Concentrations In Clams Research Articles

Biomonitoring of rare earth elements in Southern Norway: Distribution, fractionation, and accumulation patterns in the marine bivalves Mytilus spp. and Tapes spp.

Growing extraction and usage of rare earth elements and yttrium (REY) for medical and industrial applications has resulted in increased discharges into the marine environment. Using Mytilus spp. Mussels and Tapes spp. clams as bioindicator organisms, we analyzed 15 REY in soft tissues of specimens collected at two potentially polluted sites in Southern Norway: in the vicinity of an industry producing gadolinium-based MRI contrast agents (GBCAs) (Lindesnes) and in an industrially-affected fjord (Porsgrunn). The spatial distribution of REY and shale-normalized fractionation patterns were determined to assess the potential anthropogenic contribution of REY at the sites. At both sites, the REY fractionation pattern in soft tissue was characterized by enrichment of light rare earth elements (LREE) over heavy rare earth elements (HREE), while also displaying negative cerium and small positive gadolinium (Gd) anomalies. LREEs contributed to over 80% of the total REY concentrations, with increasing relative enrichment following higher total REY. Gd anomalies remained conserved in most sites despite significant differences in total REY; however, a high Gd anomaly (Gd/Gd* = 4.4) was found downstream of the GBCA industry spillwater outlet, indicating biotic uptake of excess anthropogenic Gd at this site. Total REY concentrations in clams in Porsgrunn were one order of magnitude higher than in mussels in Lindesnes. This may be attributable to freshwater influences in Porsgrunn, where clams collected closer to the river mouth had significantly higher total REY concentrations. This study constitutes the first assessment of REY concentrations in marine bivalves in Norway and can provide useful information for future biomonitoring studies on REY contamination.

Tissue-based trace element pollution of clam Ruditapes philippinarum in China: Hotspot identification and multiple nonlinear analysis

Considering the complexity of coastal and estuarine systems, a great challenge of environmental health assessment is to distinguish between natural and anthropogenically induced stress. Quantification of trace element accumulation in the tissues of sedentary bivalves with subsequent hotspot identification is important to assess the pollution status. The present study conducted a nationwide mapping of bioavailable macro- and trace elements in a widely distributed biomonitoring clam Ruditapes philippinarum from China. Ag, As, Cd, Cr, Cu, and Zn concentrations in the clams showed similar levels as those documented previously in mussels, but were lower than those in oysters at similar sites from China. Notably, the total As concentrations in clams at Xinkai Estuary and Beibu Bay were relatively higher than those at other sites in China. After normalization by tissue biomass, salinity (Na) and nutrient (P), some hotspots were identified with high pollution of trace elements at Liaodong Bay of Bohai Sea, Gold Beach of Qingdao, Dongling Port of Yellow Sea, Hangzhou Bay and adjacent coasts of East China Sea, and Pearl River Estuary and Beibu Bay of South China Sea. This study demonstrated that most trace elements had a path-dependent effect of biomass, except for Cd which showed an indirect pathway of AgNi related accumulation. Results showed significant correlations between Cd, Zn, Ag and Ni, and between Pb/Cr and Ti in clams. After mass normalization, all trace elements displayed significantly positive correlations with Na or P. Simultaneously, the clam biomass played an intermediary role in trace element accumulation in non-linear patterns related to salinity and nutrient. These results are important in evaluating the composite ambiguous information of the historical data of trace element biomonitoring.

Baseline health risk assessment of trace metals in bivalve shellfish from commercial growing areas in the estuaries of Ashtamudi and Vembanad (Kerala, India).

