Trace Metal Levels in Chironomid Larvae and Sediments from a Bolivian River: Impact of Mining Activities

The effect of mining activity on metal accumulation in sediments and Chironomidae in a river in Bolivia was assessed. Surficial sediments and midge larvae (Chironomidae, Diptera) were collected at five sampling sites. Concentrations of the trace metals Cd, Cu, Cr, Ni, Pb, and Zn were measured in organisms and sediments by inductively coupled plasma atomic emission spectrometry. Sediments were subjected to two different extraction procedures to identify total trace metals and reducible trace metals. Geochemical characteristics of the sediment were analyzed: total organic carbon (TOC), Fe and Mn oxides, and particle size distribution. To determine the relative importance of the different sediment factors contributing to the variation in metal accumulation by the chironomid larvae, nonlinear regression models were constructed. No increase in metal concentration in sediment could be measured downstream of the mining activity. Larval concentrations, however, increased markedly. Only for zinc and chromium was a significant amount of variation (48 and 73%, respectively) found. The lack of relationship for the other metals probably was due to a unmeasured exposure route, the overlying water.     

Extraction of spiked metals from contaminated coastal sediments: a comparison of different methods

Various extraction methods have been developed to assess metal bioavailability from sediments. In this study, we compared the extraction of Cd, Cr, and Zn from contaminated sediments using different extractants (normal seawater, acidic seawater of pH = 5. seawater with 1% sodium dodecyl sulfate [SDS], and gut digestive fluids collected in vitro from deposit-feeding peanut worm Sipunculus nudus) coupled with concurrent metal speciation measurements. The influences of sediment aging on metal extraction were also examined using radiotracer-spiked techniques. Sediments aging up to 100 d did not significantly affect the partitioning of spiked Cd and Cr in different geochemical phases, but the spiked Zn was partitioned more into the reducible fraction and less into the carbonate phase with increasing sediment aging. There was a major difference in the partitioning into different geochemical phases between the spiked metals and the native metals within the 100-d sediment aging. The difference between the spiked and native Cd and Zn extraction using gut juices was somewhat smaller than the strong geochemical contrast. Metals bound with the anoxic sediments were hardly extracted by different extractants. There was a significant relationship between the extraction of spiked Cd and its distribution in the exchangeable phase (positive correlation) or in the reducible phase (negative correlation). For Cr and Zn, extraction was not correlated with their partitioning in any of the geochemical phases. Further, extraction of all three metals by digestive gut fluids was not correlated with the concentrations of simultaneously extractable metals (SEM), nor with the difference between SEM and acid volatile sulfide (AVS). Our study suggests that there were large differences in extraction among metals using different extractants and only Cd extraction was significantly related to its geochemical speciation in sediments.     

Anthropogenic Sources of Heavy Metals in the Indian Ocean Coast of Kenya

Water and surface sediment samples from Rivers Sabaki, Ramisi and Vevesi that flow into the Indian Ocean coast of Kenya were analysed for heavy metals. The sediment concentrations of exchangeable cations (in μg/g) for Co, Cu, Mn, Ni, Pb, Sn and Zn ranged from 0.10 to 506.75 (for Mn at Sabaki), constituting between 2% and 20% of the total metal concentrations obtained by digestion with strong acid. Cu, Mn, Ni, Pb and Zn were more leachable with 0.1 N HCl. The total dissolved metal in water and the total sediment concentrations for Ag, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sn and Zn are given in the text. For dissolved metals, the metal/Mn ratios indicated higher concentrations of Ag in Sabaki River, Cd in Ramisi, Ni in Sabaki and Pb in Ramisi, respectively. In sediments, the metal/Mn ratios showed higher enrichment of Ag in Ramisi, Cd in Sabaki and Vevesi, and Zn in Sabaki, respectively. Enrichment factors showed elevated levels of Cd, Pb and Zn in sediment in River Sabaki and River Vevesi that were due to anthropogenic inputs through Athi River. The total dissolved metal concentration ranges for the three rivers were comparable with those ranges reported in rivers in South Africa but the sediment concentrations were below those of rivers in Europe and Asia where anthropogenic addition of some of the toxic elements such as Cu, Pb and Cd is evidently higher.     

