Linking contaminant distribution to hydrodynamic patterns in an urban estuary: The Douro estuary test case

Physicochemical dataset from Lima and Douro estuaries (Northwest Portugal)

This article presents a comprehensive dataset of physicochemical data from two urban estuaries on the northern Portuguese coast, based on five sampling campaigns conducted between October 2021 and November 2022. The dataset includes: a) in-situ vertical profiles of water physicochemical parameters (temperature, salinity, pH, turbidity, dissolved oxygen concentration and saturation) collected at 8 sampling stations along the Lima estuary (during both ebb and flood tides) and at 11 stations along the Douro estuary (during flood tides); and b) chemical analyses data, including nutrients (nitrate, nitrite, phosphate, ammonium, and silica), chlorophyll a, total particulate matter, particulate organic matter, and key metal (copper, zinc, cadmium, iron, nickel, lead, manganese, and chromium) concentrations. For the Lima estuary, additional data on dissolved metals concentrations are provided, offering a detailed picture of metal contamination. This dataset provides valuable insights into the estuarine dynamics of two important temperate systems, with a particular focus on anthropogenic influences such as nutrient enrichment and metal contamination. The data have strong reuse potential in environmental monitoring, providing a baseline for assessing anthropogenic changes and offering quality-assured references for studies linking contaminant distribution with hydrodynamic patterns in estuarine environments. Furthermore, such data are relevant to supporting the implementing of environmental policies, such as the EU Water Framework Directive for transitional waters.

Salinity-Driven Stratification Enhances Riverine Mercury Export to the Coastal Ocean

Rivers transport 300 to 5,000 Mg of mercury (Hg) annually to coastal oceans through estuaries, contributing 20-45% of total Hg input, with 100 to 1,500 Mg reaching the open ocean. However, the impact of estuarine circulation and stratification on Hg transport and methylation remains uncertain despite their known influence on other metal exports. This study developed three models to assess Hg transformation under different salinity-driven stratification regimes-well-mixed, slightly stratified, and highly stratified-using data from the Chesapeake Bay (CPB) and Hudson River Estuary (HRE), U.S.A. Results show that stratification increases riverine Hg export by 19% in CPB and 20% in HRE, with shorter Hg residence times promoting faster export. Unstratified estuaries favor Hg burial in sediments due to longer residence times and increased particle settling. Seasonal river discharge variations further influence stratification, with higher discharge enhancing stratification and Hg export. Methylmercury (MeHg) production and export also respond to stratification, with slightly stratified conditions in CPB increasing MeHg production by 11.5% and export by 16.4%. As climate change is expected to intensify stratification in many estuaries, these findings suggest potential increases in Hg and MeHg export to coastal oceans.

Potential of fishing nets for adsorption of inorganic (Cu and Pb) and organic (PAHs) pollutants

This study aimed to evaluate metals and polycyclic aromatic hydrocarbons (PAHs) adsorption on new plastic fishing nets in both laboratory and quasi-real scenario (nets submersed in marina seawater) experiments as well as in situ monitoring of these contaminants in water and sediments in lost fishing gears hotspots. The latter was inconclusive as environmental contaminants levels were very low. Laboratory experiments showed metals (copper and lead) and PAHs adsorption depended on the thickness and polymeric composition of the net, being lower in thinner nylon nets. Experiments in the marina, also showed significant contaminants adsorption, which increased over time, probably due to biofilm formation on net surface. This work showed the potential role of fishing gears as skins of pollutants, increasing organisms' exposition to contaminants present in the environment. So, initiatives to prevent the loss of fishing gear and to retrieve them are needed to reduce and/or eliminate their environmental impact.

