Biomonitoring of trace metals in the Black Sea (Romania) using mussels Mytilus galloprovincialis

In a preliminary biomonitoring study, accumulated trace metal concentrations (Cd, Cu, Zn, Hg, Fe, Mn) have been measured in the mussel Mytilus galloprovincialis collected in the Black Sea, at 100 km from the Danube Delta in February 2001 and February 2002. Mussels were collected from four sites. In 2001 metal concentrations were determined in the whole soft body whereas, in 2002, the distribution of metals was evaluated in three different organs (gills, visceral mass and remaining tissues). The results obtained in 2002 confirmed those of 2001. For a given site, concentrations were always higher in the gills and visceral mass of mussels than in the remaining tissues. Principal component analysis allowed separating stations as a function of the metal concentrations in the organs. It is concluded that the mussels M. galloprovincialis are suitable biomonitors to assess changes in metal pollution in this coastal area of the Black Sea.     

Distribution of micro-essential (Fe, Cu, Zn) and toxic (Hg) metals in tissues of two nutritionally distinct hydrothermal shrimps

Hydrothermal ecosystems of the Mid Atlantic Ridge (MAR) are dominated by shrimps and mussels that are naturally exposed to elevated levels of heavy metals providing unique in situ laboratories for ecotoxicological investigations. This study reports on the tissue compartmentalization of both micro-essential (Fe, Zn, Cu) and toxic metals (Hg) in two nutritionally distinct cariddean vent shrimps: Rimicaris exoculata and Mirocaris fortunata, in order to shed light on organism-biota interactions at hydrothermal vents. High metal concentrations in shrimps confirmed extreme exposure levels at both geochemically different hydrothermal vents (Rainbow and Lucky Strike). However, Hg concentrations were below those reported in species for human consumption that may either suggest low bioavailability of the metal, or its effective detoxification/depuration by the hydrothermal shrimp that needs to be confirmed by post-capture toxicological investigations. Distribution of metals in different tissues had very similar patterns in both shrimp species, the target organs being gill and pylorus. Tissue levels correlated well with end-member fluid composition with regard to element ratios, i.e. Fe/Zn and Fe/Cu ratios in end-member fluids reported for Rainbow and L. Strike were conserved in the gills of M. fortunata. Moreover, R. exoculata that lives closer to venting exits as compared to M. fortunata, had similar or often less metals accumulated in selected organs, possibly owing to its higher degree of adaptation to hydrothermal conditions. Despite of high concentrations in tissues micro essential metals only represented a small fraction (14-36%) of the whole body burden indicating preponderance of minerals on the surface and/or in the gut, and thus points to improper use of whole body concentration in metal bioavailability interpretations at hydrothermal vents.     

The effect of size on trace metal levels in raft cultivated mussels (Mytilus galloprovincialis)

Mussels are farmed in the coastal inlets of Galicia by means of floating raft culture. The growth of these bivalves is due to their great capacity to filter the water column, which unfortunately, also exposes them to dangerous contaminants, including heavy metals. Thus, it is imperative that mussels be monitored for metals. Size has sometimes been shown to be an important variable, but contradictory results have been found. In order to monitor metals in raft mussels, it is necessary to compile information regarding the number of size classes according to shell length, which must be taken into account to obtain a representative sampling, as well as the number of sample replicates that must be included. Also, to be considered is the cost incurred by carrying out the collection, preparation and analysis per sample. The purpose of this study is to provide information about the effect of size, indicated by shell length on the metal content of raft mussels. The ability of 10 mussel-pooled samples to discriminate real differences in metal concentration was also studied. In general, a positive relationship between metal content and shell length was observed; a similar relation was found between the weight of soft tissues and shell length. As expected from the similarity encountered between relationships of metal content and dry weight-length, the concentrations of the different metals in the soft tissues would not seem to depend on the shell length. Metal concentrations, in this study, were found to be approximately 45 ppm of Hg, 0.5 ppm of Cd, 0.7 ppm of Pb, 0.5 ppm of Cr, 0.6 ppm of Ni, 8 ppm of As, 5 ppm of Cu and 122 ppm of Zn; on a dry weight basis. No significant differences between metal concentrations at different shell lengths were detected. Another important observation was the high variability observed within one size, indicating poor homogeneity in subgroups of similar size, which must be minimized if the number of samples is not enhanced as indicated by power and size analysis.     