Trace Metals in Sediments and Zostera marina of San Ignacio and Ojo de Liebre Lagoons in the Central Pacific Coast of Baja California, Mexico

San Ignacio and Ojo de Liebre lagoons in central Baja California, Mexico are nursery and grazing grounds for whales and turtles. Ojo de Liebre Lagoon also supports a salt mine operation. By concentrating trace metals via evaporation, this activity might harm biota. Consequently, salt mining might be incompatible with the lagoon’s ecological role. Eelgrass can incorporate these elements and reroute them to other organisms. Trace metals in sediments (Cd, Co, Cu, Mn, Ni, Pb, Zn, and Fe) were measured at both lagoons. Some (Cu, Mn, Pb, and Zn) were also measured in Zostera marina patches at both lagoons. The results did not show elevated metal concentration at any lagoon, either for sediments or eelgrass. No statistically significant differences between lagoons were found. However, eelgrass at both lagoons showed larger concentration ranges than in sediments. Also, a correlation exists between sediment metal concentration and its concentration in eelgrass. Surprisingly, several sediment metal concentrations are higher than those considered as elevated for the Southern California Bight.     

Heavy Metal Concentrations in Marine Fishes Collected from Fish Culture Sites in Hong Kong

The levels of six heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) in different tissues of three species of cultured marine fishes (Epinephelus areolatus, Lutjanus russelli, and Sparus sarba) collected from three fish culture sites in Hong Kong were evaluated. Metal pollution problems in the fish culture sites were serious, as reflected by the high metal concentrations recorded in sea water, sediments, and the biomonitor Perna viridis. In general, tissues of all three species contained high concentrations of Zn and Cu, but much lower concentrations of Ni, Pb, Cd, and Cr. Similar pattern of heavy metal concentrations was observed in sea water, sediment, and P. viridis. Metal concentrations in various tissues varied greatly among species and among fish culture sites. Different tissues showed different capacity for accumulating heavy metals. Gonad of all three species contained high concentrations of Zn. On the other hand, liver seemed to be the primary organ for Cu accumulation. Overall, metal concentrations in the tissues of culture marine fishes were much lower than those in P. viridis. Despite high metal levels in sea water and sediments, concentrations of Cd, Cr, and Pb in edible tissues, including muscle and skin, did not exceed permissible levels recommended by the Hong Kong Government for human consumption. Received: 3 December 1999/Accepted: 13 June 2000     

Distribution and Accumulation of Metals in Tadpoles Inhabiting the Metalliferous Streams of Eastern Chalkidiki, Northeast Greece

The present study investigates the accumulation of heavy metals [copper (Cu), lead (Pb), zinc (Zn), magnesium (Mn), cadmium (Cd), nickel (Ni), and chromium (Cr)] in tadpoles inhabiting the metalliferous streams flowing within the Asprolakkas River basin (northeast Chalkidiki peninsula, Greece) and the effect of potentially harmful elements in stream water and sediment on the corresponding levels in their tissue. Animals were collected from six sampling sites influenced by a wide range of surface water and stream sediment trace element concentrations. The results of the chemical analyses showed that tadpoles accumulated significant levels of all of the examined metals. The range of whole-body mean measured concentrations were (in dry mass) as follows: Cu (46-182?mg/kg), Pb (103-4,490?mg/kg), Zn (494-11,460?mg/kg), Mn (1,620-13,310?mg/kg), Cd (1.2-82?mg/kg), Ni (57-163?mg/kg), and Cr (38-272?mg/kg). The mean concentrations of Pb, Zn, Mn, Ni, Cr, and Cd in Kokkinolakkas stream, which drains a currently active mining area, were the highest ever reported in tadpoles. Our results indicate that whole-body levels of Pb, Zn, Cu, and Cd increase with stream sediment concentrations and that these organisms tend to accumulate metals bound to Fe and Mn oxides. In addition, high dissolved concentrations and significant concentrations associated with more labile geochemical phases of sediments for specific metals were contributing factors determining whole-body levels. Given the observed bioconcentration factors, as well as the correlation with sediment concentrations, it is proposed that these organisms could be considered as bioindicators of environmental contamination and may be used for monitoring purposes within this metal-rich zone and, perhaps, within other rivers affected by metal mining.     

