Distribution and relationships of selected trace metals in molluscs and associated sediments from the Gulf of Aden, Yemen

Metal pollution in seaweed and related sediment of the Persian Gulf, Iran

Nickel, cadmium, copper and lead in the sediment and seven species of algae from six locations in the Bushehr Province on the Coast of the Persian Gulf were determined. Sampling sites represent areas of importance in seaweed harvest and areas near sources of anthropogenic pollution. The mean concentrations of metals in the sediment (across all six collection sites, and collection periods) were: Pb (42.4 ± 2.7), Cd (7.4 ± 1), Ni (38.1 ± 3.7), and Cu (8.3 ± 1.2) μg g(-1) dry weight. High significant positive correlations existed between metals in cervicornis, corticata, and pavonica algae and the sediment, suggesting these species of algae are suitable for biomonitoring of the area.

Biomonitoring of Cd, Cr, Hg and Pb in the Baluarte River basin associated to a mining area (NW Mexico)

With the purpose of knowing seasonal variations of Cd, Cr, Hg and Pb in a river basin with past and present mining activities, elemental concentrations were measured in six fish species and four crustacean species in Baluarte River, from some of the mining sites to the mouth of the river in the Pacific Ocean between May 2005 and March 2006. In fish, highest levels of Cd (0.06 μg g ⁻¹ dry weight) and Cr (0.01 μg g⁻¹) were detected during the dry season in Gobiesox fluviatilis and Agonostomus monticola, respectively; the highest levels of Hg (0.56 μg g⁻¹) were detected during the dry season in Guavina guavina and Mugil curema. In relation to Pb, the highest level (1.65 μg g⁻¹) was detected in A. monticola during the dry season. In crustaceans, highest levels of Cd (0.05 μg g⁻¹) occurred in Macrobrachium occidentale during both seasons; highest concentration of Cr (0.09 μg g⁻¹) was also detected in M. occidentale during the dry season. With respect to Hg, highest level (0.20 μg g⁻¹) was detected during the rainy season in Macrobrachium americanum; for Pb, the highest concentration (2.4 μg g⁻¹) corresponded to Macrobrachium digueti collected in the dry season. Considering average concentrations of trace metals in surficial sediments from all sites, Cd (p<0.025), Cr (p<0.10) and Hg (p<0.15) were significantly higher during the rainy season. Biota sediment accumulation factors above unity were detected mostly in the case of Hg in fish during both seasons. On the basis of the metal levels in fish and crustacean and the provisional tolerable weekly intake of studied elements, people can eat up to 13.99, 0.79 and 2.34 kg of fish in relation to Cd, Hg and Pb, respectively; regarding crustaceans, maximum amounts were 11.33, 2.49 and 2.68 kg of prawns relative to levels of Cd, Hg and Pb, respectively.

Influence of diffuse and chronic metal pollution in water and sediments on edible seafoods within Ondo oil-polluted coastal region, Nigeria

The bioconcentration levels of 3 non-essential elements (Pb, Cd and Ni) have been investigated in three different seafoods; Fish (Tilapia zilli), Crab (Callinectes sapidus) and periwinkle (Littorina littorea), to investigate the ecosystem health status in Ondo oil-polluted coastal region, Nigeria. The seafood samples were chosen based on their popularity as a food source and the potential of the species to contain high levels of metals based on past research results. Metal concentrations in the biota showed marked interspecific differences with C. sapidus recording the highest concentrations of all the metals. The bioconcentration factor (BCF) showed that C. sapidus and T. zilli have the greatest potential to concentrate Cd (BCF = 3-10) and Pb (BCF = 11-84) respectively. Lead uptake from both water and sediment (BCF ≈ BSAF: 0.003-0.018) were abysmally low in L. littorea as compared with other organisms. The high concentrations of Pb in fish species, effective bioaccumulation of Cd in species of crab and periwinkles, as well as very high BSAF of Ni found in species of crab indicated a strong influence from anthropogenic pollutant source on the biotic community. Oil pollution appears to be a major source of bioavailable metal contaminants for the selected biota. The study shows that C. sapidus and L. littorea can effectively compartmentalize potentially toxic metals such as Cd, Pb and Ni within their tissues. In terms of toxicity, C. sapidus had Cd concentrations greater than the 3,000 ng/g limit set by the Commission of the European Communities while Pb concentration exceeded their limits in both C. sapidus and T. zilli. All levels of Ni were below the U.S. Food and Drug Administration action levels for these metals in fish, crustaceans and shellfish. The study revealed anthropogenic enrichment of the metals studied which can possibly pose potential threats to the ecology of the area.