Microplastics in marine mussels, biological effects and human risk of intake: A case study in a multi-stressor environment

This study documented seasonal levels of microplastics (MPs) and biomarkers (condition index, neurotoxicity, energy, oxidative stress) in mussels (Mytilus galloprovincialis), and water physico-chemical parameters in the Douro estuary (NE Atlantic coast), and estimated the human risk of MP intake (HRI) through mussels. Mussel stress was determined through the Integrated Biomarker Response (IBR). HRI was estimated from mussel MP concentrations and consumer habits. MPs were mainly micro-fibres (72 %) with varied chemical composition. Seasonal MP means (±SEM) in mussels ranged from 0.111 ± 0.044 (spring) to 0.312 ± 0.092 MPs/g (summer). Seasonal variations of mussel stress (IBR: 1.4 spring to 9.7 summer) and MP concentrations were not related. MeO-BDEs, PBDEs, temperature, salinity and other factors likely contributed to mussel stress variation. HRI ranged from 2438 to 2650 MPs/year. Compared to the literature, MP contamination in mussels is low, as well as the human risk of MP intake through their consumption.

Spatial and temporal variations of geochemical processes and toxicity of water, sediments, and suspended solids in Sibuti River Estuary, NW Borneo

A comprehensive geochemical study was conducted in the Sibuti River estuary by considering water, suspended solids (SS), and sediment samples from 36 stations during southwest monsoon (SWM) and northeast monsoon (NEM). In this study, the distribution of in situ parameters, major ions, nutrients, trace metals, and isotopes (δD, δ18O) were analyzed in water samples, whereas sediments and SS were studied for trace metals. The distribution revealed that suspended solids were the major carrier of Cd, Zn, and Mn, whereas sediments worked as a major source of Co, Cr, Ba, Se, Cu, and Pb. Na-Cl water type and ion exchange dominated the lower part of the estuary during both seasons. However, the mixed mechanism of Ca-Cl, Ca-Mg-Cl, and higher weathering indicated reverse ion exchange in the intermediate and upper parts of the estuary. Isotopic signatures of δD and δ18O in estuarine water indicate that the precipitation over the Limbang area dominates during SWM, whereas higher evaporation was confirmed during NEM. The factor analysis revealed that seawater influence in the estuary majority controlled the water chemistry irrespective of seasons. Major ions were mainly regulated by the tidal influence during the low flow time of the river (SWM), whereas the mixing mechanism of weathering and seawater controlled the concentrations during NEM. Nutrients such as NO3, SO42-, NH3, and NH4+ mainly originated from the agricultural fields and nitrification along with ammonification were responsible for the recycling of such nutrients. Trace metals except Cd were found to be geogenic in nature and originating mainly from the oxidation of pyrites present in the sandstone and mudstones of the Sibuti Formation. Redox condition was catalyzed by microorganisms near the river mouth, whereas Al-oxyhydroxides and Fe-oxyhydroxides complexes in the intermediate and upper part under oxygenated conditions controlled the absorption of metals. Overall, the estuary was found to be absorptive in nature due to ideal pH conditions and was confirmed by the saturation index (SI) of minerals.

Bioaccumulation of Trace Elements in the Muscle of the Blackmouth Catshark Galeus melastomus from Mediterranean Waters

Environmental pollution, particularly in the marine environment, has become a significant concern due to the increasing presence of pollutants and their adverse effects on ecosystems and human health. This study focuses on the bioaccumulation of trace elements in the muscle tissue of the blackmouth catshark (Galeus melastomus) from different areas in the Mediterranean Sea. Trace elements are of interest due to their persistence, toxicity, and potential for bioaccumulation. This research aims to assess the distribution and accumulation of trace elements in the muscle tissue of G. melastomus and investigate their potential impact on the deep-sea environment of the Mediterranean. The focused areas include the Ligurian Sea, the northern and central Tyrrhenian Sea, the southern Tyrrhenian Sea, the Ionian Sea, the Pantelleria Waters, and the Gela Waters. Samples were collected following established protocols, and trace element analysis was conducted using inductively coupled plasma mass spectrometry. The study provides data on the concentrations of 17 trace elements, namely aluminum, arsenic, cadmium, cobalt, copper, manganese, molybdenum, nickel, zinc, selenium, strontium, lead, chromium, iron, barium, bismuth, and uranium. The findings contribute to a better understanding of trace element bioaccumulation patterns in elasmobranch species, specifically G. melastomus, and highlight the potential risks associated with chemical contamination in the Mediterranean Sea. This research emphasizes the importance of studying the impacts of pollutants on marine organisms, particularly those occupying key ecological roles, like sharks, to support effective conservation and management strategies.

