Multivariate statistical study of heavy metal enrichment in sediments of the Pearl River Estuary

Hydrodynamics and dissolved organic matter components shaped the fate of dissolved heavy metals in an intensely anthropogenically disturbed estuary

Anthropogenic activities and natural erosion caused abundant influx of heavy metals (HMs) and organic matter (OM) into estuaries characterized by the dynamic environments governed by tidal action and river flow. Similarities and differences in the fate of HM and OM as well as the influences of OM on HMs remain incomplete in estuaries with seasonal human activity and hydrodynamic force. To address this gap, dissolved HMs (dHMs) and fluorescence dissolved OM (FDOM) were investigated in the Pearl River Estuary, a highly seasonally anthropogenic and dynamic estuary. It aimed to elucidate the effects of hydrodynamic conditions and DOM on the seasonal fate of dHMs via the multivariate statistical methods. Our findings indicated dHMs and FDOM exhibited consistently higher levels in the upper estuarine and coastal waters in both seasons, predominantly controlled by the terrestrial/anthropogenic discharge. In the wet season, dHMs and humic-like substances (HULIS) were positively correlated, showing that dHMs readily combined with HULIS. This association led to a synchronous decrease offshore along the axis of the estuary and the transport following the river plume in the surface affected by the salt wedge. Contrarily, dHMs were prone to complex with protein-like components impacted by the hydrodynamics during the dry season. Principal component analysis (PCA) results revealed the terrestrial/anthropogenic inputs and the fresh-seawater mixing process were the most crucial factors responsible for the fate of dHM in wet and dry seasons, respectively, with DOM identified as a secondary but significant influencing factor in both seasons. This study holds significance in providing valuable insights into the migration, transformation, the ultimate fate of dHMs in anthropogenically influenced estuaries, as well as the intricate dynamics governing coastal ecosystems.

Tracing the land use specific impacts on groundwater quality: a chemometric, information entropy WQI and health risk assessment study

Understanding the nexus of land use and water quality can potentially underline the influences within the groundwater management. The study envisages land use-specific qualitative assessment of the groundwater resources in Ghaziabad district, in western Uttar Pradesh, India. For encountering the relative impacts of land use on the groundwater quality, chemometric analysis has been employed to apportion the pollution sources. The integration of quality parameters, in the information entropy index modeling, has segregated the quality classes and visualized the seasonal suitability trends as per potability standards along with non-carcinogenic health hazard risk assessment (HHRA). The qualitative assessment of the groundwater resources, along with spatial distribution, has deciphered a polluting impact, specifically in western and south western parts of district, and observed the linkages with direct and indirect discharges/seepages from densely populated residential and industrial land use types localized in urbanized areas. Statistically significant annual and seasonal variations have been found exclusively for EC, Mg2+, F-, Cd, Cr(total), Ni, and Pb which inferred variable concentrations, whereas land use types showed a non-significant variation within groundwater quality. Chemometric-based source apportioning and hierarchical cluster analysis (HCA) have derived salinization and enrichment of dissolved salts, arising from mixed sources and contributes to metal pollution, i.e., mainly from anthropogenic sources. Information EWQI derived poor to extremely poor category represented degraded potability specifically for fewer sites located within western and southern parts on the Yamuna-Hindon flood plains for limited sites of residential, industrial, and agricultural in an urbanized region. However, majority of the samples fall under excellent to good groundwater quality, recommendable in the north and north-eastern (peri-urban) regions. Non-carcinogenic HHRA has shown that majority of the samples categorized under unsafe value for hazard index (HI > 1), for females and children and thus, presumed probable health hazard risk from metal groundwater pollution in south-western part, eastern, and northern regions.

Distribution of potentially toxic elements in soils and sediments in Pearl River Delta, China: Natural versus anthropogenic source discrimination

Although anthropogenic contamination has been regarded as the most important source of potentially toxic elements (PTEs) in soils of large river delta plains, the extent to which human activities affect PTEs in soils is worth exploring. This study used high density geochemical data to distinguish source patterns of PTEs in soils of the Pearl River Delta Economic Zone, a large industrialized and urbanized area in China. Enrichment factor, discriminant analysis, principal components analysis, cumulative distribution function, and positive matrix factorization were used to identify sources of PTEs in soils. The results indicated that parent material was the most significant factor affecting geochemical characteristics of PTEs in soils. Median concentrations of Cd, Cr, Cu, Hg, Pb, and Zn were 0.400, 88.5, 40.5, 0.143, 43.0, and 116.0 mg/kg for stream sediments, 0.333, 75.7, 39.0, 0.121, 42.6, and 98.5 mg/kg for deep soils, and 0.365, 74.0, 45.1, 0.143, 44.6, and 119.5 mg/kg for surface soils, respectively, all of which exceed relevant reference standards. Compared with stream sediments and deep soils, surface soils exhibit substantial concentrations of PTEs. Chemical weathering and erosion of parent materials distributed in the Pearl River Delta were the main sources of PTEs in soils. Diffuse contamination and many small local contamination sources distributed throughout the study area were the most significant anthropogenic sources of PTEs in surface soils. Intensive human activities failed to change the soil geochemical characteristics derived from the parent material at the regional scale. However, it could induce non-point source pollution and local severe PTEs pollution in surface soils.

Seasonal and spatial contamination of trace elements in sediments and fish tissues (Mugil Chephalus) from Annaba gulf (North East of Algeria)

This research is devoted to assessing the pollution within a Mediterranean Sea area in the East coast of Algeria, which is known for its port and industrial activities. This study aims to assess the health status of the Gulf of Annaba located in the extreme North-East of Algeria by examining the contamination level by trace elements (Cu, Zn, Pb, Cd, Hg) in the sediments and muscles of Mugil cephalus fish. The obtained results manifest significant variations in metal levels in the sediments throughout the stations and the sampling seasons. The contamination by (Zn, Cu, Pb, Cd) of Joannonville and Sidi Salem stations is observed during both seasons whereas at the Chapuis station occurs only during the summer. The contamination indices are higher than 3, hence classifying the sediments of these three stations as "sediments at risk". Joannonville station manifests high levels of Hg only during the summer. For the muscles of M. cephalus, the contamination levels are found to be dependent on the species and the studied station. The fish inhabiting Joannonville and Sidi Salem show higher levels of (Zn, Pb, Cd) compared to the FAO/WHO standards, whereas the Pb level at Chapuis exceeds the standard during summer. Accordingly, the consumption of fish from Joannonville, Sidi Salem and Chapuis stations presents a serious threat regarding the toxicological risks based on the observed levels of contamination.

Composition, distribution and enrichment of trace metals in sediments from the muddy area off the southern Shandong Peninsula in the Northwestern South Yellow Sea of China since 10,000 years

We analyzed ten trace metals (Cu, Pb, Zn, Cr, Cd, Hg, As, Ni, V, Co and Ni) in sediments of the upper 14.98 m of core WHZK01 from the muddy area off the Shandong Peninsula, northwestern South Yellow Sea, to analyze their content, vertical distribution, and the enrichment status. Except for Hg and As, the other metals (Cu, Pb, Zn, Cr, Cd, Ni, V, Co and Ni) were mainly controlled by grain size. When the sediment particle size became smaller, the metal content reached a high level. Moreover, oxides and hydroxides of Al, Ti, Fe, and Mn also contributed to the metal enrichments due to their strong adsorption to the metals. Over the past four stages of 10-7 kyr BP, 7-4.5 kyr BP, 4.5-2.5 kyr BP, and 2.5 kyr BP to date, the metal values have shown a trend of increasing - fluctuating to high values - decreasing - re-increasing, respectively. However, since 4.5 kyr BP, Hg concentrations have been on an increasing trend, associated with the release of large amounts of contaminants into the environment from ancient human metal mining and smelting activities. As concentrations, despite the fluctuating changes, have remained relatively stable at high levels since 5.5 kyr BP, associated with their high background values.

