Preferential deposition of buoyant small microplastics in surface sediments of the Three Gorges Reservoir, China: Insights from biomineralization

Sediments act as sinks of microplastics (MPs) derived from terrestrial ecosystems. However, the fate and transport of MPs at the zone of sediment-overlying water in reservoir environment are poorly understood. Here, the MPs distribution patterns in surface sediments of the Three Gorges Reservoir (TGR) and dominant mechanisms responsible for the sinking of MPs at the zone of sediment-overlying water were comprehensively investigated. The predominant occurrence of small microplastics (<300 µm, SMPs) in surface sediments of the TGR was found, with buoyant polyethene (PE) was dominant polymer types. Interestingly, the high abundance of SMPs in sediments correlated well with the Ca2+/Mg2+ in overlying water, suggesting that divalent cations in overlying water may enhance the preferential deposition of SMPs. Simulation sinking experiments under the presence of Microcystis aeruginosa and two divalent cations using different-sized PE MPs demonstrated that the greater deposition of SMPs was mainly the result of the formation of biogenic calcite on the surface of MPs rather than magnesium minerals, which provides stronger ballasting effects for SMPs than for large MPs. This study first highlights that the impact of biomineralization on preferential sinking of SMPs and enhances the understanding of the transport behaviour of MPs in aquatic environment.

Trace metals and pesticides in water-sediment and associated pollution load indicators of Netravathi-Gurupur estuary, India: Implications on coastal pollution

Various environmental indicators were used to evaluate the water and sediment quality of the Netravathi-Gurupur estuary, India, for trace metals and pesticide pollution. The descended order of studied metal concentrations (μg/L) in the water was Fe (592.71) > Mn (98.35) > Zn (54.69) > Cu (6.64) > Cd (3.24) > Pb (2.38) > Cr (0.82) and in sediment (mg/kg) was Fe (11,396.53) > Mn (100.61) > Cr (75.41) > Zn (20.04) > Cu (12.77) > Pb (3.46) > Cd (0.02). However, pesticide residues were not detected in this estuarine environment. The various metal indexes categorised the water as uncontaminated, whereas contamination factor, enrichment factor, geo-accumulation index, degree of contamination and pollution load index indicated low to moderate sediment contamination. Multivariate statistics showed that the dominance of natural sources of trace metals with little anthropogenic impact. Improvement in water/sediment quality during the study period might be due to COVID-19 imposed lockdown.

Spatial distribution, conversion, and ecological risk assessment of hexabromocyclododecanes in the sediments of black-odorous urban rivers nationwide in China

Hexabromocyclododecanes (HBCDs) have become a global pollution problem, particularly in China-a major producer and user of HBCDs. However, little is known about the HBCD pollution status in urban rivers nationwide in China. In this study, we comprehensively investigated the pollution characteristics of HBCDs in 173 sediment samples from black-odorous urban rivers across China. Total HBCD concentrations ranged from not-detected to 848 ng/g dw, showing significant differences among the various sampling cities, but generally increasing from west to east China. This distribution pattern of HBCDs was strongly associated with the local industrial output, gross domestic product, and daily wastewater treatment capacity. α-HBCD was the predominant diastereoisomer in most sediments, with an average proportion of 63.8 ± 18.8 %, followed by γ-HBCD (23.8 ± 19.5 %) and β-HBCD (12.4 ± 6.49 %), showing a significant increase of the α-HBCD proportions relative to those in HBCD commercial mixtures and an opposite trend for that of γ-HBCD. These results suggested that HBCDs might undergo isomerization from γ- to α-HBCD and biotic/abiotic degradation with preference for γ-HBCD. Of these conversions, the microbial degradation of HBCDs was further verified by the preferential transformation of (-)-α-, (+)-β-, and (-)-γ-HBCDs and the detection of HBCD-degrading bacteria, including Dehalococcoides, Bacillus, Sphingobium, and Pseudomonas. A risk assessment indicated that HBCDs pose low to moderate risks to aquatic organisms in most black-odorous urban river sediments.

Microplastic contamination in Thai vinegar crabs (Episesarma mederi), giant mudskippers (Periophthalmodon schlosseri), and their surrounding environment from the Bang Pu mangrove forests, Samut Prakan province, Thailand

The mangrove ecosystem becomes the receptacle for both land- and marine-based plastic waste. This study examines MPs contamination in the Bang Pu mangrove forests (BPMFs) in the inner Gulf of Thailand. For this, Thai vinegar crabs (TVCs) (Episesarma mederi) and giant mudskippers (GMs) (Periophthalmodon schlosseri) were investigated with their surrounding environment in both rainy and dry seasons. Two-step digestion was employed for biota samples. MPs abundance ranged from 7.5 ± 3.8 to 15.9 ± 6.7 items/individual in TVCs and 6.2 ± 5.0 to 10.6 ± 2.6 items/individual in GMs. MPs in small-size ranges (<0.5 mm) were predominant. Fiber MPs were mostly detected in the rainy season. Most MPs were transparent with polyethylene and polypropylene as dominant polymers in all samples. Bioaccumulation was not observed in GMs. The results indicated the imperiled status of MPs contamination in TVCs and GMs with contaminated surrounding environments.

Correlation between polycyclic aromatic hydrocarbons and total organic carbon in surface sediments of the Bohai Sea and the North Yellow Sea

The correlation between polycyclic aromatic hydrocarbons (PAHs) and organic carbon is an important indicator of the marine environment. In this paper, twenty-six surface sediment samples were collected from the Bohai Sea and the North Yellow Sea as the study area, and the contents of sixteen PAHs ranged from 71.34 ng·g-1 to 240.78 ng·g-1 with an average of 143.26 ng·g-1 by gas chromatography. The source analysis indicated the source of PAHs in the surface sediments of the study area was more complex, and the percentage of combustion sources was higher than that of petroleum sources, which might cause less negative ecological risks. The average content of total organic carbon (TOC) was 5.25%, as determined by automatic potentiometric titration, and the content of TOC was higher in the Bohai Sea than in the North Yellow Sea. TOC was significantly correlated with HWM-PAHs but was not correlated with LWM-PAHs, which proved organic matter was more effective in controlling high-molecular-weight PAHs than low-molecular-weight PAHs in the surface sediments of the Bohai Sea and the North Yellow Sea.

Distribution, contamination assessment, and sources of heavy metals in surface sediments from the south of the North Yellow Sea, China

This paper reports the contents of six heavy metals and particle sizes in the surface sediments of 120 sampling stations in the southern North Yellow Sea to reveal heavy metal distribution characteristics, contamination assessment, and sources. Cu and Cr enrichments were mainly found in coastal areas with high mud content (silt and clay). However, Zn, Cd, Pb, and Hg were enriched in Weihai Bay and Dongpu Bay, which have denser populations, estuaries, and shipyards. The geoaccumulation index and principal component analysis showed that Cu and Cr contamination was low, and the sources were mainly natural processes. In addition, Zn and Cd pollution in the nearshore area was moderate, and its provenance was natural processes and human activity. However, most areas exhibited Pb and Hg contamination due to waterborne traffic and industries, including shipbuilding and gold mining.

Spatio-temporal distribution of microplastic pollution in surface sediments along the coastal areas of Istanbul, Turkey

Microplastics (MPs) have become prevalent in various environmental compartments, including air, water, and soil, attracting attention as significant pollutant parameters. This study investigated the prevalence of MP pollution in surface sediments along Istanbul's Marmara Sea, encompassing the megacity and the Bosphorus. A comprehensive sampling approach was employed, covering 43 stations across four seasons and depths ranging from 5 to 70 m. The objective was to assess the impact of terrestrial, social, and industrial activities on MPs. The average concentrations varied per season, with fall, winter, spring, and summer values recorded as 2000 ± 4100, 1600 ± 3900, 4300 ± 12,000, and 9500 ± 20,300 particles/kg-DW. The study identified river stations in the Golden Horn and sea discharge locations as hotspots for high concentrations. Notably, the dominant shape shifted from fibers in fall, winter, and spring to fragments during summer, coinciding with mucilage occurrences. The study identified 11 different polymers, with polyethylene (44 %) and polypropylene (31 %) being the most common.