Trace element accumulation in bivalve mussels Anodonta woodiana from Taihu Lake, China

Data are presented for 13 trace metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Mo, Ag, Cd, and Pb) in 38 bivalve mussels Anodonta woodiana from four separate sites (Huzhou, Dapu, Sansandao, and Manshan) around the Taihu Lake of China. All elemental concentrations generally ranked in decreasing order, Mn > Fe > Zn > As ≈ Cu ≈ Cd ≈ Se > Pb > Mo ≈ Ag, except that Cr, Co, and Ni were not detected. Anodonta woodiana was able to bioaccumulate essential Mn and toxic Cd to the extremely high level of 19,240 and 53 mg/kg dry weight, respectively. Geographical differences in the concentrations of trace elements were usually significant between sampling sites except for As and Pb, and the mussels from Sanshandao site had mostly accumulated or were contaminated with essential and toxic elements. The residue level of Cd in A. woodiana from the Sanshandao and Manshan sites appeared to be even higher than those of the essential elements Cu and Se, and exceeded the corresponding maximum residue limits of China. The present study provides the most recent information on trace element bioaccumulation or contamination in Taihu Lake and, further, suggests that A. woodiana can be used as a suitable bioindicator for inland water environmental monitoring.

Measuring bioaccumulation of contaminants from field-collected sediment in freshwater organisms: a critical review of laboratory methods

To be effective, decision-making frameworks require data from robust and reliable test methods. Using standard methods allows for more effective comparison between studies and application of data, and it reduces unnecessary duplication of efforts. Laboratory methods to assess the toxicity of sediment have been standardized and extensively used; however, procedures for measuring the bioaccumulation of contaminants from sediment into aquatic organisms need further standardization. Bioaccumulation methods using freshwater invertebrates and fish exposed to field-contaminated sediment were reviewed to identify important similarities and differences in method protocols, test conditions that need to be controlled, and data gaps. Although guidance documents are available, great variation still exists in exposure techniques used in tests, which may potentially affect the estimation of bioaccumulation. The techniques most consistent across studies include the use of Lumbriculus variegatus as a test species, test temperatures between 20 and 25°C, and a 28-d exposure with no addition of food, followed by purging of organisms. Issues that were inconsistent between studies or remained unspecified, which should be addressed, include the bioaccumulation potential of other test species, loading density of organisms, and sediment-to-water ratio. In addition to proper evaluation of the various exposure techniques and conditions, a need exists for more consistent inclusion of quality control procedures during testing.

Copper, zinc and lead bioaccumulation in marine snail, Strombus gigas, from Guacanayabo Gulf, Cuba

Levels of copper, zinc and lead were determined in sediments and edible muscle of marine snail Strombus gigas collected from Guacanayabo Gulf, Cuba. The concentration range of each metal in marine snail muscle on mg kg(-1) wet weight varied as follows: Cu = 6.4-32.6, Zn = 20.4-31.1 and Pb = 0.2-2.3; and in corresponding sediments (on mg kg(-1) dry weight) as: Cu = 157-186, Zn = 56-94 and Pb = 20-37. The average biota-sediment accumulation factors (BSAFs) obtained for studied metals are less than unity in all cases, indicating that only a little fraction of metal content in the sediments is bioavailable, independently of their possible enrichments in the sediments. The concentrations of copper and lead in some of the marine snails are above typical public health recommended limits.

Heavy metals monitoring in the southernmost mussel farm of the world (Beagle Channel, Argentina)

Water quality surrounding the mussel farm of Mytilus edulis chilensis at Brown Bay (Beagle Channel) was evaluated. The levels of five heavy metals in sediment and in gill and digestive gland of mussels were examined to consider potential risks to human health. Cd showed the highest enrichment factor in relation to its level in Earth crust (3.85-21.58), which could be related to an upwelling phenomenon. A seasonal trend was found regarding metal bioaccumulation, being higher in winter than in summer. The bioaccumulation pattern in gill was Zn>Fe>Cu>Cd, meanwhile in digestive gland was Fe>Zn>Cu>Cd. Despite Pb was measured in sediment (15.59-23.91 microg/g dw), it was not available for being incorporated by mussels. In all cases it was below the detection limit (2.37 microg/g dw). With regard to human consumption of mussels from Brown Bay, none of the elements analyzed should cause concern for consumers. Values measured in tissue mussels were below the limit of 10 microg/g dw for Cd and Pb established by SENASA for molluscs. Considering that studied mussels are for human consumption and the relatively high levels of metals in sediment may vary their availability if physical parameters changes, periodical monitoring must be carried out to avoid human risks and to produce food in a responsible manner that complies with the food safety standards.