Trace metal concentrations were monitored in the yellow clam (Paphia malabarica), green mussel (Perna viridis) and edible oyster (Crassostrea madrasensis) from growing areas in the Ashtamudi and Vembanad estuaries, Kerala. Samples of shellfish (clams n=26, mussels n=18, oysters n=36) and environmental parameters (salinity, temperature, pH and rainfall) were measured in these growing areas from July 2012 to December 2014. Ranges of mean annual concentrations (mg/kg) were Ni (0.46-0.65); Co (2.87-3.49); Fe (80.0-119.4); Mn (3.88-9.38); Zn (40.8-76.2); Pb (1.28-2.00); and Cu (1.59-4.38). In Ashtamudi, clams had higher mean concentrations of Ni, Co, Fe, Mn and Pb than oysters. Mean concentrations of Ni, Pb (in all species), Zn (in clams and mussels) and Cu (in mussels) did not exceed maximum permissible limits mandated by the Food Safety and Standards Authority of India. Mean Mn concentrations exceeded the World Health Organization guideline (1 mg/kg)in the three species while mean Fe concentrations in clams and oysters did not exceed the guideline(100 mg/kg). Target hazard quotients were generally ≤ 1, except for a few Pb results in clams and mussels. Although results suggest no health risk to consumers for the reference doses, daily intakes and elements considered, regular monitoring of trace metals is recommended to maintain consumer protection given increasing anthropogenic and climatic pressures on the shellfish growing areas.

Determination and characterization of metal nanoparticles in clams and oysters.

With the extensive application of nanotechnology, metal nanoparticles (MNPs) have been widely used, thus are universally detected in the environment. This has caused increasingly concerns due to their toxicity and the potential health risks they pose to humans. In this work, the concentrations and particle size distributions of MNPs and concentrations of associated metal ionic species in shellfish seafood (clams and oysters) were investigated using single particle inductively coupled plasma mass spectrometry (sp-ICP-MS) and inductively coupled plasma mass spectrometry (ICP-MS). The MNPs in the clam and oyster tissues were extracted via an alkaline digestion method with a recovery rate of 95.9% (for gold nanoparticles (AuNPs)). Then total concentrations of 41 metal elements were measured in the two types of seafood, of which 20 were selected for sp-ICP-MS analysis. The results showed that 5 types of MNPs were detectable in clams (Y, La, Ce, Pr, Gd) and 5 types of MNPs were detectable in oysters (Y, La, Ce, Pr, Nd). Size distributions of MNPs in clams and oysters were in the range of 35-55nm and 30-65nm, respectively. Nanoparticle concentrations in clams and oysters ranged from 0.6 to 37.7ng/g and 4.2-19.7ng/g, and accounted for 3.4%-50% and 5.5%-46% of the total metal content, respectively. Based on this analysis, the health risks of metals in the two kinds of seafood were evaluated by comparing the Provisional Tolerable Weekly Intake (PTWI) with limits recommended by the World Health Organization (WHO)/Food and Agriculture Organization (FAO). These results provide important information about the presence of metal nanoparticles in seafood and, to the best of our knowledge, this is the first time that the nanoparticles of rare earth elements have been detected and reported in bivalve mollusc tissues.

Perfluorinated carboxylic acids in edible clams: A possible exposure source of perfluorooctanoic acid for Japanese population

We investigated the profiles and levels of perfluoroalkyl carboxylic acids in edible clams from five fishing sites in Japan (Hokkaido, Himakajima-Aichi, Atsumi-Aichi, Kyoto, and Kumamoto) and one site in Vancouver, Canada in 2017. The mean concentrations of perfluoroalkyl carboxylic acids with 6–15 carbon atoms (C6–C15) in edible clams from Japanese coastal waters ranged from 197 to 1757 pg/g wet weight, but were only 48 pg/g wet weight in clams from the site in Canada. Total perfluoroalkyl carboxylic acid concentrations in clams collected in Japanese waters were 4–40 times higher than concentrations in clams from Canada. Perfluorooctanoic acid (C8) contributed 53% of total perfluoroalkyl carboxylic acid concentrations in the clams from Japanese waters, which may be contaminated from terrestrial sources though river effluents, but was not detected in the clam samples from Canada. Principal component analysis separated shorter- and longer-chain perfluoroalkyl carboxylic acids, suggesting differing emission sources or environmental fate. Consumption of clams may be an exposure pathway of perfluorooctanoic acid in the Japanese population.

