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BackgroundThe ecotoxicological risk posed by metals and their mixtures in sediments depends on their bioavailability. Many methods for evaluating the bioavailability of metals in sediments/soils are time-consuming and expensive, and frequently result in equivocal outcomes. The diffusive gradients in thin films (DGT) technique is a good measure of bioavailability for metals that can avoid the above drawbacks. Therefore, more effective approaches to this method should be developed that focus on metal bioavailability. No studies have been conducted using DGT to assess metal mixtures to aquatic biota in sediments. This study is therefore the first attempt to assess sediment toxicity of metals and their mixtures to aquatic biota based on the DGT technique. The intertidal zone of the Pearl River Estuary is selected as a case study.ResultsThe bioavailable (DGT-labile) concentrations of metals range as follows (μg/L): Cd, 0.34–3.62; Pb, 1.35–1.92; Ni, 0.67–92.83; Cu, 0.74–10.30; Zn, 28.60–296.94; Co, 0.03–58.85; Fe, 7.23–4539.36; and Mn, 19.40–6626.83. The risk quotient (RQ), which is the ratio between the measured metal concentrations in the environment (MEC) and the predicted no-effect concentration (PNEC), is conducted to evaluate the single metal risk. The RQ based on summing up the MEC/PNEC ratios (RQMEC/PNEC) and the RQ based on sum of toxic units (RQSTU) are used to assess risk of metal mixture. TheRQ values of Cd, Pb, Ni, Cu, Zn, Fe, and Mn significantly exceed 1, indicating that the adverse effects of the metals are not negligible. Regarding the toxicity of metal mixtures, the values of RQMEC/PNEC and RQSTU are both between 62.45 and 743.48, revealing that the possible risk has already occurred in the study area.ConclusionsThe two methods of RQMEC/PNEC and RQSTU based on DGT-labile metal concentrations are effective and suitable to estimate the toxicity of metal mixtures in sediments.

The existing methods of measuring combined toxicity of heavy metal mixtures in environment do not fully consider three major factors (i.e., number of heavy metal species, aquatic biota, all investigated sites as an entity). Herein, a new method named joint probabilistic risk (JPR) method is proposed for evaluating the combined toxicity of heavy metal mixtures to aquatic biota. In this new method, the above three factors are fully taken into account. In order to evaluate the feasibility of the new method, the Pearl River Estuary (PRE) is selected as a case study. Concentrations of heavy metals (Cd, Pb, Cr, Ni, Cu, and Zn) in surface sediments of PRE are investigated and toxic equivalent factors (TEFs) of these heavy metals are calculated. Based on TEFs, sedimental concentrations of heavy metals of PRE are converted to Cd toxic equivalent concentration (Cdeq), while the Cd toxicity data (Cdto) are extracted from the literature. The probability density curves for Cdeq and Cdto are constructed and the overlap area is quantified as 0.2497. This indicates that the surface sediments of PRE have a 24.97% probability of toxic effect towards aquatic biota. Finally, this new method is validated by two indirect methods of mERMq and mPELq.

Freshwater lakes in China face increasing environmental pressures due to rapid urbanization and industrialization, with metal pollution emerging as a significant concern. Despite this, the ecological risk assessment of metal mixtures in lake sediment remains limited. The current study addresses this gap by utilizing the diffusive gradients in thin films (DGT) technique to investigate the distribution and ecological risk of metals and arsenic in surface sediment of Hongze Lake, China. Substantial variations in metal concentrations were found across sampling sites, with average values of manganese (Mn) (1,730.56 μg/L) and iron (Fe) (930.58 μg/L) being notably high. The ecological risk quotient (RQ) values for Mn and Fe exceeded 1 at all sites, indicating substantial ecological risks, while copper (Cu) and arsenic (As) had RQ values near or above 1 at most sites. A joint probabilistic risk assessment using the species sensitivity distribution (SSD) method revealed a 30.31% probability of concurrent toxic effects on aquatic organisms. These results highlight the pressing need for proactive measures to mitigate metal contamination risks in Hongze Lake. The current study provides critical insight into the ecological risks associated with metal pollution and underscores the importance of effective environmental management to preserve the lake's ecosystem. [Display omitted] •The metals in sediments from Honze Lake were investigated with DGT.•Mn and Fe had RQ values > 1 at all sites, indicating significant ecological risk.•Cu and As had RQ values near or >1 at most sites, indicating potential risks.•Sediments had a 30.31% combined risk from 15 metals to aquatic biota.