Magnetic susceptibility and heavy metal contents in sediments of Riam Kiwa, Riam Kanan and Martapura rivers, Kalimantan Selatan province, Indonesia

Kalimantan Selatan is proud of the Martapura River's natural and cultural history. Martapura tributaries include Riam Kanan and Kiwa. The Martapura River is essential because it provides clean water and a livelihood for riverside residents. Human-caused river pollution grows with population density (also known as anthropogenic pollutants). This study characterizes surface sediment magnetic characteristics and heavy metal contents along the Riam Kanan, Riam Kiwa, and Martapura rivers. The purpose of this research is to evaluate the magnetic signal with respect to heavy metal contents found in surface sediments taken from rivers and to confirm the use of the rock magnetism method in environmental studies in the study area. Surface sediment samples were gathered and tested for magnetic, heavy metal, and mineralogical content. According to the findings, the pseudo-single domain (PSD) magnetite mineral predominates among the magnetic minerals that can be found in the surface sediments of the rivers Riam Kanan, Riam Kiwa, and Martapura. This substantially greater grain size may be due to magnetic particles produced by erosion along the river banks. The mass-specific magnetic susceptibility of surface sediments ranges from 103.11 to 1403.64 × 10^-8 m³/kg, with an average value of 355.67 × 10^-8 m³/kg due to the peatland environment. Magnetic susceptibility strongly negatively correlates with heavy contents like Cu, Zn, and Hg, according to Pearson correlation analysis. Due to this correlation, magnetic susceptibility may indicate heavy metal pollution in certain rivers. This current study demonstrates the novelty of the relationship between magnetic susceptibility and the contents of heavy metals in surface sediments from rivers in peatland and tropical environments by illustrating how the relationship affects the magnetic susceptibility of the sediments.

Seasonal variation and provenance of organic matter in the surface sediments of the three gorges reservoir: Stable isotope analysis and implications for agricultural management

The construction of the Three Gorges Dam has altered the hydrology and increased the trapping of sediment in the reservoir. This has also changed the composition and export of particulate organic matter in the Yangtze River. To understand the seasonal variations and sources of organic matter in sediments, total organic carbon (TOC), total nitrogen (TN), δ¹³C_org and δ¹⁵N in surface sediment samples from the mainstream and tributaries of the Three Gorges Reservoir were measured in the summer (July) and winter (December) of 2017, respectively. The results showed that the concentrations of TOC and TN in the surface sediments of the Three Gorges Reservoir were 0.79 %-1.46 % and 0.07 %-0.13 %, respectively. The ranges of δ¹³C_org and δ¹⁵N were - 26.35 ‰ to-24.70 ‰ and 2.59 ‰ to 5.67 ‰, respectively. According to δ¹³C_org and the TOC/TN ratio, the source range of organic matter was determined, and the contributions of different organic matter sources were quantified using a Bayesian mixed model. The results showed that soil organic matter and river plankton were the main sources of surface sediment organic matter in summer, whereas soil organic matter and aquatic vascular plants were the main sources in winter. The source of organic matter is related to biological factors in summer, whereas it is mainly caused by hydrodynamic conditions in winter. The analysis of δ¹⁵N further reveals that there are obvious external pollutants in the Three Gorges Reservoir, mainly related to artificial nitrogen fertiliser and domestic sewage. This study highlights the influence that soil nitrogen loss may be an important reason for the impact of agricultural non-point source pollution in the reservoir area, showing seasonal differences which were mainly affected by rainfall in summer and controlled by impoundment in winter. Hence, fine nitrogen management is required to reduce pollution in the Three Gorges Reservoir.

Influence of land cover, point source pollution, and granularity on the distribution of metals, metalloids, and organic matter in the river and stream sediments in the Republic of Korea

With increasing anthropogenic activities, rivers and streams have become vulnerable to pollution; therefore, monitoring potential contaminants and the pollution status of surface sediments is essential. This study analyzed the concentrations of organic matter, metals, and metalloids; indices for organic, metal, and metalloid pollution; and ecological risk in river and stream sediments at 82 stations across Korea in 2017, 2018, and 2020. We performed bootstrapped analysis of variance, principal component analysis, and cluster analysis and used a structural equation model (SEM) to investigate spatiotemporal changes in the pollution status, main pollutant chemicals, and the exogenous factors affecting pollution status. The results suggest no significant differences in any of the twelve single chemical parameters and three pollution indices across the surveyed years. Metals, metalloids (Cu, Zn, Pb, and Hg), and organic matter with nutrients were identified as the main pollutants. The SEM demonstrated the significant influence of pollution sources-water used for industrial purposes, landfill wastewater discharge, and industrial wastewater discharge-on organic pollution, metal and metalloid pollution load, and environmental toxicity. This study identified consistently polluted areas, proposed additional management policies and stricter regulations on major point pollution sources rather than on broader land-use types, and suggested the combined consideration of metal toxicity risk with nutrient accumulation for future risk assessments.

Insights about levels and source appointment of petroleum hydrocarbons in Brazilian semi-arid coastal: baseline status assessment for ocean decade targets

The Ocean decade (2021-2030) for sustainable development proclaimed in 2017 by the UN, seeks to promote and conserve the sustainable use of oceans, seas, and marine resources. For this, the distribution of n-alkanes, polycyclic aromatic hydrocarbons (PAHs), and biomarkers, in sediments from the Fortaleza coastal zone (Mucuripe harbor (MH) and Inner Continental shelf (ICS)) were used to assess the impacts of anthropogenic activities in the area. The concentrations of total n-alkanes (Σ16 n-alkanes) in MH and ICS sediments varied from 35.9 to 94.9 and 17.9 to 197.3 μg g^-1, respectively, while the isoprenoids phytane and pristane in MH and ICS sediments ranged from 0.1 to 1.69 ug g^-1 and from 0.14 and 1.20 μg g^-1, respectively. Most of the sediment samples presented carbon preference index (CPI) values close to unity, indicating that the area is submitted to petroleum-related sources. The concentrations of Σ16 PAHs in MH and ICS sediments varied from 87.0 to 562.0 and 98 to 288.0 ng g^-1. This work presents the first investigation of the petroleum biomarkers hopanes and steranes in the Fortaleza coastal zone, in which ΣBiomarkers varied from 0.10 to 1.79 and 0.02 to 0.24 ug g^-1 in MH and ICS sediments, respectively. The presence at stations of biomarkers also indicates petrogenic input. The diagnosis of the distribution of pollutants in the investigated zones of the Fortaleza coast suggests contamination from urban areas and oil spills and vessel traffic.

Bacterial community composition of the sediment in Sayram Lake, an alpine lake in the arid northwest of China

Sediment bacterial communities play a critical role in biogeochemical cycling in alpine lake ecosystems. However, little is known about the sediment microbial communities in these lakes. In this study, the bacterial community composition (BCC) and their relationships with environmental factors of the sediment in Sayram Lake, the largest alpine and cold-water inland lake, China was analyzed using Illumina MiSeq sequencing. In total, we obtained 618,271 high quality sequences. The results showed that the bacterial communities with 30 phyla and 546 genera, were spread out among the 5 furface sediment samples, respectively. The communities were dominated by Proteobacteria, Acidobacteria, Planctomycetes, Gemmatimonadetes, Chloroflexi, Actinobacteria, Verrucomicrobia and Bacteroidetes, accounting for 48.15 ± 8.10%, 11.23 ± 3.10%, 8.42 ± 2.15%, 8.37 ± 2.26%, 7.40 ± 3.05%, 5.62 ± 1.25%, 4.18 ± 2.12% and 2.24 ± 1.10% of the total reads, respectively. At the genus level, the communities were dominated by Aquabacterium, Pseudomonas, Woeseia, MND1, Ignavibacterium and Truepera, accounting for 7.89% ± 8.24%, 2.32% ± 1.05%, 2.14% ± 0.94%, 2% ± 1.22%, 0.94% ± 0.14% and 0.80% ± 0.14% of the total reads, respectively. Statistical analyses showed the similarity of the sediment bacterial communities at our field sites was considerably low, far below 35%, and total organic carbon (TOC) was the dominant environmental factor affecting the spatial changes of BCC in the sediment. Thus, this study greatly improving our understanding of the microbial ecology of alpine lake in the arid and semi-arid ecosystems today so seriously threatened.

