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.

The efficiency of trace element uptake by seagrass Cymodocea serrulata in Rabigh lagoon, Red Sea

The search for solutions to environmental pollution has been on the increase, with many questions recently as to which marine organisms can bioaccumulate trace elements in the marine ecosystem. Cadmium, Cr, Cu, Fe, Mn, Ni, Pb, and Zn concentrations in sediment, seawater, and seagrass compartments (root, rhizome, and leaf blade) were determined at Rabigh lagoon, Red Sea. This is to provide an insight into the potential of Cymodocea serrulata to bioaccumulate trace elements and as a good candidate to biomonitor these elements in a natural aquatic ecosystem. Results revealed significant variations in trace element concentrations across the three compartments of C. serrulata and the sites, with site S8 located in the most closed part of the lagoon recording the highest concentrations for all the trace elements. The translocation factor (TF_rhizome/root = 1.00) of trace elements was higher in the root compartment. This implies that the root compartment is a better bioindicator of trace elements and has more potential to be utilized for biomonitoring. A significant positive correlation (p < 0.01) was established between the trace element concentrations in sediment, seawater, and the three compartments of C. serrulata except for Mn concentration in the compartments. The seagrass C. serrulata can be used for biomonitoring of trace elements in marine ecosystems as our results provide information on its capacity to bioaccumulate these elements. This is one of the key characteristics of a typical bioindicator of aquatic pollutants.

Diffusive gradients in thin films (DGT): A suitable tool for metals/metalloids monitoring in continental waterbodies at the large network scale

The contribution of Diffusive Gradients in Thin films (DGT) passive sampling to continental water quality monitoring was assessed in a real measurement network (6 sampling campaigns, 17 stations). Ten metals/metalloids (Al, Zn, Ni, Cd, Cu, Pb, Cr, As, Se and Sb) were studied using the control laboratory's working conditions with grab and DGT passive sampling. The DGT field deployments were robust, with a 3% sampler loss rate and a <65% average relative deviation between duplicates. Compared to grab sampling, DGT showed a similar quantification frequency for half of the targeted elements but showed a higher frequency for the other half (e.g., Cd quantification at 20% with grab sampling vs. 97% with DGT). Similar concentration trends were established using DGT and grab sampling at most sites throughout the year. Notably, for some elements, trends were only provided by DGT sampling. A study of several DGT blanks showed that the device contamination was occasional and originated primarily from cross-contamination during the disassembly step. Considering this contamination, the operational sensitivity by DGT was at least between 1 and 5 times greater in comparison to that by grab sampling. Estimations of the economic cost revealed that measurement networks cost 2 to 3 times more when monitored by DGT compared to standard grab monitoring. However, the information obtained based on each type of sampling method is different. Grab sampling is easy to implement and can highlight high contamination peaks. The DGT concentrations are averaged over time and are relevant to chronic exposure evaluations. Considering the good performance of the DGT sampling highlighted in this study and its complementarity with grab sampling in terms of water quality assessments, a combination of these two types of sampling, which can be affordable, should improve the water quality evaluation within monitoring networks.

Tracing iron ore tailings in the marine environment: An investigation of the Fundão dam failure

This work aims to characterize, in mineral and chemical terms, the ore tailings related to the Mariana disaster (MG, Brazil), occurred on 5 November 2015, and assess its correlation with sediments found in the continental shelf adjacent to the Doce River mouth (ES, Brazil). This study uses samples of tailings and seabed sediments collected at the mouth of the Doce River from 2012 to 2019. Elemental compositions of all samples were determined by X-ray fluorescence measurements; however, Synchrotron Resonant X-Ray Diffraction proved to be a remarkable technique to characterize the crystallographic phases of iron present in sediments. Studies and analyzes of the sediment samples showed that the tailings have a notable feature of the iron-crystallographic phases, mainly observed in the period after the Fundão dam failure, as compared with sediments collected in the period before. This set of iron-containing mineral phases, here called the Iron Mineralogical Set (IMS), consists of the main phases of hematite and magnetite and the minority phases of goethite and greenalite and it is used as a marker of tailings. Mass ac magnetic susceptibility measures supported the concept of the IMS as a marker. It is suggested a relationship between the content of the IMS in the sediment samples as a function of the measures of mass magnetic susceptibility. The IMS had shown the influence of tailings on the sea bed sediment indicating that there is no possibility, at the current stage, of predicting how many years this material will still be at the seabed.