Correlations, partitioning and bioaccumulation of heavy metals between different compartments of Lake Balaton

Correlations between trace metals in dissolved and particulate phases, zooplankton, mussels and sediments in Lake Balaton were investigated. The degree of correlation between the various metals was different in each of the investigated compartments. Particulate metal concentrations (microg g(-1)) were anti-correlated with suspended particulate matter (SPM) (mg l(-1)), indicating a dilution effect, while total metal concentrations in the water column (microg l(-1)) were highly correlated with SPM, implying a major influence of the turbidity on the total metal concentrations. Between compartments, not many significant correlations were recognized. Only Ba, Ca, Sr and Mg are correlated in the sediments and in the particulate phase, suggesting common sources for both compartments. Partitioning coefficients (Kd) of trace metals between dissolved and particulate phases are generally low, typical for natural water and fairly stable over the lake. Most of the trace metals (Zn, Co, Cd and Pb) exist in the particulate phase (for about 70% of the total metal load). Cu and Ni are exceptions, showing a more equal distribution. Bioconcentration factors (BCF) of zooplankton and mussels were comparable to those of other natural waters. A negative biomagnification from suspended particulate matter to zooplankton and from sediment to mussel was recognized for all trace metals, except a small enrichment of Zn in zooplankton and Cd in mussel. Four factors were recognized in SPM and in sediments but they did not contain the same group of metals. Cluster analysis showed that metal accumulations in the sediments were different between northern and southern shores and in SPM between western and eastern areas.     

Residual effects of lead and zinc mining on freshwater mussels in the Spring River Basin (Kansas, Missouri, and Oklahoma, USA)

Concentrations of selected trace elements in surface water and fluvial sediment were investigated as possible factors limiting the distribution and abundance of freshwater mussels in the Spring River Basin, a 6600 km(2) watershed overlapping a former Pb and Zn mining and ore processing district in the central USA. Mussel taxa richness surveys and supporting physical habitat assessments were performed in 23 stream reaches dispersed throughout the basin and above and below former mining sites. Quantitative mussel density surveys were performed in the Spring River at one upstream reference location and one downstream location. Concentrations of 16 trace elements in the soft tissues of mussels and Asian clams (Corbicula fluminea) were determined at most survey sites. Comparable analyses were performed on surface water samples collected during base flow and peak flow synoptic surveys and sediment samples collected during base flow periods. Sites on the Spring River immediately upstream of heavily mined areas supported at least 21-25 species of mussels, whereas sites near the lower terminus of the river yielded evidence of 6-8 extant species. Between the upper and lower quantitative survey sites, mean mussel and clam densities declined by 89% and 97%, respectively. Tributary reaches below heavily mined areas lacked evident bivalve communities and contained concentrations of Cd, Pb, and Zn that continually or sporadically exceeded hardness-dependent water quality criteria and consensus-based sediment quality guidelines (probable effect concentrations). In less contaminated stream reaches supporting bivalves, concentrations of Cd, Pb, and Zn in mussels and clams were correlated spatially with the levels occurring in surficial sediment (0.50 < or = tau < or = 0.64, p < or = 0.03). In non-headwater perennial stream reaches, sediment Cd, Pb, and Zn levels were related inversely to mussel taxa richness (-0.80 < or = tau < or = -0.64, p < or = 0.004). Metal contaminant burdens in mussels and clams fluctuated measurably in association with variable stream flow conditions and accompanying changes in surface water and sediment chemistry. Concentrations of Cd, Pb, and Zn in mussels approximately paralleled the levels measured in composite clam samples (0.74 < or = tau < or = 0.79, p<0.001), implying C. fluminea could serve as a possible surrogate for native mussels in future metal bioaccumulation studies. Overall, streams draining heavily mined areas exhibited depauperate (or fully extirpated) mussel assemblages and correspondingly elevated concentrations of Cd, Pb, and Zn in water, sediment, and bivalve tissue. Other evaluated environmental chemistry parameters, and physical habitat conditions assessed at the stream reach scale, demonstrated little general relationship to the degraded status of these assemblages. We conclude that pollution attributable to former mining operations continues to adversely influence environmental quality and impede the recovery of mussel communities in a large portion of the Spring River Basin.     

The effects of dissecting tools on the trace element concentrations of fish and mussel tissues

A comparison of the effects of dissecting tools composed of various materials on the trace element content of the muscle of the marine bluefish, Pomatomus saltatrix, and the soft tissues of freshwater mussels, Eliptio complanatus and Lampsilus radiata, is presented. The fish were dissected with blades made of stainless steel, Lexan plastic, titanium, and Teflon-coated stainless steel. The mussels were dissected with stainless and Teflon tools only. Elements measured included As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sn, Te, V, and Zn. Significant concentration differences (P = 0.01) were not found for any element in fish or mussel samples dissected by the different tools.     