Geochemical distribution and forms of phosphorus in the surface sediment of Netravathi-Gurupur estuary, southwestern coast of India

Estuaries are the most productive transition ecosystem and phosphorus (P) plays an important role in these ecosystems. Therefore, in the present study, sequential extraction method was used to determine the abundance of five sediment P fractions (calcium (Ca-P), Iron (FeP), aluminum (AlP), exchangeable (Ex-P) and organic (OrgP) bound P) in Netravathi-Gurupur estuary, India. Total phosphorus (TP) content varied from 435-810 mg/kg (non-monsoon) and 258-699 mg/kg (monsoon). Inorganic P was dominant part. Different P fractions followed similar order (Fe-P > Ca-P > Al-P > Org-P > Ex-P) with respect to seasons. FeP was dominant fraction, indicating probable anthropogenic stress. Sediment may act as source of P as bioavailable P constituted 40-69.2 % of TP. Molar ratio of OC to Org-P in sediment indicated terrestrial sources of organic matter. However, the estimated phosphorus pollution index were lower than one except a few cases indicating less ecological risk with respect to sedimentary TP load.

Occurrence, spatial distribution, and risk assessment of short- and medium-chain chlorinated paraffins in sediment from black-odorous rivers across China

Chlorinated paraffins (CPs) were massively produced for varied industrial purposes, of which improper handling and consequent environmental release resulted in worldwide contamination. The present study investigated the occurrence and spatial distribution of short- and medium-chain chlorinated paraffins (SCCP/MCCPs) in 171 sediment samples from black-odorous urban rivers across China. Total SCCP and MCCP concentrations ranged from 8.3 to 9.4 × 10⁴ (median: 1.1 × 10³) ng/g dw, and from not-detected-value to 1.0 × 10⁶ (median: 1.3 × 10⁴) ng/g dw, respectively. No clear spatial distribution of SCCPs and MCCPs was observed since black-odorous urban rivers were polluted by point-sources of the SCCP/MCCPs. Significant positive correlations were identified between SCCP/MCCPs and total organic carbon, and between SCCP/MCCPs and other persistent organic matter, including polybrominated diethyl ethers, polychlorinated biphenyls, antibiotics, and plasticizers. The average ratios of MCCPs to SCCPs in most samples were divided into 11 and 16, implying the manufacturing and use of at least two types of CP technical mixtures in China. The composition of SCCP/MCCPs were similar to that in their commercial products. Ecological risk assessments by two approaches, including the Federal Environmental Quality Guidelines and Risk Quotient, both revealed that SCCP/MCCP in surface sediments confer an ecological risk. ENVIRONMENTAL IMPLICATION: SCCPs and MCCPs can be considered "hazardous materials" because of their massive production and their potential persistence, long-distance transfer, bioaccumulation potential, and toxicity. This research conducted a comprehensive study on SCCP/MCCP in black-odorous urban river sediments across China and revealed their environmental risk, which may improve understanding of SCCP/MCCP contamination characteristics.

Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Seawater and Sediments, Human and Ecological Risks, Northern Coastline of Persian Gulf

This study aimed to assess 13 PAHs concentrations and induced human and ecological risks in seawater and surficial sediments of eight estuaries in the northern coastline of the Persian Gulf, Iran, 2021. The range of Σ13 PAHs concentration was 0.24-8.83 µg L^-l and 3.1-11.46 µg g^-1 dry weight, and the mean value was 4.99 µg L^-l and 6.06 µg g^-1 dry weight in seawater and sediment, respectively. Two, three and four rings PAHs were dominant with 29.33% and 41.33% of ΣPAHs in seawater and sediment, respectively. The primary source of PAHs was both pyrolytic and petrogenic. Most PAHs' calculated health (DCR, HQs, TEF, MEF) and ecological risks (SQGs) values in seawater were in the moderate range or high-risk values for damage to the marine environment. It is concluded that the pollution of PAHs should be carefully considered, and the government should make a proper action plan to minimize the pollution.

Geochemical characteristics of heavy metals in surface sediments of the Bohai Strait, China

The heavy metal (Cr, Cu, Ni, Pb, and Zn) content and particle size of surface sediment samples taken from 123 sites in the Bohai Strait of China were analyzed. All five heavy metals showed a similar distribution in the Bohai Strait, with lower concentrations in the middle and higher concentrations at the sides of the strait. The amount of heavy metals was lowest in the Laotieshan Channel due to the rapid current in this channel. According to our calculated values of the pollution index (Pi), only 1.6 % of the sample sites were polluted by Cr and Cu. The calculated geo-accumulation index (Igeo) values showed that few of the sites were polluted by heavy metals. The level of Pb was controlled by both terrigenous inputs and clay adsorption, while the levels of the other heavy metals (Cr, Cu, Ni, and Zn) were mainly controlled by terrigenous inputs.

Determination of PCDD/F and DL-PCB pollution levels, source appointment and risk assessment of surface sediments in dam lakes in Istanbul, Türkiye

The current situation of the water resources of Istanbul, which is one of the important metropolises of Europe, should be known and constantly monitored by the reasons of the rapid increase in the city population, the acceleration of production-related industrial activities, the expansion of the city with construction activities, and the decrease in precipitation. The purpose of this study was to reveal the situations of surface sediments collected from Istanbul water reservoirs in terms of PCDD/Fs and DL-PCBs, to identify possible sources, and to conduct their ecological risk assessment. Total PCDD/Fs and DL-PCBs concentrations varied between 28.13 and 457.4 pg/g (average 136.8 pg/g) and 12.19-340.1 pg/g (average 72.09 pg/g). The corresponding TEQ values of PCDD/Fs and DL-PCBs were between 0.53 and 5.37 pg TEQ/g (average 2.23 pg TEQ/g) and 0.02-0.44 pg TEQ/g (average 0.12 pg TEQ/g), respectively. Octachlorodibenzo-p-dioxin (OCDD) is the dominant congener by constituting about 75% of the total PCDD/Fs on average, while congener distributions of DL-PCBs showed the dominance of PCB-118 and PCB-105. The sediments taken from Kazandere dam have the lowest pollution levels for both PCDD/Fs and DL-PCBs. The highest PCDD/F and DL-PCB amounts were measured in sediments of Alibey and Elmalı dams (closest to highly populated settlements of Istanbul), which are most affected by the air pollution caused by the traffic, commercial/industrial combustion (like waste incineration facility) and combustion for residential heating. Almost all the sediments have total dioxin-like toxicity levels higher than the safe threshold level (with two exceptions) of 0.85 pg TEQ/g dw, proposed for ecological risk. Health risk assessment shows that levels of dioxin-like compounds would result in a total intake of 0.33 pg TEQ/kg bw/day even in the worst-case scenario, not exceeding the tolerable daily intake value of 1 pg TEQ/kg bw/day. Among exposure pathways, consumption of fish constitutes almost all the total intake, while contributions of other pathways are minimal.

Mercury and other trace elements distribution and profiling of microbial community in the surface sediments of East Siberian Sea

In this study, total mercury (THg), methylmercury (MeHg), various trace elements, and microbial communities were measured in surface sediments of the East Siberian Sea (ESS). The results showed that the average values of THg and MeHg were 58.8 ± 15.21 μg/kg and 0.50 ± 0.22 μg/kg, respectively. The notable levels of trace elements present in both surface sediment and porewater were Al, Fe, and Mn. The enrichment factor and geoaccumulation index analyses found that both natural phenomena and anthropogenic activities contributed to elevated concentrations of metals in the ESS. The redox proxy metals, pH, and SO₄^2- were the major factors influencing the THg and MeHg distributions. Microbial profiles were substantially affected by metals and other abiotic factors. Proteobacteria and Thaumarchaeota were the most abundant phyla. Overall, the findings presented here facilitate the understanding of the current status of metal contamination, its influencing factors, and metal-microbiota-interactions in ESS.