Metal accumulation in Asiatic clam from the Lower Min River (China) and implications for human health

Considering growing concerns regarding polluted estuaries and their adverse effects on public health, this study aimed to identify concentrations of metal (Zn, Fe, Cr, Ni, Cd, Mn, As, Cu, and Pb) in Asiatic clams sampled along the Lower Min River, China. Multivariate methods were used to identify and apportion pollution sources. Noncarcinogenic and carcinogenic health risk assessments were performed to gauge adverse consumer health effects. Results showed that Cr, Pb, and Zn concentrations were higher than the limits prescribed in Chinese government guidelines. In comparison with concentrations of selected metals in other rivers, Cr, Pb, Zn, and As concentrations in clams were generally higher. Pollution assessment using the metal pollution index showed that sampling sites surrounding developing industrial and residential areas were the most polluted. Principal component analysis indicated significant anthropogenic metal contributions in clams. Health risk assessment indicated significant risk for clam consumers along the Lower Min River in terms of hazard quotient and carcinogenic risk and, thus, clam consumption from the study area should be avoided. The present findings would help in establishing environmental monitoring plans and contribute to preserving public health as well as the development of water conservation strategies to alleviate the metal pollution.

Toxic effects of multi-walled carbon nanotubes on bivalves: Comparison between functionalized and nonfunctionalized nanoparticles

Despite of the large array of available carbon nanotube (CNT) configurations that allow different industrial and scientific applications of these nanoparticles, their impacts on aquatic organisms, especially on invertebrate species, are still limited. To our knowledge, no information is available on how surface chemistry alteration (functionalization) of CNTs may impact the toxicity of these NPs to bivalve species after a chronic exposure. For this reason, the impacts induced by chronic exposure (28days) to unfunctionalized MWCNTs (Nf-MWCNTs) in comparison with functionalized MWCNTs (f-MWCNTs), were evaluated in R. philippinarum, by measuring alterations induced in clams' oxidative status, neurotoxicity and metabolic capacity. The results obtained revealed that exposure to both MWCNT materials altered energy-related responses, with higher metabolic capacity and lower glycogen, protein and lipid concentrations in clams exposed to these CNTs. Moreover, R. philippinarum exposed to Nf-MWCNTs and f-MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defense mechanisms (superoxide-dismutase, glutathione peroxidase and glutathione S-transferases) in exposed clams. Additionally, neurotoxicity was observed by inhibition of Cholinesterases activity in organisms exposed to both MWCNTs.

Assessment of relationship between rainfall and Escherichia coli in clams (Chamelea gallina) using the Bayes Factor.

Consumption of bivalve shellfish harvested from water contaminated with sewage pollution presents a risk of human infections and targeting control measures require a good understanding of environmental factors influencing the transport and the fate of faecal contaminants within the hydrological catchments. Although there has been extensive development of regression models, the point of this paper, focused on the relationship between rainfall events and concentrations of Escherichia coli monitored in clams, was the use of a Bayesian approach, by the Bayes Factor. The study was conducted on clams harvested from the south coast of Marche Region (Italy), a coastal area impacted by continuous treated effluents, intermittent rainfalldependent untreated sewage spillage - as a consequence of stormwater overflowing - and rivers with an ephemeral flow regime. The work compared the different interpretation criteria of Bayes Factor, confirmed that E. coli concentrations in clams from the studied area varied in correlation with rainfall events, and demonstrated the effectiveness of Bayes Factor in the assessment of shellfish quality in coastal marine waters. However, it suggested that further investigations would be warranted to determine which environmental factors provide the better basis for accurate and timely predictions. Furthermore the gathered data could be useful, to the local authorities of Marche Region, in the definition of flexible monitoring programmes, taking into account the atmospheric events that could affect the correct functioning of sewage managing systems and the flow of tributary rivers.