Platinum Group Element distribution in water and marine biota from two impacted estuarine environments (Douro and Ave estuaries, Portugal)

Platinum Group Elements (PGEs) are contaminants of emerging environmental concern considering their continuous increasing use and subsequent release in the environment. While recent field studies provided PGE levels in seawater, scarce knowledge still exists regarding PGE contamination in marine organisms, especially for rhodium (Rh). Water, macroalgae and mussels were sampled along two representative urbanized estuarine systems and adjacent coastal areas (Douro and Ave estuaries, Portugal). Rhodium and platinum (Pt) concentrations were quantified through both stripping voltammetry and mass spectrometry in collected samples. Spatial mapping of PGE contamination was, to a certain extent, correlated with proxies of urban effluents. The use of Pt/Rh ratios reflected the dominant influence of PGE traffic emissions along the Douro and inputs from various sources (including industries) on the Ave Estuary. Macroalgae and mussels PGE concentrations reflected urban pressure, amplifying environmental signals, and supporting their relevant use as bioindicators of PGE contamination in estuarine/coastal systems.

Are microplastics contributing to pollution-induced neurotoxicity? A pilot study with wild fish in a real scenario

Pollution-induced neurotoxicity is of high concern. This pilot study investigated the potential relationship between the presence of microplastics (MPs) in the brain of 180 wild fish (Dicentrarchus labrax, Platichthys flesus, Mugil cephalus) from a contaminated estuary and the activity of the acetylcholinesterase (AChE) enzyme. MPs were found in 9 samples (5% of the total), all of them from D. labrax collected in the summer, which represents 45% of the samples of this species collected in that season (20). Seventeen MPs were recovered from brain samples, with sizes ranging from 8 to 96 μm. Polyacrylamide, polyacrylic acid and one biopolymer (zein) were identified by Micro-Raman spectroscopy. Fish with MPs showed lower (p ≤ 0.05) AChE activity than those where MPs were not found. These findings point to the contribution of MPs to the neurotoxicity induced by long-term exposure to pollution, stressing the need of further studies on the topic to increase 'One Health' protection.

Pollution status and risk assessment of trace elements in Portuguese water, soils, sediments, and associated biota: a trend analysis from the 80s to 2021

Pollution of water bodies and sediments/soils by trace elements remains a global threat and a serious environmental hazard to biodiversity and human's health. Globalization and industrialization resulted in the increase and availability of these substances in the environment posing unpredictable adverse effects to living organisms. To determine pollution status and risk contamination by trace elements, data available in the literature of the last 40 years on trace elements occurrence in three environmental matrices (water bodies, sediments/soils, and biota) from Continental Portugal were collected (about 90 studies). Data were compared to water and sediment quality guidelines to assess potential ecological risks. Most environmentally relevant hazardous elements include Zn, Cu, Cd, Pb, and As. Various studies found trace elements at levels higher than those considered safe by environmental guidelines. In surface waters, Al, Zn, Se, and Ag were found above aquatic life limits in about 60% of the reviewed papers, while Cu, Zn, and As exceed those values in more than 60% of mining waters. Hg and Cd in sediments from mining areas exceeded aquatic life limits and potential ecological risk showed extremely high risk for most of the elements. The data compiled in this review is very heterogenous, varying in terms of sampling schemes, trace elements analysed, and spatiotemporal settings. This heterogenicity leads to data differences that make meaningful comparisons difficult. Nevertheless, the compilation of scattered environmental spatial and temporal trace elements data, of either natural sources or human activity as well as the ultimate effect on biological systems, is of the upmost importance to broaden its knowledge, risk assessment, and implementation of mitigation measures.