Seasonal dynamics of metal phase distributions in the perennial tropical (Brahmaputra) river: Environmental fate and transport perspective

An evaluation of the seasonal dynamics of metal (Cd, Cr, Cu, Pb and Zn) phase distribution and speciation, along with different hydrogeochemical facies, was conducted along the entire stretch of a perennial tropical (Brahmaputra) River. Water samples were collected from twelve locations during the monsoon, post-monsoon and pre-monsoon seasons. A characteristic trend in bioavailability was observed in the sequence of Zn > Cu > Pb > Cr > Cd, reflecting non-significant seasonal changes in dissolved and particulate phase metal fractions at all twelvelocations. Partition (or distribution) coefficients (K_ds) for Cu (5.30-6.50), Zn (4.47-6.44), Pb (3.69-4.97) and Cr (3.25-5.15), reflect the influences of anionic inorganic constitutents (aqua ion complexes), environmental variables, and river hydrology. MINTEQA2 calculations showed that metal forms complexes with other inorganic ions such as Cl^-, SO₄^2-, HCO^3- and strong binding as organic complexes (for Cu and Pb) reduces their leaching potential to groundwater system. High log K_d values (≥5.3) and significant spatial variations at locations R3 to R8 of Pb, Cu, and Zn during pre-monsoon period may be explained by the formation of complexes with organic ligands in sewage and domestic wastes (humic and fulvic acids). Multivariate statistical analysis revealed multi-metal co-contamination, mainly of Zn, Cu, Cd and Pb and dissolved nutrients, loading in different clusters, emphasizing the importance of climatic, anthropogenic, terrigenous and lithological sources as controlling factors for seasonal metal dynamics in the river water.

Water Framework Directive programmes of measures: Lessons from the 1st planning cycle of a catchment in England

The European Union's Water Framework Directive (WFD) required Member States to establish programmes of measures to achieve good water status formally by 2015, but on postponing the deadline by two six-year periods, by 2027 at the latest. With many Member States facing problems with developing such measures in the first planning cycle, and limited change in ecological status since the first river basin management plans were reported, we look at the implementation of the Directive in England, where only 17% of the surface water bodies were found at good status in 2015, a reduction of 4% since 2009. Using as a case study the Broadland Rivers catchment, we examine the measures taken for Cycle 1 and changes in the classifications of water body status, to investigate whether the way the measures were developed could have limited their potential to deliver WFD objectives. While the WFD was adopted to succeed and replace management practices targeting individually non-compliant element, findings indicate that little had changed in the way measures were developed. Although considerable progress has been made on the implementation of these measures, the limited progress in improving classifications demonstrates the limits of this approach and further makes the case for what the WFD was introduced for: the harmonised transposition of the Integrated River Basin Management paradigm, as the key for delivering good ecological status.

The Transition of EU Water Policy Towards the Water Framework Directive's Integrated River Basin Management Paradigm

Introduced in 2000 to reform and rationalise water policy and management across the European Union (EU) Member States (MS), the Water Framework Directive (WFD), the EU's flagship legislation on water protection, is widely acknowledged as the embodiment and vessel for the application of the Integrated River Basin Management (IRBM) paradigm. Its ecological objectives, perhaps even more challenging than the prospect of statutory catchment planning itself, were for all EU waters to achieve 'good status' by 2015 (except where exemptions applied) and the prevention of any further deterioration. In support of the upcoming WFD review in 2019, the paper reviews the transition of EU policies that led to the adoption of the WFD, to identify the reasons why the Directive was introduced and what it is trying to deliver, and to place progress with its implementation into context. It further investigates reasons that might have limited the effectiveness of the Directive and contributed to the limited delivery and delays in water quality improvements. Findings reveal that different interpretations on the Directive's objectives and exemptions left unresolved since its negotiation, ambiguity and compromises observed by its Common Implementation Strategy and lack of real support for the policy shift required have all been barriers to the harmonised transposition of the IRBM paradigm, the key to delivering good ecological status. The 2019 WFD review offers a unique opportunity to realign the implementation of the Directive to its initial aspirations and goals.