Bioaccumulation of heavy metals in mullet (Mugil cephalus) and oyster (Crassostrea madrasensis) from Pulicat lake, south east coast of India

The accumulation of six heavy metals (Cr, Cd, Cu, Zn, Pb and Ni) in sediment, water and in tissue parts of Mugil cephalus and Crassostrea madrasensis was studied in two locations of Pulicat lake, Southeast coast of India, which receives considerable quantity of effluents from industries located in North Chennai coastal region. The results reveal that the metal concentration in water is decreasing in the following order of Zn > Ni > Cu > Cr > Pb > Cd both in lake and barmouth and highest concentration was observed for Zn (32.5 μg L(-1) in lake and 25.2 μg L(-1) in bar mouth). Metals were highly concentrated in sediments when compared to water and biota. Metals abundance in sediments has following sequential order of Cr > Ni > Zn > Cu > Pb > Cd and the accumulation pattern in barmouth showed minor variation indicating the following pattern of Zn > Ni > Cr > Cu > Pb > Cd. The geoaccumulation index (I(geo)) for Pulicat lake sediments indicate that the sediments are extremely contaminated with Cd and moderately contaminated with Cu and Ni. Bioaccumulation of heavy metals in Mugil cephalus and Crassostrea madrasensis showed marked differences in the accumulation patterns. It is observed that Zn, Cu and Pb are accumulated in elevated concentrations in various parts of the fish and oyster when compared with other metals.     

Influences of aging on the bioavailability of sediment-bound Cd and Zn to deposit-feeding sipunculans and soldier crabs

The radiotracer technique was used to assess the influences of sediment-metal contact time or aging (up to two years) on the bioavailability and geochemical speciation of Cd and Zn in sediments. Bioavailability was quantified by measuring the assimilation efficiency of metals in two deposit-feeding invertebrates (sipunculans and soldier crabs) and the extraction by the sipunculans' gut juices. Sediment aging generally did not significantly affect the Cd speciation in the sediments, Cd assimilation, and Cd extraction. In contrast, sediment aging significantly affected the Zn distribution in different geochemical phases and the Zn bioavailability. With increasing aging, the Zn distributed in the carbonate phase decreased, whereas that in the reducible phase increased. Accordingly, the Zn gut-juice extraction decreased significantly. Two years of aging were not sufficient for Zn to be associated with the organic and residual phases. A significant positive correlation was found between Cd gut-juice extraction and assimilation efficiency. Gut-juice extraction of Cd and Zn generally increased with metal distribution in the exchangeable and carbonate phases but decreased with that in the reducible phase. Our results suggest that different metals are influenced by sediment aging differently and that geochemical speciation analysis is useful in studying the bioavailability of sediment-bound metals. This study may have implications for designing sediment toxicity tests using spiking techniques and for understanding the fates of anthropogenically derived metals in sediments.     