Copper, zinc and lead enrichments in sediments from Guacanayabo Gulf, Cuba, and its bioaccumulation in oysters, Crassostrea rhizophorae

Levels of iron, copper, zinc and lead were determined in sediments and soft tissue of the oyster Crassostrea rhizophorae collected from Guacanayabo Gulf, Cuba. Metal-to-Iron ratio in sediments shows an average enrichment for Cu (5,1), Pb (11,7) and Zn (1,3) in the last 20 years. Metal concentrations found in soft tissue of C. rhizophorae are site dependent. The average biota-sediment accumulation factors (BSAFs) obtained for Fe, Cu and Pb are less than unity in all cases, indicating that only a little fraction of Cu and Pb in the sediments is bioavailable, independently of their enrichments. Zinc has an average BSAF value of 2.4 and may represent a serious impact in the area. The concentrations of zinc and copper in some of the oysters are above typical public health recommended limits.

Cd, Cu, Pb and Zn in clams and sediments from an impacted estuary by the oil industry in the southwestern Gulf of Mexico: concentrations and bioaccumulation factors

With the objective of estimating the temporal variation and bioavailability of Cd, Cu, Pb and Zn in Coatzacoalcos estuary, the biota-sediment accumulation factors (BSAF) were calculated. For this purpose, surficial sediments and clams from 14 selected sites were collected during three climatic seasons. In surficial sediments, highest levels of Cd and Cu were measured during the rainy season near to the industrial area of Minatitlan, while highest concentrations of Pb and Zn were registered during the windy season in sediments collected near to the industrial area of Coatzacoalcos. Considering all the sampling seasons and bivalve species, average metal concentrations followed the order Zn > Cu > Cd > Pb. BSAF ranged from 0.01 (Pb) in Corbicula fluminea during the hot season to 25.1 (Cd) in Polymesoda caroliniana during the windy season. BSAF of Cd, Cu and Zn were higher during the windy season; in the case of Pb, the dry season was the time when such figure was more elevated. It can be stated that Polymesoda caroliniana is a net accumulator of Cd and Zn and a weak accumulator of Pb for the studied estuary.

Biomonitoring study of heavy metals in biota and sediments in the South Eastern coast of Mediterranean sea, Egypt

Concentrations of Cd, Cu, Co, Zn, Mn and Fe were determined in biota and sediment samples collected from the Eastern Harbour and El-Mex Bay in the Mediterranean Sea, Egypt. The levels of Cu, Co, Zn, Mn and Fe in the macroalgae, Ulva lactuca, Enteromorpha compressa (green algae) and Jania rubens (red algae), recorded high concentrations except for Cd. Moreover, Fe was the most predominant metal in the seaweed. The two species of bivalves, Donax trunculus and Paphia textile, showed different amounts of metals in their tissue. The abundance of heavy metal concentrations in the mussel samples was found in the order Fe> Zn> Mn> Cu> Co> Cd and Fe> Zn> Mn> Cu> Cd> Co, respectively for the two species. The metals concentrations were generally higher compared with the previous studies in mussels from the same area. The levels of metals accumulated in the investigated fish samples, Saurida undosquamis, Siganus rivulatus, Lithognathus mormyrus and Sphyraena sphyraena, were higher than those of Marmara Sea (Turkey), for Co and Cd and lower for Cu, Zn, Mn and Fe. El-Mex Bay having the highest metals concentration in sediments as their order of abundance were Fe> Zn> Mn> Cu> Cd> Co. Nevertheless, a high variability in the metal levels occurs among the studied algae and biota and also between the investigated Harbour. A significant correlations (p < 0.05) were found for each of Zn and Fe in P. textile and of Co in D. trunculus relative to their concentrations in surficial sediments.