Risk Assessment and Source Identification of Arsenic in Surface Sediments from Caohai Lake, China

Urban freshwaters containing arsenic are facing an increasing problem of eutrophication. This study evaluated the spatial distribution, ecological risk, and origin of As in surface sediments obtained from Caohai Lake, a typical hypertrophic urban lake in China. It revealed that the total As concentration in surface sediments decreased gradually from north to south, consisted with the lake eutrophication status. The average As level was 161 mg/kg, dominated by reducible and oxidisable fractions. The analyses of geoaccumulation index and enrichment factor indicated that As ranged between moderately-to-heavily and heavily contamination, was severely influenced by anthropogenic factors, i.e. industrial discharges and agricultural activities. Risk assessment code and potential ecological risk index results showed moderate to high potential ecological risk could be observed although the current As risk was low, supporting by the experimentally quantified As release data.

Assessment of trace element contamination in the historical nesting grounds of green sea turtle (Chelonia mydas) in Hainan Island, China

Trace element pollution is a potential threat to the reproduction of sea turtles. Hainan Island was previously the most important nesting ground of green sea turtles in China before they disappeared approximately 36 years ago. The Chinese government has encouraged restoration work on historical nesting grounds, and it is necessary to evaluate the status of these sites before conducting habitat restoration. This study analyzed the concentrations of seven trace elements in the surface sediments of 13 historical nesting grounds in Hainan. The average concentrations were 19.47 (Cr), 4.67 (Ni), 6.99 (Cu), 0.08 (Cd), 16.68 (Pb), 0.02 (Hg), and 5.27 (As) mg/kg, which were lower than the first-grade limit values of the GB (18668-2002) national standard in China. The concentrations were close to the background value, except for the relatively high Cd value. The potential ecological risk was ranked as Cd > Hg > As > Cu > Pb > Cr. The spatial distribution of trace element contamination in Hainan was uneven, with high potential ecological risk levels of Cd and Hg contamination in Longwan'gang, Shimeiwan, Yazhou Qu, and Fushicun. Marine mariculture, wastewater discharge, and fishing boats are the main sources of trace element contamination in Hainan. We recommend strengthening the control of Hg and Cd contamination sources, monitoring trace elements in relevant/interest areas, and the environmental protection department should curb local residents from directly discharging mariculture wastewater and domestic sewage into the sea.

Assessing spatiotemporal sources of biogenic and anthropogenic sedimentary organic matter from the mainstream Haihe River, China: Using n-alkanes as indicators

Sedimentary organic matter (SOM) plays an important role in the transportation and transformation of various pollutants and the carbon cycle in aquatic and terrestrial ecosystems, especially for seagoing rivers. However, few studies have focused on the sources and factors of SOM in rivers under the significant pressure of high urbanization and industrialization. In this study, we adopted the molecular markers of n-alkanes and their proxies in the mainstream Haihe River to reveal the spatiotemporal distributions and biogenic and anthropogenic sources of SOM. The concentrations of Σ₂₉n-alkanes, Σ_biogenicn-alkanes, and Σ_{anthropogenic}n-alkanes were 4985.6 (127.5-26,296.6), 1872.1 (38.1-9216.9), and 3113.5 (89.4-18,259.7) ng·g^-1 dw (dry weight), respectively. Hybrid sources of n-alkanes were found in this study. The composition distribution and proxies of n-alkanes showed that woody and herbaceous plants are the main sources of biogenic SOM, while incomplete fossil fuel burning and heavy oil emissions served as the main contributors to anthropogenic SOM in the mainstream Haihe River, especially through industrial activities. The average chain length of biogenic n-alkanes (ACL_bio) was verified to quantify the relative contributions of biogenic sources of SOM and proxies; the average chain length of anthropogenic n-alkanes (ACL_anthro), and the ratio of unit short‑carbon to unit long‑carbon anthropogenic n-alkanes (L/H) were verified to quantify the relative contributions of anthropogenic sources of SOM in the river system. Impacts from sedimentary geochemistry (such as total organic carbon (TOC) and grain size of sediments) on n-alkanes were explored, and the correlations of Σ₂₉n-alkanes with TOC and grain size of the river sediment indicated that terrestrial organic matter was the main source of SOM, while emissions from incomplete combustion and intensive manufacturer activities should also not be neglected.

Distribution and ecological risk assessment of phthalic acid esters in surface sediments of three rivers in Northern Vietnam

Pollution status and distribution characteristics of ten typical phthalic acid esters (PAEs) were investigated in 36 sediment samples collected from three rivers in Northern Vietnam from June to October 2020. The total concentrations of PAEs in sediment samples collected from the To Lich River (n = 9), the Nhue River (n = 12), and the Day River (n = 15) were in ranges of 11,000-125,000 ng/g-dwt (mean/median: 50,000/42,200 ng/g-dwt), 2140-89,900 ng/g-dwt (mean/median: 29,300/20,700 ng/g-dwt), and 1140-43,100 ng/g-dwt (mean/median: 13,800/10,400 ng/g-dwt), respectively. Among ten PAEs studied, di-(2-ethylhexyl) phthalate (DEHP) was found at the highest levels in all samples meanwhile dimethyl phthalate (DMP), diethyl phthalate (DEP), and dipropyl phthalate (DPP) were detected at low frequency and concentration. Significant correlations have existed between the median-chain (C₄-C₇) PAE pairs in sediment samples. Due to the high accumulation in the sediments, the median-chain PAEs had a higher ecological risk than the short-chain (C₁-C₃) PAEs. These contaminants may present a longstanding influence on organisms and ecosystems.

Distribution and assessment of heavy metal in sediments of Malacca Strait

In this study, we explored the heavy metal elements in 42 surface sediments from the Malacca Strait in terms of distribution, controlling factors, environmental quality, and primary sources. An analysis of grain size revealed finer sediments near the coast of Malaysia, which gradually thickened toward offshore. In addition, heavy metal elements were abundantly distributed near the coastal area of Malaysia, with a gradual decrease toward the sea; their content increased within waters close to the Perak estuary. Source analysis of heavy metals showed that Cr, Hg, Zn, Cd, and Cu were mostly derived from natural weathering, and their distribution was significantly influenced by sediment grain size. As and Pb were affected by human activities. The environmental quality assessment results showed that Cu, Cr, Cd, and Zn in our study regions were pollution-free. Pb elements showed low-to-moderate pollution, and Hg showed a certain degree of ecological risk due to its high toxicity coefficient. The content of As elements in surface sediments increased significantly when compared to the background value, with several evaluation methods indicating a high-risk index. According to these findings, the area near the mouth of the Perak River is the most polluted, followed by the surrounding coastal areas.

Ecotoxicological assessment of toxic elements contamination in mangrove ecosystem along the Red Sea coast, Egypt

Identifying biochemical aspects of the potentially toxic elements (PTEs) is of particular concern in mangrove ecosystems, Avicennia marina (Forssk.) Vierh., due to their importance as natural buffers in coastal areas. Nonetheless, the microbial community dynamics and potential scavenging responses of mangrove ecosystems to the phytotoxicity of PTEs remain questionable. This study assesses the ecological risk benchmarks of some PTEs, including aluminum (Al), boron (B), barium (Ba), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn), and their microbial responses in the bottom sediments of mangrove ecosystems along Egypt's Red Sea coast. In particular, we assessed the role of microbial metabolites in biochemical cycling of nutrients and scavenging against phytotoxicity hazards. We quantified a spectrum of ecological risk assessment indices, which suggested elevated levels of PTEs in sediment, particularly Cr, Hg, and Pb. Canonical correspondence analysis and generalized linear mixed effects models indicate that the spatial biodiversity of microbial taxa is impacted significantly by the physicochemical characteristics of sediments and concentrations of PTEs. Results demonstrate that the microbial communities and their metabolites exert a significant influence on organic matter (OM) decomposition and the biochemical cycling of phytoavailable nutrients including nitrogen (N), phosphorus (P), and potassium (K). Spatially, nitrogenase activities were higher (411.5 μmoL h^-1 mL^-1) in the southern sites of the Red Sea coast relative to the northern locations (93.8 μmoL h^-1 mL^-1). In contrast, higher concentrations of phytohormones, including indole-3-acetic acid (IAA) (61.5 mg mL^-1) and gibberellins (534.2 mg mL^-1), were more evident in northern sites. Siderophores correlated positively with Fe concentration in sediments and averaged 307.4 mg mL^-1. Overall, these findings provide insights into the biochemical signals of PTEs contamination in hostile environments, contributing to a better understanding of the future prospects of PTEs bioremediation in contaminated coastal environments.