Bioaccumulation of heavy metals in two wet retention ponds

Metal accumulation in stormwater ponds may contaminate the inhabiting fauna, thus jeopardizing their ecosystem servicing function. We evaluated bioaccumulation of metals in natural fauna and caged mussel indicator organisms in two wet retention ponds. Mussel cages were distributed throughout the ponds to detect bioaccumulation gradients and obtain a time-integrated measure of metal bioavailability. We further investigated if sediment metal concentrations correlate with those in the fauna and mussels. Metal concentrations in the fauna tended to be higher in the ponds than in a reference lake, but statistical significance was only shown for Cu. Positive correlations were found for some metals in fauna and sediment. Sediment metal concentrations in one pond decreased from inlet to outlet while no gradients were observed in the mussels in either pond. These findings indicate that metal accumulation in the examined ponds currently does not pose a threat to their habitat function.     

Bioaccumulation of pollutants in the zebra mussel from hazardous industrial waste and evaluation of spatial distribution using GAMs

In the Flix Reservoir (Ebro River, Spain), ca. 300,000 tons of industrial waste were dumped because of the activity of a factory plant in Flix. Within the recovery program implemented, this exceptional situation provides a unique opportunity to test the value of zebra mussel as sentinel organism. Ten metal concentrations were measured in mussels from different sites to assess spatial redistribution of metals and bioavailability to the food web. Our results showed an important metal uptake by mussels; metal concentrations (except As) measured in impacted sites were up to 10 times higher than in control sites, and Mn and Hg exceeded several times the levels previously reported for polluted waters. Concentrations increased downstream showing the metal mobilization from polluted sediments in Flix Reservoir. The higher metal concentrations measured in zebra mussel individuals clearly indicated their bioavailability to the food web, allowing the toxics transfer to predators and occasionally to humans. Thus, zebra mussel is a valuable sentinel organism to identify highly polluted waters, transport routes and trophic transfer.     

Field validation of autometallographical black silver deposit (BSD) extent in three bivalve species from the Lagoon of Venice, Italy (Mytilus galloprovincialis, Tapes philippinarum, Scapharca inaequivalvis) for metal bioavailability assessment

The autometallographic approach was applied to three filter-feeder bivalves from differently polluted sites of the Lagoon of Venice. The area density (AD) values of black silver deposits (BSDs) were therefore seasonally quantified by image analysis in digestive cell lysosomes. Sediments were characterised in terms of grain size, organic content and metal concentrations (Cd, Cu, Ni, Pb, Zn). The physiological status of the bivalves was also evaluated by applying the "survival in air" test as a generic stress index. Chemical results showed that Zn contributed to the total metal load for more than 60% in sediments and for 85%-94% in mussel and clam digestive glands, respectively (data processed from published results obtained on the same samples). Regression analyses between extent of BSDs and both total metal and Zn concentrations in digestive gland followed a linear pattern in mussels and clams, but not in arks. Similarly, in mussels and clams only, BSD amount was significantly correlated with total metal concentrations in sediments according to a logarithmic model. Consequently, results obtained from autometallography can discriminate sites on the basis of their metal pollution levels, like chemical analyses on both sediments and digestive glands, evaluations being supported by the results of the physiological stress index. As a conclusion, it is suggested that autometallography in bivalves may provide overall estimates of metal fractions moving from sediments towards organisms through the ingestion of metal-enriched particles. Future work is needed to define the bioaccumulation model in arks and to clarify their possible use as metal biomonitors.     

The bioaccumulation of cadmium by the Blue Swimmer Crab Portunus pelagicus L.

The Blue Swimmer Crab (Portunus pelagicus) accumulates only cadmium in the hepatopancreas after being presented elevated levels of the metals Cd, Cu, Zn, As, Fe and Al via a food source, the mussel Trychomya hirsuta. Over 8 weeks, crabs were fed a controlled diet to determine the accumulation of metals. Significant (P = 0.05) Cd accumulation was detected after 4 weeks of feeding. Food mussels were sourced from either 'contaminated' or 'uncontaminated' sites. Mussels from uncontaminated sites had an average Cd level of 0.07 microg/g wet weight and contaminated mussels had an average of 5.2 microg/g wet weight. The usefulness of presenting metals in this way to assess potential bioaccumulators is further considered against other presentation methods.     