Hydrochemistry and quality appraisal of groundwater in Birr River Catchment, Central Blue Nile River Basin, using multivariate techniques and water quality indices

Due to the continuous population growth and the expansion of industry and agriculture in Ethiopia, groundwater demand has been increasing to supplement the erratic surface water. Therefore, the availability of sufficient and clean groundwater should be appraised and tracked regularly to secure its multi-purposes. This work aims to assess the appropriateness of groundwater for drinking, and irrigation uses and identifies the key factors controlling groundwater quality in the Birr River Catchment (BRC), Blue Nile River Basin, Ethiopia. For this purpose, a total of 79 groundwater samples were assessed for physicochemical parameters. Major ion analysis, multivariate techniques (MCA, HCA, and PCA), and multi-hydrochemical indices were applied in the analysis of groundwater quality data. Hydrochemical analysis indicated that the principal cation and anion were Ca²⁺ and HCO₃^-, respectively. The spatial analysis of the major ions revealed a positive trend for Mg²⁺, Na⁺, K⁺, HCO₃^-, Cl^-, and SO₄^2- along the groundwater flow path from the upland to the Birr river valley. Conversely, Ca²⁺ shows a deleterious tendency along the groundwater flow direction. The aquifer has three principal hydrochemical facies: Ca-HCO₃, Ca/Mg-HCO₃, and Na-HCO₃. The water quality analysis indicates that with the exception of TDS, Ca²⁺, Mg²⁺, and HCO₃^- in a few locations, most of the parameters analyzed are within the WHO allowable limits and are thus considered suitable for drinking water. The combined use of Gibbs and ionic ratio plots confirmed that silicate weathering was invariably prevailing in the region. The Chloro-Alkali Indices (CAIs) have indicated that cation exchange occurs in more than 85% of groundwater samples. However, there were indications of the influence of reverse ion exchange in the rest of the data. The MCA, PCA, and HCA disclosed that geo-genic sources accompanied by human activities mainly control the groundwater quality of the catchment. However, water quality assessment indices show that groundwater in the highest proportion of the catchment is suitable for human consumption and agricultural use.

Saltwater intrusion regulates the distribution and partitioning of heavy metals in water in a dynamic estuary, South China

The mixing processes of fresh-salt water in estuarine and coastal regions have a substantial impact on the characteristics of heavy metals. A study was conducted in the Pearl River Estuary (PRE), located in South China, to examine the distribution and partitioning of heavy metals and the factors that influence their presence. Results showed that the hydrodynamic force, caused by the landward intrusion of the salt wedge, was the major contributor to the aggregation of heavy metals in the northern and western PRE. Conversely, metals were diffused seaward at lower concentrations along the plume flow in surface water. The study found that some metals, including Fe, Mn, Zn and Pb, were significantly higher in surface water than in bottom water in eastern waters, but the reverse was true in the southern offshore area, where limited mixing hindered the vertical transfer of metals in the water column. The partitioning coefficients (K_D) of metals varied, with Fe exhibiting the highest K_D (1038 ± 1093 L/g), followed by Zn (579 ± 482 L/g) and Mn (216 ± 224). The highest K_D values of metals in surface water were observed in the west coast, while the highest K_D in bottom water was found in eastern areas. Furthermore, re-suspension of sediment and the mixing of seawater and freshwater offshore, caused by seawater intrusion, resulted in the partitioning of Cu, Ni and Zn towards particulate phases in offshore waters. This study provides valuable insights into the migration and transformation of heavy metals in dynamic estuaries influenced by the interaction of freshwater and saltwater and highlights the importance of continued research in this field.

Effects of sedimentary heavy metals on meiobenthic community in tropical estuaries along eastern Arabian Sea

The central west coast of India comprises the 720 km long coastline of Maharashtra state and houses widespread industrial zones along the eastern Arabian Sea. Sediments from seven industrial-dominated estuaries along the central west coast were studied for metal enrichment and benthic assemblages to determine sediment quality status and ecological effects in these areas. The suit of geochemical indices highlighted the contamination of sediment in the estuaries concerning heavy metals. Positive correlations of Hg with Co, Zn, Ni, Cr, and Pb indicated the source similarity and effect of anthropogenic activity. non-Metric Multidimensional Scaling (n-MDS) based on meiofaunal abundance showed a cleared separation of clusters through the gradient of heavy metal concentrations. The Canonical Correspondence Analysis (CCA) results with the Monte Carlo test signified those heavy metals influenced the meiobenthic community. Heavy metals (Cr, Ni, Zn, Cd, Pb, and Hg) were the main drivers shaping the meiofaunal community with a significant (p < 0.05) reduction in taxa richness, diversity, and evenness. Dominant meiofaunal assemblages evidence the tolerance of foraminiferans and nematodes. However, these taxa were affected by decreased abundance at impacted sites compared to other fauna. In conclusion, results demonstrated that impairment occurred in the meiofaunal community in most estuaries (except AB and KK).

Land-Water Transport and Sources of Nitrogen Pollution Affecting the Structure and Function of Riverine Microbial Communities

The characterization of variations in riverine microbiota that stem from contaminant sources and transport modes is important for understanding biogeochemical processes. However, the association between complex anthropogenic nitrogen pollution and bacteria has not been extensively investigated owing to the difficulties faced while determining the distribution of nitrogen contaminants in watersheds. Here, we employed the Soil and Water Assessment Tool alongside microbiological analysis to explore microbial characteristics and their responses to complex nitrogen pollution patterns. Significant variations in microbial communities were observed in sub-basins with distinct land-water pollution transport modes. Point source-dominated areas (PSDAs) exhibited reduced microbial diversity, high number of denitrification groups, and increased nitrogen cycling compared with others. The negative relative deviations (-3.38) between the measured and simulated nitrate concentrations in PSDAs indicated that nitrate removal was more effective in PSDAs. Pollution sources were also closely associated with microbiota. Effluents from concentrated animal feeding operations were the primary factors relating to the microbiota compositions in PSDAs and balanced areas. In nonpoint source-dominated areas, contaminants from septic tanks become the most relevant sources to microbial community structures. Overall, this study expands our knowledge regarding microbial biogeochemistry in catchments and beyond by linking specific nitrogen pollution scenarios to microorganisms.

Assessment of heavy metals remobilization and release risks at the sediment-water interface in estuarine environment

The influence of overlying hydrodynamics on the exchange behaviour and fluxes of heavy metals at the sediment-water interface (SWI) is poorly understood. In the study, metals exchange behaviour and exchange rate at the SWI under resuspended and undisturbed scenario were investigated The results showed that dissolved Cr, Cu, Zn, and Pb concentrations increased rapidly to attain maximum values between 0.3 and 0.5 N·m^-2 after the sediment resuspended. Following the quick release, metals concentrations gradually decreased and remained at relatively low levels, especially for Cu and Zn. Meanwhile, Cu, Zn, and Pb had higher potential remobilization potential in the undisturbed case. Calculating with the hydrodynamics in the Modaomen, the metals efflux under the resuspension scenario could reach 0.55 to 4130.83 mg·m^-2·yr^-1, which were 1-3 orders of magnitudes higher than the undisturbed case. Whether or not resuspension events occurred, estuarine sediments were source of heavy metals, especially in the weakly mixed zone.

Integrative toolbox to assess the quality of freshwater sediments contaminated with potentially toxic metals

The Guadiana Basin is a transnational basin, presenting historical contamination with potentially toxic metals (PTM), which origin can be both natural and anthropogenic. This study explores the use of a set of observational, chemical and ecotoxicological assays with Heterocypris incongruens, Vibrio fischeri, Pseudokirchneriella subcapitata, Thamnocephalus platyurus, identifying the most sensitive to be included in a toolbox to analyze the quality of freshwater sediments related to this type of contamination. The study included the analysis of a reservoir and streams sediments of Guadiana basin, in two consecutive years with different climate conditions 2017 (dry year) and 2018 (normal year). The results showed high chemical variability along the basin, with greater contamination with PTM in the reservoir sediments. The calculated Enrichment Factors (EF) indicated high anthropogenic contamination by Cd, followed by Pb (EF > 1.5). The geoaccumulation index (Igeo) revealed that the sediments were severely polluted with Cd, and slightly polluted with Pb and Cu, inducing a higher sublethal toxicity to Heterocypris incongruens. Among the parameters evaluated, and after the use of multivariate statistical techniques, the toolbox for assessing sediments quality, in similar climate and geological conditions, should include the analysis of: meteorology, land use/cover in the area, granulometry, organic matter content, PTM concentrations, contamination indices (e.g., Igeo and EF), and sublethal bioassays with H. incongruens (total sediment analysis) and Vibrio fisheri luminescence inhibition (pore water analysis).