Anthropogenic (PBDE) and naturally-produced (MeO-PBDE) brominated compound levels in Bizerte Lagoon clams (Ruditapes decussatus): Levels and human health risk assessment

Information on the occurrence of organobrominated compounds in bivalves from Tunisia is scarce. To the best of our knowledge, this is the first report of these compounds in clams from Tunisia. The aim of this study is to measure natural and synthetic organobrominated compound concentrations and evaluate congener distribution and pollution sources in a clam species (Ruditapes decussatus) from three sites of the Bizerte Lagoon. Total synthetic organobrominated pollutant levels in clam ranged from 34.8 to 188ngg−1lw. For natural organobrominated compounds, concentrations varied from 18.2 to 49.5ngg−1lw. Total PBDE and MeO-PBDE concentrations in clams from the Bizerte Lagoon were similar or slightly lower than those reported for other species from other locations around the world. The health risks associated with the consumption of this species were assessed and posed no threat to public health concerning PBDE intakes.

The impacts of emergent pollutants on Ruditapes philippinarum: biochemical responses to carbon nanoparticles exposure

Multi-walled carbon nanotubes (MWCNTs) are one of the most important carbon Nanoparticles (NPs). The production and use of these NPs are increasing rapidly and, therefore, the need to assess their presence in the environment and associated risks has become of prime importance. Recent studies demonstrated the impacts of different NPs on bivalves, a taxonomic group where species tolerance to anthropogenic stressors, such as pollutants, is widely variable. The Manila clam Ruditapes philippinarum is one of the most commonly used bivalve species in environmental monitoring studies and ecotoxicology tests, however, to our knowledge, no information is available on biochemical alterations on this species due to MWCNTs exposure. Thus, the present study aimed to assess the toxic effects of different MWCNT concentrations (0.01; 0.10 and 1.00mg/L) in R. philippinarum biochemical (energy reserves, metabolic capacity, oxidative status and neurotoxicity) performance, after 28days of exposure. The results obtained revealed that exposure to MWCNTs altered energy-related responses, with higher metabolic capacity and lower glycogen and protein concentrations in clams exposed to these carbon NPs. Moreover, R. philippinarum exposed to MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defence mechanisms in exposed clams. Additionally, neurotoxicity was observed by inhibition of cholinesterases activity in organisms exposed to MWCNTs. The present study provides valuable information regarding how these emerging pollutans could become a potential risk for the environment and living organisms.

A comparison of the physiological responses, behaviour and biotransformation of paralytic shellfish poisoning toxins in a surf-clam (Paphies donacina) and the green-lipped mussel (Perna canaliculus)

The accumulation of paralytic shellfish toxins (PSTs) in bivalves is species specific. We compared the physiological responses and the toxin profiles in tissues of the burrowing surf clam, Paphies donacina, and the green-lipped mussel, Perna canaliculus, exposed to the toxic dinoflagellate Alexandrium tamarense. Bivalves were supplied with the toxic algae for 10 days, then allowed a detoxification period of 8 days. Clearance rates of mussels and clams were similar when fed either with toxic A. tamarense or non-toxic A. margalefi. Byssus production in the mussel was inhibited and exhalent siphon activity in clams was erratic following exposure to A. tamarense. There were considerable differences in the toxic profile between the dinoflagellate A. tamarense, and tissues of the mussel and the surf clam, indicating that bioconversion of the PSTs had taken place. Toxin profiles of the tissues were both species and tissue specific. Following an 8-day detoxification period, total PSTs in mussels had fallen to safe concentrations below 50µg per 100g, whereas concentrations in clams remained high, with an average value greater than 600µg STX di-HCL equivalents per 100g. The results confirmed that mussels and clams are important monitoring organisms for toxic algal blooms and can be used to minimise the health risk of PSTs to humans.

The endocrine-disrupting effect and other physiological responses of municipal effluent on the clam Ruditapes decussatus.