Trace Metal Concentrations in Sediments and Oysters of Botany Bay,NSW, Australia

Surfical sediment (< 63 µm) trace metal concentrations (Zn, Cu, Pd, Cd, As) were analyzed from seven sites in Botany Bay, NSW, Australia, to assess the extent of contamination from the surrounding urban areas. The northwest shoreline of Botany Bay contained high surfical sediment trace metal concentrations relative to the southern shoreline. Surfical sediment Pb concentrations (10–120 µg/g) were above the current ANZECC/ARMCANZ interim sediment guideline value (50 µg/g) for the protection of benthic ecosystems at the northwest sites. Cooks River was identified as a major source of trace metals. Oysters grown in Botany Bay have greater Zn, Cu, and Cd concentrations than two relatively pristine reference locations, Jervis Bay and Batemans Bay, indicating that the Botany Bay region has elevated biologically available metal concentrations. Oyster tissue trace metal concentrations were below the Australian and New Zealand Food Authority standards. Translocation of oysters to sites around the bay identified Pb and Cd as the only trace metals to be accumulated over 3 months. Copper concentrations in transplanted oysters declined at most sites, indicating that the sites investigated in this study have less bioavailable copper than Woolooware Bay, the source of the oysters. The shallow waters along the southern shoreline are protected from the tidal flow that carry contaminated sediments and the biologically available trace metals appear to be low.Received: 31 May 2002/Accepted: 13 December 2002     

Monitoring of Trace Metal Contamination in the Souss Estuary (South Morocco) Using the Clams <Emphasis Type="Italic">Cerastoderma edule</Emphasis> and <Emphasis Type="Italic">Scrobicularia plana</Emphasis>

Concentrations of seven metals (Cd, Cu, Cr, Pb, Ni, Zn, Hg) were monitored monthly during 2 years in two bivalves, Cerastoderma edule and Scrobicularia plana collected from the Souss estuary (South Morocco) before and after the commissioning of a sewage treatment plant in November 2002. According to trace metals, changes in concentrations were observed mainly in S. plana, characterised by a decrease of Cu, Hg and Pb when Cd was clearly increasing. Conversely, no clear changes were observed in C. edule during the same periods. This study suggests the use of S. plana in the monitoring of trace metal contamination of such coastal marine environments.     

Heavy Metals in Sediments and Lobster (<Emphasis Type="Italic">Panulirus gracilis</Emphasis>) from the Discharge Area of the Submarine Sewage Outfall in Mazatlán Bay (SE Gulf of California)

Concentrations of selected heavy metals in lobster (Panulirus gracilis) tissues and sediments (bulk and bioavailable fractions) from an area influenced by sewage discharge in Mazatlán Bay were determined. Cd, Cu, Fe, Pb, and Zn in the sediments showed enrichment factors higher than one related to the discharge and were higher than the lower values of the sediment quality guidelines proposed by NOAA and CCME. In addition to the high levels, relatively high bioavailability in the sediments was estimated for Cd, Cu, Mn, Pb, and Zn, suggesting a possible adverse effect on the associated benthic organisms. A high concentration of Cr, Fe, Mn, and Ni was found in the exoskeleton of P. gracilis. The hemolymph, hepatopancreas, gills, and gonads concentrate Cu, Cd, and Zn to levels higher than the available concentration in the sediments (BCF > 1). However, most of the metals studied in the edible muscle tissue in P. gracilis ranged within the recommended limits for human consumption, except Pb, which was found to be above the acceptable level for shellfish and represents a health risk.     

Bioavailability of metals to the amphipod Monoporeia affinis: interactions with authigenic sulfides in urban brackish-water and freshwater sediments

Could reduced eutrophication be a potential environmental threat because of increased mobility and bioavailability of trace metals? This question was addressed by oxygenating intact sediment cores, varying in redox potential and salinity, in a test system containing the amphipod Monoporeia affinis. Results show a low mobility of metals during oxygenation, and despite high concentrations of metals in sediments, only Pb showed a notable degree of bioaccumulation. Cadmium was bioaccumulated particularly in freshwater sediment, and body burden of Cd was related to salinity, porewater, and sediment concentrations. Despite high sediment and porewater concentrations of Cu and Zn, no relationship was recorded to body burden. For three of four tested metals, Cd, Pb, and Zn, metals in sediment were more important for body burdens in amphipods as compared to metals in porewater. Food, rather than interstitial water, therefore seems to be the main route of metal contaminants to these amphipods. Furthermore, this observed low release of metals from sediments and low body burden significance of porewater metals indicate that ameliorated oxygen conditions in contaminated sediments may be regarded as a minor environmental threat for one of the most important Baltic benthic organisms.     