Risk assessment, spatial distribution, and source identification of heavy metals in surface soils in Zhijin County, Guizhou Province, China

Zhijin County is a typical mineral resource-based city in Southwest China. The problem of heavy metals (HM) in the soil in Zhijin County must be considered during regional economic and ecological development. A total of 2436 soil samples (0‒20 cm depth) were collected to analyze the soil pH, organic matter content, and HM spatial distribution and sources. The HM concentrations in the surface soil were found to be higher than the national surface soil background values. Absolute principal component sore-multivariate linear regression (APCS-MLR) showed that the HM sources in the surface soil of Zhijin County were industrial and agricultural activities (48.09%), natural sources (34.47%), and atmospheric deposition (17.43%); 65.53% of HM were produced by anthropogenic activities, which were mainly associated with the mineral industry. The impact of anthropogenic pollution decreased in the following order: paddy field (66.45%) > rainfed cropland (65.91%) > barren land (61.98%) > garden land (61.82%) > forest land (59.11%) > grassland (53.31%). The potential ecological risk of surface soil is moderate, while low-risk areas were mainly distributed in mountainous regions in the north, southwest, and east. The study emphasizes the source and risk assessment of HM in the surface soil of Zhijin County. The results can be used for environmental management planning, decision-making, and risk assessment.

Determination of the Heavy Metal Bioaccumulation Patterns in Muscles of Two Species of Mullets from the Southern Caspian Sea

Simple Summary

Fish are an important source of proteins of a high biological value, of some vitamins and minerals, and of polyunsaturated omega-3 fatty acids. However, fish products can also allow harmful substances, like heavy metals, to enter the diet. Such substances are recognized as being the most serious contaminants for aquatic ecosystems at the present time. Their non-biodegradability allows them to accumulate in fish tissues, and then pass into human diets. Therefore, our study aimed to determine the concentrations of heavy metals (As, Cd, Cu, Hg, Ni, Pb, and Zn), and to evaluate the bioaccumulation patterns in the different types of musculature in two species of fish of commercial interest, Chelon auratus and Chelon saliens, from the south coast of the Caspian Sea. The results obtained emphasize the need to continue to monitor and evaluate the degree of pollution in the sampled area, both in fish and other species and also in the environment, as well as recommending prevention measures orientated towards limiting and/or reducing the excessive exposure of the human population to heavy metal contamination.

Abstract

Although fish is a food that supplies nutrients of a high biological value, they can also be a source of some harmful substances, such as heavy metals. In the same context, some human activities in the Caspian Sea have contaminated this ecosystem during the past few years. For those reasons, our objective consisted of determining the concentrations of heavy metals and evaluating their bioaccumulation patterns in the different types of musculature in two species of mullets of commercial interest, Chelon auratus and Chelon saliens, from the southern coast of this sea. For this purpose, 20 C. auratus and 29 C. saliens were caught off this coastline and the metal concentrations in 3 different muscle locations were analyzed: the ventral, dorsal and caudal muscles of each fish. The caudal muscle had higher concentrations of Cd, Cu, Pb, and Zn, whereas As, Hg and Ni accumulation seemed to be independent of the musculature type. Overall, the Cd, Hg, and Pb concentrations exceeded the maximum levels permitted in fish by the European Union. In addition, the relationships between pairs of metals were positive and elevated in all the cases, which could be a sign of heavy metal pollution in the region sampled. Therefore, it will be necessary to continue monitoring and evaluating the degree of pollution in the Caspian Sea.

Multi-geochemical background comparison and the identification of the best normalizer for the estimation of PTE contamination in agricultural soil

Identifying a suitable geochemical background level (GBL) and an appropriate normalizer is imperative for ensuring soil quality, health, and security. The objective of this study was to identify the appropriate normalizer and suitable GBL for determining PTE enrichment levels in agricultural soils and investigate if there are any statistical differences due to the GBL [World Average Value (WAV) European Average Value (EAV)] used. Forty-nine topsoil samples were obtained from seven agricultural communities in the Frdek-Mstek District (Czech Republic). Portable X-ray fluorescence was used to determine the total PTEs (Cr, Ni, Cu, Y, Ba, Th, As, Pb, and Zn) concentration levels in the soil. Correlation matrix analysis was used to determine the metallic relationship between the PTEs and the normalizers (Al, Fe, Ti, Zr, Sr and Rb). Pollution indices such as contamination factor (CF), geoaccumulation index (Igeo) and enrichment factor (EF) analysis were used to determine the most suitable GBL. Al, Fe, Sr, Ti and Rb strongly correlated with the CF, Igeo and EF, whereas WAV performed better than the other geochemical background (EAV). The results indicated that Rb was the suitable normalizer and WAV was the appropriate GBL for agricultural soil and provided a foundation for evaluating and surveilling soil quality and health in agricultural soil.

Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef

Toxic metal exposure is a threat to green sea turtles (Chelonia mydas) inhabiting and foraging in coastal seagrass meadows and are of particular concern in local bays of the Great Barrier Reef (GBR), as numerous sources of metal contaminants are located within the region. Seagrass species tend to bioaccumulate metals at concentrations greater than that detected in the surrounding environment. Little is known regarding ecotoxicological impacts of environmental metal loads on seagrass or Chelonia mydas (C. mydas), and thus this study aimed to investigate and describe seagrass metal loads in three central GBR coastal sites and one offshore site located in the northern GBR. Primary seagrass forage of C. mydas was identified, and samples collected from foraging sites before and after the 2018/2019 wet season, and multivariate differences in metal profiles investigated between sites and sampling events. Most metals investigated were higher at one or more coastal sites, relative to data obtained from the offshore site, and cadmium (Cd), cobalt (Co), iron (Fe) and manganese (Mn) were found to be higher at all coastal sites. Principle Component Analysis (PCA) found that metal profiles in the coastal sites were similar, but all were distinctly different from that of the offshore data. Coastal foraging sites are influenced by land-based contaminants that can enter the coastal zone via river discharge during periods of heavy rainfall, and impact sites closest to sources. Bioavailability of metal elements are determined by complex interactions and processes that are largely unknown, but association between elevated metal loads and turtle disease warrants further investigation to better understand the impact of environmental contaminants on ecologically important seagrass and associated macrograzers.

Identification of Water Pollution Sources for Better Langat River Basin Management in Malaysia

The shutdown of drinking water treatment plants (DWTPs) at the Langat River Basin, Malaysia, which provides drinking water to almost one-third population in the basin, is very frequent, especially due to chemical pollution in the river. This study explored the pollution sources in the Langat River based on eight specific water intake points of the respective DWTPs to suggest an integrated river basin management (IRBM). Analysis of Al (250.26 ± 189.24 µg/L), As (1.65 ± 0.93 µg/L), Cd (1.22 ± 0.88 µg/L), Cr (0.47 ± 0.27 µg/L), and Pb (9.99 ± 5.38 µg/L) by ICP-MS following the Chelex® 100 column resin ion exchange method found that the mean concentrations except Al were within the water quality standard of the Ministry of Health (MOH) as well as the Dept. of Environment (DOE) Malaysia. However, the determined water quality index based on physicochemical parameters (2005–2015) at the midstream of Langat River was Class III, which needs substantial treatment before drinking. The linear regression model of Al, As, Cd, and Pb suggests that water quality parameters are significantly influencing the increase or decrease in these metal concentrations. Moreover, the principal component analysis (PCA) and the hierarchical cluster analysis (HCA) also support the regression models that the sources of pollution are both natural and man-made activities, and these pollution sources can be clustered into two categories, i.e., upstream (category 1) and mid to downstream (category 2) in the Langat River. The degraded water quality in the midstream compared to up and downstream of the river is mainly due to human activities apart from the natural weathering of minerals. Therefore, the implementation of policies should be effective at the local level for pollution management, especially via the proactive leadership roles of local government for this transboundary Langat River to benefit from IRBM.

Source-specific ecological risk assessment and quantitative source apportionment of heavy metals in surface sediments of Pearl River Estuary, China

In this study, surface sediments of the Pearl River Estuary were collected from 29 stations and investigated the spatial distribution, pollution level, quantitative source apportionment, and source-specific ecological risk of 10 heavy metals. The mean concentrations followed the order of Mn > Zn > Cr > Cu > Ni > Pb > As > Co > Cd > Hg. In terms of spatial distribution, it showed that the heavy metals were enriched in the inner Pearl River Estuary with 'extremely high' level of Hg, whereas, Cd and Zn posed 'moderate to high' contamination potential. We apportioned four main sources using positive matrix factorization model, in which natural geogenic and industrial manufacturing sources accounted for 36.84% and 27.11% of the total, respectively. However, the source-specific risk assessment suggested that mixed anthropogenic sources were the main contributors, and ecological risks were strongly affected by anthropogenic imports from the surrounding cities.

