lakes is small and ranges from 7 to 15% with respect to the total concentration of the metal.

Nitrite accumulation and anammox bacterial niche partitioning in Arctic Mid-Ocean Ridge sediments

By consuming ammonium and nitrite, anammox bacteria form an important functional guild in nitrogen cycling in many environments, including marine sediments. However, their distribution and impact on the important substrate nitrite has not been well characterized. Here we combined biogeochemical, microbiological, and genomic approaches to study anammox bacteria and other nitrogen cycling groups in two sediment cores retrieved from the Arctic Mid-Ocean Ridge (AMOR). We observed nitrite accumulation in these cores, a phenomenon also recorded at 28 other marine sediment sites and in analogous aquatic environments. The nitrite maximum coincides with reduced abundance of anammox bacteria. Anammox bacterial abundances were at least one order of magnitude higher than those of nitrite reducers and the anammox abundance maxima were detected in the layers above and below the nitrite maximum. Nitrite accumulation in the two AMOR cores co-occurs with a niche partitioning between two anammox bacterial families (Candidatus Bathyanammoxibiaceae and Candidatus Scalinduaceae), likely dependent on ammonium availability. Through reconstructing and comparing the dominant anammox genomes (Ca. Bathyanammoxibius amoris and Ca. Scalindua sediminis), we revealed that Ca. B. amoris has fewer high-affinity ammonium transporters than Ca. S. sediminis and lacks the capacity to access alternative substrates and/or energy sources such as urea and cyanate. These features may restrict Ca. Bathyanammoxibiaceae to conditions of higher ammonium concentrations. These findings improve our understanding about nitrogen cycling in marine sediments by revealing coincident nitrite accumulation and niche partitioning of anammox bacteria.

Stormwater Pond Evolution and Challenges in Measuring the Hydraulic Conductivity of Pond Sediments

Stormwater ponds are intended to be used for mitigating floods, improving water quality, and recharging groundwater. The sediment-water interface (SWI) of stormwater ponds exhibits properties that influence surface water–groundwater exchanges similar to naturally occurring surface water bodies. However, these ponds are rarely monitored over time to account for their functionality. As organic and inorganic sediments accumulate on the pond bed, the ability of the SWI to conduct water is influenced by sediment deposition, accumulation, and compaction, as well as organic matter content and other biological processes. Two augmented methods, a sediment core permeability cell and an in situ aluminum tube and manometer, were evaluated for measuring the hydraulic conductivity of the SWI. The grain size, hydraulic conductivity, and percentage of organic matter were compared between two ponds constructed 22 years apart. Both methods were effective at measuring the hydraulic conductivities, especially in challenging encountered field situations, albeit with some shortcomings. The in situ method yielded data from sediments with low hydraulic conductivities due to thermal heating, expansion of the water, and the release of biogenic-derived gas from the sediments within the aluminum tube. The converted sediment core permeability cells generated the most consistent measurements. Grain size and hydraulic conductivities were correlated to pond age. The mean and effective grain sizes, as well as hydraulic conductivities of the older pond, were statistically lower than the younger pond in both shallow and deeper depths. Measurement of the changes in the SWI of stormwater ponds is important to protect urbanized areas from flood damage, control the quality and quantity of runoff, and maintain their groundwater recharge function.

The sediment budget and migration of 137Cs in Chernobyl affected area: 30 years of investigations in the Plava River basin, Tula region

The Plava River basin (Tula region) is considered the most polluted with Chernobyl fallout region in Russian Federation. Detailed studies of sediment redistribution and migration of 137Cs produced by Chernobyl were conducted in the basin. The article provides an overview of results from various studies conducted during the last 30 years estimating the rate of erosion and sediment redistribution based on different methodology including 137Cs. Sediment budgets for different parts of the fluvial network were developed based on estimated rates of erosion and accumulation of sediments within the Plava River basin for the post-Chernobyl period. It has been established that eroded from agricultural fields sediments accumulate on the slopes of interfluves (38.4%) and in the bottoms of dry valleys (2738%). Part of the sediment delivered by slope runoff and temporary watercourses from the slopes of the interfluves to the bottoms of river valleys was redeposited on river floodplains (1011%), and the remaining part (13.124.7%) passed into the river sediment load. The value of basin contribution of sediments to the Plava River sediment runoff is somewhat overestimated due to the specifics of the erosion models used to calculate soil erosion from arable land. It has been established that for the period of more than 25 years since the Chernobyl accident, 5% of 137Cs deposits were lost due to soil erosion (less than 0.2% annually). According to evaluated sediment budget, only a quarter of mobilized material leaves basin as a sediment yield. Thus, only about 1% of the initial 137Cs fallout was removed from the Plava basin. The perspective directions for research on sediment redistribution in the plain river basins located in the temperate zone using 137Cs as a technogenic tracer are outlined.

