Influence of prey type on nickel and thallium assimilation, subcellular distribution and effects in juvenile fathead minnows (Pimephales promelas)

Variation in the burden and chemical forms of thallium in non-detoxified tissues of tilapia fish (Oreochromis niloticus) from waterborne exposure

Thallium (Tl) is highly toxic to aquatic ecosystems, but information about its concentration and distribution characteristics in different fish tissues is limited. In this study, juvenile tilapia (Oreochromis niloticus) were exposed to Tl solutions with different sub-lethal concentrations for 28 days, and the Tl concentrations and distribution patterns in the fish non-detoxified tissues (gills, muscle, and bone) were analyzed. The Tl chemical form fractions, Tl-ethanol, Tl-HCl, and Tl-residual, corresponding to easy, moderate, and difficult migration fraction, respectively, in the fish tissues were obtained by sequential extractant approach. The Tl concentrations of different fractions and total burden were determined using graphite furnace atomic absorption spectrophotometry. Exposure-concentration effect determined the Tl burden in the fish tissues. The average Tl-total concentration factors were 360, 447, and 593 in the bone, gills, and muscle, respectively, and the limited variation during the exposure period indicates that tilapia have a strong ability to self-regulate and achieve Tl homeostasis. However, Tl fractions varied in tissues, and the Tl-HCl fraction dominated in the gills (60.1%) and bone (59.0%), switchover Tl-ethanol fraction dominated in the muscle (68.3%). This study has shown that Tl can be easily taken up by fish during 28-days-period and largely distributed in non-detoxified tissues especially muscle, in which concurrent risks of high Tl-total burden and high levels of Tl in the form of easy migration fraction, posing possible risks to public health.

Role of prey subcellular distribution on the bioaccumulation of yttrium (Y) in the rainbow trout

Our knowledge of the processes leading to the bioaccumulation of rare earth elements (REE) in aquatic biota is limited. As the contamination of freshwater ecosystems by anthropogenic REE have recently been reported, it becomes increasingly urgent to understand how these metals are transferred to freshwater organisms in order to develop appropriate guidelines. We exposed rainbow trout (Oncorhynchus mykiss) to an REE, yttrium (Y), to either a range of Y-contaminated prey (Daphnia magna) or a range of Y-contaminated water. For the feeding experiment, the relationship between the Y assimilation by O. mykiss and the Y subcellular fractionation in D. magna was evaluated. Assimilation efficiency of Y by O. mykiss was low, ranging from 0.8 to 3%. These values were close to the proportion of Y accumulated in D. magna cytosol, 0.6-2%, a theoretical trophically available fraction. Moreover, under our laboratory conditions, water appeared as a poor source of Y transfer to O. mykiss. Regardless of the source of contamination, a similar pattern of Y bioaccumulation among O. mykiss tissues was revealed: muscles < liver < gills < intestine. We conclude that the trophic transfer potential of Y is low and the evaluation of Y burden in prey cytosol appears to be a relevant predictor of Y assimilation by their consumers.

The continuous physiological changes of zebrafish (Danio rerio) based on metabolism under controlled thallium stress

In this research, the continuous physiological changes of zebrafish (Danio rerio) in 0.1 μg/L thallium (Tl) in 15 days were investigated. The results showed that Tl(I) stress had a significant positive linear correlation with zebrafish ammonia nitrogen excretion (ANE) (p < 0.001), and the mean value of ANE in Tl(I) treatment (435 ± 227 mg/kg/h) was approximately 2 times higher than in the control group (239 ± 168 mg/kg/h), which suggested that ANE was suitable for Tl(I) stress assessment. A substantial difference based on oxygen consumption rate (OCR) between the control group (587 ± 112 mg/kg/h) and Tl(I) treatment (260 ± 88 mg/kg/h) with a high significance p < 0.001 could be observed, and the results indicated that Tl(I) played a negative role in OCR of zebrafish. The characteristics of both ANE and OCR changes under slight Tl(I) stress could be reflected by the ammonia quotient (AQ). It was noteworthy that AQ increased rapidly in first 6 h from 0.66 to 4.50, which was 3 times higher than 1.2, indicating rapid increase in both anaerobic energy utilization and protein metabolism in 0.1 μg/L Tl(I) exposure. It is concluded that the physiological changes of zebrafish based on metabolism can be regarded as a sensitive biological indicator of Tl(I) pollution, which could work as a substitute of potassium that disrupts the normal biological metabolism in the process of transport.

