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The "pseudo-durability" of antibiotics in estuaries is gaining increasing interest, especially in the Yangtze Estuary, a vital water supply source for the Shanghai city. To clearly describe the pollution level and risk of antibiotics in this estuary, the contents of 8 typical antibiotics in the surface water and the sediment along the nearshore zone and in the estuarine channel in the estuary were comprehensively analyzed. The results revealed that sulfonamides and tetracycline are the predominant antibiotics in the surface water, while tetracyclines and fluoroquinolones are the dominant ones in the sediments. The ranges of the eight antibiotic concentrations between the nearshore zone (not detected to 7.06 ng/L for water, below LOD to 10.94 ng/g for sediment) and the estuarine channel (not detected to 8.46 ng/L for water, not detected to 14.84 ng/g for sediment) showed no notable differences, but the degree of scatter was different for each antibiotic. The spatial distribution was different for each antibiotic in the north branch and the south branch; higher values for most of the target antibiotics were observed in the south branch of the estuary. The distribution and source analysis from a GIS map using the kriging method indicated that runoff input and the antibiotic residues from aquaculture were the two major sources of the antibiotic pollution in the Yangtze Estuary. A risk assessment of the individual antibiotic exposure in the surface water showed that sulfamethoxazole, ofloxacin and ciprofloxacin, tetracycline and oxytetracycline, and sulfadiazine, roxithromycin and erythromycin in this area exhibited a medium risk, low risk and almost no risk to the selected aquatic microorganisms, respectively. Unlabelled Image • Estuary cities have an important contribution for antibiotic pollution in the Yangtze Estuary. • Runoff input and aquaculture discharge are the two main sources of antibiotics. • Organic carbon is a key factor controlling antibiotic concentrations in water and sediment. • Most of the studied antibiotics showed relatively low ecological risk. [ABSTRACT FROM AUTHOR]

The partitioning of ten heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, and Zn) between the water, suspended particulate matter (SPM), and sediments in seven channel sections during three hydrologic seasons in the Yangtze Estuary was comprehensively investigated. Special attention was paid to the role of tides, influential factors (concentrations of SPM and dissolved organic carbon, and particle size), and heavy metal speciation. The SPM – water and sediment – water partition coefficients ( K p ) of the heavy metals exhibited similar changes along the channel sections, though the former were larger throughout the estuary. Because of the higher salinity, the K p values of most of the metals were higher in the north branch than in the south branch. The K p values of Cd, Co, and As generally decreased from the wet season to the dry season. Both the diagonal line method and paired samples t -test showed that no specific phase transfer of heavy metals existed during the flood and ebb tides, but the sediment – water K p was more concentrated for the diagonal line method, owing to the relatively smaller tidal influences on the sediment. The partition coefficients (especially the K p for SPM – water) had negative correlations with the dissolved organic carbon (DOC) but positive correlations were noted with the particle size for most of the heavy metals in sediment. Two types of significant correlations were observed between K p and metal speciation (i.e., exchangeable, carbonate, reducible, organic, and residual fractions), which can be used to identify the dominant phase-partition mechanisms (e.g., adsorption or desorption) of heavy metals. [ABSTRACT FROM AUTHOR]

The temporal–spatial changes in the concentration and health risk of eight dissolved heavy metals in the Yangtze Estuary over a 5-year period were discussed based on large-scale sampling data. Special attention was paid to the differentiation of metal sources. Concentrations of the metals were present in the following order: Zn ≫ As > Cu > Cr > Ni > Pb > Cd > Hg, but the hazard quotient indices could be obviously divided into three gradients. More attention should be paid to As, Ni, Pb, and Cr because they increased yearly. Cu, Ni, Pb and As had higher health risks in the nearshore zones, while higher health risks of Zn, Cr, Cd, and Hg were observed in the estuarine channel. Correlations and hierarchical cluster analysis results of metal sources were consistent well with those obtained by temporal–spatial distributions. Shipping activities were the largest contributor to the elevated Zn concentrations in the estuary, while Megacity Shanghai significantly affected the Ni, Cu and As pollution. Yangtze River runoff was the primary source of Cu and As in the estuary. Cd and Cr pollution were closely related to the sediment release under the drive of the “salt-out effect”. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chronological records of metal deposition at different estuarine sites were studied. [•] Sedimentary metal speciation reveal responses to upstream hydrological events. [•] The transformation of metal speciation can explain the intercepting role of dams. [•] Sediment particles and organic carbon are the proxies for the metals deposition. [Copyright &y& Elsevier]