In order to document the potential endocrine disrupting and toxic effect of the municipal wastewater effluents discharged into the Sfax coastal area (South of Tunisia), specimens of clam R. decussatus were collected from a reference site and were in vivo exposed to treated sewage effluent for 30 days. To this end, estrogenic and androgenic activities were measured in the gills to assess potential accumulation and regulation of active compounds. After effluent exposure androgenic activity in organic extracts increased up to fivefold compared to controls and remained elevated, while estrogenic activity was not significantly affected by exposure. As a consequence, remarkable disruptions in the gametogenesis activity, glycogen content, and Vitellogenin-like protein levels in male clams were observed. A parallel analysis of heavy metals in clam tissues was determined. A significant uptake of Ni, Zn, and Pb in soft tissues of exposed clams was observed. The significant increase of malondialdehyde (MDA) concentrations as a function of exposure time implies that clams have been exposed to an oxidative stress probably due to the presence of high metal concentrations in sewage effluent. Correlation analysis has revealed a statistically significant and positive relationship between MDA levels and metal concentrations in clams' tissues. The acetylcholinesterase activity was not significantly affected by exposure. Altogether, these results showed that a short-term exposure to a mixture of chemical compounds released by the Sfax wastewater treatment plant induce adverse physiological and reproductive effects in R. decussatus. Further studies are underway in order to evaluate its long-term impacts on aquatic wildlife in the gulf of Gabes area.

Methylmercury Bioaccumulation in Stream Food Webs Declines with Increasing Primary Production.

Opposing hypotheses posit that increasing primary productivity should result in either greater or lesser contaminant accumulation in stream food webs. We conducted an experiment to evaluate primary productivity effects on MeHg accumulation in stream consumers. We varied light for 16 artificial streams creating a productivity gradient (oxygen production =0.048-0.71 mg O2 L(-1) d(-1)) among streams. Two-level food webs were established consisting of phytoplankton/filter feeding clam, periphyton/grazing snail, and leaves/shredding amphipod (Hyalella azteca). Phytoplankton and periphyton biomass, along with MeHg removal from the water column, increased significantly with productivity, but MeHg concentrations in these primary producers declined. Methylmercury concentrations in clams and snails also declined with productivity, and consumer concentrations were strongly correlated with MeHg concentrations in primary producers. Heterotroph biomass on leaves, MeHg in leaves, and MeHg in Hyalella were unrelated to stream productivity. Our results support the hypothesis that contaminant bioaccumulation declines with stream primary production via the mechanism of bloom dilution (MeHg burden per cell decreases in algal blooms), extending patterns of contaminant accumulation documented in lakes to lotic systems.

Influence of Rainfall on E. Coli Concentrations in Clams: Results of Collaboration Between Competent Health Authority and Producers' Association in the Province of Fermo (Italy).

The Area Vasta di Fermo (the competent health authority of the Marche Region), in collaboration with the local producers’ Association conducted a series of studies on the presence of E. coli as an indicator of faecal contamination in the environment, in shellfish and in fishery waters, and on the factors that can affect their presence. These studies, carried out from 2008 to 2011, included an assessment of the currents along the coast, of the precipitations, and data from the monitoring of E. coli on shellfish harvested in the collection areas were examined. The results showed that in most cases, small concentrations of microorganisms in shellfish corresponded to little or no precipitations, while an increase in the levels of E. coli was preceded by more or less abundant rainfalls. The conclusions suggest that it is advisable to carry out a more detailed risk analysis which should take into account the above-mentioned factors. Furthermore, monitoring alone based on the determination of indicator organisms, especially when carried out as a single analysis or with a small number of E. coli determinations, does not provide a satisfactory indication of safety. The regional surveillance plans should be applied timely and rigorously, together with onsite investigations aimed at identifying changes that can affect the presence of E. coli in shellfish. Food business operators themselves could implement good manufacturing practices to verify whether the microbiological parameters are within the prescribed limits after rainfalls, especially if heavy.