Water quality assessment in two lakes of Panchkula, Haryana, using GIS: case study on seasonal and depth wise variations

Water is the most important commodity available on earth and exists as both surface and sub-surface sources, but increased water pollution has reduced its potability. In this context, it has become imperative to regularly monitor the water quality. In situ and laboratory experimental procedures involve point wise collection of samples for quality determination which are too elaborative and time consuming. As such, the use of methods like Geographic Information System (GIS) modelling if used in collaboration with the traditional methods can prove to be a great tool as they are less expensive and gives a complete spatial resolution of the study site. Therefore, the present study focuses on the determination of water quality using traditional methods in collaboration with GIS modelling system using the inverse distance weighing (IDW) method for two natural lakes in Haryana. The IDW technique was used to interpolate parameters like temperature, dissolved oxygen (DO), nitrates (NO₃) and total phosphorous (TP) as they represent the effects of recent and old pollution in lake waters at different depths. These parameters were interpolated for determining the overall water quality status for the lakes. The collaboration can prove to be of great practical significance in today's time by giving an elaborative view of the present water quality status, easing daily telemetric monitoring of the sites as well as give an opportunity for futuristic modelling. The technique can work for almost all the sites around the globe which have either not been evaluated from quality aspect or are inaccessible for monitoring. Parameters like temperature and DO show significant depth wise and seasonal variations for both the lakes with highest values observed at the surface levels, whereas the NO₃ and TP represented effects of point pollution sources to a smaller extent. The maximum value of temperature was determined to be of 30.7 °C and 9 mg/l for DO and was recorded at the surface of lakes 2 and 1, respectively. Further, nitrate and phosphorous concentrations were observed to have maximum values of 0.99 and 0.5 mg/l at the centre of the lake 1 for monsoon season due to influx of pollutants and settlements in the bed. The primary reason for the variation of water quality may be attributed to increased sedimentation at the bottom of lake due to agricultural activities in the vicinity which creates impacts on different hydrodynamic processes leading to increased levels of TP and NO₃ concentrations. Further, increased recreational activities lead to induced variations in the water quality as well.

Hydrogeochemical Survey along the Northern Coastal Region of Ramanathapuram District, Tamilnadu, India

Ramanathapuram is a drought-prone southern Indian district that was selected for conducting a hydrogeochemical study. Groundwater samples from 40 locations were collected during January 2020 (pandemic interdiction according to COVID) and January 2021. The hydrogeochemical properties of the groundwater samples were evaluated and compared with drinking water regulations to assess their water quality. The order of cation dominance was as follows: Na+ > Ca2+ > K+ > Mg2+ in January 2020 and Na+ > Ca2+ > Mg2+ > K+ in January 2021 with respect to the mean value. The order of anion dominance was as follows: Cl− > HCO3− > SO42− > NO3− > F− in January 2020 and Cl− > SO42− > HCO3− > NO3− > F− in January 2021 with respect to the mean value. In the study area, the southern coastal region was identified as a groundwater-polluted zone through spatial analysis based on all analysis results. The irrigation water quality was analyzed using various calculated indices, such as Na% (percent sodium), SAR (sodium absorption ratio), PI (permeability index), MgC (magnesium risk), RSC (residual sodium concentration), and KI (Kelly ratio), demonstrating the suitability of the groundwater for irrigation in most parts of the study area. This was also confirmed by the Na% vs. EC Plot, USSL, and Doneen’s Plot for PI. In addition, the WQI results for drinking water and irrigation confirmed the suitability of the groundwater in most parts of the study area, except for the coastal regions. The dominant hydrogeologic facies of Na+-Cl−, Ca2+-Mg2+-SO42−, and Ca2+-Mg2+-Cl− types illustrated by the Piper diagram indicate the mixing process of freshwater with saline water in the coastal aquifers. Rock–water interaction and evaporation were the main controllers of groundwater geochemistry in the study area, as determined using the Gibbs plot. Ion exchange, seawater intrusion, weathering of carbonates, and the dissolution of calcium and gypsum minerals from the aquifer were identified as the major geogenic processes controlling groundwater chemistry using the Chadha plot, scatter plot, and Cl−/HCO3− ratio. Further, multivariate statistical approaches also confirmed the strong mutual relationship among the parameters, several factors controlling hydrogeochemistry, and grouping of water samples based on the parameters. Appropriate artificial recharge techniques must be used in the affected regions to stop seawater intrusion and increase freshwater recharge.

Element partitioning, emissions, and relative risk during disposal processes of diverse litters, fruit tree branches, and crop straws: dry distillation, incomplete combustion, and sufficient combustion

This study reports the release behaviors, enrichment characteristics, contamination level, and health risk of twenty-one elements in biomass, when dry distillation, incomplete combustion, and sufficient combustion. Results indicate that the element concentration in different kinds of biomass varies greatly. Even for the same kind of biomass, concentration in three products of dry distillation, incomplete combustion, and sufficient combustion is also different: fifteen elements (K, Ca, Mg, Al, Fe, Mn, B, Cu, Zn, Mo, Cd, Cr, Pb, Sb, Sn) have no significant difference in concentration but other six elements (As, Co, Ni, V, Na, P) are the opposite. Multivariate statistical approaches were used to assess five significant factors which affect element concentration, suggesting the contributes from biomass type, moisture content, soil, biomass age or organ, and disposal methods. Disposal methods and biomass type result in significant differences in element enrichment factor. More elements will release during sufficient combustion rather than dry distillation. The increasing of supplied oxygen during disposal process may increase the overall toxicity from elements release. The data of excess lifetime cancer risk (ELCR) suggests that Cr, Ni, Co, Cd, and Pb are the largest contributors to cancer risks during biomass application.

Appraisal of Environmental Health and Ecohydrology of Free-Flowing Aghanashini River, Karnataka, India

Rivers are vital freshwater resources that cater to the needs of society. The burgeoning population and the consequent land-use changes have altered the hydrologic regime with biophysical and chemical integrity changes. This necessitates understanding the land-use dynamics, flow dynamics, hydrologic regime, and water quality of riverine ecosystems. An assessment of the land-use dynamics in the Aghanashini River basin reveals a decline in vegetation cover from 86.06% (1973) to 50.78% (2018). The computation of eco-hydrological indices (EHI) highlights that the sub-watersheds with native vegetation had higher infiltration (and storage) than water loss due to evapotranspiration and meeting the societal demand. The computation of water quality index helped to assess the overall water quality across seasons. The study provides insights into hydrology linkages with the catchment landscape dynamics to the hydrologists and land-use managers. These insights would aid in the prudent management of river basins to address water stress issues through watershed treatment involving afforestation with native species, appropriate cropping, and soil conservation measures.

Uptake of a plasticizer (di-n-butyl phthalate) impacts the biochemical and physiological responses of barley

BACKGROUND

DBP is one of the most commonly used plasticizers for imparting desirable properties to polymers. The introduction of phthalates is reported to have occurred in the late 1920s, and there has been a significant rise in their release into the environment in past decades due to a lack of covalent bonding with the parent matrix. Because of their numerous applications in day-to-day life, phthalates have become ubiquitous and also classified as endocrine disruptors. Hence, several studies have been conducted to investigate the phthalate-mediated toxicities in animals; however, plants have not been explored to the same amount.

METHODS

Therefore, in the present study, the accumulation and translocation along with morpho-physiological perturbations in barley plants after 15, 30, 60, and 120 days of exposure to di-n-butyl phthalate (DBP) are investigated using standard protocols.

RESULTS

The maximal accumulation and translocation of DBP in the roots and shoots of barley plants was observed after 60 days of exposure. The exposure of DBP from 15 to 120 days was recorded to decline all the morphological indices (i.e., dry weight, net primary productivity, seed number per spike, and seed weight) of barley plants. The pigments content declined under DBP treatment for all exposure durations except 120 days exposure. Carbohydrate content increased after 15-30 days of exposure afterward it was observed to be decreased under 60 and 120 days of exposure. The protein content was declined in DBP stressed plants for 15-120 days. Proline content was increased in all exposure durations and maximal percent increase was recorded in 120 days of exposure. MDA content showed an increase at earlier exposure durations then followed by a decline in long-term exposure. Hydrogen peroxide content increased at all exposure durations. There were significant alterations observed in the activities of all antioxidative enzymes in comparison to the control. Furthermore, DBP stressed plants after 60 days were analyzed for the macromolecular variations using Fourier transform infrared spectroscopy (FTIR).