Chemical extractions of heavy metals in sediments as related to metal uptake by grass shrimp (Palaemonetes pugio) and clam (Mercenaria mercenaria)

Sediments from four sites in the Hampton Roads Harbor and Elizabeth River system were subjected to solid phase bioassays usingPalaemonetes pugio andMercenaria mercenaria. Metal levels in both organisms after exposure to the sediments varied little between sites; there was no difference in metal uptake between organisms exposed to the test sediments and to the reference sediment. All of the test sites would be acceptable for ocean disposal with respect to the tested metals. Metals concentrations inPalaemonetes were generally greater thanMercenaria. The amounts of metals extracted from the sediments were in the order of Conc HNO₃+H₂O₂>1N HNO₃>DTPA. Differences in metal levels in the Conc HNO₃+H₂O₂ and DTPA extracts from different sediments were generally significant and related to sediment type and sampling location. Since there was no significant difference in the concentrations in tissue for either organism, there was no correlation of metal uptake with the sediment extraction method. Out of four sites and metals studied with two test organisms, there were only four instances of bioaccumulation. Data from sediment extractable metals and metal/Fe ratios indicatedPalaemonetes were enriched with respect to the sediment in Cr, Cu, Ni, Pb, and Zn;Mercenaria were enriched with Pb and Zn.     

Spatial and Temporal Variations of Heavy Metals in Surface Sediments in Bohai Bay, North China

Characteristics of the spatial and temporal distributions of selected heavy metals (Cu, Zn, Cd, Pb and Hg) in Bohai Bay, north China was examined. Surface sediment samples from 15 sites were collected and analyzed for the selected metals with atomic absorption spectrometry (AAS) from the year of 1997–2007. Mean concentrations of metals in the 11-year period showed that Hg and Zn concentrations slightly fluctuated, while Cu, Cd and Pb concentrations in sediments varied with time. High levels of heavy metals occurred not only along the shoreline but also at some site in the inner part of the bay, suggesting the contamination sources of heavy metals from both terrestrial inputs and the atmospheric deposition. Compared with the environmental background values of selected heavy metals it indicated that anthropogenic activities influenced the sediment quality. The contamination factor \textCⁱ_f {\text{C}}^{i}_{f} , which is used to evaluate the pollution of the environment, showed that the contamination by selected heavy metals was moderate. Cd, Zn and Pb were the main polluting elements in this area.     

Tidal Creek and Salt Marsh Sediments in South Carolina Coastal Estuaries: I. Distribution of Trace Metals

Twenty-eight tidal creeks were sampled along the South Carolina coast in the summer of 1995 to determine the levels of sediment trace metal contamination associated with different types and varying levels of human development in their watersheds. The particle size and total organic carbon (TOC) content of creek sediments in developed watersheds (i.e., industrial, urban, and suburban) were similar to that in watersheds with little or no development (i.e., forested or reference). Those trace metals commonly associated with urban and industrial sources, including Cu, Cr, Pb, Zn, Cd, and Hg, were in significantly higher concentrations in tidal creeks located in industrial/urban watersheds compared to the suburban and forested watersheds. Sediment trace metal concentrations were similar for creeks located in suburban and forested watersheds and 2 to 10 times lower than the creeks located in industrial/urban watersheds. Concentrations of trace metals primarily associated with the natural weathering of basement rock, including Al, Fe, As, Ni, and Mn, were not significantly different among watershed types. Four of the tidal creek–salt marsh systems were extensively sampled from the creek channel to the marsh-upland interface to characterize sediment trace metal spatial distributions within creek-marsh systems. Sediment particle size, TOC, and trace metal concentrations varied spatially within each creek-marsh system depending on the type of development in the watershed and the probable source of metals. The creek-marsh system selected to represent the industrial development had significantly higher “anthropogenic” trace metal concentrations compared to the other creek-marsh systems. This system also had trace metal distributional patterns that appeared to be associated with several localized sources of metals on the marsh surface. Both the “anthropogenic” and “natural” trace metal concentrations andspatial distributions were similar among and within the forested and suburban creek-marsh systems. Received: 8 December 1998/Accepted: 1 April 1999     

