The euryhaline pygmy mussel, Xenostrobus securis, is a useful biomonitor of key metal contamination in the highly urbanised Sydney Estuary, Australia

Differential response of heavy metal accumulation in freshwater aquatic organisms to organic matter pathway (δ13C) and trophic level (δ15N)

The migration of heavy metals into aquatic ecosystems is a concern for the safety of aquatic organisms and human health. However, the migration of heavy metals from habitats to the food chain in freshwater ecosystems requires extensive exploration. We extensively investigated the levels of heavy metals in multiple media of freshwater ecosystems and explored their migration from freshwater habitats to the food chain. The results showed that the concentrations of Cr, Cu, Cd, Zn, Sb, and Pb in sediments, Cr in mollusks, and Cd in clams exceeded their standard limit values. Feeding habits, species, and body length considerably affected heavy metal levels in fish, whereas regional differences, body length, and weight considerably affected heavy metal levels in mollusks. The bioconcentration capacity (improved biotawater (sediment) accumulation factors) of the muscles was higher than that of the gills and visceral mass. Mollusks were strongly enriched in Cu, Cd, Zn, and Mn in their habitats, whereas fish were more favourable for the accumulation of Cu, Zn, and Cr. Heavy metals in sediments pose a higher risk to aquatic organisms than those in the overlying water. Trophic level (TL) (δ15N) considerably diluted levels of most metals, whereas Cu and Zn levels increased along the organic matter pathway (δ13C) in the entire aquatic food chain. The levels of typical pollutants, such as Cu, Zn, As, Cd, Pb, and Cr changed considerably along the organic matter pathway in mollusks. The levels of heavy metals in fish were not affected by TL or organic matter pathway, except for Cu. The potential risk of consuming aquatic organisms from Poyang Lake was ranked as clams > snails > fish for adults and children and As in aquatic organisms was the primary contributor to health risk.

Bioaccumulation patterns of trace elements by native (M. galloprovincialis) and invasive (X. securis) mussels in coastal systems (Vigo Ria, NW Iberian Peninsula)

A number of trace elements (Mn, Fe, Co, Ni, Cu, Zn, As, Nb, Mo, Ag, Cd, Pb, U and the rare earth elements - REE) were analyzed in the dissolved phase, suspended particulate matter and in different organs (gills, hepatopancreas, and the rest of soft tissue) in mussels of the native Mytilus galloprovincialis and invasive Xenostrobus securis species in the Vigo Ria (NW Iberian Peninsula) in order to assess potential differences in their bioaccumulation patterns. Results obtained do not show significant differences in the bioaccumulation of trace elements by M. galloprovincialis and X. securis, except for Zn and Ag. In the case of Zn, a 4-fold enrichment in M. galloprovincialis compared to X. securis was found. The most important differences between species were observed for Ag, with approximately 40-fold higher concentrations in X. securis. Such elevated Ag bioaccumulation by X. securis can be useful for Ag biomonitoring using these invasive species in this area.

Biochemical and Histological Biomarkers in Crassostrea sp. (Bivalvia, Ostreidae) for Environmental Monitoring of a Neotropical Estuarine Area (São José Bay, Northeastern Brazil)

This study aimed to compare biochemical and histological biomarkers in oysters to identify impacted areas in a Brazilian port region. Oysters belonging to the Crassostrea genus were collected in two points in São José Bay (Brazil): (A1) Curupu Island (control area) and (A2) Braga Port (impacted area). Digestive glands from oysters were used to analyze the enzymatic activity of glutathione S-transferase and Catalase. The gills were used for standard histology analyses. Water samples were collected for metal analyses. Our results indicated that there was a change in the activity of oyster GST and CAT enzymes, especially in A2. Histological gill analysis indicated more frequent changes in A2. The analyzed metals presented higher values in A2. The results of this study suggest that enzymatic alterations, histological changes and higher metal values are indicative of initial stress caused by contaminants in São José Bay, especially in the port region.

A Commentary on the Use of Bivalve Mollusks in Monitoring Metal Pollution Levels

The objective of this commentary is to promote the use of bivalves as biomonitors, which is a part of the continual efforts of the International Mussel Watch. This commentary is an additional discussion on "Bivalve mollusks in metal pollution studies: From bioaccumulation to biomonitoring" by Zuykov et al., published in Chemosphere 93, 201-208. The present discussion can serve as a platform for further insights to provide new thoughts and novel ideas on how to make better use of bivalves in biomonitoring studies. The certainty of better and more extensive applications of mollusks in environmental monitoring in the future is almost confirmed but more studies are urgently needed. With all the reported studies using bivalves as biomonitors of heavy metal pollution, the effectiveness of using Mussel Watch is beyond any reasonable doubts. The challenge is the development of more accurate methodologies for of heavy metal data interpretation, and the precision of the biomonitoring studies using bivalves as biomonitors, whether in coastal or freshwater ecosystems. Lastly, inclusion of human health risk assessment of heavy metals in commercial bivalves would make the research papers of high public interest.

Spatial and seasonal variability of human and fish viruses in mussels inside and offshore of Ravenna's harbour (Adriatic Sea, Italy)

AIMS

This study aims to investigate the presence and spatial-seasonal variability of human and fish viruses in coastal marine systems using Ravenna's harbour area (Adriatic Sea, Italy) as a model.