Abstract: The contamination and ecological risks of six metals (i.e., As, Cu, Mn, Pb, Sb and Zn) in sediments of the Yangtze Estuary were assessed using two typical index approaches, (i.e., total content and speciation indices). Special attention was paid to the relationships between the two index methods. The ecological risk of each sampling site was uniformly low to moderate in degree. The contamination levels of these sites were low to moderate according to the speciation index used, while the total content indices indicated a moderate to considerate contamination. A significant positive relationship existed between the two index methods when assessing the risks of Cu, Pb and Zn, while negative correlations and inconsistencies existed for As, Mn and Sb. The correlation behaviors were mainly dependent to three metal factors: the fractional distribution, the enrichment degree and the toxic response factors. Significant correspondences were observed between the total content and the speciation indices when assessing the ecological risks of each sampling site and each metal (Cu, Pb or Zn), while discrepancies were found between the two approaches when assessing the contamination of specific sites in the estuary area. [Copyright &y& Elsevier]

Abstract: Correlation of heavy metals in the tissues of typical organisms (i.e., fishes and crabs) and those in their living environments (i.e., surface water, bottom water, and sediment) in Yangtze River Estuary has been qualitatively and quantitatively analyzed. Metal levels followed the trend: sediments >Eriocheir sinensis > Eriocheir leptognathus >benthic fish>pelagic fish>bottom water>surface water. Tissues in fishes and crabs of different species and sizes had diverse metal bioaccumulation characteristics, which was significantly affected by environment factors and their living habits. Metal levels in legs of crabs, and heads and skins of fishes showed significant correlations with those in their living environments. Collichthys lucidus is an effective bioindicator for assessing metal levels in water. No significant health risk was identified by the estimated daily intake and target hazard quotients analyses. [Copyright &y& Elsevier]

Abstract: Spatial distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Yangtze Estuary, especially the North Branch, have been fully investigated. PAH concentrations increased with the descending distance from the inner estuary to the adjacent sea, and varied significantly in various estuarine regions. Water currents (e.g., river runoff and ocean current) greatly affected the distribution pattern. In addition, ambient sewage and traffic also contributed to the PAH pollution in the estuary. In the adjacent sea, PAH values along the −20m isobath were higher than those along the −10m isobath due to the “marginal filter” phenomenon formed by different water currents. In most sites, PAHs had poor correlations with sediment size, but had positive correlations with total organic carbon. Based on the qualitative and quantitative analysis results, PAH sources were proved to be mainly from a mixture of petroleum combustion, biomass, and coal combustion. [Copyright &y& Elsevier]

To determine whether the discharge control of heavy metals in the Yangtze River basin can significantly change the pollution level in the estuary, this study analyzed the sources (upper river, the estuarine region, and the adjacent sea) of ten heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, and Zn) in dissolved and particulate phases in the surface water of the estuary during wet, normal, and dry seasons. Metal sources inferred from section fluxes agree with those in statistical analysis methods. Heavy metal pollution in the surface water of Yangtze Estuary primarily depends on the sediment suspension and the wastewater discharge from estuary cities. Upper river only constitutes the main source of dissolved heavy metals during the wet season, while the estuarine region and the adjacent sea (especially the former) dominate the dissolved metal pollution in the normal and dry seasons. Particulate metals are mainly derived from sediment suspension in the estuary and the adjacent sea, and the contribution of the upper river can be neglected. Compared with the hydrologic seasons, flood-ebb tides exert a more obvious effect on the water flow directions in the estuary. Sediment suspension, not the upper river, significantly affects the suspended particulate matter concentration in the estuary. [ABSTRACT FROM AUTHOR]

Highlights: [•] The distribution and sources of CDOM in the Yangtze Estuary were studied. [•] 3D fluorescence spectra combined with PARAFAC–PCA analysis was developed. [•] Two humic-like components and one tryptophan-like component were identified. [•] Pore water CDOM was mainly from the sediment release and deposition effects. [•] Surface and bottom water CDOM was from microbial degradation of external wastes. [ABSTRACT FROM AUTHOR]