CONCLUSION

Thus, the outcomes of the current work provide an appraisal of phthalates' uptake and translocation mediated phytotoxic responses in barley plants. These observations can help in developing genetically modified edible plants that are resistant to phthalates uptake, thereby ensuring food security.

Anthropogenic influences on sedimentary geochemistry of Itapessoca Estuarine Complex, Pernambuco, Brazil

The Itapessoca Estuarine Complex is characterized by a history of intense economic activities developed on the banks of its tributary rivers, often exercised without any control or planning. In order to relate natural and/or anthropic events to the sediment age, radiometric dating method was performed by determining excess ²¹⁰Pb in the sediment using the proportional gas flow technique. To investigate possible disturbances in recent sedimentation processes in studied area, 20 surfaces sediment samples and 2 sediment cores were collected for determination of concentrations of the chemical elements. Al, Ca, Fe, K, Mg, Mn, Ni, Pb, Si, Sr, Ti and Zn concentrations were determined by the energy-dispersive X-ray fluorescence (EDXRF) technique. Through the enrichment factors and ratios among some elements associated with geochronological data, it was possible identify geochemical changes in sedimentation of sampled points, with increase of minerals associated with fine fractions and decrease of the proportions of elements associated with coarse fractions. The radiometric dating reveals that Pb enrichment and the exacerbated increase of Ca and Sr enrichment factors are strongly related to the anthropic activity in the region.

Occurrence, spatial distribution and ecological risk assessment of trace elements in surface sediments of rivers and coastal areas of the East Coast of Bangladesh, North-East Bay of Bengal

Coastal and estuarine ecosystems provide habitats for many organisms. Recently, the estuaries and coastal areas of the East Coast of Bangladesh have become heavily contaminated due to dumping of untreated wastewater into the rivers from a number of different industries. The current study analyzes potentially toxic elements contamination in surface sediments of the Karnaphuli, Sangu, Bakkhali and Naf Rivers, Kutubdia and Moheshkhali Channel, and St. Martin's Island, and assesses the consequent ecological risks. The pollution load index (PLI), geoaccumulation index (I_geo) and potential ecological risk (PER) indices show that the contaminated sediments have negative effects on the aquatic environments. The PLI values ranged between 0.45 and 1.67, which suggests the severity of trace-element contamination. The mean I_geo values showed the sediments range from uncontaminated to heavily contaminated state. The Enrichment Factor (EF) values suggested that the sediments were contaminated by anthropogenic sources, and PER values demonstrate that sites at Sangu, Naf and St Martin's Island are less contaminated compared to sites at Karnaphuli, Bakkhali, Kutubdia and Moheshkhali. Overall, results showed that Karnaphuli river is the most contaminated and St Martin's Island is the least based on the spatial distribution of PLI, C_d, PER and ∑TUs of trace metals in surface sediments. Comparing with the neighboring countries, the concentrations of Cd and Pb were found to be higher while Cr is lower in the East Coast of Bangladesh than the estuarine and coastal waters of the Bay of Bengal rim countries. The present study reveals that the lack of water quality guidelines in Bangladesh for the coastal, estuarine and marine water escalated the dumping of untreated wastewater. Immediate measures need to be taken to address the ecological risks so that an effective management program can be undertaken. A systematic approach for collecting pollutant data and use of isotopes to trace anthropogenic sources of contamination is recommended for pollutants like toxic metals, pesticides and other contaminants in sediment and aquatic products in the entire coastal waters of the Bay of Bengal.

Hydrogeochemical and salinity appraisal of surficial lens of freshwater aquifer along Lagos coastal belt, South West, Nigeria

In order to determine the hydrogeochemical processes and salinity status of the surficial lens of freshwater aquifer in the Lagos coastal basin, physicochemical parameters and hydrogeochemical tools were employed in this study. These tools include existing methods such as Piper diagram, Durov diagram, Gibb's diagram, statistical analysis and geochemical modelling, and the newly proposed cationic contribution evaluation and ionic ratio bivariate plots. The Piper plot revealed that chemical facies is rich in (Ca, Mg, Cl and HCO₃) and (Ca and HCO₃) for the groundwater in both wet and dry seasons while Mg–Cl and Na–Cl water types characterised the lagoon and the Ocean, respectively. The surficial aquifer is an essentially freshwater in the dry season and partly saline in the wet season due to flash flood, marine aerosol precipitation and infiltration from the surrounding brackish surface waters. The Ca²⁺+Mg²⁺ vs total cation (TZ⁺); HCO₃^-/Ca²⁺vs Ca²⁺/Mg²⁺ and HCO₃^-/Ca²⁺ vs Ca²⁺/Na⁺ plots as well as geochemical modelling indicated that carbonate weathering is the dominant chemical process controlling the groundwater chemistry for both seasons. In a descending order, water-rock interaction, ion exchange and evaporation are the geochemical processes controlling the groundwater quality in the area. Besides the natural processes, factor analysis revealed the imminent influence of anthropogenic activities (industrial and domestic) on the groundwater chemistry indicated by the presence of Mn, Fe, Ni, Cd, Pb, Cu and NO₃ above the permissible limit of drinking water standard, particularly in the wet season. In addition to the successful application of the proposed ionic plots, the study justifies the importance of multiple tools application in the hydrogeochemical deductions and recommends consistent monitoring of the shallow aquifers in the Lagos coastal basin.

Distribution, Risk Assessment, and Sources of Trace Metals in Surface Sediments from the Sea Area of Macao, South China

Due to rapid economic development in the Pearl River Delta, South China, trace metals pose a significant threat to the coastal ecosystems. In this study, we investigated the spatial distribution, contamination status, ecological risk, and possible sources of trace metals in 150 surface sediment samples from the Macao sea area. The results showed that concentrations of Ag, Pb, Cu, Zn, and Cd were highest in the Inner Harbour, whereas Cr, Co, As, and Ni were mainly accumulated in the downstream area of the Maliuzhou Waterway and the eastern area of Macao International Airport. Sediment grain composition, organic matter, total phosphorus, and hydrological regime were key factors influencing the spatial distribution patterns of trace metals. According to the environmental contamination indices of the enrichment factor, geo-accumulation index, and contamination factor, moderate contamination of trace metals occurs in the study area, while Ag and Pb contribute significantly to the contamination. Based on the potential ecological risk index, trace metals in surface sediments pose a low ecological risk. Correlation analysis and principal component analysis indicated that Cr, Co, Ni, and As were mainly derived from natural sources, whereas Ag, Pb, Cu, Zn, and Cd were mainly associated with anthropogenic sources.

Ecological Risk from Toxic Metals in Sediments of the Yangtze, Yellow, Pearl, and Liaohe Rivers, China

In this study, the concentrations of six toxic metals (Cd, Cr, Cu, Ni, Pb, and Zn) in surface sediments within the Yangtze, Yellow, Pearl, and Liaohe rivers, China, were analyzed, and their associated pollution statuses and potential ecological risks were assessed using the geoaccumulation index (I_geo), sediment quality guidelines (SQGs), and the potential ecological risk index (RI). Relatively high toxic metal concentrations were observed in the Pearl and Yangtze rivers, whereas relatively low concentrations were observed in the Yellow and Liaohe rivers. In the Yangtze, Pearl, and Liaohe rivers, the concentrations of these six toxic metals were higher than their background values. Based on the SQGs, the concentrations of Cd, Cr, and Cu in the four rivers were found to be higher than the threshold effect levels (TELs) but lower than the probable effect levels (PELs); however, the concentration of Ni exceeded the PEL in the Pearl River sediments. The I_geo index indicated that all four rivers were heavily contaminated with Cd. The RI of the Pearl and Yellow rivers was classed as high and low, respectively, and that of the Yangtze and Liaohe rivers as moderate. The pollution status of the sediments in the four major rivers was explored in relation to the geochemical background, the ecological toxicity of metals, and the sensitivity of the local benthic communities. These results provide meaningful information for directing river management priorities.