A method to assess the evolution and recovery of heavy metal pollution in estuarine sediments: Past history, present situation and future perspectives

A methodology to assess the historical evolution and recovery of heavy metal pollution in estuarine sediments was developed and is presented here. This approach quantifies the distribution of heavy metals in sediment cores, and investigates the influence of anthropogenic activities and/or core locations on the heavy metal pollution, by proposing and using sediment quality indices and polynomial regressions. The method has been applied to the Suances Estuary confirming its suitability as a comprehensive and practical management tool. In this estuary, the evolution of heavy metal pollution (since 1997-1998 to 2015) pointed out the deeper the sediments, the more polluted, indicating a recovery at the upper layers due to the closure and ending of washing discharges from mining, and the reduction of metal loads from industrial wastewaters. In terms of global pollution, the intertidal and subtidal sediments will require 43.1±2.8 and 8.6±0.6years to be unpolluted, respectively.

Using seagrasses to identify local and large-scale trends of metals in the Mediterranean Sea

To manage trace metal pollution it is critical to determine how much temporal trends can be attributed to local or large-scale sources. We tracked changes in metal content in the seagrass Posidonia oceanica, along the NW Mediterranean from 2003 to 2010. While Cu, Cd and Ni showed a large inter-site variation, likely due to local factors, Fe, Mn and Pb showed little local variation and synchronous interannual variability across sites, most likely due to large-scale sources. Zn showed equal importance of local and large-scale sources of variation. Temporal trends of Ni, Zn, Cd, Cu remained almost stable. In contrast, Fe, Mn and Pb slightly increased in the last decade. These trends suggest that metals like Cu, Cd, Ni can be effectively managed at local scale. Whereas, elements like Fe, Mn and Pb have an important large-scale component that needs to be managed across the frontiers of national jurisdictions.

Heavy Metals in Surface Soils in the Upper Reaches of the Heihe River, Northeastern Tibetan Plateau, China

The upper reaches of the Heihe River have been regarded as a hotspot for phytoecology, climate change, water resources and hydrology studies. Due to the cold-arid climate, high elevation, remote location and poor traffic conditions, few studies focused on heavy metal contamination of soils have been conducted or reported in this region. In the present study, an investigation was performed to provide information regarding the concentration levels, sources, spatial distributions, and environmental risks of heavy metals in this area for the first time. Fifty-six surface soil samples collected from the study area were analyzed for Cr, Mn, Ni, Cu, Zn, As, Cd and Pb concentrations, as well as TOC levels. Basic statistics, concentration comparisons, correlation coefficient analysis and multivariate analyses coupled with spatial distributions were utilized to delineate the features and the sources of different heavy metals. Risk assessments, including geoaccumulation index, enrichment factor and potential ecological risk index, were also performed. The results indicate that the concentrations of heavy metals have been increasing since the 1990 s. The mean values of each metal are all above the average background values in the Qinghai Province, Tibet, China and the world, except for that of Cr. Of special note is the concentration of Cd, which is extremely elevated compared with all background values. The distinguished ore-forming conditions and well-preserved, widely distributed limestones likely contribute to the high Cd concentration. Heavy metals in surface soils in the study area are primarily inherited from parent materials. Nonetheless, anthropogenic activities may have accelerated the process of weathering. Cd presents a high background concentration level and poses a severe environmental risk throughout the whole region. Soils in Yinda, Reshui daban, Kekeli and Zamasheng in particular pose threats to the health of the local population, as well as that of livestock and wildlife.

Metal contamination recorded in the sediment of the semi-closed Bakar Bay (Croatia)

This study presents metal levels in the sediments of the Bakar Bay, with its main goal to evaluate recent anthropogenic influence, as well as over previous decades. Sediment profiles at 7 sampling points were taken. Chemical contents in bulk sediment were obtained using ICP, ICP-MS, and AAS methodologies, and 20 most significant elements were presented. Concentrations of selected elements were evaluated by factor statistical analyses to identify their source. Also, metal enrichment factor and geoaccumulation index were calculated, and spatial distribution maps for three sediment layers were constructed. Measured metal concentrations in sediment were compared with concentrations in other sediments from the Adriatic Sea. In addition, a set of sediment quality guidelines were also applied in order to predict the probability of adverse biological effects on the benthic community: This was found not to be very serious. Factor analysis clearly demonstrates the segregation between metals of natural origin resulted from soil and bedrock weathering (Li, Al, Cr, Sc), and with two anthropogenic sources originating from the city of Bakar and bulk cargo terminal (Hg, Pb, Zn, Ag, Sn, and Fe). Mercury (max 0.65 μg g(-1)) is found to be the heaviest contaminant, followed by lead (max 71.5 μg g(-1)), copper (89.3 μg g(-1)), and zinc (156 μg g(-1)). However, this study shows that Bakar Bay is considerably less polluted with toxic metals than it was believed.