Relationship between seawater pollution and qualitative changes in the extracted proteins from mussels Mytilus galloprovincialis

The aim of this study was to find a reliable biomarker of seawater pollution. For this purpose the contents of Zn and Cu, proteins and antioxidant activity in mussels Mytilus galloprovincialis collected from polluted and non-polluted sites of the Bulgarian Black Sea coast were compared. To determine the above-mentioned indices atomic spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, fluorescence, differential scanning calorimetry (DSC), and two antioxidant tests were used. It was found that the amounts of Zn and Cu were significantly higher in the mussel proteins from the polluted than from the non-polluted sites (P<0.05). FT-IR spectroscopy and fluorescence revealed specific qualitative changes in secondary and tertiary structures in mussel proteins in the samples from polluted sites. The thermodynamic properties of proteins and the changes upon denaturation were correlated with the secondary structure of proteins and disappearance of alpha-helix. Purified protein scavenging activity against 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) radical cation (ABTS(*+)) was significantly higher in mussel samples from polluted than from non-polluted sites. Therefore, the changes in Zn and Cu concentration, in protein's secondary and tertiary structures and antioxidant activity in mussels M. galloprovincialis from polluted sites can be a reliable biomarker of the level of the seawater pollution.     

Heavy metal contents (Cd,Cu, Zn) in spiders (Pirata piraticus) living in intertidal sediments of the river Scheldt estuary (Belgium) as affected by substrate characteristics

Metals are transferred into the food web by ground-dwelling organisms, among others. This study aimed to identify the most important factors that determine the bioavailability of heavy metals to the spider Pirata piraticus living in the intertidal sediments of the Scheldt estuary (Flanders, Belgium). At five locations, which represent a varying degree of metal contamination and salinity, the superficial layer of sediments was characterised for physico-chemical properties and heavy metal (Cd, Cu, Zn) content and extractability. Spiders were sampled at the same locations and analysed for Cd, Cu and Zn. Higher Cd, Cu and Zn contents were found in spiders on sites with lower total metal contents in the sediment. These sites were closest to the river mouth and were characterised by a higher salinity. Significant, positive correlations were found between the chloride content of the sediments and the Cd, Cu and Zn content of P. piraticus. Similarly, a strong relationship was observed between the ratio of exchangeable Cd and Zn to the total cation exchange capacity and the contents of these elements in P. piraticus. These field data indicated that salinity, cation exchange capacity and exchangeable metal contents were of most importance in determining bioavailability of heavy metals in these intertidal sediments.     

Metallothionein concentrations in a population of Patella aspera: variation with size

The determination of metallothionein (MT) concentrations in species with different feeding habits is important from the ecotoxicological point of view because it provides a better understanding of the role of these proteins in metal uptake pathways. The main objective was study the variation of MT and metal (Cd, Cu and Zn) concentrations with size and weight in the limpets Patella aspera. In addition investigate the relationship between MT and metal concentrations in limpets from different metal load environments of the south coast of Portugal with the aim to use MT in P. aspera as a biomarker of metal exposure. MT concentrations in the whole soft tissues of P. aspera increased with size and weight while metals decrease with size and weight. MT concentrations showed no significant relationship with Cd or Cu concentrations in the limpets from the South Portuguese Coast. However, a negative exponential relationship detected between MT and Zn concentrations suggest that Zn bound to MT might be displaced by Cd or Cu ions. The ability of limpets to store both Cd and Cu bound to MT may be responsible for the tolerance of this species to contaminated environments. The relationship between MT concentrations and Zn indicates that MT seems to play a minor role in binding Zn in Patella species.     

Assessment of metal pollution in Onsan Bay, Korea using Asian periwinkle Littorina brevicula as a biomonitor.

