Caihuan Ke

Bioaccumulation of Cd, Se, and Zn in an estuarine oyster (Crassostrea rivularis) and a coastal oyster (Saccostrea glomerata)

We compared the bioaccumulation of Cd, Se, and Zn in an estuarine oyster (Crassostrea rivularis) and a coastal oyster (Saccostrea glomerata) from both the dissolved and particulate phases. A bioenergetic-based kinetic model was used to predict the exposure pathways of metals in the oysters. The assimilation efficiencies (AEs) of metals, determined for four species of phytoplankton and natural sediment, were in the range of 30-75% for Cd, 25-75% for Se, and 30-80% for Zn, respectively, in the two oysters. There was little difference in metal AE between the two oysters and among the three metals on the same particle type. Metal uptake rate constant, determined from the log-log relationship between metal influx rate and metal concentration in the dissolved phase, was higher for Cd and Zn in the estuarine oyster C. rivularis than in the coastal oyster S. glomerata. The uptake rate constants quantified for Cd, Se, and Zn were the highest among different bivalve species studied so far. The calculated metal absorption efficiency from the dissolved phase was similar to those found in other bivalve species. The measured efflux rate constant in the estuarine oyster C. rivularis was in the range of 0.01-0.03 day(-1) for Cd, Se, and Zn, and were comparable to those found in mussels and clams. In contrast, the efflux rate constant of Cd and Zn in the coastal oyster S. glomerata was 0.003-0.004 day(-1), which may be responsible for the high Cd and Zn concentrations in the oysters. The bioenergetic-based kinetic model predicts that under most circumstances likely experienced by oysters in nature, the majority of Se and Zn in the two oysters stem from uptake from the dietary phase. Dissolved uptake contributes significantly to metal accumulation only when the metal concentration factor (CF) in the particles is in the lower portion of the range typically found in nature. Sensitivity analysis indicates that the metal CF is a critical parameter in determining the exposure pathways of metals in the oysters. Our study demonstrated that estuarine and coastal oysters differed in their strategies in accumulating a high metal concentration in their tissues.

Copper and zinc contamination in oysters: Subcellular distribution and detoxification

Metal pollution levels in estuarine and coastal environments have been widely reported, but few documented reports exist of severe contamination in specific environments. Here, we report on a metal-contaminated estuary in Fujian Province, China, in which blue oysters (Crassostrea hongkongensis) and green oysters (Crassostrea angulata) were discovered to be contaminated with Cu and other metals. Extraordinarily high metal concentrations were found in the oysters collected from the estuary. Comparison with historical data suggests that the estuary has recently been contaminated with Cr, Cu, Ni, and Zn. Metal concentrations in blue oysters were as high as 1.4 and 2.4% of whole-body tissue dry wt for Cu and Zn, respectively. Cellular debris was the main subcellular fraction binding the metals, but metal-rich granules were important for Cr, Ni, and Pb. With increasing Cu accumulation, its partitioning into the cytosolic proteins decreased. In contrast, metallothionein-like proteins increased their importance in binding with Zn as tissue concentrations of Zn increased. In the most severely contaminated oysters, only a negligible fraction of their Cu and Zn was bound with the metal-sensitive fraction, which may explain the survival of oysters in such contaminated environments.

Trace elements in two marine fish cultured in fish cages in Fujian province, China

Two cultured marine fish, the Japanese seabass (Lateolabrax japonicus) and red seabream (Pagrus major) were collected from eight fish cage sites along the coast of Fujian province in China. The concentrations of Ag, As, Cd, Co, Cu, Fe, Mn, Se, and Zn in their muscle, stomach and liver tissue were quantified. The risk of these trace elements to humans through fish consumption was then assessed. The highest concentrations of As, Cd, Se and Zn in fish feed from fish cages were found in Dongshan Station. Moreover, the As levels in the muscles of both species at all sites were generally higher than Chinas national standard (>1.0 microg/g). Trace element concentrations in two marine fish followed the order of livers > stomachs > muscles. Although the As levels in two marine caged fish exceeded the permissible standards, the estimated daily intake of As did not exceed the reference dose guideline established by US EPA. For other trace elements examined in this study, their concentrations did not exceed the permissible concentrations of the international standards.

Effects of cooking and subcellular distribution on the bioaccessibility of trace elements in two marine fish species.