Migratory crustaceans as biomonitors of metal pollution in their nursery areas. The Lesina lagoon (SE Italy) as a case study

The Lesina lagoon is located on the southern Adriatic coast of Italy; many marine species, such as the shrimp M. kerathurus, use the Lesina lagoon as a nursery, spending their initial growth phase there. In order to assess the usefulness of migratory species as biomonitors of the environmental quality of this nursery area, we evaluated the metal content of the M. kerathurus juveniles at the end of their growth phase in the lagoon (October), when they are assumed to have bioaccumulated the maximum level of metals from the lagoon environment. The concentrations of Cr, Cd, Pb, Zn, Mn and Cu were measured in the muscle and exoskeleton of the shrimp, and in the sediments and waters of three areas of the Lesina Lagoon. Both the water and sediment levels of the investigated metals tended to fall within the ranges recorded for other lagoon environments characterized by similar anthropic impact and texturally similar sediment; the juveniles of the shrimp M. kerathurus proved to be strong bioaccumulators of heavy metals such as Zn and Cu (biota-sediment accumulation factors - BSAFs - 6.01 and 25.0 respectively), which derive from agricultural activities; therefore, at the end of their growing phase in the lagoon they can be considered useful biomonitors of metal contamination of agricultural origin in their nursery area.

Trace metals accumulation patterns in a mangrove lagoon ecosystem, Mazatlan Harbor, southeast Gulf of California

Water, surface sediments, the mussel Mytella strigata, the mangrove oyster Crassostrea corteziensis, and the green macroalgae Caulerpa sertularioides from four locations in Mazatlan Harbor on the southeast coast of the Gulf of California, were analyzed to determine concentrations and distribution patterns of cadmium, copper, mercury, lead, and zinc. Total metal concentrations in water in the present study exceed the background levels in open sea and coastal waters. Total metal concentrations in sediments were ordered as follows: Zn > Pb > Cu > Cd > Hg, but for the bioavailable fraction were ordered as Zn > Cu > Pb > Cd > Hg. The concentrations in bioavailable levels fall between the Threshold Effects Level (TEL), and Probable Effects Level (PEL), criteria for sediment quality. Distribution patterns for metals in organisms were ordered Zn > Cu > Pb > Cd > Hg with seasonal variations for Pb and Zn. Correlations between Cd, Cu, Pb and Zn were indicative of similar assimilation and storage mechanisms and common sources of contamination. These correlations also indicated that bioavailability was not simultaneous for Cd and Pb. Bioconcentration factors (BCF) show different patterns in different organisms. For the oyster the metals were ordered Zn >> Cu > Cd approximately Hg > Pb, for the mussel Hg > Cu approximately Zn approximately Cd > Pb and for the macroalgae Zn >> Cu > Pb > Cd > Hg. Based on BCF results in the lagoon system, the oyster C cortezienzes can be used as a biomonitor of Zn and Cu exposure, the mussel M. strigata of Hg exposure and the green macroalgae C. serticularioides of exposure to all five metals studied.

Assessment of the exposure of two fish species to metals pollution in the Ogun river catchments, Ketu, Lagos, Nigeria

The concentrations of metals (Ca, Cd, Fe, Mn, Pb and Zn) were determined by flame atomic absorption spectrophotometry in water, sediments and fish samples in the Ogun river catchments, Ketu, Lagos, which is an important bird nesting, fishing and drinking water source. The results show that the southern tip bothering the Lagos lagoon is where the highest metal concentrations are found in the fish species (Tilapia sp. and Chrysichthys sp.), whereas the Agboyi creek segment near the lagoon with higher surrounding human population density recorded higher levels of metals in sediments and water samples. The two fish species accumulated different amounts of metals. However, the differences were not statistically different at p < 0.05. There is a significant correlation (p < 0.05) for Cd concentration in water. The concentrations of Pb in sampling points 3 and 4 as well as Cd, Mn and Fe in all six sampling points exceeds the World Health Organization (WHO) limits for drinking water. Levels of metals obtained for sediments are within the range reported for Nigeria's river sediments. Based on this study, the human risks for heavy metals in the harvested fish species from the Ogun river catchments, Ketu, are low for now as the concentrations were below the recommended Food and Agriculture Organization (FAO) maximum limits for Pb (0.5 mg/Kg), Cd (0.5 mg/Kg), and Zn (30 mg/Kg) in fish.

