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

Legacy of anthropogenic activity recorded in sediments by microtechnofossils and chemical markers

This overview presents comparison of common microtechnofossils with other geochemical markers that may have the great potential to be the anthropogenic signatures for recent and future sediment strata. The novel man-made products encompass spherical and spheroidal fly-ash particulates, microplastics, synthetic crystals, and more recently examined glass microspheres. Due to their low specific gravity and small size varying from a tiny fraction of millimeter to approximately 5 mm, microtechnofossils may be transported over a long distance from their primary or secondary sources by water and wind. Of these technogenic materials, among the most resistant to physical and chemical degradation are glass microbeads, and additionally synthetic crystals and some types of fly-ash particulates derived mostly from coal/oil combustion, metal ore smelting operations and cement/lime manufacturing. Nonetheless, synthetic glass microspheres have found exponentially growing applications as reflective ingredients in traffic-related paints and building facades, as well as in a variety of applications mostly as low-density fillers of many materials. In contrast to anthropogenic fly-ash and microplastic particles, glass microspheres resemble in many respects common detrital quartz grains. Moreover, like quartz, they are resistant to depositional and diagenetic processes, which is a prerequisite for future geologic archives preserving anthropogenic signals. These and other characteristics make glass microspheres a more widely used product in various fields thus assigning them to a new emerging and globally spreading chronostratigraphic marker of human-impacted sediments.

Soil source, not the degree of urbanization determines soil physicochemical properties and bacterial composition in Ningbo urban green spaces

Urban green spaces provide multiple ecosystem services and have great influences on human health. However, the compositions and properties of urban soil are not well understood yet. In this study, soil samples were collected from 45 parks in Ningbo to investigate the relationships among soil physicochemical properties, heavy metals and bacterial communities. The results showed that soil dissolved organic matter (DOM) was of high molecular weight, high aromaticity, and low degree of humification. The contents of heavy metals were all below the China's national standard safety limit (GB 3660-2018). The bioavailability of heavy metals highly correlated with soil pH, the content of DOC, the fluorescent component, the degree of humification and the source of DOM. The most abundant genera were Gemmatimonadaceae_uncultured, Xanthobacteraceae_uncultured, and Acidothermus in all samples, which were related to nitrogen cycle and bioavailability of heavy metals. Soil pH, bioavailability of Zn, Cd, and Pb (CaCl2 extracted) were the main edaphic factors influencing bacterial community composition. It should be noted that there was no significant impact of urbanization on soil physicochemical properties and bacterial composition, but they were determined by the source of soil in urban green spaces. However, with the passage of time, the effect of urbanization on urban green spaces cannot be ignored. Overall, this study provided new insight for understanding the linkage among soil physicochemical properties, heavy metals, and bacterial communities in urban green spaces.

Long-term sediment records reveal over three thousand years of heavy metal inputs in the Mar Menor coastal lagoon (SE Spain)

The Mar Menor lagoon combined high biological production and environmental quality, making it an important economic engine. However, the pressure of human activities put its ecological integrity at risk, the oldest environmental impact being mining activity recorded since Roman times, about 3500 years ago, reaching its maximum intensity in the 20th century, contributing heavy metals to the lagoon sediments for almost 30 centuries. This work reviews the spatiotemporal evolution of the main heavy metals in this coastal lagoon using data from 272 surface sediment samples obtained during the last 40 years and two deep cores covering the total history of the lagoon (c. 6500 yrs BP), so as their incidence in the lagoon trophic web. The observed patterns in sedimentation, sediment characteristics and heavy metal content respond to the complex interaction, sometimes synergistic and sometimes opposing, between climatic conditions, biological production and human activities, with mining being mainly responsible for Pb, Zn and Cd inputs and port activities for Cu. High Fe/Al, Ti/Al and Zr/Al ratios identify periods of mining activity, while periods of arid climatic conditions and deforestation that increase erosion processes in the drainage basin and silt concentration in the lagoon sediments are determined by high Zr/Rb and, to a lesser extent, Zr/Al and Si/Al ratios. After the cessation of direct discharges into the lagoon in the 1950s, the recent evolution of heavy metals concentration and its spatial redistribution would be determined by hydrographic and biogeochemical processes, solubility of different elements, and coastal works in harbours and on beaches. The bioconcentration factor decreases along the trophic levels of the food web, suggesting that the lagoon ecosystem provides an important service by retaining heavy metals in the sediment, largely preventing their bioavailability, but actions involving resuspension or changes in sediment conditions would pose a risk to organisms.

Quantitative source apportionment of heavy metals in sediments from the Bohai Sea, China

In this study, the sources of nine heavy metals (Cd, As, Hg, Cu, Pb, Ni, Cr, Zn, and Co) in the sediments of the Bohai Sea were quantitatively identified through a positive factor matrix to provide better advice for marine and coastal management. In Bohai Sea sediments, most metals fell below detectable contamination levels, including As, Cu, Pb, Ni, Cr, Zn, and Co. Unfortunately, Bohai Sea sediments were moderately to significantly enrich with Cd and Hg, posing potentially adverse ecological risks to aquatic ecosystems. Our modeled results showed three factors representing natural, anthropogenic, and atmospheric deposition sources. Enriched Cd and Hg were likely derived from anthropogenic activities through river runoff and atmospheric deposition due to adjacent Zn smelting and chlor-alkali production, respectively. The other metals were mainly derived from natural sources.