Profile of trace metals accumulation in core sediment from Seine river estuary (docks basin)

The Seine is one of the most polluted rivers in Europe with respect to potentially harmful elements. It receives effluents from the upstream Paris urban and industrial area, and also local inputs from the heavily industrialized Rouen and Le Havre regions. The present study deals with this environmental topic and the concentrations of Cd, Ni, Pb, Hg, Zn and Cu were determined in sediment cores collected in the docks basin of Rouen harbour in 2008. The intensity of metal pollution during recent decades was evaluated using an enrichment factor (EF) and a geoaccumulation index (Igeo). The results of vertical distribution showed that the metal pollution in the past is much higher than in the surface sediment. Mercury was found to be the heaviest pollutant (with Igeo and EF exceeding 4 and 20, respectively), and Cd and Pb were the second most important pollutants. A slight contamination in Ni was observed with very low Igeo values. To estimate the sediment toxicity, simultaneously extracted metals/acid volatile sulfides ratio (SEM/AVS) was calculated. Low values of the toxicity index SEM/AVS were observed in the core sediments indicating the inexistence of metal potential toxicity. Also the concentrations of these trace metals were lower than the probable effect concentration values reported as consensus-based sediment quality guidelines for fresh water ecosystems.

A risk-based approach to prioritise catchments for diffuse metal pollution management

Catchment management integrates a wide range of water management aspects taking into account the interaction between land-use and water quality. While most sources of pollution can be identified, monitoring and tackling diffuse pollution are difficult due to the abundance of its sources and pathways. As a result, the application of risk assessment of diffuse pollution at the catchment level has been limited. This study aimed to develop a risk-based approach to rank and prioritise catchments based on the need for managing diffuse metal pollution, using a multi-criteria evaluation framework. Source-pathway-receptor linkages were the basis for the selection of criteria and associated indicators. The methodology was applied to eight catchments located in the Humber River Basin District (RBD) that were comparatively evaluated, and difficulties in selecting weightings for the criteria used were discussed. Results showed that Don and Rother, Aire and Calder and Trent were the three catchments with the highest risk of diffuse metal pollution in this RBD. The findings demonstrate the potential of the proposed risk-based approach to inform more detailed investigations to follow and prioritise the need for investments on relevant programmes to prevent diffuse metal pollution in catchments where these are needed most.

The role of sediments as a source of metals in river catchments

Aquatic sediments are a known source of pollutants, but their impact on the quality of overlying waters is not easily quantified. Sediments are generally considered to behave as a sink for pollutants such as heavy metals in the aquatic environment, frequently acting as a source for their presence in waters, with implications for catchment management. This study aimed to calculate the contribution of sediments to metal levels in overlying waters, helping understand their role as a source of metals in river catchments. An aquivalence mass balance approach was modified to take into account both natural and anthropogenic influences and applied to assess sediment contribution in a reach of the River Yare in the UK. The rates of total metal transport from sediments to overlying waters were estimated to be 29.89 g d(-1) for cadmium (Cd), 1633.39 g d(-1) for lead (Pb), 8.29 g d(-1) for mercury (Hg) and 357.56 g d(-1) for nickel (Ni). The results from the case study demonstrated that sediments could be a significant source of metal emissions in river catchments. The calculations proposed in the paper could be useful in developing strategies for sediment management, not only to improve and/or maintain quality of sediments but also to inform the selection of measures of pollution control for the catchment.

