The Akoya pearl oyster shell as an archival monitor of lead exposure

Assessing lead toxicity in the clam Ruditapes philippinarum: Bioaccumulation and biochemical responses

Lead (Pb) is a non-essential metal. Its occurrence in the environment is related principally to anthropogenic contamination. Pb is toxic to aquatic organisms and can provoke damage to membranes and inhibit the activity of essential enzymes. The filter-feeding, Manila clam Ruditapes philippinarum is widely used as a biomonitor organism to assess metal toxicity. Among biomarkers related to the Pb toxicity, the enzymatic activity of δ-aminolevulinic acid dehydratase (δ-ALAD) has been adopted as a specific tool. Metallothionein (MT), lipid peroxidation (LPO) and antioxidant enzymes activities, such as catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR) and glutathione S-transferase (GST) and superoxidase dismutase (SOD) have also been employed to assess the toxic effect of metals. Two target tissues, the gills and the digestive gland, were selected to examine biomarker responses. In order to assess the effects of Pb accumulation and the mechanisms involved in the recovery from it, clams were exposed at two Pb levels (10 and 100 µg/L) for 7 days and were later maintained in clean water for 7 days as a depuration period. Pb accumulation was dependent on the exposure concentration and higher Pb levels were observed in the gills compared to the digestive gland. Inhibition of δ-ALAD, GST and SOD and the induction of MT and LPO over the exposure period were observed in the gills and the digestive gland of R. philippinarum. The depuration period showed a continuous inhibition of the δ-ALAD activity and induction of MT and LPO in both tissues. These results demonstrate that lead induced an exposure effect and the 7 days of depuration were not sufficient to recover the basal health status of the clams.

Evaluating a 5-year metal contamination remediation and the biomonitoring potential of a freshwater gastropod along the Xiangjiang River, China

Effective remediation of heavy metal pollution in aquatic systems is desired in many regions, but it requires integrative assessments of sediments, water, and biota that can serve as robust biomonitors. We assessed the effects of a 5-year metal contamination remediation along the Xiangjiang River, China, by comparing concentrations of trace metals in water and surface sediments between 2010-2011 and 2016. We also explored the trace metal biomonitoring potential of a freshwater gastropod (Bellamya aeruginosa). Metal concentrations in water (means and ranges) dropped over time to within permissible limits of drinking water guidelines set by China, USEPA, and WHO in 2016. Although sediment means and ranges of Cd, Pb, Zn, and Mn also diminished with remediation, those for Cr and Cu slightly increased, and all six metals retained concentrations higher than standards set by China. All metals in sediments could also be associated with anthropogenic inputs using a hierarchical clustering analysis, and they generate high potential ecological risks based on several indices, especially for Cd and As. The bio-sediment accumulation factors of all measured trace metals in gastropod soft tissues and shells were lower than 1.0, except for Ca. Trace metal contents in gastropods were positively correlated with those in water and surface sediments for As (soft tissues) and Cr (shells). Collectively, our results do not yet highlight strong beneficial effects of 5-year remediation and clearly illustrate the heavy metal pollution remaining in Xiangjiang River sediment. Additional physical, chemical, and biological measurements should be implemented to improve sediment quality. We further conclude that gastropod soft tissues and shells can be suitable biomonitors of spatial differences in some heavy metals found within river sediments (e.g., As, Cr).

Improving data resolution and statistical rigor in the analysis of bivalve shells as environmental archives

Bivalves secrete their shells in an annual fashion, resulting in discrete bands of growth within each shell. In doing so, they may incorporate trace elements in concentrations reflecting exposure. This may make it possible to use them as archives of environmental information, such as contamination events. In this study, we used laser ablation inductively coupled plasma-mass spectrometry to analyze trace elements (Cd, Cu, Mn, Pb and Zn) on a fly-scanning transect perpendicular to the growth annuli of the freshwater bivalve Elliptio hopetonensis collected from the Altamaha river system. Concentrations of Mn from multiple shells at each site were correlated and average Mn data series were formed. Periodicity of Mn data was determined and sampling errors removed using an autoregression model. The Mn data series at each site were shown to have regular fluctuations of high and low concentrations. Fluctuations were similar between the shells from the same site but different between shells from different sites, demonstrating that Mn deposition in the shells of E. hopetonensis follows a regular, seasonal pattern but that growth differs between sites with different environments. Cd, Cu, Pb and Zn could not be analyzed in a statistically robust manner. This is the first study to attempt to improve data resolution by using the fly-scanning approach and, additionally, the first to apply an autoregression model to Mn data from bivalve annuli. Further study is required to develop this approach for environmental monitoring.

A proteomic analysis of the effects of metal contamination on Sydney Rock Oyster (Saccostrea glomerata) haemolymph

The current study uses proteomics to assess the effects of metal contamination on Sydney Rock oyster haemolymph. Saccostrea glomerata were exposed in aquaria for four days to three environmentally relevant metals (copper, lead or zinc). Oyster haemolymph proteins from metal-exposed oysters were then compared to haemolymph from non-exposed controls using 2-dimensional electrophoresis to identify proteins that differed significantly in intensity. These proteins were then subjected to tandem mass spectrometry so that putative protein identities could be assigned. The data suggest that there are unique protein expression profiles for each metal. Exposure to 100 μg/l of copper, lead or zinc yielded a total of 25 differentially expressed proteins. However, only one of these protein spots exhibited altered intensities in response to all three metals. Eighteen of the 25 spots were significantly affected by just one of the three metals. Differentially expressed proteins were assigned to five different categories of biological function. Proteins affecting shell properties were the most common functional group accounting for 34% of the identified proteins. Cytoskeletal activities and metabolism/stress responses each accounted for a further 25% of the proteins.

Rapid detection of toxic metals in non-crushed oyster shells by portable X-ray fluorescence spectrometry

The aim of this study was the multi-elemental detection of toxic metals such as lead (Pb) in non-crushed oyster shells by using a portable X-ray fluorescence (XRF) spectrometer. A rapid, simultaneous multi-element analytical methodology for non-crushed oyster shells has been developed using a portable XRF which provides a quick, quantitative, non-destructive, and cost-effective mean for assessment of oyster shell contamination from Pb. Pb contamination in oyster shells was further confirmed by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). The results indicated that Pb is distributed in-homogeneously in contaminated shells. Oyster shells have a lamellar structure that could contribute to the high accumulation of Pb on oyster shells.

Different effects of Pb(2+) and Cu(2+) on immune and antioxidant enzyme activities in the mantle of Pinctada fucata

The aim of this study was to investigate the natural role of the mantle in pearl oyster, Pinctada fucata. The mantle is believed to be the tissue responsible for shell and pearl formation. However, our current study on lead and copper accumulation in tissues of the oyster showed that the secondary tissue for lead accumulation was not the digestive gland but the mantle. In view of high lead concentrations in the mantle, its general metabolic condition (including immune and antioxidant defense systems) as affected by the two metals was studied. The results indicated that activities of antioxidant enzymes (superoxide dismutase, SOD; Se-dependent glutathione peroxidase, Se-GPx) were altered by lead and copper in the similar way. However, the immune enzyme activities (acid phosphatase, AcPase; phenoloxidase, PO) were perturbed differently by two metals. Therefore, the mantle of P. fucata was predicted to participate in immune processes and accumulation or detoxification of lead besides shell formation. Our observations described here may also provide important clues to further understanding of the biomarker responses of bivalves.