Cadmium (Cd), lead (Pb), copper (Cu) and zinc (Zn) concentrations in the marine gastropod, Littorina brevicula Philippi, were determined to assess the metal pollution in Onsan Bay, Korea. Samples of L. brevicula employed as a biomonitor and seawater were collected from 12 to 20 stations of Onsan Bay in November 1997, respectively. Dissolved metal concentrations in surface seawater were highest at the station near Onsan Non-ferrous Industrial Complex: 1.15 micrograms l-1 for Cd, 2.49 micrograms l-1 for Pb, 3.75 micrograms l-1 for Cu and 23.98 micrograms l-1 for Zn. These values were 1-2 orders higher than those shown at outer regions of the Bay. Metal concentrations in the soft body of periwinkles were highly variable at different sampling locations: 0.48-27.11 micrograms g-1 for Cd, 1.41-24.91 micrograms g-1 for Pb, 57-664 micrograms g-1 for Cu and 83-246 micrograms g-1 for Zn. The values from stations near the industrial complex were higher than those expected from relationships between body sizes and metal body burdens in periwinkles collected from the whole Korean coast. Spatial distribution of metal concentrations in the periwinkle and seawater indicated that Onsan industrial complex near the Bay is the input source of these metals. Especially, Cd and Pb concentrations in the periwinkle and seawater were distinctly decreased with distance from the Onsan industrial complex. Non-essential metals such as Cd and Pb in the periwinkle showed a strong correlation with dissolved metal concentrations in seawater. Conversely, essential Cu and Zn in the periwinkle were hardly explained by those in seawater, except at the most contaminated sites.     

Heavy metal content of oysters from the Lynher Estuary,U.K.

The concentrations of As, Cd, Cu, Hg, Pb and Zn have been determined in oysters and sediments from the Lynher Estuary, U.K. The sediments contained high levels of Cu, Fe, Pb and Zn probably associated with run off from a metalliferous catchment area and high Hg associated with a local sewage input. In contrast, the analyses of the oyster tissue showed that only Cu and Zn were concentrated in the flesh. The majority of samples contained coliform bacteria in excess of 1000 organisms per ml of tissue. It is concluded that the quality of the oysters from this fishery was limited by the bacteriological cleanliness rather than toxic metal content.     

The effect of graded doses of cadmium on lead,zinc and copper content of target and indicator organs in rats

Eleven groups of inbred Wistar rats, five males and five females in each group, received graded doses of CdCl₂, from 0–25 ppm, in the drinking water from conception until sacrifice at the age of ten weeks. The Pb, Zn and Cu levels of various indicators and target organs were recorded by atomic absorption spectrophotometry. Cd concentrations above 5 ppm caused a significant increase in Zn content of kidneys, liver, spleen, heart and adrenal glands in most of the experimental groups, and in addition a significant positive correlation between Cd and Zn in the same tissues. With concentrations above 10 ppm, Zn contents of epiphyses and diaphyses decreased significantly, and through all groups there was a significant negative correlation between Zn and Cd in diaphysis. This local Zn deficit may cause a retarded growth of long bones. Cd supply resulted in a significant decrease in Zn content of incisors and molars, but did not significantly affect the Cu content. Neither were Zn nor Cu concentrations in hair affected. Cd supply led to a significantly increased storage of Cu in liver, spleen, heart and skeletal muscle and a positive correlation between Cd and Cu content in the same tissues. Cd administration caused a significant decrease of Pb concentrations in molars, hair, kidney cortex, heart, skeletal muscle and adrenal glands in several of the experimental groups, and also a significant negative correlation between Pb and Cd content of molars, hair, kidney cortex, liver and heart. This can be a result of decreased uptake, increased excretion or changes in the distribution pattern of Pb.     

Clams as pollution bioindicators in Kuwait''s marine environment: metal accumulation and depuration

This study has developed and verified clam transplantation for marine pollution monitoring in Kuwait and has assessed its reliability for monitoring pollution by heavy metals through laboratory and field transplantation experiments. In field experiments, live specimens of the clam Circenita callipyga were transplanted, either suspended in seawater or buried in sand, to 11 coastal sites in Kuwait; subsamples of transplanted clams were recovered at intervals over a 6-month period. In laboratory experiments, heavy metal accumulation for 36 days and depuration (body's release of pollutants) for 60 days in small and big clams were investigated. Clams subsampled in laboratory and field experiments were analyzed for Hg, Cu, V, Cd and Pb. Results showed the ability of clams to survive under the transplantation conditions. Accumulation of biofouling materials was a problem at only two transplantation sites and was overcome by periodic cleaning. Statistical analysis of laboratory experimental data showed significant accumulation of all test metals and significant depuration of Hg, Cu, V and Cd. Rates of metal accumulation and depuration differed in relation to clam size class. Field experiments indicated statistically significant increases in Hg and Cu concentrations in the transplanted clams at most stations, no change in Cd concentrations and an increase or, occasionally, a decrease in V and Pb concentrations.     