Heavy metals in sediment and their accumulation in commonly consumed fish species in Bangladesh

Six heavy metals (chromium [Cr], nickel [Ni], copper [Cu], arsenic [As], cadmium [Cd], and lead [Pb]) were measured in sediments and soft tissues of eleven commonly consumed fish species collected from an urban river in the northern part of Bangladesh. The abundance of heavy metals in sediments varied in the decreasing order of Cr > Ni > Cu > Pb > As > Cd. The ranges of mean metal concentrations in fish species, in mg/kg wet weight (ww), were as follows: Cr, 0.11–0.46; Ni, 0.77–2.6; Cu, 0.57–2.1; As, 0.43–1.7; Cd, 0.020–0.23; and Pb, 0.15–1.1. Target hazard quotients (THQs) and target carcinogenic risk (TR) showed the intake of As and Pb through fish consumption were higher than the recommended values, indicating the consumption of these fish species is associated with noncarcinogenic and carcinogenic health risks.     

Heavy Metal Levels in Suspended Sediments, Crassostrea gigas, and the Risk to Humans

Wild Pacific oyster (Crassostrea gigas) and sediment, both resuspended and suspended (RSS) samples (<53 μm), were collected over an 8-month period from a coastal estuary in Baynes Sound, BC, Canada. Stable isotope analysis (δ¹³C, δ¹⁵N) was used to determine, first, if RSS sediments was an important dietary source to C. gigas and, second, if so, whether it served as a significant dietary exposure route for Cd, Cu, Pb, and Zn. Although RSS sediments were high in trace metals such as Cd, Pb, Zn, and notably Cu, stable isotope signatures for oyster tissues did not correspond to those of RSS sediments. These results indicate that RSS sediments are not a significant source of metal to the oysters. In addition, we compared the potential risk to humans ingesting C. gigas with levels of Cd, Cu, Pb, and Zn from this study to the current Agency for Toxic Substances and Disease Registry (ATSDR) chronic oral minimal risk levels (MRLs) using current Canadian consumption guidelines of three oysters/week. Cu, Pb, and Zn levels were below MRL levels, with Cd exceeding the recommended 0.2 μg/kg/day MRL level fourfold. Total daily intake levels (TDI) for Cd were additionally calculated and either reached or exceeded the Food and Agriculture Organization/World Health Organization (FAP/WHO) reference dose of 1 μg/kg/day for Cd consumption in Canadians. Our results indicate that the current Canadian Cd consumption guidelines do not protect individuals consuming the maximum recommended levels of wild oysters.     

Bioaccumulation and Distribution of Metals in Sediments and Avicenna marina Tissues in the Hara Biosphere Reserve, Iran

The metal pollution in Sediments and Avicenna marina tissues in the Hara Biosphere Reserve was monitored for Lead (Pb), Cadmium (Cd), and Nickel (Ni) with atomic absorption spectrometer. The results showed that the mean concentration of Pb, Cd, and Ni in the water and sediments were much higher than the recommended threshold limits in the most stations, also the highest means of Pb, Cd, and Ni were observed in Avicenna roots and it were 25.26?±?4.86, 2.17?±?0.74, and 26.72?±?6.17 (μg?g(-1)) respectively. Calculating BCF (bioconcentration factor) index illustrates that A. marina accumulates Pb, Cd, and Ni 1.62, 1.52 and 0.73 times greater than sediment levels respectively, So it can show that A. marina may be employed as a biological indicator exposure of Cd, Pb, and Ni with temporal monitoring, also the factories were main sources of metals contamination in the Hara Biosphere Reserve.     