Regional background determination and pollution assessment of heavy metals in the semi-closed Bohai Sea sediments

Background metal concentrations are important in assessing pollution level of marine sediments; however, they can be significantly altered by local depositional environments, resulting in significant errors in regional pollution assessment. This study was based on the investigation of the background levels of heavy metals in the Bohai Sea sediments using sediment core, 2-sigma outlier, and regression methods. We also estimate the ecological risks of heavy metals for surface sediments collected from the Bohai Sea using the three methods mentioned above. Ecological risks of heavy metals calculated using the regression method show wide disparities and significant differences from those calculated using the sediment core and 2-sigma methods, indicating that the regression method is not suitable for the Bohai Sea, likely as a result of its complex sources. Conversely, the estimated ecological risks using the sediment core method are moderate, and most heavy metals, except for Hg and Cd, have negligible contamination.

Effects of hydrological connectivity project on heavy metals in Wuhan urban lakes on the time scale

Metal pollution in lakes threatens the ecological environment and human health. When environmental conditions change, heavy metals (HMs) in lake sediments can cause secondary pollution. At present, the implementation of the Hydrological Connectivity Project (HCP) is a significant means of lake governance. In this study, the accumulation, potential ecological risk, and sources of HMs in Four lakes (Houguan Lake, Tangxun Lake, Moshui Lake, and Chen Lake) in Wuhan city were compared before and after the completion of the HCP. The results indicated that the HCP reduced the enrichment factor of HMs and the potential ecological risk in the heavily polluted Moshui Lake but caused secondary pollution in the less polluted Houguan Lake. Moreover, the degree of purification of lakes that took a longer time to complete the HCP (Moshui Lake) was significantly higher than that of lakes with a shorter HCP completion time (Tangxun Lake). Water exchange caused by the HCP leading to exchange of the primary pollution source between Houguan Lake and Moshui Lake to a certain extent. This study provides a reference for evaluating the implementation effect of the HCP on HM pollution in lakes and for future governance planning.

Halogenated organic pollutants (HOPs) in marine fish from the Beibu Gulf, South China Sea: Levels, distribution, and health risk assessment

Six marine fish species, collected from the Beibu Gulf were statistically analyzed for polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and dichlorodiphenyltrichloroethanes (DDTs). The concentrations of ∑₁₄PBDEs, ∑₂₆PCBs, and ∑₆DDTs ranged from 11.8-1431, 8.74-495, and 9.47-1263 ng g^-1 lipid weight (lw), respectively. In general, PBDEs were the predominant halogenated organic pollutants (HOPs) in the Beibu Gulf. The homologues profiles of Mugil cephalus and Trichiurus nanhaiensis differed from other four species. For example, the contributions of deca-BDEs in M. cephalus (14 %) and T. nanhaiensis (1 %) were lower than other four species (56 %). The ratio of (DDE + DDD)/ΣDDTs in all samples was >0.5, indicating that DDTs were mainly derived from historical residues. Intakes of HOPs through the consumption of the marine fish from the study areas might not subject residents of the coastal areas in the Beibu Gulf to health risks.

Potentially hazardous metals in the sediment of a subtropical bay in South China: Spatial variability, contamination assessment and source apportionment

Potentially hazardous metals (PHMs) in the coastal environment have become a great concern due to their easy bioaccumulation, poor biodegradability and high toxicity. Surface sediment samples were collected in a subtropical bay in South China to analyse the spatial variations, contamination level and potential sources of PHMs. The results indicated that the order of average contents of PHMs in Qinzhou Bay sediment was Zn > Pb > Cr > Cu > As > Hg > Cd. The most important potential ecological risk factor was Hg pollution in the Qinzhou Bay sediments. The positive matrix factorization (PMF) model results indicated that Cu, Pb, Zn, Cd and Cr mainly originated from natural sources while Hg and As were related to coal fired industrial inputs and petroleum production activities. The results could provide a basis for marine management to formulate relevant pollution prevention and control measures.

Accumulation and fluxes of potentially toxic elements in a large coastal lagoon (southern Gulf of Mexico) from 210Pb sediment chronologies

Three ²¹⁰Pb-dated sediment cores were used to evaluate the contamination degree and flux ratios of potentially toxic elements (PTEs; As, Cd, Cr, Cu, Ni, Pb, V, and Zn) in seagrass meadows from the northern margin of Términos Lagoon (TL), southern Gulf of Mexico. The sediments displayed minor Cd, Ni, V, and Zn enrichments but moderate to strong enrichment by As. Results from a chemometric analysis revealed that: 1) salinization and grain size, along with 2) the terrigenous inputs are the major factors influencing the PTEs accumulation. The historical trends of PTEs flux ratios nearly follow the large-scale land-use changes around TL, linked to the growth of the Mexican oil industry in the area since the 1970s. Our findings showed the critical role of seagrass meadows as PTEs sinks. This information is useful for decision-makers to develop restoration projects for a vulnerable site within the largest coastal lagoon ecosystem in Mexico.