Distribution of Cd, Zn, Cu and Fe among selected tissues of the earthworm (Allolobophora caliginosa) and Eurasian woodcock (Scolopax rusticola)

We have measured the concentrations of heavy metals in soils, earthworms and tissues of woodcocks in Quaderna Valley, northern Italy. The soil concentration of metals analysed in this research is consistent with data reported by other authors for uncontaminated or slightly contaminated soils. In earthworms, metals were mostly accumulated in the encapsulating chloragogenous tissue; the positive correlation between Cu concentration in the soil and in earthworms is noteworthy. Heavy metal distribution in the tissues of woodcock showed that Cd accumulation in the kidney was linked to the diet. Cu and Fe were preferentially concentrated in the liver and Zn in the testis. Kidney Cd and Zn concentrations were higher in adults than in juveniles. In addition, a main kidney metallothionein isoform, containing Cd and Zn, was isolated. In the kidney, Cd levels were linearly correlated with the concentration of metallothionein. Of the investigated metals, Cd raises the greatest concern, due to the increasing soil contamination by human activities.     

Mammalian hair as an accumulative bioindicator of metal bioavailability in Australian terrestrial environments

The current study represents the first investigation of the suitability of marsupial and eutherian mammalian hair as indicator tissue for metal exposure and accumulation within contaminated Australian terrestrial ecosystems. A soil metal contamination gradient was established across 22 sites at increasing distances from a decommissioned Lead/Zinc smelter in NSW, Australia. Within each site, soil and small mammal populations were sampled. An Australian native marsupial, the insectivorous Brown Antechinus, Antechinus stuartii: Dasyuridae, and introduced rodents, the omnivorous Brown or Norway Rat, Rattus norvegicus: Muridae and the Black Rat, Rattus rattus: Muridae were assessed for hair concentrations of Cadmium (Cd), Copper (Cu), Lead (Pb) and Zinc (Zn). Metals in soil were most elevated at sites within close proximity to the smelter, with soil metal concentrations decreasing with distance from the smelter. The non-essential metals Pb and Cd were accumulated in hair, both metals exhibiting positive linear relationships with environmental exposure (soil metal concentrations). When the variables of weight and snout-vent length were considered, no further contribution in terms of explaining the variability in hair Cd or Pb was observed for all species examined. The essential metals Cu and Zn were regulated in hair, remaining similar across the metal contamination gradient. A significant negative correlation between snout-vent length and hair Cu concentration was found for the Brown Rat; greater hair Cu concentrations were found in smaller individuals of this species. Accumulation of Pb to hair was similar among species while concentrations of Cd in Brown Rat hair were higher than both Black Rat and Brown Antechinus hair. As each of the three aforementioned species exhibit similar bioaccumulation relationships for Pb, we suggest that sampling hair from introduced rodents (pest species) may provide a suitable proxy for the assessment of Pb bioavailability for a range of small mammals within Australian urban remnants.     

Human dietary exposure to heavy metals via the consumption of greenshell mussels (Perna canaliculus Gmelin 1791) from the Bay of Islands, northern New Zealand

Cadmium (Cd), mercury (Hg), arsenic (As), lead (Pb) and tin (Sn) concentrations were determined using ICP-MS in soft tissues (wet wt.) from whole greenshell mussels (Perna canaliculus) collected from Urapukapuka-Rawhiti Island, Opua Marina, Waitangi Bridge and Opua Wharf from the Bay of Islands, northern New Zealand (NZ). All samples had metal concentrations well below the Food Standards Australia and New Zealand (FSANZ) maximum limits and were comparable to, or less than, concentrations observed in previous NZ studies. Based on the average values detected in the current study, the concentrations of heavy metals ingested in a ‘typical diet’ containing greenshell mussels are below the provisional tolerable weekly intake (PTWI). However, Māori (indigenous people of New Zealand), Pacific Islanders and Asians consume a far greater quantity of seafood (and therefore heavy metals) than the general public of New Zealand and could potentially consume enough shellfish to exceed the PTWI for Cd (but not for Hg, As, Pb or Sn). Although our results, based on the current PTWIs, indicate no significant health risk to greenshell mussel consumers in this region, PTWIs change over time; concentrations which were thought to be safe are later found to be harmful. Additionally, differences in individual human susceptibilities to various toxins could increase the risk of harm for consumers with low tolerance to heavy metals. We suggest that a survey of the frequency, amount and species consumed by groups whose diet may be largely shellfish-based is required to enable a more comprehensive risk assessment to be made.