Distribution profile of heavy metals and associated contamination trend with the sedimentary environment of Pakistan coast bordering the Northern Arabian Sea

Spatiotemporal distributions of heavy metals (HMs) and their contamination status linked with the sedimentary environment were investigated in 2 monitoring years (MY-I and MY-II) along the Pakistan coast. The concentrations of HMs in sediments were analyzed through an atomic absorption spectrometer and presented the following order: Fe > Zn > Cu > Pb ≈ Cr > Ni > Co > Cd in MY-I and Fe > Cr > Zn > Ni > Cu > Pb > Co > Cd in MY-II. In the coastal sediments, all HMs surpassed the edges of shale values and sediment quality guidelines, excluding Fe. The burial flux (F_B), mass inventory (M_I), and deposition flux (F_D) of HMs were evaluated and compared to explore the potential of sediments to adsorb and desorb the metals into the marine environment during the last decade. Metal-specific pollution indices (I_geo, EF, C_f, and E_r) presented moderate contamination of Cu, Zn, Cr, Ni, and Co but considerable contamination of Pb and Cd in sediments. However, site-specific geoindicators (CD, RI, and PLI) signified the Sandspit as the highest polluted site along the coastal vicinity. Multivariate analyses via principal component analysis (PCA) and cluster analysis (CA) also highlighted the significant interactions between geochemical properties. The current study concluded the high pollution state toward the HMs and rendered the knowledge for policymaking and conserving the coastal and estuarine environment of Pakistan bordering the Northern Arabian Sea.

Trend analysis of global usage of digital soil mapping models in the prediction of potentially toxic elements in soil/sediments: a bibliometric review

The rising and continuous pollution of the soil from anthropogenic activities is of great concern. Owing to this concern, the advent of digital soil mapping (DSM) has been a tool that soil scientists use in this era to predict the potentially toxic element (PTE) content in the soil. The purpose of this paper was to conduct a review of articles, summarize and analyse the spatial prediction of potentially toxic elements, determine and compare the models' usage as well as their performance over time. Through Scopus, the Web of Science and Google Scholar, we collected papers between the year 2001 and the first quarter of 2019, which were tailored towards the spatial PTE prediction using DSM approaches. The results indicated that soil pollution emanates from diverse sources. However, it provided reasons why the authors investigate a piece of land or area, highlighting the uncertainties in mapping, number of publications per journal and continental efforts to research as well as published on trending issues regarding DSM. This paper reveals the complementary role machine learning algorithms and the geostatistical models play in DSM. Nevertheless, geostatistical approaches remain the most preferred model compared to machine learning algorithms.

Assessing environmental pollution levels in marinas

Despite the growing interest in recreational boating and the increasing number of marinas along the world's coastlines, environmental knowledge of these ecosystems is still very scarce. Detailed data of pollutants in marinas are necessary to provide a global approach of environmental risks in the context of international management strategies. In the present study, a set of 64 variables (30 in seawater and 34 in sediments) were measured to compare marinas from the Southern Iberian Peninsula (SIP). Uni and multivariate analyses showed significant differences among marinas, evidencing the importance of management on a local scale. The most relevant variables determining these differences were turbidity and the biocide Irgarol 1051 in seawater, and granulometry, hydrocarbons and faecal coliforms in sediment. The use of normalization techniques with Al or Fe, and the suitability of different methodologies to measure Total Organic Matter in marinas were also discussed. Additionally, we perform a comprehensive literature review of worldwide marina stressors and develop a simple and straightforward method for assessing environmental quality. The method was tested using SIP marinas and was based on the comparison of 15 selected sediment stressors with background values, concentrations of worldwide sediment quality guidelines (SQGs), and reference conditions/security thresholds established by the programme of coastal waters in port areas (ROM 5.1). A global score was assigned using a new proposed index, Marinas Environmental Pollution Index (MEPI), ranging from 0 to 150 points according to the environmental quality (<90: bad, 90-120: moderate, >120: good). MEPI of marinas from SIP ranged from 60 to 110 points indicating bad or moderate levels of pollution. Environmental quality is one of the decisive factors for awarding eco-labels or eco-certifications, such as Blue Flags in marinas. Therefore, pollution baseline information and environmental tools are mandatory for correct assignation of these awards and necessary for assessing the efficiency of management actions.

Heavy metal contamination prediction using ensemble model: Case study of Bay sedimentation, Australia

Lead (Pb) is a primary toxic heavy metal (HM) which present throughout the entire ecosystem. Some commonly observed challenges in HM (Pb) prediction using artificial intelligence (AI) models include overfitting, normalization, validation against classical AI models, and lack in learning/technology transfer. This study explores the extreme gradient boosting (XGBoost) model as a superior SuperLearning (SL) algorithms for Pb prediction. The proposed model was examined using historical data at the Bramble and Deception Bay (BB and DB) stations, Australia. The model was trained at one of the stations and transferred to a cross-station and vice versa. XGBoost showed higher reliability with less declination in (R²: coefficient of determination), i.e., 0.97 % over the testing phase, among others models at BB. At the cross-station (DB), the performance of the XGBoost model was decreased by 2.74 % (R²) against random forests (RF). The mean absolute error (MAE) observed 40 % (XGBoost) and 47 % (RF) less than artificial neural network (ANN). The XGBoost model performance declined by 3.44 % (R²) over testing (DB), which is minor among validated models. At the cross-station (BB), the XGBoost model showed the least decrement in terms of R², i.e., 7.99 % against the ANN (8.31 %), RF (10.26 %), and support vector machine (SVM, 36.19 %).

Potential Ecological Risk of Heavy Metals in a Typical Tributary of the Three Gorges Reservoir

Water and sediment samples were collected from a tributary (Ruxi River) of the Three Gorges Reservoir (TGR) to analyze the concentrations of seven heavy metals (HMs) and their fractions for better understanding the migration, bioavailability and potential environmental risk of HMs. The results indicated that the concentrations of HMs in water were lower than the Environmental Quality Standards for Surface Water Class I standards, except for Ni. Cd in sediment was found to be more sensitive to environmental changes, as the acid-soluble fraction of Cd accounted for about 40% of total Cd, and the sediment-water partition coefficient of Cd was the smallest among all the HMs. Meanwhile, multiple risk assessment methods of HMs indicated that sediment Cd in most sampling sites, significantly influenced by human activities, exhibited heavy pollution, suggesting that the Cd pollution should be attached great importance in the Ruxi River.

Insights into leaded gasoline registered in mud depocenters derived from multivariate statistical tool: southeastern Brazilian coast

Lead has been widely used since antiquity, but its uses drastically increased during the Industrial Revolution. The global emission of Pb into the environment was mainly due to tetraethyl lead added to gasoline as an antiknock additive. Because of its toxicity and neurological effects, the compound was phased out in the 1980s. Isotopic signatures are widely applied to differentiate sources of Pb; however, this is an expensive and sophisticated analysis compared to elemental analysis. Thus, this study aims to gain insight into leaded gasoline registered in mud depocenters from the southeastern Brazilian coast using multivariate statistical tools on elemental analysis data of trace elements. Seven multiple cores were collected on board the Research Vessel Alpha Crucis. Al, As, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, P, Pb, Sc, Sr, V and Zn were analyzed by acid digestion and quantified by ICP-OES. Levels and enrichment factors of Pb resulted in homogeneous columns, indicating that small variations in concentrations can be attributed to grain size differences, not presenting contaminated levels. From statistical results, the highest contribution on the first component was represented by a lithogenic source with the leaching of continental rocks. Lead content was notable in its high loadings in other components, which suggests atmospheric deposition. An increase in these components in subsurface samples from vertical profiles between 1935 and 1996 could represent a fingerprint of the consumption of leaded gasoline in Brazil between 1923 and 1989. Thus, statistical analysis of elemental data enabled to infer possible sources and pathways of Pb to the environment, without isotopic analysis.