Seasonal Variation and Contamination Risk Assessment of Heavy Metals in Surface Sediment of an Estuary Alluvial Island in Eastern China

The heavy metal pollution of estuary wetlands caused by industrial and agricultural production activities has aroused widespread concern. The Hakanson Pollution index, Geo-accumulation index (I_geo) and Redundancy analysis were used to explore the seasonal variation and contamination risk of heavy metals in surface sediments. Results showed that the heavy metal concentrations were ranked in descending order: Cd > Cu > Zn > Pb > Cr. The analysis result of HPI and I_geo showed that there was a low level of heavy metal contamination both in summer and winter. Redundancy analysis showed that the correlation between heavy metals and physicochemical properties of sediment was significantly different in winter and summer. Our findings provide scientific support for the prevention of heavy metal pollution in estuary wetlands.

Spatial distribution, source identification and ecological risk assessment of POPs and heavy metals in lake sediments of Istanbul, Turkey

Istanbul needs to be protected and constantly monitored water resources due to its increasing population and the decrease in precipitation. This study aims to comprehensively reveal surface sediments collected from reservoirs that supply water to Istanbul concerning POPs (PAHs, PCBs, and OCPs) and heavy metals; to identify possible sources of PAHs, and conduct their ecological risk assessment. Pollution indices in this study were used as contamination degree (CD) contamination factor (CF), geoaccumulation index (I_geo), pollution load index (PLI) and Sediment Quality Guidelines (SQGs). Total PAH concentrations of surface sediments at the sampling points ranged from 46.29 ng/g (A7) to 403.9 ng/g (A15). Benzo(b)fluoranthene (5.647-59.42 ng/g), Pyrene (3.625-83.10 ng/g), Fluoranthene (3.363-66.48 ng/g), Phenanthrene (3.115-52.48 ng/g), Chrysene (3.532-43.98 ng/g), Naphthalene (6.606-36.20 ng/g), Benzo(g,h,i)perylene (3.316-41.73 ng/g) and Indeno(1,2,3-c,d)pyrene (3.453-38.84 ng/g) are the dominant PAH compounds. PAH pollution may be caused by the village-town settlements near the dam and the O7-D020 highway. Total OCP concentration ranged from 2.233 ng/g (A12) to 7.337 ng/g (A1), while total PCB concentration ranged from 0.246 ng/g (A13) to 3.708 ng/g (A1). The lowest total OCP and PCB concentrations were found in surface sediments taken from Kazandere, Papuçdere and Alibey Dam lakes. DDT p,p (0.072-5.177 ng/g) has the highest concentration among all sediment samples. While the most dominant OCP compounds in the samples were DDT p,p, DDE p,p and DDD p,p, HCH alpha, HCH beta, respectively, PCB 153, 138 and 180 were the highest detected PCB congeners in the same samples. Total heavy metal concentration varied from 77,812 mg/kg to 267,072 mg/kg. According to PAH diagnostic analysis, the surface sediments of Terkos, Büyükçekmece, Elmalı, Darlık, Sazlıdere, Alibey and Ömerli Dams were polluted by petrogenic sources, while the surface sediments of Kazandere and Papuçdere Dams were affected by pyrogenic sources. None of the levels of POPs in the samples exceeded the ERM values. Slight and moderate contamination of heavy metals, such as Pb and Zn, were present in most of the sampling points according to CD, CF, PLI and I_geo values. The quality criteria of heavy metals showed that almost all of the sampling points had Cd, Pb and Hg concentrations below the ERL values. The Ni concentrations at most of the sampling points significantly exceeded the ERM values. The concentrations of As, Cr, Cu and especially Ni and Zn exhibit a significant toxic risk to aquatic organisms to sediment quality criteria.

Distribution, source identification and environmental risk assessment of potentially toxic elements (PTEs) in the surface sediment of Sanmen Bay, Zhejiang Province, China

In this paper, the distribution, degree of pollution and sources of Cu, Pb, Zn, Cd, Cr, As, Co, Ni and Hg in the surface sediment of Sanmen Bay were studied. The average concentrations of the identified potentially toxic elements (PTEs) were in the following order: Zn > Ni > Cr > Cu > Pb > Co > As>Cd > Hg. Almost all PTEs had a significant positive correlation with TOC, clay and Al; Cr had no significant correlations. Apart from Hg, the contamination levels of 8 PTEs were at those considered to be low-to-no pollution. Comparatively, the contamination level of Hg was much higher than the background value, which indicated moderate pollution. The source of this pollution may have included industrialization, urbanization and/or transport of industrial waste materials. Both geoaccumulation index (I_geo) and potential ecological risk (RI) values suggested that Hg was the major contributor to the ecological risk posed by the selected PTEs.

Assessing heavy metals in surface sediments of the Seomjin River Basin, South Korea, by statistical and geochemical analysis

We investigated particle size distribution and heavy metal concentrations in surface sediments of streams and lakes in the Seomjin River Basin by comparison with Sediment Quality Guidelines (SQGs). Origins were identified using statistical and geochemical approaches. Sand was prevalent in mean particle size of surface sediments (except lakes). Mean concentrations of Pb, Zn, Cd, and Hg were similar for the Seomjin and Boseong rivers, while those of Cu, As, Cr, and Ni were approximately 1.5-2.0 times higher in the Boseong. SQGs revealed no serious pollution in the basin's site concentrations, although As and Ni levels in the Boseong had some potential for benthos toxicity. Correlation and principal component/factor analysis showed that concentrations of Cu, As, Cr, and Ni were dominant from geological origins rather than anthropogenic. The reducible fraction bound to Fe and Mn-oxides was prevalent in Pb, while the water- and acid-soluble fractions were easily exchangeable or bound to high Cd carbonates. The fraction bound to the highest lattice in residual prevailed in Zn, Cu, Cr, and Ni, accounting for 64%, 65%, 87%, and 86%, respectively. Similarly, results indicated geological origins. Risk assessment to benthos based on labile fractions (F1 + F2 + F3) were Cd (72%) < Pb (66%) < Zn (36%) ≈ Cu (35%) < Ni (14%) ≈ Cr (13%). While Cd and Pb showed the highest risk, their concentrations were relatively lower. However, Cr and Ni showed the highest concentrations but low risk levels, suggesting their pollution is unlikely to have adverse effects on benthos.

Spatial distribution, contamination assessment and potential ecological risk of some trace metals in the surface sediments of the Gulf of Tunis, North Tunisia

To evaluate the trace metals contamination status in the Gulf of Tunis, forty one sediment samples were analyzed using different approaches. According to certain contamination and ecological risk indices (Contamination Factor, Geoaccumulation index and Ecological risk index), Hg has the highest contamination level while pollution by Ni, Pb, Cd and Cr was absent. The highest concentrations of trace metals were found in sediments collected from the offshore and coastal areas located opposite the main exchange points with the gulf particularly, the Mejerda and Meliane Rivers, the Khalij Channel, Ghar El Melh and El Malah lagoons, Tunis Lake and Sebkhat Ariana. However, further ecological indices (Potential ecological risk index, Toxic unit and Mean effect-range median quotient) and comparison with sediment quality guidelines suggest that in addition to Mercury, Cr, Pb and Ni concentrations are detrimental to biota in both the offshore and areas near to the exchange points with the gulf. Moreover, in these areas the results from sequential extraction and individual contamination factor calculation pointed to the mobility and bioavailability of Cr, Pb and Ni.

Levels and ecological risk of heavy metals in the surface sediments of tidal flats along the North Jiangsu coast, China

We investigated the contamination levels of nine heavy metals (Mn, Pb, V, Cr, Co, Ni, Cu, Zn, and As) in 153 surface sediment samples collected along five tidal flats on the North Jiangsu coast, China. The spatial distributions of most heavy metals gradually decreased from the northern Sheyang region to the southern Jianggang region, while slightly increasing in the Rudong region. Principal component analysis indicated that Co, Ni, Cu, Zn, and As were mainly derived from the natural environment, V and Cr were mainly derived from human activities. Additionally, Mn and Pb influenced by both natural and human sources. The geo-accumulation index and the contamination factor indicated that heavy metal contamination in the sediments exhibited little to no pollution levels. The potential ecological risk index exhibiting low ecological risks. Meanwhile, the mean probable effect level quotient values indicating slight toxicity. Cr and Ni were the major contributors to toxicity.