In current human health risk assessment, the maximum acceptable concentrations of contaminants in food are mostly based on the total concentrations. However, the total concentration of contaminants may not always reflect the available amount. Bioaccessibility determination is thus required to improve the risk assessment of contaminants. This study used an in vitro digestion model to assess the bioaccessibility of several trace elements (As, Cd, Cu, Fe, Se, and Zn) in the muscles of two farmed marine fish species (seabass Lateolabrax japonicus and red seabream Pagrosomus major ) of different body sizes. The total concentrations and subcellular distributions of these trace elements in fish muscles were also determined. Bioaccessibility of these trace elements was generally high (>45%), and the lowest bioaccessibility was observed for Fe. Cooking processes, including boiling, steaming, frying, and grilling, generally decreased the bioaccessibility of these trace elements, especially for Cu and Zn. The influences of frying and grilling were greater than those of boiling and steaming. The relationship of bioaccessibility and total concentration varied with the elements. A positive correlation was found for As and Cu and a negative correlation for Fe, whereas no correlation was found for Cd, Se, and Zn. A significant positive relationship was demonstrated between the bioaccessibility and the elemental partitioning in the heat stable protein fraction and in the trophically available fraction, and a negative correlation was observed between the bioaccessibility and the elemental partitioning in metal-rich granule fraction. Subcellular distribution may thus affect the bioaccessibility of metals and should be considered in the risk assessment for seafood safety.

Dominance of dietary intake of cadmium and zinc by two marine predatory gastropods.

Marine gastropods are known to accumulate high metal concentrations in their tissues, especially in the digestive glands. Although bindings with metallothioneins and granules are proposed to be responsible for the accumulation of high metal concentration, routes and rates of metal accumulation in these animals are not known. In this study, we determined the biokinetics of Cd and Zn in two predatory marine gastropods (Babylonia formasae habei and Nassarius teretiusculus), including metal assimilation efficiency (AE) from ingested clam tissues, metal uptake rate from the dissolved phase, and metal efflux rate constant. The metal AEs were 87-99% for Cd and 50-79% for Zn in B. formasae habei, and were 84-94% for Cd and 79-81% for Zn in N. teretiusculus, respectively, feeding on clams radiolabeled from both the aqueous and dietary phases. The uptake rate constants from the dissolved phase were 0.0562 l g(-1) per day for Cd and 0.122 l g(-1) per day for Zn in N. teretiusculus, and 0.0292 l g(-1) per day for Cd and 0.0573 l g(-1) per day for Zn in B. formasae habei, respectively. The efflux rate constants were 0.0011 per day for Cd and 0.0138 per day for Zn in N. teretiusculus, and 0.0055 per day for Cd and 0.0057 per day for Zn in B. formasae habei, respectively. Using a simple kinetic model, we showed that the trophic transfer factor, defined as the ratio of metal concentration in predatory gastropods and metal concentration in prey organisms (bivalves), was greater than one under most circumstances, suggesting that Cd and Zn may be biomagnified during their trophic transfer from bivalves to gastropods. Furthermore, our model predicted that the dietary exposure dominated (>90%) the overall Cd and Zn accumulation in the two predatory gastropods. Our study also highlights the interspecies difference in metal biokinetics in marine gastropods.

Rapid Assessments of Metal Bioavailability in Marine Sediments Using Coelomic Fluid of Sipunculan Worms

A suitable test organism for assessing the bioavailability of sediment-bound metals should accumulate metals mainly from the sediment instead of other sources such as water. The deposit-feeding sipunculan worms, which indiscriminately ingest sediment particles and have a very low uptake rate of dissolved metals, appear to be such good candidates. The worms have additional advantage due to simple anatomy and are like little sacs full of liquid, that is, coelomic fluid, which can be easily collected for metal analysis after simple sample treatment. We measured the metal concentrations in a sipunculan worm, Phascolosoma arcuatum and in sediments collected from intertidal zones of Xiamen City, China. Significant correlations were found for the concentrations of chromium, nickel, copper, zinc, cadmium, and lead in sediments and their concentrations in both somatic tissue and coelomic fluid of the worms. Analyzing the metals in coelomic fluid led to similar results as the somatic-tissue metals for assessing the bioavailability of sediment-bound metals and the spatial pattern of sediment-bound metal contamination. Therefore, measuring coelomic-fluid metal concentrations can be used to provide a rapid assessment of metal bioavailability in marine sediments.