METHODS AND RESULTS

Human viruses (noroviruses and hepatitis A virus) and one of the most threatening finfish pathogens, the nervous necrosis virus (NNV), were investigated in mussels living inside and offshore Ravenna's harbour. Thirty-three and 36·7% of tested mussel samples resulted contaminated by human and fish viruses respectively. A different spatial-seasonal distribution was observed. Human viruses were detected mainly in inner port sites during colder months, while NNV was detected in both inside and offshore of Ravenna's harbour, mainly during warmer months.

CONCLUSIONS

The presence of human viruses in the inner port close to the city centre could be attributed to wastewaters carrying pathogens in the port environment and this arises public health concerns, however, the presence of these viruses limited to the canal port during the winter can greatly reduce the risk to human health. Regarding NNV, the accumulation and release of viable virus by mussels, could represent a viral source for susceptible finfish. These findings reflect the different epidemiological features of these infections and indicate the importance to choose the correct indicator to monitor viral contaminations.

SIGNIFICANCE AND IMPACT OF THE STUDY

The high frequency of viral contamination pointed out in the study stresses the imperative to monitor the viral presence in all coastal habitats where the high natural value meets several recreational and commercial activities such as the Ravenna's harbour area. Particularly, this study could represent a novel starting point for the development of a more structured bio-monitoring program, in order to ensure improved environmental management and safety of coastal areas.

Intertidal mussels do not stop metal bioaccumulation even when out of water: Cadmium toxicokinetics in Xenostrobus atratus under influences of simulated tidal exposure

Intertidal bivalves are periodically exposed in air. It is tempting to speculate that the organisms would temporarily escape from contaminants when they are out of water and thus have lower risks. In this study, we tested this speculation by investigating cadmium (Cd) toxicokinetics in an intertidal mussel, Xenostrobus atratus, under the effects of tidal exposure using simulated tidal regimes. The uptake rate constant (k_u) of Cd ranged from 0.045 L g^-1 d^-1 to 0.109 L g^-1 d^-1, whereas the elimination rate constant (k_e) of Cd ranged from 0.029 d^-1 to 0.091 d^-1. Cd bioaccumulation was slightly higher in the continuously immersed mussels than the alternately immersed mussels, but much lower than what would be expected if assuming bioaccumulation being proportional to immersion duration. Cd uptake was observed even when mussels were exposed in air, due to uptake of Cd dissolved in mantle cavity fluid and internalization of Cd adsorbed on mussel tissues. Overall, tidal height showed limited effects on Cd bioaccumulation, consistent with the trend of Cd concentrations found in X. atratus collected from different tidal heights. The mantle cavity uptake mechanism is expected to be applicable to other contaminants and bivalves, and should have important implications in risk assessments for intertidal environment.

Dataset of genotoxic and cytotoxic effects on the pygmy mussel, Xenostrobus securis, from the highly urbanised Sydney Estuary, Australia: Relationships with metal bioaccumulation

This article contains a dataset of the genotoxic (DNA damage, via the micronucleus frequency test) and cytotoxic (lysosomal membrane stability (cellular integrity), via the neutral red retention test) effects on the pygmy mussel, Xenostrobus securis (Bivalvia: Mytilidae) from variably contaminated sites (primarily from cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn)) in the highly urbanized Sydney Estuary, south-eastern Australia. Data were collected 15 years apart (June 2004 and June 2019) to assess any change in (i) the “health” of mussels (based on the above two toxicity endpoints) and (ii) their metal contaminant status (measured as whole soft tissue concentrations of Cd, Cr, Cu, Pb and Zn). Linear relationships between both toxicity endpoints and metal concentrations in the whole soft tissue were also investigated. Multivariate statistical techniques, including principal components analysis, multidimensional scaling and cluster analysis, were also explored to reduce dimensional data, investigate patterns and assess similarities among study sites with respect to tissue metal concentrations and toxicity effects in X. securis. Enrichment factors were calculated by dividing the mean whole soft tissue metal concentration at each site in the Sydney Estuary, by its mean baseline metal concentration from near-pristine (reference) sites in the adjacent Hawkesbury Estuary. Salinity, pH, temperature, turbidity, dissolved oxygen and chlorophyll a were measured in the surface waters at each site

Physico-chemical and key metal data for surface waters and sediments of the Sydney and Hawkesbury estuaries, Australia

This article contains general physico-chemical data (salinity, pH, redox potential, temperature, dissolved oxygen, suspended particulate matter (SPM), dissolved organic carbon and chlorophyll a concentrations) for surface waters at 15 near-pristine sites in the Hawkesbury Estuary and 24 sites (encompassing a wide range of metal contamination) in the highly urbanized Sydney Estuary, south-eastern Australia. Data on concentrations of five key metals (cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn)) in filtered (<0.2 μm) surface water, suspended particulate matter (>0.2 μm) and surface sediments (<2 mm) at each study site are also provided. The concentrations of Cd, Cr, Cu, Pb and Zn in SPM and sediment at each site were normalised for aluminium (Al) concentration (e.g. Cd/Al), to account for natural variation in particle size and mineralogy. Enrichment factors (EFs) were calculated from these data by dividing the mean metal concentration at each site in the Sydney Estuary, for each environmental matrix (i.e., filtered water, SPM and sediment), by its mean baseline metal concentration from near-pristine reference sites in the adjacent Hawkesbury Estuary. A thorough knowledge of the general physico-chemistry and key metal concentrations in surface waters and sediments in the Sydney Estuary provide a baseline to assess anthropogenic change and better manage estuarine/marine ecosystems.