Efficiency of Fez WWTP: multi-parameter evaluation of water and sediment quality

In order to assess the impact of the proper functioning of wastewater treatment plants (WWTPs) and sanitation networks on the quality of water and surface sediments of the Oued Fez River and its tributaries, and ultimately their outlet in the Sebou River, physico-chemical, geochemical and mineralogical analyses were performed. The components were studied in high- and low-water regimes at eight sites. Seven heavy metals (As, Cd, Cr, Cu, Ni, Pb and Zn) were investigated in the sediments, with a decreasing trend being identified as Zn > Cu > Pb > Cr > As > Ni > Cd, and a mobility sequence as Cu > Pb > Zn > Ni > Cr. A comparison of the total heavy metal concentrations in the Oued Fez and Sebou River sediments with those of previous studies indicated a reduction in the harmful and polluting contribution of the Oued Fez to the Sebou River. The heavy metal assessment was achieved using environmental indices and sediment quality guidelines. The obtained results indicate that the presence of heavy metals in the sediment mainly comes from anthropogenic activities. Based on these results and their comparison with those from previous studies, the contribution of WWTPs and sanitation networks to improving the water quality of the middle Sebou River is clearly noteworthy.

Characterization and distribution of microplastics in estuarine surface sediments, Kayamkulam estuary, southwest coast of India

The present study aims to formulate the characterization and distribution of microplastic in the estuarine surface sediments of Kayamkulam estuary, southwest coast of India. The sediments were dominated by fibre and film shaped microplastic substances. The surface sediments were dominated by <1000 μm microplastics. The composition of microplastics in descending order was as follows: polyester > polypropylene > polyethylene. The distribution of microplastics was significantly higher than that observed in the other study regions, except for Pearl river estuary and Guanabara Bay. The distribution of microplastics was chiefly controlled by estuarine inundating water and the distance of the sampling site from the open sea.

Distribution and assessment of heavy metal contents in surface sediments of the western Sunda Shelf

The heavy metal contents (Cr, Cu, Zn, Cd, Pb, Hg, and As) of 88 surface sediment samples from the western Sunda Shelf were analyzed to determine their spatial distribution patterns and contamination status. The results demonstrated that high enrichment regions of heavy metals were focused in the Kelantan, Pahang, and Ambat river estuaries, and deep water regions of the study area. These high enrichment regions were mainly controlled by riverine inputs and their hydrodynamic conditions. The enrichment factor (EF), geoaccumulation index (I_geo), and potential ecological risk index (PERI) were used to assess heavy metal accumulation. The results indicated that the study area was not significantly contaminated overall at the time of the study; however, Cd, As, and Hg were at levels corresponding to moderate contamination at many stations located in the Pahang River estuary, Kelantan River estuary, and north-eastern region of the study area, primarily because of anthropogenic activities.

Pollution and ecological risk assessment, and source identification of heavy metals in sediment from the Beibu Gulf, South China Sea

The Beibu Gulf is an important passageway between China and the Association of Southeast Asian Nations, where there has been an increase in pollution of heavy metals (HMs). High concentrations of Pb, Cr, Cd, Cu, Zn, As, and Hg in surface sediment were found in Qinzhou Bay, Fangchenggang, and other coastal areas. Stochastic geo-accumulation analyses identified the pollution to be "uncontaminated"; however, it had an 18% probability of deterioration. The Cd, Hg, and As pollution were relatively serious. Principal component analysis, positive matrix factor model, and mercury isotopes demonstrated that the HMs could mainly be attributed to industrial sources including petrochemical, coal-fired, metal and metalloid processing, leather tanning, and human activities: anthropogenic sources accounted for approximately 70% of all the contaminations. This study demonstrates the contribution of terrigenous input to HMs even at a low level and provides basic data for the coordinated development of land and marine resources.

Potential linkage between sedimentary oxygen consumption and benthic flux of biogenic elements in a coastal scallop farming area, North Yellow Sea

Surface sediments were collected from a mariculture area adjacent to the Yangma Island suffering from hypoxia in summer, and a laboratory static incubation was conducted to study the sedimentary oxygen consumption (SOC) and the benthic fluxes of nutrients and fluorescent dissolved organic matter (FDOM). Compared with some coastal areas, the SOC of the studied area was relatively low in summer with the value of 2.34-6.03 mmol m^-2 d^-1. Sediment acted as an important source of nutrients (except for nitrate) and FDOM for the overlying water. Dissolved oxygen (DO) in the overlying water could affect the decomposition mode of sedimentary organic matter (SOM), i.e. aerobic and anaerobic decomposition and subsequently dominated the release of nutrients and FDOM. When DO > 50 μmol l^-1, it was beneficial to the release of ammonium, silicate and FDOM. In contrast, low oxygen conditions, i.e. DO < 100 μmol l^-1, stimulated sediment phosphate efflux. In addition, scallop farming activities also affected the SOC and benthic flux of nutrients and FDOM mainly through biological deposition.

Sources of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethanes (DDTs) found in surface sediment from coastal areas of Beibu Gulf: A reflection on shipping activities and coastal industries

The presence of polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethanes (DDTs) was determined in the sediments of Beibu Gulf, a newly developing industry and port in South China, to evaluate whether the rapid development of coastal cities has accelerated the organic pollution in the region. The levels of PCBs and DDTs ranged from 1.17 to 8.00 ng g^-1 and ND (not detected) to 3.82 ng g^-1, respectively. The levels were higher in the east of Beibu Gulf than in the west, which influenced by the industrialisation and urbanisation in the east. Additionally, penta-PCBs were the dominant PCB congeners, which are related to shipping activities, and DDTs may have originated from the historical use of technical DDT. The levels of pp'-DDD and PCBs did not have the potential to cause ecological risks in Beibu Gulf; however, residues of DDTs were at relatively higher ecotoxicological levels, thereby having the potential to cause adverse biological effects.

Spatial patterns and co-occurrence networks of microbial communities related to environmental heterogeneity in deep-sea surface sediments around Yap Trench, Western Pacific Ocean

Microbial communities are a large component of abyssal and hadal benthic environments, especially in deep-sea areas like Yap Trench, they provide a continuous source of nutrients and energy in their unique ecosystems. However, due to sampling difficulties, these microbial communities are relatively understudied. In the summer of 2017, sediment samples were collected from 21 stations around Yap Trench in the Western Pacific Ocean (mostly in the West Caroline Basin), at depths ranging from 3156 to 7837 m. Sediment samples from deep water depths and shallow water depths differed in organic matter content, median grain size, silt-clay content, and biodiversity. The structure of the microbial communities in the surface sediments had distinct relationships with environmental factors and their co-occurrence networks exhibited a clear spatial pattern. In addition, for both prokaryotes or eukaryotes, a combination of variables including silt-clay content, organic matter content, median grain size, and depth had the greatest impact on community structure. It was notable that fungi played important roles in the co-occurrence networks of deep water depth sediment samples while bacteria dominated those of shallow water depth samples. The differences in structure and ecological niches in the different networks were due to differences in sediment texture and organic matter content. Since clay had a positive effect on the diversity of bacteria, it had an indirect positive effect on fungi, leading to differences in biodiversity among different groups. More organic matter meant more nutrients were available for the growth and reproduction of microbes, which led to fewer niche overlaps. This study conducted an extensive and systematic sequencing survey of surface sediments around Yap Trench in the Western Pacific Ocean, providing insight into microbial responses to environmental heterogeneity in deep-sea benthic ecosystems.