Heavy Metal Distribution in Surface Sediments of the Coastal Pearl Bay, South China Sea

Six heavy metals (As, Cu, Cd, Zn, Cr, and Pb) in surface sediments (0–5 cm) from the twenty selected sites of the coastal Pearl Bay (South China Sea) were analyzed to assess the distribution pattern and potential ecological risk. Overall concentrations (mg/kg, dw) in the sediment samples were: As (10.88 ± 6.50), Cu (24.16 ± 18.63), Cd (0.55 ± 0.78), Zn (48.53 ± 30.06), Cr (35.78 ± 28.66), Pb (31.28 ± 18.50). Results showed that the overall mean values of Cd concentrations exceeded the standard of China Marine Sediment Quality, caused by significantly high levels of Cd contents in five sites (S8, S11, S13, S16, and S17) at the offshore area of Pearl Bay. Generally, the metal concentrations showed a decreasing trend from the offshore area to the inner bay. Various index values such as the geo-accumulation index (Igeo), the ecological risk index (Eri), and the contamination factor (CF) demonstrated that the coastal Pearl Bay was not polluted by the examined metals except for Cd, which might cause contamination and ecological risk in the region. Principal component analysis (PCA) results indicated that Cu, Zn, and Cr might originate from natural sources inland, and Pb and As might come from the gasoline and diesel fuel from engine boats. It is recommended that further research should focus on detecting the acute source and transferring mechanisms of the toxic metal Cd.

Historical records of trace metals in two sediment cores of Jiaozhou Bay, north China

To investigate the long-term effects of urbanization and industrialization on coastal trace metal contamination, two sediment cores, Q21 (representing 1965-2018) and Q23 (representing 1986-2018), collected from the adjacent coasts of the east old town and west new area of Qingdao were analyzed. Although the concentrations of As, Cd, Co, Cr, Cu, Ni, Pb, Sc, and Zn were higher in Core Q21, the increasing trends in their concentrations and contamination levels were more obvious in Q23, especially since the 2000s. Moreover, the urbanization rates of the new area (1978-2017) were significantly positively correlated with the historical metal concentrations in Q23. Affected by the rapid socio-economic development in the new area, the combined excessive concentrations of the eight metals (excluding Sc) increased faster in Q23 (0.14-78.4 mg/kg) than Q21 (0.58-45.3 mg/kg). Overall, the sediment Core Q23 experienced higher trace metal contamination and ecological risks than Core Q21.

Assessment of seasonal and spatial variation responses of integrated biomarkers in two marine sentinel bivalve species: Agadir Bay (Southern of Morocco)

The present study aims to assess the effects of contamination of the Agadir bay coasts using bivalves as a biomonitoring sentinel species. Seasonal variations of biochemical composition in terms of total protein content and oxidative stress biomarkers including glutathione-S-transferase, malondialdehyde, catalase and acetylcholinesterase were evaluated in the soft tissues of Scrobicularia plana and Donax trunculus specimens. The latter were collected from two sites in Agadir bay during two-year span (2018-2020). The Integrated Biomarker Response Index (IBR) was performed to classify the stress response in both species and to assess the level of exposure to xenobiotics. The data showed maximum annual values of acetylcholinesterase and malondialdehyde for Donax trunculus in Agadir beach (AG) with 6.25 nmol/mn/mg and 3 nmol/mg of protein, respectively. Those of catalase and glutathione-S-transferase for Scrobicularia plana in Oued Souss estuary (OS) were of 4.41 μmol/mn/mg and 14.43 nmol/mn/mg of protein, respectively. The studied species are considered good indicators in aquatic ecosystems.

Elucidating the Quenching Mechanism in Carbon Dot-Metal Interactions-Designing Sensitive and Selective Optical Probes

Overexposure to metals has significant adverse effects on human and animal health coupled with nefarious consequences to the environment. Sensitive tools to measure low contaminant levels exist, but often come at a high cost and require tedious procedures. Thus, there exists a need for the development of affordable metal sensors that can offer high sensitivity and selectivity while being accessible on a global scale. Here, carbon dots, prepared in a one-pot synthesis using glutathione and formamide, have been developed as dual fluorescent metal sensing probes. Following extensive characterization of their physico-chemical properties, it is demonstrated that dual fluorescence can be exploited to build a robust ratiometric sensor with low-ppb detection sensitivity in water. This investigation shows that these optical probes are selective for Pb2+ and Hg2+ ions. Using steady-state and dynamic optical characterization techniques, coupled with hard and soft acid-base theory, the underlying reason for this selective behavior was identified. These findings shed light on the nature of metal-carbon dot interactions, which can be used to tailor their properties to target specific metal ions. Finally, these findings can be applicable to other fluorescent nanoparticle systems that are targeted for development as metal sensors.