Selective Pressurized Liquid Extraction Technique Capable of Analyzing Dioxins, Furans, and PCBs in Clams and Crab Tissue

A selective pressurized liquid extraction technique (SPLE) was developed for the analysis of polychlorodibenzo-p-dioxins, polychlorodibenzofurans (PCDD/Fs) and dioxin-like polychlorobiphenyls (dl-PCBs) in clam and crab tissue. The SPLE incorporated multiple cleanup adsorbents (alumina, florisil, silica gel, celite, and carbopack) within the extraction cell. Tissue extracts were analyzed by high resolution gas chromatography coupled with electron capture negative ionization mass spectrometry. Mean recovery (n = 3) and percent relative standard deviation for PCDD/Fs and dl-PCBs in clam and crabs was 89 ± 2.3 and 85 ± 4.0, respectively. The SPLE method was applied to clams and crabs collected from the San Jacinto River Waste Pits, a Superfund site in Houston, TX. The dl-PCBs concentrations in clams and crabs ranged from 50 to 2,450 and 5 to 800 ng/g ww, respectively. Sample preparation time and solvents were reduced by 92 % and 65 %, respectively, as compared to USEPA method 1613.

Relative Importance of Burrow Sediment and Porewater to the Accumulation of Trace Metals in the Clam Amiantis umbonella

The objectives of this study were to evaluate the infaunal, facultative deposit-feeding clam Amiantis umbonella as a bioindicator of trace-metal contamination and the relative importance of clam burrow sediment and porewater to total accumulation in an urban/industrial coastal environment. Concentrations of eight trace metals (cadmium [Cd], chromium, copper, mercury [Hg], nickel, lead [Pb], vanadium, and zinc) were measured in the soft tissues of clams and in sediment and porewater from clam burrows along a 5-km transect from desalination/power plant discharges in inner Kuwait Bay. All metals had significantly greater concentrations in clams collected near the desalination/power plant discharges than from the reference site and exhibited decreasing trends with distance from the point source in clam soft tissues and burrow sediment and porewater. Concentrations of Hg (1-9ppm [dry weight]) and the highest concentrations of Pb (3ppm) and Cd (7ppm) in clams from contaminated sites in Kuwait Bay were greater than human consumption limits. Metal concentrations in clams were correlated with those in burrow sediment and porewater across all sites and at sites closest to the point source but not within the reference site. The concentrations of all metals, except Pb, in clams from the contaminated sites were more highly correlated with those in clam burrow sediment than porewater. Concentrations of Pb in clam soft tissues were more strongly correlated with those in burrow porewater than sediment. These results indicate that A. umbonella is an excellent bioindicator of trace metal contamination and that sediment is an important source of contaminant metals to this infaunal clam; however, the source of each metal must be evaluated separately.

Availability of Venerid Clam, Amiantis umbonella as potential metal bioindicator in Bandar Abbas coast, the Persian Gulf

Abstract Concentration of thirteen metals were measured in the clam Amiantis umbonella and its parasite crab Arcotheres tivelae , sediment and water collected at two stations of the Northern coast of the Persian Gulf. Magnesium and iron were the two most abundant measured metals in clams, crabs, sediments and water. The maximum and minimum metal concentrations in clams were attributed to Mg (3541–5445 μgg −1 dry wt) and Ag (0.30 μgg −1 dry wt). Regarding metal concentration in different clam’s compartments, Pb in shell, As in digestive gland and Cu, Ag and Zn in remaining soft parts were more than other clam’s parts, crab, water and sediment as well. A. umbonella could be a useful bioindicator for As, Pb, Cu, Ag and Zn metal elements. A. tivelae could also be used as a valuable bioindicator for Cd in addition to the mentioned metals to survey metal concentration. There was insignificant difference between metal concentration in infested and non-infested clams. However, the average concentrations of metals in infested clams were less than non-infested during the study. A significant positive correlation was occurred between clam length and concentrations of Cd, Mn, Pb and Ag. There was also a positive significant correlation between accumulation of metals in clams, crabs, water and sediment. This study showed that variable metal concentrations were related to station and season interactions. However, stations and seasons did not affect metal concentration in clam, crab and water separately.