Characterization of polycyclic aromatic hydrocarbons in the surface sediments around the sunken Sanchi oil tanker

The Sanchi oil tanker collision has attracted worldwide attention for its uniqueness in history. This study investigates the contamination level, spatial distribution, sources, and ecological risk level of polycyclic aromatic hydrocarbons (PAHs) present in the surface sediments collected from around the sunken tanker. The results indicated that the total PAH contents in the study area were in the range of 26.42-226.94 ngˑg^-1, with an average of 106.86 ngˑg^-1. The highest PAH concentration was observed at the station closest to the Sanchi wreckage, indicating potential PAH contamination due to the accident. The PAH ratios and statistical analysis revealed that the PAHs were mainly generated by coal and fuel oil combustion, with certain petrogenic inputs. The ecological risk assessment results suggested that adverse ecological effects to the benthic ecosystem due to PAH contamination was rare. However, long-term monitoring of the local sedimentary environment is highly recommended because of the prominent presence of high molecular weight PAHs.

Ecological risk assessment of persistent organic pollutants (POPs) in surface sediments from aquaculture system

Organochlorinated pesticides (OCPs) and Polychlorinated biphenyls (PCBs) in the surface sediments from shrimp ponds in four regions of the northern part of the Central Java coast (namely Brebes, Tegal, Pemalang, and Pekalongan) were investigated. The highest concentration of ∑ OCPs was found in Brebes Regency, ranging from 68.1 ± 3.4 to 168.1 ± 9.8 μg kg^-1 dw. As indicated by the DDT ratio and chlordane ratio, the value suggested that those compounds may mainly originate from historical inputs rather than a recent application. The concentrations of Ʃ 7 indicator PCBs were determined, with the concentration ranged from 1.2 ± 0.7 μg kg^-1 dw (Pekalongan) to 2.2 ± 0.4 μg kg^-1 dw (Tegal). The most toxic PCB congener, PCB 118, was detected in all studied regions, with the highest proportion found in Tegal. Source analysis indicated that PCBs in the sediments mainly originated from Aroclor 1254 and Aroclor 1248. Compared to sediment quality guidelines (SQGs), some OCPs were found with concentrations which potentially posed an adverse effect. Our findings suggested that more attention should be paid to ensure sustainable shrimp culture facing such a risk of the OCPs and PCBs.

Concentrations, spatial distribution, and pollution assessment of heavy metals in surficial sediments from upstream of Yellow River, China

Surface sediments were collected from 122 sites in the upstream of the Yellow River, China. The concentration of Fe, Mn, Cu, Ni, Zn, Cr, Pb, and Cd in sediments was investigated to explore the spatial distribution based on statistics and interpolation method. The results suggested that the concentrations of heavy metals were lower than potential effect levels (PEL). The samples above threshold effect level (TEL) for Pb and Zn were less than 10%, while almost 50% of samples for Ni exceeded PEL. Pb and Zn in sediments performed little or no adverse effects on the aquatic ecosystems. Higher concentrations of all heavy metals occurred in Qinghai and Gansu sections; the concentrations of Cu, Ni, and Zn were significantly higher than the Inner Mongolia section. Lower concentration of Fe, Mn, Cu, Ni, and Zn appeared in Qinghai section; the concentrations of Fe, Mn, Cr, and Pb manifested relatively steady and similar distributions and approximately decreasing tendency along the upstream of Yellow River.

Metal pollution assessment in surface sediments of Namak Lake, Iran

Desiccation of the Namak Lake (NL) can result in the release of fine-grained dust contaminated with heavy metals, while there is little information available on the propagation of metals in the bed sediments of this lake. In this study, contamination of metals in the surface sediments of the NL was analyzed and the pollution status of sediments was assessed using geo-accumulation index (I_geo), enrichment factor (EF), the consensus-based sediment quality guidelines (CBSQGs), and mean probable effect concentration quotient (mPECQ). Results indicated that metal concentrations at the southern part were higher than at the middle and northern parts of the lake. Possible reasons are (i) pollution loads mainly entered the lake through the rivers at the west and northwest, but accumulated at the southern parts, (ii) hard layer of salt covering the bottom of the NL at the northern part suppresses adsorption of metals to the sediment, and (iii) the muddy nature of sediments at the southern part makes it easier for metals to be absorbed. EF results showed that sediments at the southern part of the lake were moderately enriched with lead (Pb). The low I_geo values suggested no pollution with the metals, and CBSQG values showed that the sediments of the NL were not toxic, while the mPECQ index suggested a toxicity probability of less than 25%. Cluster analysis classified the metals into two clusters. In general, the results showed that metal pollution in the surface sediments of NL was generally low although the concentration of Pb at the southern part of the lake was worrisome.

Beta radioactivity of urban surface-deposited sediment in three Russian cities

Study of gross beta activity was conducted in Russian cities Ekaterinburg, Rostov-on-Don, and Nizhny Novgorod. The cities were characterized by continental climate, although they are located in different geographical zones. The bulk urban samples were fractionated with three size fractions: dust (0.002-0.1 mm), fine sand (0.1-1 mm), and coarse sand (> 1 mm). Measurement setup equipped with beta radiometer BDPB-01 was designed to measure the low levels of gross beta-activity in a small amount of the obtained size-fractionated samples. According to the results of the study, the gross beta activity depends on the size fraction and the city. The highest beta activity concentration was found in the dust fraction which is about the same in all cities 0.8-0.9 Bq g^-1. In size fractions of fine sand and coarse sand, the beta activity depends on the city. Among other cities, the highest average beta concentration was found in Ekaterinburg (0.8 and 0.6 Bq g^-1 in fine and coarse sand fractions, respectively), while the lowest is 0.28 and 0.44 Bq g^-1, respectively. The relationship of beta activity concentration with mineral and chemical composition is studied. Average beta activity in the different fractions of the surface-deposited sediment correlates with uranium, thorium, and organic matter concentration. The gross beta activity may be considered an indicator of high contribution of dust and high pollution with Pb, Cu, and Zn in the urban environment.

Hexabromocyclododecane in riverine and estuarine sediments from Osaka, Japan: spatial distribution and concentration variability within identical samples

In this study, hexabromocyclododecane (HBCD) in riverine and estuarine sediments was investigated in Osaka, Japan. The mean total HBCD concentration detected in sediments ranged from < 0.50 to 130 ng g^-1 dry weight. This exceeded the ubiquitous HBCD contamination level found globally but was lower than that in areas affected by point sources, such as textile industries and expanded polystyrene plants. Sewage effluent was one of the suspected point sources of HBCD in the study area. The HBCD concentrations in sediments were highly dependent on certain factors, such as the location of the sampling site (proximity to possible emission sources), sediment properties (silt or sand), and organic substance content. The range of the diastereomer composition of α- and γ-HBCD was wider than that in other studies. Repeatability tests (n = 3) were conducted for all samples to assess the variability in the HBCD concentrations within identical sediment samples. Some variations were observed in the HBCD concentrations and diastereomer compositions within the repeatability test results at some sampling sites; nevertheless, the same samples were extracted and analyzed in triplicate. The bromine contents of the extracts of these samples were analyzed by X-ray fluorescence, and the results agreed well with those estimated from the LC-MS/MS results. From these results, it was confirmed that several sediment samples contained heterogeneously distributed HBCD. The risk characterization ratios (predicted environmental concentration/predicted no-effect concentration) of sites with high HBCD concentrations ranged from 0.1 to 1; thus, further information is required, and the sediment HBCD levels in this region should be continuously studied.

Spatial Variability and Source Apportionment of Aliphatic Hydrocarbons in Sediments from the Typical Coal Mining Area

Fifty-four surface sediments from the typical coal mining area were analyzed for pristane, phytane and C₈-C₄₀ n-alkanes using gas chromatography-mass spectrometry (GC-MS). The spatial distribution, homolog profiles and source apportionment of aliphatic hydrocarbons were investigated. Bimodal distribution pattern, centered at C₁₆-C₂₀ and C₂₇-C₃₃ n-alkanes, were observed in all sediment samples with an obvious dominance of low molecular weight homologues. Principal component analysis-multiple linear regression (PCA-MLR) was used to predict the contributions of different sources. The result implied that natural input was the main source, contribution of which accounted for 60.8%, and the contributions of different sources were estimated as follow: 21.8% for terrestrial higher plants, 24.1% for algae and photosynthetic bacteria, 14.9% for submerged/floating macrophytes, 23.5% for fossil fuel combustion and 15.7% for petroleum hydrocarbons. Moreover, relatively high median concentrations of fossil fuel combustion were observed in Shou County and Fengtai County, indicating the high contribution of fossil fuel combustion in these two areas.