Trace metals assessment in water, sediment, mussel and seagrass species--validation of the use of Posidonia oceanica as a metal biomonitor

The accumulation of trace metals (Cd, Co, Cr, Hg, Ni and Pb) was measured in water, sediment, the mussel Mytilus galloprovincialis and the seagrass Posidonia oceanica. Samples were collected in three locations of the north-western Mediterranean (Canari, Livorno and Porto-Torres) which present different levels and sources of human impact. Analyses in the different compartments (water, sediment, M. galloprovincialis and P. oceanica) have allowed to identify Canari as the most Cd, Co, Cr and Ni contaminated site; Livorno as the most Hg contaminated and Porto-Torres as the most Pb contaminated. Furthermore, for the first time, metal concentrations found in P. oceanica have been compared with those found in the water column, in the sediment and in the recognized metal bio-indicator species M. galloprovincialis and the results obtained have led to the same conclusions. Thus, this study allows to validate the use of P. oceanica as metal biomonitor of coastal waters.

A comparative assessment of heavy metal accumulation in soft parts and byssus of mussels from subarctic, temperate, subtropical and tropical marine environments

Existing data on metal concentrations in mussels from subarctic, temperate, subtropical and tropical waters were analyzed using multivariate statistics in order to assess regional variations in metal contamination. Potential errors were reduced by only analyzing data from surveys that employed the same protocols, analytical methodologies and analysts. Factor analysis demonstrated that mussels inhabiting extremely contaminated areas (e.g. from Japanese and Swedish metallurgy sources) could be separated from mussels from other contaminated areas, and that metals such as Cd, Pb, Cu and Zn could be used to identify heavily contaminated samples while Co, Fe, Cr and Ni concentrations were good markers for exposure to inputs from different industrial sources. Furthermore byssus, like soft tissue, selectively and sensitively reflects variations of certain metal concentrations in ambient waters and thus serves as a reliable biomonitor for these contaminants in a variety of coastal and estuarine areas.

Mercury in surface sediments and benthic organisms from Guaymas Bay, east coast of the Gulf of California

In order to know the concentration of mercury in surface sediments, macroalgae and clams from Guaymas Bay, Mexico, 20 surface sediment samples and several individuals of Codium amplivesciculatum (3), Enteromorpha clathrata (4), Gracilaria subsecundata (2), Ulva lactuca (2), Chione subrugosa (80) and Crassostrea gigas (40) were collected and their Hg concentration was measured by a cold vapor Hg analyzer, after acid digestion. In addition, granulometric analysis and quantification of total organic carbon, aluminum, iron and manganese contents in sediments were performed. A Pearsons correlation matrix was determined and, the enrichment factor, the geoaccumulation index and the biota-sediment accumulation factor were calculated. Mercury concentrations in sediments ranged from 0.3 to 2.3 microg g(-1), with the central and northern portions showing the highest values. Macroalgae had a content of Hg that oscillated from 0.058 to 0.134 microg g(-1), while the average concentrations of this metal for clams and oysters were 0.063 and 0.230 microg g(-1), respectively. A clear effect of Guaymas City and the anthropogenic activities carried out around the Guaymas Bay has been observed and the enrichment factor and the geochemical index suggest that sediments from this coastal ecosystem are moderately to strongly contaminated with Hg. However, according to the figure of the maximum human consumption of Hg per week recommended by the World Health Organization, people can ingest clams without risk to their health.

Study on the contamination of heavy metals and their correlations in mollusks collected from coastal sites along the Chinese Bohai Sea

Mollusks living in seas can accumulate heavy metals, and may serve as excellent passive biomonitors. During a period of 1 year, bioaccumulation of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn was examined in nine kinds of mollusks (Rapana venosa, Neverita didyma, Scapharca subcrenata, Mytilus edulis, Amusium, Crassostrea talienwhanensis, Meretix meretrix, Ruditapes philippinarum, and Mactra veneriformis), which were collected at eight coastal sites along the Chinese Bohai Sea. Metal concentrations were directly determined by inductively coupled plasma mass spectrometer (ICP-MS). Two certified reference materials, dogfish muscle (DORM-2) and mussel (GBW 08571), were used to validate the methods, and the recoveries were within 83.72-112.30% of the certified values. Bioaccumulation of metals varied strongly among sampling sites and species. Statistical analysis (one-way ANOVA) indicated that different species examined showed different bioaccumulation of metals, and perhaps they could be used as potential biomonitors to investigate the contamination levels of heavy metals. Principal component analysis (PCA) and correlation analysis were used to study the relationships between these heavy metals. The results showed that, in nine mollusks' tissues, there are significant correlations between these elements in adjacent main group or subgroup in periodic table of elements.