Metal Pollution in Huayuan River in Hunan Province in China by Manganese Sulphate Waste Residue

The Huayuan River in Hunan Province in China is subject to ongoing mining activity with Mn extraction. In this study, the level and environmental significance of metals (including Mn, Cd, Pb, Cu, Zn, Ni and Fe) concentrations in the surface water and river sediments have been investigated along a 187 km reach of the Huayuan River. Using the X-ray fluorescence (XRF) analysis, we analyzed the characterization of metals in manganese sulphate waste residue (MSWR) deposited along the bank of Huayuan River. The speciation of metals in both sediment and MSWR was established using the BCR-three step sequential extraction procedure. In the water samples, the average concentrations of Mn, Cd and Pb exceeded the acceptable concentrations for drinking water in the WHO Guidelines for drinking water quality, Vol. 1, Recommendations, Geneva (2004) and Chinese (GB 5749-2006) guidelines, respectively. The average concentrations of Mn, Cd, Pb and Zn in the river sediments were found to be considerably higher than the corresponding world average shale values. The percentages of Cd (31.4%), Mn (31.1%), Zn (12.8%) and Pb (8.1%) associated with exchangeable and weak acid fraction in the sediments were higher than other metals. Mn (5.81%), Zn (0.208%), Pb (0.0292%) and Cd (0.0113%) were identified in MSWR by XRF analysis. The percentages of Mn, Cd, Zn and Pb associated with the exchangeable and weak acid soluble fraction in MSWR were 41.9%, 31.1%, 23.8% and 9.8%, respectively. The peak solute and sediment-bound metal concentrations were found at the sites of MSWR deposited along the bank of Huayuan River. The results suggested that MSWR deposited along the bank may have a closely relation with the metal pollution of Huayuan River. The results obtained may be useful to assess both short and long-term environmental impact of the MSWR deposited activities and support decisions for a future remediation of this river.     

Sediment geochemical controls on CD, CR, and ZN assmilation by the clam Ruditapes philippinarum

Several important sediment geochemical factors (particle size, contact time, artificial sediment composition, acid volatile sulfide, and pure inorganic particles coated or uncoated with humic acid) were examined for their influences on the assimilation of Cd, Cr, and Zn in the marine clam Ruditapes philippinarum. Metal desorption and phase speciation were concurrently measured for these particles. Differences in particle size did not significantly affect metal assimilation. Increasing contact time with sediments decreased assimilation by the clams of Cr and Zn, but not of Cd. A significant positive relationship was found between the metal assimilation efficiency (AE) and the metal partitioning in the exchangeable fraction of sediments for Cd and Zn. The assimilation of metals was negatively dependent on the metal distribution in the reducible (Fe oxide) fraction, indicating that Fe oxide reduced metal bioavailability to the clams. Metal AEs measured with artificially prepared sediments were comparable to those measured with natural sediments. The AEs were significantly higher in artificial sediment without Fe oxide. Humic acid coating appeared to have no major and consistent influence on metal assimilation by the clams. The AEs measured for pure inorganic particles were much higher than those measured for sediments or artificially prepared sediments, except for the Fe oxide particles, indicating that digestion may behave differently for pure particles. Metals bound to artificially synthesized acid volatile sulfide were much less bioavailable to the clams. The AEs were as low as 4% for Cd and 7% for Zn, whereas the AE for Cr was somewhat similar to those measured for other types of particles. When all particle types (natural sediments, artificial sediment, and pure particles) were considered, a significant relationship was found between Cd AE and its desorption in seawater. This study has demonstrated that several geochemical fractions of the sediments, particularly the exchangeable, Fe oxide, and sulfide fractions, are important in determining metal bioavailability from sediments to clams.