Multi-element signatures in solid and solution phases in a tropical mixing zone: A case study in the Cai River estuary, Vietnam

This study provides baseline concentrations of major, trace, and rare earth elements (REEs) in the solid and solution phases of the tropical Cai River estuary under influence of multiple stresses. The application of the selected multivariate analysis tools (principal component analysis and redundancy analysis) to the enrichment factor and partitioning coefficients (K_SPM/Water and K_SPM/Sed) calculated from the bulk element contents highlighted the strongest relationships (considered as multi-element signatures) according to the efficiency of the transfer across the estuarine gradients (considered as a selective geochemical filter). Thus, most of the major and trace elements, and REEs studied mainly settle within the mixing zone due to the association with terrigenous aluminosilicate clay minerals, whereas Co, Ni, Cu, As, and Mo are transferred seaward because of their association with the most labile fraction of the fluvial particulate load (such as clays, organic colloids, and carbonates). The major and trace elements, and REEs investigated in this study are mainly introduced in the Cai River and its estuary via basement rock weathering under enhanced monsoonal precipitation, whereas Bi showed the most severe enrichment in the non-weathering distribution pattern. The fractionation of the fluvial element load within the estuarine geochemical filter is mainly controlled by the differential settling of fluvial mineral element-bearing phases along with estuarine colloid dynamics - a topic that must warrants further investigation.

Quantitative and qualitative determination of microplastics in oyster, seawater and sediment from the coastal areas in Zhuhai, China

Microplastics as a new class of environmental contaminants have become the hot issue of global concern. We conducted quantitative and qualitative experiments to investigate microplastics in oyster, seawater and sediment along the Zhuhai coastline. The soft tissues of oysters were digested with potassium hydroxide (10%) and hydrogen peroxide (30%), seawaters and sediments with hydrogen peroxide (30%) to degrade organic matter, and analyzed using a digital camera, optical microscopy and micro-ATR-FTIR. The abundance of microplastics were in the range of 0.14-7.90 n/g in oysters (wet weight), 10.00-27.50 n/L in seawaters and 0.053-0.26 n/g in sediments. The fiber and fragment shape, black color, 101-500 μm of size and polyethylene composition were all classified as the major constituents of microplastics. The level of contaminants in oysters was correlated to those in their surrounding environments. Therefore, oysters may serve as a promising sentinel species for the indication of microplastic pollution in the coastal zone of Zhuhai.

Investigation on trace metal speciation and distribution in the Scheldt estuary

The biogeochemical behavior of Cd, Co, Cr, Cu, Ni and Pb along the historically polluted Scheldt estuary (Belgium - The Netherlands) was investigated in this study. As never studied before in this area, labile trace metals were measured using the passive sampling technique of Diffusive Gradients in Thin-films (DGT), while total dissolved and particulate trace metal concentrations were assessed using classic active sampling techniques. This dual approach allowed us to highlight the variations of trace metal speciation and distribution in the estuarine surface waters, considering environmental and physicochemical gradients along the transect. The large data set obtained was then compared with literature data of historical measurements along the Scheldt (from 1980 until now), but also from other estuaries. As emphasized by our results, trace metal mobility and partitioning along the Scheldt estuary was mainly driven by biogeochemical reactions which were strongly influenced by gradients of specific estuarine physico-chemical parameters, such as salinity, turbidity, temperature and so on. Hence, all species of trace metals displayed a non-conservative behavior. More precisely, dissolved labile fractions of trace metals showed higher levels in the middle estuary, where many solubilization and remobilization processes occurred due to turbulent mixing mechanisms and an increasing salinity. Our study confirmed the decreasing trend historically observed for particulate metals along the Scheldt, as well as the rising concentrations recorded for dissolved trace metals which might also lead to an increase of their labile fraction measured by the DGT. Finally, these preliminary results suggested that a more regular monitoring of labile metal along the Scheldt estuary is essential to have an in-depth understanding of trace metal speciation and to review bioavailability of trace metals within estuarine ecosystems.