The occurrence, multi-index assessment, and sources of heavy metals in surface sediments of Zhelin Bay were investigated. Average heavy metal concentrations (mg/kg) were 81.89 (Cr), 770.76 (Mn), 16.81 (Co), 62.25 (Ni), 96.30 (Cu), 162.04 (Zn), and 73.40 (Pb), with the concentrations of studied seven heavy metals being significantly higher than their corresponding background values. Geo-accumulation index (Igeo) and pollution load index (PLI) were implemented to assess degree of heavy metal contamination. The Igeo and PLI indicated that Cr, Mn, Co, Zn, and Pb were slightly polluted, and Cu and Ni were moderately polluted in the region. Potential ecological risk index (RI) and mean possible effect level (PEL) quotient were conducted to assess ecological risk. The RI and mean PEL quotient demonstrated that surface sediments of Zhelin Bay were slight ecological risks and exhibited a 21% probability of toxicity. Principal component analysis (PCA) combined with the correlation analysis (CA) and hierarchical cluster analysis (HAC) revealed that the heavy metal contamination in Zhelin Bay might originate from three type sources.

Changes in zooplankton composition, abundance, and some species in response to environmental variation were investigated over four seasons (2020) in Daya Bay. In total, 129 taxa of zooplankton (16 groups of planktonic larvae and 20 indeterminate species) were identified. Zooplankton communities exhibited a significant seasonal shift in abundance and taxonomic composition. The maximum number of zooplankton species was recorded in winter (72 species) and the lowest in spring (42 species). However, the abundance was highest in spring (1,372.01 ± 1,071.14 individuals/m³) and lowest in autumn (50.93 ± 34.05 individuals/m³). Pearson correlation analyses demonstrated that the zooplankton abundance and the variations of indicator species were obviously correlated with environmental parameters ( e . g ., salinity, temperature, pH, and chlorophyll- a ). Based on specificity and occupancy analysis, a total of eight species were selected as indicator species. It is noteworthy that some kollaplankton (such as Dolioletta gegenbauri and Doliolum denticulatum ) could potentially cause disaster to the nuclear power plant cooling system because of their relatively large body size and huge blooms in spring. In addition, Centropages tenuiremis blooms in spring and Penilia avirostris blooms in summer could attract assemblages of larval or adult pelagic fish, which would also threaten the cooling system security in Daya Bay. In conclusion, our results suggest that zooplankton communities and some species may be considered as favorable indicators of the marine environment.

Polycyclic aromatic hydrocarbons (PAHs) in urban soils may pose a serious threat to human health via oral ingestion, dermal absorption, and particulate inhalation, especially in public parks and playgrounds, with children and senior citizens showing the highest susceptibility. Several studies have been undertaken identifying PAHs in urban soils, but no studies to date have assessed PAHs in urban parks, in particular in exposed-lawn soils. In recent decades, unprecedented rates of urbanization and industrialization in China have resulted in significant levels of urban environmental pollution. However, concentrations, sources, and the health risk associated with PAH exposure via urban park lawn soils in China remain unknown. The concentrations, sources, and health risk of exposure to 16 PAHs in surface-exposed lawn soils were studied in 28 urban parks in Guangzhou. Concentrations of Σ16PAHs ranged from 76.44 to 890.85 ng/g with a mean of 286.11 ng/g. PAH composition was mostly characterized by 2- and 4-ring PAHs in most sampling parks; Nap, Flua, Pyr, Phe, and Chr were the dominant constituents. Principle component analysis coupled with multivariate linear regression indicated that vehicular and coal combustion emissions contributed to 50.53 and 49.46% of PAHs in Guangzhou’s urban park soils, respectively. Total cancer risk (TCR) analysis found that 22 parks (accounting for 78.57% total parks) designed for children’s use and general-use park areas presented a potentially high risk (>1 × 10 −4 ) for all users.