Trends and Sources of Heavy Metal Pollution in Global River and Lake Sediments from 1970 to 2018

Heavy metal pollution is a global problem although its sources and trends differ by region and time. To data, no published research has reported heavy metal pollution in global rivers and lakes. This study reviewed past sampling data across six continents from 1970 to 2018 and analyzed the trends and sources of 10 heavy metal species in sediments from 289 rivers and 133 lakes. Collectively, river sediments showed increasing trends in Cd, Cr, Ni, Mn, and Co and decreasing trends in Hg, indicating that rivers acted as a sink for the former and a source for the latter. Lake sediments showed increasing trends in Pb, Hg, Cr, and Mn, and decreasing trends in Cd, Zn, and As, indicating that lakes acted as a sink for the former and a source for the latter. Due to difference in natural backgrounds and development stage in continents, mean metal concentrations were generally higher in Europe and North America than in Africa, Asia, and South America. Principal component analysis showed that main metal source was mining and manufacturing from the 1970s to 1990s and domestic waste discharge from the 2000s to 2010s. Metal sources in sediments differed greatly by continent, with rock weathering dominant in Africa, mining and manufacturing dominant in North America, and domestic waste discharge dominant in Asia and Europe. Global trends in sediment metal loads and pollution-control measures suggest that the implementation of rigorous standards on metal emissions, limitations on metal concentrations in manufactured products, and the pretreatment of metal-contaminated waste have been effective at controlling heavy metal pollution in rivers and lakes. Thus, these efforts should be extended globally.

Distribution, source, and pollution assessment of heavy metals in Sanya offshore area, south Hainan Island of China

Forty-four surface sediments from Sanya offshore area are analyzed for assessing heavy metals (Cu, Pb, Zn, Cr, Cd, Hg, and As) pollution. High metal values except for As are located in the southern areas which have fine-particle presence. However, high values of the metal As appear at a depth of 15-30 m in the Yazhou Bay. As and Pb show moderate contamination, and other metals show low contamination. The metals (except for As) are confirmed not to be enriched to slightly enriched, which are controlled by the grain size and mainly derived of the natural weathering products. The moderately severe to severe enrichment of As occurs in the Yazhou Bay and the nearshore area of the Sanya Bay. The reason is due in part to the excessive use of agricultural fertilizers. Further, it is also likely to be related to the high background value of As in the sea area.

Recent history of metal contamination in the Fangcheng Bay (Beibu Gulf, South China) utilizing spatially-distributed sediment cores: Responding to local urbanization and industrialization

In this study, the recent history of heavy metal pollution in the Fangcheng Bay (South China) was reconstructed utilizing three ²¹⁰Pb-dated sediment cores. The metal concentration profiles display three trends since the 1970s and clearly reflect local urbanization and industrialization. The metals in the Fangcheng Bay started to accumulate in the 1970s but remained relatively low until the 1990s which corresponds to the slow urbanization and industrialization. The metal accumulation in the eastern Fangcheng Bay peaked in the early 2000s following the steep increases in accordance with the rapid industrialization of the eastern Fangcheng Bay where the core HSL was collected. Conversely, the heavy metal profiles in the western Fangcheng Bay present slight step increases in the early 2000s followed by a dramatic metal enrichment in the late 2000s; the expansion of these two cores, which begins in the early 2000s, concurs well with the rapid local urbanization and industrialization.

Concentrations of Metals in Tissues of Cockle Anadara granosa (Linnaeus, 1758) from East Java Coast, Indonesia, and Potential Risks to Human Health

This study reports the presence of Cd, Pb, Zn, Hg, Cu, and Cr in the cockles (Anadara granosa, Linnaeus, 1758) harvested along the East Java Coast, Indonesia. The concentrations of metals were determined by atomic absorption spectrometer and expressed in mg kg⁻¹ wet weight. The concentrations of metals ranged from 0.11 to 0.82 mg kg⁻¹ for Cd, 0.10 to 0.54 mg kg⁻¹ for Pb, 10.22 to 19.04 mg kg⁻¹ for Zn, 0.02 to 1.47 mg kg⁻¹ for Hg, 1.79 to 4.76 mg kg⁻¹ for Cu, and 1.64 to 3.79 mg kg⁻¹ for Cr. The metal concentrations in the whole tissues of cockles were in the order Zn>Cu>Cr>Hg>Cd>Pb. The Cd and Pb levels in cockles were found to be higher than the permissible limit for human consumption according to EC and FAO; the levels of Hg exceeded the EC, Hong Kong, Australia, and Indonesia standards; and the levels of Cr exceeded the Hong Kong standard. The estimated weekly intake (EWI) of cockles indicates that the concentrations of Cd and Hg in the cockle tissues from Gresik were higher than the provisional tolerable weekly intake (PTWI); meanwhile, the concentrations of Cr of cockles from all locations were higher than and close to the PTWI. The THQ values for Cd at Gresik, for Hg at Gresik, Surabaya, and Pasuruan, and for Cr at all locations were higher than one indicating that these metals pose potential noncarcinogenic effects to consumers. Reducing the consumption of cockles should be done in order to minimize the adverse effects of metals especially Cd, Hg, and Cr to human health.

Spatial and seasonal distribution of multi-elements in suspended particulate matter (SPM) in tidally dominated Hooghly river estuary and their ecotoxicological relevance

The present work represented first study of the spatio-seasonal distribution of the multi-elements in the suspended particulate matter (SPM) of the tropical Hooghly river estuary (HRE), eastern part of India. The high load of SPM (20-3460 mg/l) might have induced negative impact on the phytoplankton density. The relative abundance of the studied elements exhibited the following decreasing trend (concentration in μg/g and %): Si(26.44 ± 3.75%) > Al(7.94 ± 1.52%) > Fe(6.17 ± 1.9%) > K(3.05 ± 1.5%) > Ca(1.97 ± 1.11%) > Mg(1.57 ± 1.71%) > Na(1.45 ± 8.40%) > Mn(1273 ± 2003) > Zn(178.43 ± 130.95) > V(151.54 ± 27.13) > Cr(147.08 ± 32.21) > Cu(62.06 ± 14.03) > Ni(49.64 ± 12.09) > Pb(21.5 ± 10.45). The accumulation of Ni, Cr, Pb, and Cu is mainly controlled by the formation of Fe hydroxides along with particulate organic carbon (POC) and salinity. The average geo-accumulation index (I_geo) and enrichment factor (EF) endorsed the substantial input of Cr (I_geo = 0.037; EF = 1.61) and Zn (I_geo = 0.123; EF = 2.07) from diffused pollution sources. From ecotoxicological point of view, the quality guidelines (QGs) suggested that Cr and Ni might possess frequent adverse biological effects. However, the mean probable effect level (PEL) quotient values revealed 49% probability of toxicity to the aquatic biota for five toxic elements (Cr, Ni, Cu, Zn, and Pb). The geochemical approaches, pollution indices, and statistical evaluation together revealed low to moderate contamination in the estuary. This baseline data would be beneficial in adopting proper management strategies for sustainable utilization and restoration of the water resources. The authors strongly recommend continuous systematic monitoring and installation of treatment plants for management of this stressed estuary.

What Controls the Flushing Efficiency and Particle Transport Pathways in a Tropical Estuary? Cochin Estuary, Southwest Coast of India

Estuaries with poor flushing and longer residence time retain effluents and pollutants, ultimately resulting in eutrophication, a decline in biodiversity and, finally, deterioration of water quality. Cochin Estuary (CE), southwest coast of India, is under the threat of nutrient enrichment by the anthropogenic interventions and terrestrial inputs through land runoff. The present study used the FVCOM hydrodynamic model coupled with the Lagrangian particle module (passive) to estimate the residence time and to delineate site-specific transport pathways in the CE. The back and forth movements and residence time of particles was elucidated by using metrics such as path length, net displacement and tortuosity. Spatio-temporal patterns of the particle distribution in the CE showed a similar trend during monsoon and post-monsoon with an average residence time of 25 and 30 days, respectively. During the low river discharge period (pre-monsoon), flood-ebb velocities resulted in a minimum net transport of the water and longer residence time of 90 days compared to that of the high discharge period (monsoon). During the pre-monsoon, particle released at the southern upstream (station 15) traversed a path length of 350 km in 90 days before being flushed out through the Fortkochi inlet, where the axial distance was only 35 km. This indicates that the retention capacity of pollutants within the system is very high and can adversely affect the water quality of the ecosystem. However, path length (120 km) and residence time (7.5 days) of CE were considerably reduced during the high discharge period. Thus the reduced path length and the lower residence time can effectively transport the pollutants reaching the system, which will ultimately restore the healthy ecosystem. This is a pioneer attempt to estimate the flushing characteristics and residence time of the CE by integrating the hydrodynamics and Lagrangian particle tracking module of FVCOM. This information is vital for the sustainable management of sensitive ecosystems.