Simultaneous determination of 22 antibiotics in environmental water samples by solid phase extraction-high performance liquid chromatography-tandem mass spectrometry

The widespread and frequent use of antibiotics to treat diseases or encourage animal growth has resulted in their persistence and accumulation in water, soil, and sediments. As a typical emerging pollutant in the environment, antibiotics have become an important research focus in recent years. Antibiotics are commonly found at trace levels in water environments. Unfortunately, the determination of various types of antibiotics, all of which exhibit different physicochemical properties, remains a challenging endeavor. Thus, developing pretreatment and analytical techniques to achieve the rapid, sensitive, and accurate analysis of these emerging contaminants in various water samples is an essential undertaking.In this paper, a solid phase extraction-high performance liquid chromatography-tandem mass spectrometry (SPE-HPLC-MS/MS) method for the simultaneous determination of 22 antibiotics including 4 penicillins, 12 quinolones and 6 macrolides in environmental water samples was developed. Based on the characteristics of the screened antibiotics and sample matrix, the pretreatment method was optimized, focusing on the SPE column, pH of the water sample, and amount of ethylene diamine tetra-acetic acid disodium (Na2EDTA) added to the water sample. Prior to extraction, a 200 mL water sample was added with 0.5 g of Na2EDTA and pH-adjusted to 3 using sulfuric acid or sodium hydroxide solution. Water sample enrichment and purification were achieved using an HLB column. HPLC separation was carried out on a C18 column (100 mm×2.1 mm, 3.5 μm) via gradient elution with a mobile phase composed of acetonitrile and 0.15% (v/v) formic acid aqueous solution. Qualitative and quantitative analyses were performed on a triple quadrupole mass spectrometer in multiple reaction monitoring mode using an electrospray ionization source. The results showed correlation coefficients greater than 0.995, indicating good linear relationships. The method detection limits (MDLs) and limits of quantification (LOQs) were in the ranges of 2.3-10.7 ng/L and 9.2-42.8 ng/L, respectively. The recoveries of target compounds in surface water at three spiked levels ranged from 61.2% to 157%, with relative standard deviations (RSDs) of 1.0%-21.9%. The recoveries of target compounds in wastewater at three spiked levels were 50.1%-129%, with RSDs of 1.2%-16.9%. The method was successfully applied to the simultaneous determination of antibiotics in reservoir water, surface water, sewage treatment plant outfall, and livestock wastewater. Most of the antibiotics were detected in watershed and livestock wastewater. Lincomycin was detected in 10 surface water samples, with a detection frequency of 90%, and ofloxacin showed the highest contents (127 ng/L) in livestock wastewater. Therefore, the present method exhibits excellent performance in terms of MDLs and recoveries compared with previously reported methods. The developed method presents the advantages of small water sample volumes, wide applicability, and fast analysis times; thus, it can be considered a rapid, efficient, and sensitive analytical method with excellent potential for monitoring emergency environmental pollution. The method could also provide a reliable reference for formulating antibiotic residue standards. The results provide strong support for and an improved understanding of the environmental occurrence, treatment, and control of emerging pollutants.

Geochemistry aspects of modern mercury accumulation in bottom sediments from the south-western Chukchi Sea

Mercury (Hg) having a high migration capacity reach the Arctic region via the atmosphere. The absorbers for Hg are sea bottom sediments. Sedimentation in the Chukchi Sea occurs under the influence of highly productive Pacific waters entering through the Bering Strait and the inflow of a terrigenous component from the western direction with the Siberian Coastal Current. The Hg concentrations ranged from 12 μg kg−1 to 39 μg kg−1 in bottom sediments of study polygon. Based on dating sediment core the background concentration was 29 μg kg−1. Concentration of Hg in fine sediment fractions was 82 μg kg−1, in sandy fractions (>63 μm) varied from 8 to12 μg kg−1. In recent decades the Hg accumulation in bottom sediments has been controlled by the biogenic component. The Hg in the studied sediments presents as sulfide form.

Human-induced metals accumulation in sediments of an industrialized bay of northern Chile. An enrichment and ecological risk assessment based on preindustrial values

Environmental assessment in marine systems is difficult because most of the time their preindustrial characteristics are not available.Four sediment cores taken in Mejillones bay (northern Chile) were used to establish preindustrial metals concentrations, and to assess the environmental status of this industrialized zone.According to historical documents, the beginning of the industrial era start in 1850 CE. Considering this, the preindustrial concentration of some metals was established, by mean of a statistical approach.Most of the metals increase their concentration from the preindustrial to the industrial period. Environmental assessment showed an enrichment of Zr and Cr, a moderately polluted condition, and a low probability of toxic effect on the biological communities.The preindustrial values derived from sediment cores are a good tool to evaluate the environmental condition of Mejillones bay. However new information (backgrounds with a higher spatial representativity, toxicological threshold, and others) it is necessary to improve the environmental assessment of this environment.