Antibiotics are emerging contaminants and widely used in human healthcare, livestock, and aquaculture. The toxicity posed by antibiotics and their mixtures in sediments depends on their bioavailability. Now, the bioavailability of organic materials can be determined accurately by the diffusive gradients in thin films (DGT) technique. This technique was used for the first time ever in this study to evaluate in detail the integral toxicity of antibiotics in sediments to aquatic biota. Zhelin Bay was selected as a case study, because it is the largest mariculture area in eastern Guangdong, South China. Two antibiotics, chlortetracycline (CTC) (A) and sulfachlorpyridazine (SCP), were detected at average concentrations of 2.83 and 1.14 ng/ml, respectively. The other fifteen antibiotics were undetectable. The single risk assessment based on the risk quotient (RQ) of CTC and SCP shows that a relatively low risk has occurred. After this careful assessment of probabilistic ecotoxicological risks, the combined toxicity of antibiotic mixtures (CTC and SCP) clearly indicates that the toxicity probability of surface sediments to aquatic organisms was relatively low (0.23%).

PurposeThe main objectives of this study were to investigate the distribution characteristics and evaluate the potential ecological hazard associated with rare earth elements (REEs) within the Pearl River Estuary (PRE) sediment. Furthermore, we still have not fully understood the contamination and potential ecological risks of REEs in aquatic sediments. Moreover, the factors influencing their distribution remain unidentified. Hence, we selected the PRE as the central focus for our case study in this paper.Materials and methodsSediment samples in this study (0–20 cm) were collected from 156 locations. The total organic carbon (TOC) and grain size were measured. The concentrations of REEs were determined by inductively coupled plasma mass spectrometry (ICP-MS). Furthermore, contamination models, including geoaccumulation index (Igeo), enrichment factor (EF), contamination factor (Cfi), and pollution load index (PLI), along with ecological risk assessment models potential ecological risk factors (Eri) and ecological risk index (RI) have been employed to evaluate pollution levels and ecological risks.ResultsThe concentrations of sum REEs (ΣREEs) were in the range of 51.21 to 567.08 mg kg−1, with an average of 299.06 mg kg−1. We identified two accumulation centers for REEs, indicating that these elements primarily originated from these two centers. It can be seen from the values of EF of REEs that these elements showed minimal enrichment. Moreover, the pollution load index (PLI), which assesses the combined contamination of REEs, was computed to evaluate the collective contamination in the study area. The PLI results indicate a slight multi-element contamination in the research region. Furthermore, based on the Eri values, it is evident that all studied REEs pose a low ecological risk.ConclusionsThe distributions of REEs were mainly controlled by TOC and median grain size. The RI was also calculated to assess the combined potential risks on the ecology. The study’s findings indicate that the PRE’s sediments produce low ecological risks.

The toxicity and mobility of metals in the environment are driven by their specific chemical forms and binding states. However, heavy metal fractionation in sediments from plateau deep lakes in China is rare. This study analyzed surface sediments collected from Fuxian Lake, the largest deep freshwater lake in China; parameters examined included total metal concentrations, chemical partitioning, and biological risk assessment. The average total concentrations (mg/kg) were 7.9 for Cd, 97.6 for Pb, 102.8 for Cr, 60.8 for Ni, 73.6 for Cu, and 112.9 for Zn; these levels were significantly higher than their corresponding background values. Cd was preferentially associated with the acid-soluble fraction; significant portions of the Pb, Cr, Ni, Cu, and Zn were mainly associated with the residual fractions. Overall, surface sediments of Fuxian Lake were associated with a 21% incidence of toxicity based on the mean effects range–median quotient. Cd was mainly at high or very high risk levels, and Cu and Zn were mainly at medium or high risk levels based on the risk assessment code (RAC).