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.

Changes in the heavy metals and petroleum hydrocarbon contents in seawater and surface sediment in the year following artificial reef construction in the Pearl River Estuary, China

Marine pollution is an important driver of ocean biodiversity loss, which can be mitigated by the construction of artificial reefs (ARs). Many studies have explored how ARs affect marine organisms, but our understanding of the changes in heavy metals and petroleum hydrocarbons after AR construction is limited. In the current study, we assessed the heavy metal and petroleum hydrocarbon contents of the seawater (surface and bottom seawater) and surface sediment before and after AR construction in AR habitat and in nearby non-reef control habitat in the Pearl River Estuary, China. AR construction tended to decrease the contents of Cu, Pb, Cd, and Hg but tended to increase Zn content in seawater and in surface sediment. Petroleum hydrocarbon content changed irregularly in seawater and surface sediment. Effects of AR construction were similar in the nearby non-reef habitat vs. the AR habitat. Seawater heavy metal and petroleum hydrocarbon contents were correlated with the seawater physicochemical properties (mainly temperature, inorganic nitrogen, chemical oxygen demand, available phosphate, and suspended particulate organic matter), and sediment heavy metal content was correlated with sediment organic matter content. Additional studies over longer time periods and at larger spatial scales are needed to clarify how AR construction affects heavy metal and petroleum hydrocarbon contents in marine environments.

The spatiotemporal contribution of the phytoplankton community and environmental variables to the carbon sequestration potential in an urban river

The phytoplankton (internal driving forces) and environmental variables that affect complex biochemical reactions (external driving forces) play an important role in regulating photosynthetic carbon fixation. Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) exists in various phytoplankton species and is an important enzyme in the photosynthetic process. To investigate the phytoplankton composition (internal driving forces), we selected the functional gene of the Rubisco large subunit (rbcL) as the target gene for this study. Phytoplankton gross primary productivity was measured using light and dark biological oxygen demand bottles to assess the carbon sequestration potential. The fundamental environmental indicators were determined to analyze the mechanisms that drive the carbon fixation process. The correlation results indicated that green algae were only controlled by nitrate, and that diatoms were positively correlated with phosphate. The cluster analysis results demonstrated that nitrite was the major driver controlling phytoplankton primary productivity. During the wet seasons (spring and summer), the contribution of the planktonic community respiration to the carbon sequestration potential was higher than net primary productivity (NPP), followed by dissolved organic carbon and nitrate. During the dry season (autumn), NPP, total nitrogen, and nitrite ranked highest in terms of carbon sequestration potential. The contributions of green algae and diatoms to the carbon sequestration potential were temporally higher than those of cyanobacteria. The maximum carbon sequestration potential occurred during autumn because of diatom production and the function of phosphate, whereas the minimum carbon sequestration potential occurred in summer. Spatially, the upstream carbon sequestration potential was higher compared with downstream because of the effect (contribution) of cyanobacteria (Phormidium), diatoms (Surirella solea and Thalassiosira pseudonana), and environmental variable (nitrite). These findings provide a better understanding of the underlying mechanisms of phytoplankton productivity and the influences of environmental variables on carbon sequestration in urban river ecosystems.

Risk for Indo-Pacific humpback dolphins (Sousa chinensis) and human health related to the heavy metal levels in fish from the Pearl River Estuary, China

Cetaceans and humans shared the same route of exposure to many anthropogenic contaminants via fish consumption. To assess the health risks associated with heavy metal levels in fishes from the Pearl River Estuary (PRE) and the seasonal dynamics, 13 fish species (n = 675) consumed by the Indo-Pacific humpback dolphins (Sousa chinensis) and humans were analyzed for concentrations of nine heavy metals. Heavy metal levels vary significantly by species and by season in the PRE fishes. The two eel goby species were the most contaminated fish species, which had the highest levels of Cu, Pb, Hg, Mn and Se. Levels of non-essential metals (As and Pb) in many different fish species were all found significantly higher in dry season than in wet season, which may reflect the dilution effect on contaminant levels in the PRE waters in rainy season. For essential metals, Cu, Cr and Se in many fish species were significantly higher in dry season compared to wet season, while Se and Mn in the other fish species showed an opposite pattern, since essential metal accumulation could be influenced by several physiological processes in life. Risk assessment for dolphins showed that inorganic-As levels in all fishes exceeded the safe limits, whereas a more conservative approach indicated that the levels of all metals in all fish samples had toxic effects on dolphins, except for Hg. Human health risk analysis showed that inorganic-As levels in tonguesole (all year) and sillago (dry season) and Cr levels in pomfret (dry season) exceeded the acceptable values.

Critical Processes of Trace Metals Mobility in Transitional Waters: Implications from the Remote, Antinioti Lagoon, Corfu Island, Greece

The Antinioti Lagoon is a karstified, rather pristine, and shallow coastal lagoon located in the northern part of Corfu Island in NW Greece. The present study examines the levels of metals (Al, Fe, Mn, Cd, Cu, Pb, and Zn) in the dissolved and particulate phase, as well as in surface and core sediments, and identifies the critical processes that define their behavior. The major transport pathway of dissolved Mn, Cd, and Pb, and particulate Mn, Cd, and Zn into the lagoon is through freshwater springs, whereas surface runoff dominates the transport of particulate Al, Fe, and Cu. Interestingly, large particles (>8 μm) contain higher amounts of Al, Fe and Mn than the finer ones (<8 μm), due to flocculation of oxyhydroxides that, eventually, scavenge other metals, as well. Cadmium and Zn bound to the large particles were found to be less prone to desorption than the smaller ones and were effectively captured within the lagoon. In the sediments, diagenetic processes are responsible for post-depositional changes in the forms of metals (particularly Fe, Mn and Cd). Enrichment factors (EFs) based on local background showed that sediments are enriched in restricted areas in Cd and Pb by maximum factors 4.8 and 10, respectively. These metals were predominantly found in potentially labile forms. Thus, any interventions introducing changes in the physico-chemical conditions may result in the release of metals, with negative implications on the lagoon’s ecological quality.

Distribution, Source Identification, and Assessment of Potentially Toxic Elements in the Sediment Core from the Estuarine Region of the Golmud River to the Qarhan Salt Lake, Qinghai, China

The Qarhan Salt Lake has attracted increasing attention due to its significant national economic status and increased human activity, especially mining. Therefore, a sediment core collected from the confluence of the Golmud River to the Qarhan Salt Lake was chosen to investigate the concentrations, pollution levels, and ecological assessment of nine targeted elements (Al, As, Cd, Cr, Cu, Ni, P, Pb, and Zn). The excess 210Pb activities were calculated and a sedimentation rate of approximately 0.041 cm/y was estimated. Elements sources were identified, and the results show that Al, As, Cu, Ni, Pb, and Zn were mainly from natural sources, Cd and P were mainly from human input, and Cr appeared to have both sources. For Cd and P there was an increasing trend from 1987 and 1975, respectively, coinciding with the Chinese economic reform, Qarhan Salt Lake development and utilization, and also with the gross domestic product of Haixi State, Qinghai Province. Though the pollution and ecological assessment showed that there was nil to very low contamination and ecological risk, which is different from previous assumptions, the obviously increasing trend of Cd and P in the surface is still a concern. More attention should be paid to Cd and P in the further development of the Qarhan Salt Lake and the Golmud City.

Lead Pollution and Isotope Tracing of Surface Sediments in the Huainan Panji Coal Mining Subsidence Area, Anhui, China

In this study, the provenance of anthropogenic lead, a major pollutant of surface sediments, was determined in Huainan Panji coal mining area. The lead concentrations and the pollution degree were investigated by the enrichment factor. Tessier five-step morphology extraction method was used to discuss its potential hazard. By comparing the lead isotope ratios of surface sediments and surrounding potential polluted end-members, the lead isotope ternary mixture model was appropriated to explore the sources and relative contribution fractions. The results showed that: (1) The lead concentrations ranged from 31.44 to 64.07 mg/kg which was mild-moderate pollution. (2) The chemical forms of lead were residue state > iron-manganese oxidation state > exchangeable state > organic state > carbonate state. (3) The anthropogenic lead in surface sediments originated from soil, vehicle exhaust, coal gangue. And the relative contribution fractions were 51.70%, 30.90%, and 17.40%.