Ecological risk assessment and source apportionment of metals in the surface sediments of river systems in Lake Taihu Basin, China

In this study, the concentrations of Zn, Cr, Ni, Cu, Pb, As, Cd, and Hg in the surface sediments of 94 sites sampled from six water systems in the Lake Taihu Basin in China were measured, and the pollution risks and sources of the metals were identified. The results showed that the mean concentrations of Zn, Cr, Ni, Cu, Pb, As, Cd, and Hg in the riverine surface sediments were 163.6, 102.5, 45.5, 44.7, 37.0, 13.3, 0.5, and 0.1 mg/kg, respectively, higher than the corresponding background values (except for Hg). According to the geoaccumulation index (I_geo), the Pb, Ni, Zn, Cu, and Cd concentrations in the riverine surface sediments were generally at low levels of pollution. Based on a pollution load index (PLI) evaluation, the Pb, Ni, Zn, and Cu concentrations in the riverine surface sediments were generally at moderate levels of pollution. According to the thresholds of potential ecological risk, the Cd and Hg concentrations in the riverine surface sediments exhibited moderate potential ecological risks. Multivariate statistical analysis indicated that the Pb in the riverine surface sediments primarily originated from domestic sewage, agricultural wastewater discharge, and petroleum combustion; the concentrations of Cr, Ni, and Zn were influenced by the electroplating and alloy manufacturing industries; the concentrations of Cu and As mainly originated from pesticide use and industrial wastewater discharge; and those of Cd and Hg primarily stemmed from industrial wastewater discharge. This research provides information regarding metallic contamination and the possible associated ecological risks to benthic organisms in the surface sediments of river systems and is useful for developing sustainable strategies for environmental pollution control and management in the Lake Taihu Basin.

Distribution characteristics, sources identification and risk assessment of n-alkanes and heavy metals in surface sediments, Tajikistan, Central Asia

Central Asia is the global hotspot resulting from either a scarcity of natural resources or environmental degradation. Tajikistan, however, is called the "central Asian water tower", is rich in water and minerals and plays a very important role in the ecology of Central Asia. Given the soil contamination issues in Tajikistan, the spatial distributions and sources of n-alkanes and heavy metals in surface sediments of Tajikistan were investigated. The evaluation of n-alkane and elemental indices helped to elucidate the origins of complex pollutants. The n-alkane indices were allowed to identify biogenic and petrogenic sources, and statistical methods were used to identify natural and anthropogenic sources of heavy metals. Enrichment factors were used to assess the contamination statuses of heavy metals. The results indicated that n-alkanes in the cluster I (sample 23) and II (samples 1, 5, 12, 14, 18, 22, 29, and 30) samples were affected by crude oil or incomplete fossil fuel combustion. Biomarker indices indicated strong contributions of petroleum sources to the n-alkanes in samples 14, 18, 23, and 29, but that n-alkanes in the other samples were mainly derived from higher plant waxes. Statistical analyses showed that cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) were originated from industrial activities. Phosphorus (P) was closely related to local agricultural activities. Manganese (Mn) was derived from mining activities and industrial wastewater. The enrichment factors indicated that sediment was zero to minor contamination with Cr, Cu, Ni, and Pb, but moderate contamination with Cd and significant contamination with Zn. Interestingly, the samples contaminated with Cd included the cluster I and II samples, meaning the source of Cd contamination had agreed with the results of n-alkanes. The combined evaluation of n-alkanes and heavy metals suggested that their pollutant sources were crude oil contamination.

Mercury pollution of riverine sediments in a typical irrigation area in the Beijing-Tianjin-Hebei region

The Beijing-Tianjin-Hebei region is China's cultural and political center. Rapid social and economic development has led to serious water pollution in this region. A comprehensive investigation of mercury (Hg) pollution in riverine sediments was carried out in a typical irrigation area in this region. The results show that the total Hg levels in the surface sediments of the Duliujian River Network (DRN) ranged from 0.169 to 1.391 mg kg^-1, with an average of 0.528 mg kg^-1. The Hg levels at most of the sample points were higher than the background. The Hg fractions were categorized as exchangeable (B1), reducible (B2), oxidizable (B3), and residual (B4). The Hg was mainly present in the B4 fraction (0.439 mg kg^-1, on average). The order of the average percentage of different fractions of Hg was B4 > B3 > B2 > B1. A risk assessment using total Hg showed that the potential ecological risk in each section of the DRN ranged from 80.4 to 662 (average = 263). A risk assessment using Hg speciation showed that the average risk for B1 was 3.28%. Because the potential ecological risk is very high, more attention should be given to this risk in the management of the river. This research also provides theoretical support for the study of Hg in the developed area of the agricultural irrigation canal. The information obtained in this study could be used to develop effective management strategies to control Hg pollution in the DRN.

Distributions, compositions, and ecological risk assessment of polycyclic aromatic hydrocarbons and phthalic acid esters in surface sediment of Songhua river, China

The distribution, composition, and ecological risk of 16 types of polycyclic aromatic hydrocarbons (PAHs) and 6 types of phthalic acid esters (PAEs) in the surface sediment of Songhua river, northeast China, were investigated. The total weight of the PAHs (∑₁₆PAHs) varied from 226.70 to 7086.62 ng/g dry weight (dw), whereas that of the PAEs (∑₆PAEs) ranged from 819.44 to 24,035.39 ng/g dw. The dominant PAHs were four-membered ring PAHs, which varied from 18.65% to 78.10% of the total PAHs. The most abundant PAEs was di-2-ethylhexyl phthalate ester (DEHP), which accounted for 65.02-99.07% of the total PAEs, followed by di-n-butyl phthalate ranging from 1.50 to 55.43%. Pyrolytic origin was the dominant PAH source. Approximately 12.70% target PAHs in the Songhua river sediment exhibited moderate ecological risk with 23.49-1404.09 ng/g carcinogenic toxicity equivalent. DEHP in 80.95% of the sediment samples exceeded the effects range low, indicating its potential harmfulness to the aquatic environment.

Occurrence and distribution of organophosphate esters in sediment from northern Chinese coastal waters

Organophosphate esters (OPEs) are used as flame retardants and plasticizers in many consumer products. Owing to OPEs' toxicity, exposure of organisms in aquatic ecosystems is a concern. Information that pertains to the occurrence and distribution of OPEs in marine aquatic environment, however, is scarce. In this study, concentrations and profiles of 14 OPE triesters were determined in sediment collected in coastal waters (Bohai Sea and East China Sea) of northern China. The total concentrations of OPEs (ΣOPEs) in surface sediment were in the range of 1.76-49.9 (median: 9.13) ng/g dry weight (dw), which were comparable to or lower than the range of concentrations reported for surface sediments worldwide. Tris(2-chloro-propyl) phosphate (TCIPP), tris(2-chloroethyl) phosphate (TCEP), tri-isobutyl phosphate (TiBP), and tri-n-butyl phosphate (TnBP) were the predominant OPEs found in surface sediment, collectively accounting for 81% of the total concentrations. ΣOPE concentrations in sediment core (range: 8.58-169, median: 31.6 ng/g dw) were generally higher than those found in surface sediment. The vertical distribution of OPEs in sediment core showed a gradual increasing trend in concentrations during the past decade.

Modern modes of sediment distribution and the anthropogenic heavy metal pollution record in northeastern Beibu Gulf, south China sea

During the expedition 908 survey in 2007, 539 seafloor surface sediment samples and two cores were collected over a narrow sector of the northeastern Beibu Gulf, South China Sea. Currently, three dynamic sedimentological processes prevail in the study area: circulation-controlled sand deposition, mud deposition under weak sediment dynamics, and fluvial input. Core A233 from the circulation-controlled sand area, with a 60 cm mixed layer, provides evidence of dynamics disturbance since the mid-Holocene. To reconstruct the anthropogenic heavy metal pollution history, we selected core A146 from the stable mud sector influenced by fluvial input. The dating of core A146 was based on ²¹⁰Pb activity analysis, showing an ~90-year historical record in the upper 40 cm. The heavy metal contamination results showed a generally low pollution level. Nonetheless, increased pollution has happened since the 1950s, especially after 1978 A.D., corresponding to the beginning of China's reform and opening up.