Uncertainty-based calibration and prediction with a stormwater surface accumulation-washoff model based on coverage of sampled Zn, Cu, Pb and Cd field data

A dynamic conceptual and lumped accumulation wash-off model (SEWSYS) is uncertainty-calibrated with Zn, Cu, Pb and Cd field data from an intensive, detailed monitoring campaign. We use the generalized linear uncertainty estimation (GLUE) technique in combination with the Metropolis algorithm, which allows identifying a range of behavioral model parameter sets. The small catchment size and nearness of the rain gauge justified excluding the hydrological model parameters from the uncertainty assessment. Uniform, closed prior distributions were heuristically specified for the dry and wet removal parameters, which allowed using an open not specified uniform prior for the dry deposition parameter. We used an exponential likelihood function based on the sum of squared errors between observed and simulated event masses and adjusted a scaling factor to cover 95% of the observations within the empirical 95% model prediction bounds. A positive correlation between the dry deposition and the dry (wind) removal rates was revealed as well as a negative correlation between the wet removal (wash-off) rate and the ratio between the dry deposition and wind removal rates, which determines the maximum pool of accumulated metal available on the conceptual catchment surface. Forward Monte Carlo analysis based on the posterior parameter sets covered 95% of the observed event mean concentrations, and 95% prediction quantiles for site mean concentrations were estimated to 470 μg/l ± 20% for Zn, 295 μg/l ± 40% for Cu, 20 μg/l ± 80% for Pb and 0.6 μg/l ± 35% for Cd. This uncertainty-based calibration procedure adequately describes the prediction uncertainty conditioned on the used model and data, but seasonal and site-to-site variation is not considered, i.e. predicting metal concentrations in stormwater runoff from gauged as well as ungauged catchments with the SEWSYS model is generally more uncertain than the indicated numbers.

A recent history of metal accumulation in the sediments of Rijeka harbor, Adriatic Sea, Croatia

We studied metal pollution in the sediments of Rijeka harbor, including anthropogenic influence during recent decades and at the present time. Sediment profiles were collected at ten sampling points. The concentrations of 63 elements in bulk sediment were obtained using ICP-MS, and the concentrations of selected elements were evaluated by statistical factor analyses. We also calculated metal-enrichment factors and geoaccumulation indices and constructed spatial-distribution maps. Mercury (Hg) was the heaviest pollutant, with concentrations exceeding 4 mg/kg. Silver (Ag) was the second most important pollutant, with constantly increasing values. The average concentrations of the most toxic elements were comparable to those found in sediments of other ports throughout the world, and their toxicity ranged from threshold values [chromium (Cr), arsenic (As)] and midrange-effect values [cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), nickel (Ni)] to extreme-effect values (Hg). Metal pollution has decreased during recent decades, except for Ag and barium (Ba).

From chemical risk assessment to environmental quality management: the challenge for soil protection

The 40 years that have passed since the beginning of the 'environmental revolution' has seen a large increase in development of policies for the protection of environmental media and a recognition by the public of the importance of environmental quality. There has been a shift from policy in reaction to high profile events, then to control of releases to single environmental media, and to the present position of moving toward integrated management of all environmental media at present. This development has moved away from classical chemical risk assessment toward environmental holism, including recognition of the ecological value of these media. This work details how policy developments have taken place for air and water, with examples from the USA and EU, in order to compare this with policy development regarding soil. Soil, with quite different policy frameworks and distinct uses, understanding, and threats compared to other environmental media, is currently attracting attention regarding the need for its protection independent of use. Challenges for soil policy are identified and evaluated, and recommendations on how these challenges can be overcome are discussed with relevance to water and air protection policy.

Risk assessment of trace elements in sediments: the case of the estuary of the Nerbioi-Ibaizabal River (Basque Country)

Long term (January 2005-January 2008) monitoring of sediments was used to investigate metal pollution in the estuary of the Nerbioi-Ibaizabal River (Bilbao, Basque Country). Sediments were collected from eight representative locations of the estuary approximately every three months. The concentration of fourteen elements was measured in sediment extracts. Different graphical representations of the data set, simple statistical methods and sediment quality guidelines were combined to investigate trends in space and time, identify pollution sources, and assess sediment quality from a toxicological point of view. In general terms, the main trend reveals a significant fall in metal concentration over the period investigated. There are still certain points of the estuary with relatively high concentration of toxic metals, but the toxicological approach suggests that the risk for living organisms is not important.