Heavy metal concentrations in molluscs from the Atlantic coast of southern Spain

Trace metals were determined in the two most abundant species of bivalve molluscs along the Atlantic coast of southern Spain (Donax trunculus and Chamelea gallina) and in the sediments where they live. The results show that the area near the mouth of the Huelva estuary is where the highest metal concentrations are found in sediments and in the two bivalve species. This is not surprising, considering that the Huelva estuary is the mouth of the Tinto and Odiel rivers, which have one of the highest levels of metal pollution of all the rivers of Europe. The two species of bivalves have different amounts of metals in their tissues. The concentrations of Cr, Cu, Pb, Zn, As and Hg in D. trunculus were significantly higher (p < 0.05) than in C. gallina; however, C. gallina contained more Ni and Cd. In both species the most abundant elements were Cu and Zn, while Hg showed the lowest values. There is a significant correlation (p < 0.05) for concentrations of Cu, Pb, Zn and Hg in D. trunculus and C. gallina relative to their concentrations in surface sediments.

Correlations between metal uptake in the soft tissue of Perna perna and gill filament pathology after exposure to mercury

The accumulation of metal in soft tissues, filtration rate and gill filament morphology are correlated in the southern African rock mussel, Perna perna, during exposure to mercury (24 days) and recovery (24 days). The amount of Hg in soft tissues increased from 0.13 to 87.5 microg/g dry weight after 24 days exposure, and declined to 13 microg/g during recovery. Mean filtration rate fell from 3,979 to 1,818 ml/h/g dry weight by day 2, but recovered slightly through days 4 and 8 (3,037 ml/h/g), with a higher average rate (5,030 ml/h/g) being maintained over the 24-48 days recovery period. The initial decline in filtration coincided with epithelial cell deterioration presented as interstitial oedema, neural and epithelial cell degeneration and reduced ciliation. Between days 8 and 24, cilia regenerated and there was a general improvement in cell morphology. Gill filament morphology returned to near normal during the metal-free recovery period. The usefulness of P. perna as an indicator of pollution is discussed.

Selected trace metals in oysters (Crassostrea iridescens) and sediments from the discharge zone of the submarine sewage outfall in Mazatlán Bay (southeast Gulf of California): chemical fractions and bioaccumulation factors

Concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn in the soft tissue of Crassostrea iridescens and the associated surface sediments (bulk and bioavailable metal concentrations) from an area influenced by a sewage outfall in Mazatlán Bay (southeast Gulf of California), were determined by atomic absorption spectrophotometry. Significant spatial differences in metal concentrations in both the bulk and bioavailable forms in the sediments were identified. An enrichment of Cu, Ni, Pb and Zn in sites located on a south-north transect was detected indicating a dominant influence of the sewage outfall toward the north. C. iridescens accumulated more Zn, Cu, Ni, Fe, Cd; and less Mn, Cr and Pb than were bioavailable in the sediments, as measured using conventional extraction analysis. The degree of enrichment and the bioavailable metal concentrations in the sediments of the south portion of Mazatlán Bay is discussed. The potential ability of C. iridescens as a biomonitor of metallic pollutants is postulated.

Metals in sediments and the edible cockle Cerastoderma edule from two Moroccan Atlantic lagoons: Moulay Bou Selham and Sidi Moussa

Metals (Cd, Cu, Pb and Zn) were determined over a 3-year period in sediments and bivales Cerastoderma edule from two lagoon ecosystems on the Moroccan Atlantic coastline, Moulay Bou Selham and Sidi Moussa. Sediment metal concentrations were seasonally influenced, and were highest, generally, in winter--possibly signifying an increased contribution from run-off from adjacent arable land and roads. Neither site can be considered highly contaminated; however, Cd was enriched at Sidi Moussa, probably as a result of waste discharge from phosphate industries 20 km along the coast to the northeast. This ability to act as a sink for metals at distance from sources demonstrates the need for surveillance in these sensitive environments. Copper and Zn concentrations in edible cockles C. edule appear to be regulated over the concentration ranges currently found in lagoon sediments. In contrast, body burdens of Pb and, to a lesser extent Cd, reflect sediment levels and might be useful in future risk assessments. Metal concentrations Cerastoderma edule are seasonally related to the reproductive cycle, however, and sample timing will need to be standardised in future monitoring exercises.