Mercury and stable isotope signatures in caged marine fish and fish feeds

Total mercury (THg) and methylmercury (MeHg) concentrations were determined in four species of marine caged carnivorous fish, one species of herbivorous fish and three types of fish feeds (dried pellet feed, forage fish and fish viscera), collected from five cage sites in the rural areas along Fujian coastline, China. For the carnivorous fish, the concentrations of THg and MeHg ranged from 0.03 to 0.31 μg/g and from 0.02 to 0.30 μg/g on wet weight basis, respectively. The concentrations were lower for the herbivorous fish with both within the range of 0.01-0.03 μg/g. Out of the three tested fish feeds, tuna viscera contained the highest level of mercury (0.20 μg/g THg and 0.13 μg/g MeHg), with pellet feed containing the lowest level (0.05 μg/g THg and 0.01 μg/g MeHg). The calculated trophic transfer factor of MeHg was the highest (12-64) for fish fed on pellet feeds, and was the lowest for fish fed on tuna viscera. A significant relationship was found between Hg concentrations in caged fish and in fish feeds, thus Hg was primarily accumulated from the diet. Furthermore, the stable isotope δ(15)N was positively correlated with the Hg concentration in two caged sites, indicating that δ(15)N may be a suitable tool for tracking mercury in caged fish. We conclude that fish farming may be a good way of reducing the human exposure to Hg because mercury levels can be carefully controlled in such farming systems.

Oyster-based national mapping of trace metals pollution in the Chinese coastal waters

To investigate the distribution and variability of trace metal pollution in the Chinese coastal waters, over 1000 adult oyster individuals were collected from 31 sites along the entire coastline, spanning from temperate to tropical regions (Bohai Sea, Yellow Sea, East China Sea and South China Sea), between August and September 2015. Concentrations of macroelements [sodium (Na), potassium (K), calcium (Ca), magnesium (Mg) and phosphorus (P)] and trace elements [cadmium (Cd), copper (Cu), zinc (Zn), nickel (Ni), lead (Pb), chromium (Cr), silver (Ag), and titanium (Ti)] in these oysters were concurrently measured and analyzed. The results showed high Ti, Zn and Cu bioaccumulation in oysters from Guangdong (South China Sea) and Zhejiang (East China Sea). Oysters at Nanji Island (Wenzhou) and Daya Bay (Huizhou) accumulated significantly high concentrations of Ni and Cr. The elements in these oysters were several times higher than the national food safety limits of China. On the other hand, the present study found that normalization of metals by salinity (Na) and nutrient (P) could reflect more details of metal pollution in the oysters. Biomonitoring of metal pollution could benefit from incorporating the macroelement calibration instead of focusing only on the total metal concentrations. Overall, simultaneous measurement of macroelements and trace metals coupled with non-linear analysis provide a new perspective for revealing the underlying mechanism of trace metal bioavailability and bioaccumulation in marine organisms.

Responses of abalone Haliotis diversicolor to sublethal exposure of waterborne and dietary silver and cadmium

In this study, we examined the chronic waterborne and dietary exposure of silver (Ag) and cadmium (Cd) to the abalone Haliotis diversicolor using various endpoints such as growth and feeding rates, metal body burden, subcellular distribution, and metallothionein (MT) concentration over a period of 7 weeks of exposure. The growth and feeding rates of abalones were inhibited during the early stage of exposure to different extents, but then recovered to nearly the control levels. A large portion of Ag was redistributed to organelles and metal-rich granules from the cellular debris fraction, whereas cellular debris and metallothionein-like protein were the dominant pools for the storage of Cd, which remained comparable during the exposure period. The MT concentrations were significantly elevated (in a dose-dependent manner) within the first 2 weeks of exposure, after which the MT concentrations started to decrease. All these results implied that abalones respond rapidly to metal exposure, but apparently developed subsequent acclimation.

Toxicological responses of the hard clam Meretrix meretrix exposed to excess dissolved iron or challenged by Vibrio parahaemolyticus

The responses of genes encoding defense components such as ferritin, the lipopolysaccharide-induced tumor necrosis factor-alpha factor (LITAF), the inhibitor of nuclear factor-κB (IκB), metallothionein, and glutathione peroxidase were assessed at the transcriptional level in order to investigate the toxicological and immune mechanism of the hard clam Meretrix meretrix (HCMM) following challenge with iron or a bacterium (Vibrio parahaemolyticus). Fe dissolved in natural seawater led to an increase of Fe content in both the hepatopancreas and gill tissue of HCMM between 4 and 15 days of exposure. The ferritin gene responded both transcriptionally as indicated by real-time quantitative PCR and translationally as shown by western blotting results to iron exposure and both transcriptional and translational ferritin expression in the hepatopancreas had a positive correlation with the concentration of dissolved iron in seawater. Both iron and V. parahaemolyticus exposure triggered immune responses with similar trends in clam tissues. There was a significant post-challenge mRNA expression of LITAF and IκB at 3h, ferritin at 24h, and metallothionein and glutathione peroxidase at 48h. This behavior might be linked to their specific functions in physiological processes. These results suggested that similar signaling pathways were triggered during both iron and V. parahaemolyticus challenges. Here, we indicated that the ferritin of Meretrix meretrix was an intermediate in the pathway of iron homeostasis and in its innate immune defense mechanism.