Occurrence of Brown Ring Disease in Carpet Shell ClamsRuditapes decussatusfrom the Gulf of Gabes (Tunisia, Central Mediterranean Sea)

The occurrence and spread of brown ring disease (BRD) to several northern Mediterranean coasts is described. We report the results of a 6-y surveillance of BRD in natural populations of carpet shell clams (Ruditapes decussatus) in 14 zones along the Gulf of Gabes in Tunisia (southern Mediterranean Sea). BRD symptoms in adult animals resulting from conchiolin deposits in inner parts of carpet shell were observed in all zones surveyed. Infestation rates within each site ranged from 65–100%, and BRD prevalence varied from 1–58% of clams in winter and from 1–33% in summer. Positive correlations were demonstrated between BRD prevalence and Vibrio spp. concentrations in clams. Vibrio tapetis was not identified among the bacterial organisms, suggesting that other marine Vibrio species are capable of causing BRD-like illness in carpet shell clams.

Bioaccumulation of Heavy Metals in the Volta Clam, Galatea Paradoxa (Born, 1778) in Relation to Their Geoaccumulation in Benthic Sediments of the Volta Estuary, Ghana

Heavy metal accumulation in aquatic ecosystems is a common phenomenon among bivalve filter feeders. This study was carried out over an 18-month period at Ada and Aveglo in Ghana, where intense clam fishing represents a major livelihood. The study sought to investigate the concentrations of some heavy metals, zinc, manganese, iron and mercury, in whole soft tissues of three different size classes of the Volta estuary clam, Galatea paradoxa, in relation to geoaccumulation of the metals in benthic sediments. The study also sought to examine whether the levels of the metals in clam tissues were within acceptable limits for human consumption. Clam sizes were categorised as small (25–40 mm) medium (41–55 mm) and large (above 55 mm) based on shell lengths and predominant sizes captured in the Volta estuary. Mercury levels in clams and sediments were determined using a Mercury Analyser while Zn, Mn and Fe were determined using an Atomic Absorption Spectrophotometer. Heavy metal concentrations in clams were within permissible limits with reference to WHO safety standards. There were no significant spatial differences (p>0.05) in the concentrations of Mn, Zn, Fe and Hg in clams at Ada and Aveglo. No relationship was observed between heavy metal concentrations in clams and geo-sediments indicating that metal accumulation in clams may not be directly or solely derived from sediments but from other sources such as dissolved metals in the water and seston. Highly significant differences (p<0.0001) were observed between the clam size-classes and sediment samples for iron. Total mercury concentrations showed highly significant variations (p<0.0001) between all the clam size-classes and the sediment samples.

Tapes philippinarum seed exposure to metals in polluted areas of the Venice lagoon

The concentration changes of 12 metals (As, Hg, Cd, Cr, Co, Cu, Pb, Mn, Ni, V, Zn, Fe, and Hg) in the soft tissues of Tapes philippinarum during growth were investigated. Clams were seeded in two contaminated areas of the Venice lagoon (San Giuliano and Fusina) and in an area of the Marano lagoon (Lignano Sabbiadoro) close to the clam-farm where the seed was produced. Metal trends were very different according to the considered element, the study site and the growth period. Arsenic was always higher in clam tissues than in surface sediments and suspended particles in all the three stations. Mercury, Cd and Cu were higher in the clams from Marano and Fusina but not in those from San Giuliano. Zinc and Co in clams exceeded the concentrations in the sediment and suspended particles only at Marano. The other elements (Cr, Pb, Mn, Ni, and Fe) were always higher in SPM and sediments. In general metal concentrations in clams were more highly correlated to concentrations in the suspended particles rather than in the surface sediments and in suspended clams rather than in bottom clams, nevertheless significant differences between stations and contaminants were found. Metal concentrations in clams were always lower than the European regulatory limits.