Geochemistry and organic petrography of the Middle Permian Lucaogou alkaline lacustrine oil shale in the southern Junggar Basin, China: Implications for formation conditions and organic matter accumulation

Organic matter (OM) accumulation in terrestrial sediments shows not only a significant carbon sink in the Earth's carbon cycle but an important origin of fossil fuels, which is closely associated with the complex and diverse depositional environments and climate conditions. The Junggar Basin developed the most laterally extensive and thickest alkaline lacustrine sediments as well as the richest hydrocarbon source rock/oil shale interval of all the world during the deposition of the Lucaogou Formation and equivalent units. In this study, the sedimentary succession of 564 m with a mudstone and dolomite matrix of the Lucaogou oil shale from the Qi 1 well located in the southern Junggar Basin was investigated, which can be divided into two members based on lithology. This paper is a synthetic use of major element oxides, trace, and rare-earth elements as well as organic petrography data as proxies to evaluate the provenance, paleotectonic setting, paleoclimate and weathering conditions, paleoenvironment, and paleoproductivity as well as origin and accumulation of OM of the Lucaogou sediments.It is suggested that no recycling sediments in all the studied samples, based on parameters including the Th/Sc vs. Zr/Sc plot, the Chemical Index of Alteration (CIA) being linearly dependent on Weathering Index of Parker (WIP), and the high Index of Compositional Variability. The provenance mainly from intermediate-felsic volcanic rocks (e.g., granodiorite, andesite and dacite) is supported by the bivariate plots of Euanom vs. Th/Sc, La/Th vs. Hf, La/Sc vs. Co/Th, Cr/Th vs. Sc/Th, Y/Ni vs. Cr/V, and Nb/Y vs. Zr/TiO2 as well as triangular diagrams of mafic–felsic–weathering, M+–4Si–R2+ and Rb/V–Zr/Zn–Sc/Nb. The continental island arc is inferred from paleotectonic setting discrimination diagrams (i.e., the La–Th–Sc, Th–Co–Zr/10 and Th–Sc–Zr/10 ternary as well as Ti/Zr vs. La/Sc binary diagrams). The chemical weathering indices (i.e., the CIA, WIP, weathering index (W), Weathering Intensity Scale, Sodium Depletion Index, and Ga/Rb vs. K2O/Al2O3 binary diagram) indicate the paleoclimate conditions were cold/arid with weak chemical weathering in a warming and/or enhanced continental weathering episode. Besides, the Sr/Ba ratios and gallium concentrations indicate the paleosalinity was brackish to hypersaline and was higher in the lower member in relation to that in the upper member. However, the suboxic environment of the benthic water (inferred from the MoEF vs. UEF co-variations and Corg/P ratios as well as large sizes of framboidal pyrites) and the moderate paleoproductivity (evaluated via the Sibio, Babio, and Pbio values, as well as Ni/Al and Cu/Al ratios) caused by predominate algae and bacteria (inferred from the organic petrography) kept stable in the paleolake during this period. The OM accumulation was mainly controlled by the preservation conditions rather than the paleoproductivity and limited detrital inputs/low deposition rates, which was indicated by the plot of Co × Mn values vs. Cd/Mo ratios and the total organic carbon contents being negatively related to stable carbon isotope compositions of OM.

Which sediment fraction mainly drives microplastics aging process: Dissolved organic matter or colloids?

Riparian sediment is the last barrier preventing contaminants from polluting aquatic ecosystems. Recently, microplastics (MPs) have frequently been found in sediments. However, the MP aging process and its impact on sediments remain unknown. This study aimed to identify the key driving factors and mechanisms of riparian sediment on MPs aging behavior. The results showed that MPs surface suffered heavy breakage and the oxygen-to-carbon ratio of MPs increased by 268% after accumulation in sediment for 214 d. The carbonyl index revealed that the degree of MP aging driven by dissolved organic matter (DOM) was 6.7-83.6% greater than that of colloids, indicating that DOM was the key sediment fraction driving MP aging. Sunlight was an important environmental factor that enhanced MPs aging by sediment fractions, because photo-irradiated DOM produced hydroxyl and superoxide radicals to damage the MPs structure. Benzoic acid, dibenzoylmethane, and 4-heptyl-4,6-diphenyl-tetrahydro-pytan-2-one were the main products during the MP aging process under the interaction of sunlight and DOM, which showed acute toxicity to aquatic organisms and caused more severe toxicity during the chronic period. These results clearly clarify the behavior and environmental risk of MPs after accumulation in sediment, providing guide information to control MP pollution in the riparian zone.