Toxicity and Subcellular Fractionation of Yttrium in Three Freshwater Organisms: Daphnia magna, Chironomus riparius, and Oncorhynchus mykiss

The demand for rare earth elements (REEs) has increased since the 1990s leading to the development of many mining projects worldwide. However, less is known about how organisms can handle these metals in natural aquatic systems. Through laboratory experiments, we assessed the chronic toxicity and subcellular fractionation of yttrium (Y), one of the four most abundant REEs, in three freshwater organisms commonly used in aquatic toxicology: Daphnia magna, Chironomus riparius, and Oncorhynchus mykiss. In bioassays using growth as an end point, C. riparius was the only organism showing toxicity at Y exposure concentrations close to environmental ones. The lowest observable effect concentrations (LOECs) of Y assessed for D. magna and O. mykiss were at least 100 times higher than the Y concentration in natural freshwater. A negative correlation between Y toxicity and water hardness was observed for D. magna. When exposed to their respective estimated LOECs, D. magna bioaccumulated 15-45 times more Y than the other two organisms exposed to their own LOECs. This former species sequestered up to 75% of Y in the NaOH-resistant fraction, a putative metal-detoxified subcellular fraction. To a lesser extent, C. riparius bioaccumulated 20-30% of Y in this detoxified fraction. In contrast, the Y subcellular distribution in O. mykiss liver did not highlight any notable detoxification strategy; Y was accumulated primarily in mitochondria (ca. 32%), a putative metal-sensitive fraction. This fraction was also the main sensitive fraction where Y accumulated in C. riparius and D. magna. Hence, the interaction of Y with mitochondria could explain its toxicity. In conclusion, there is a wide range of subcellular handling strategies for Y, with D. magna accumulating high quantities but sequestering most of it in detoxified fractions, whereas O. mykiss tending to accumulate less Y but in highly sensitive fractions.

Metal subcellular partitioning determines excretion pathways and sensitivity to cadmium toxicity in two marine fish species

Subcellular cadmium (Cd) partitioning was investigated in the liver of two marine fish species, the European sea bass Dicentrarchus labrax and the Senegalese sole Solea senegalensis, dietary exposed to an environmentally realistic Cd dose for two months followed by a two-month depuration. The two species displayed different handling strategies during the depuration period. Cd was largely bound to detoxifying fractions such as heat stable proteins (HSP) including metallothioneins (MT) in sea bass, while Cd was more linked to sensitive fractions such as organelles in sole. Whole liver concentrations and subcellular partitioning were also determined for essential elements. The greatest impairment of essential metal homeostasis due to Cd exposure was found in sole. These elements followed the Cd partitioning pattern, suggesting that they are involved in antioxidant responses against Cd toxicity. Cd consumption diminished sole growth in terms of body weight, probably due to lipid storage impairment. The contrasting partitioning patterns showed by the two species might imply different pathways for Cd elimination from the liver. In sea bass, MT-bound Cd would be excreted through bile or released into blood, crossing the cell membrane via a protein transporter. In sole, MRG-bound Cd would be sequestered by organelles before being released into the blood via vesicular exocytosis. These distinct strategies in cellular Cd handling in the liver might account for differential sensitivity to Cd toxicity and differential Cd excretion pathways between the two marine fish species.

Toxic responses of zebrafish (Danio rerio) to thallium and deltamethrin characterized in the electrocardiogram

The electrocardiogram (ECG) has been widely used to objectively address the physical condition as an index of stress. Though a numerous accounts of investigations on aquatic organisms' ECGs have been made, differentiation of ECG parameters in responding to specific toxic chemicals has not been extensively studied. In this research, it is hypothesized that zebrafish (Danio rerio) ECG parameters would differently respond to different types of pollutants, a heavy metal, thallium (Tl, 0.10 and 13.00 μg/L) and an organic chemical, deltamethrin (DM, 0.52 and 2.00 μg/L). Based on the SOM training and statistical analyses, QRS complex could be specified as an indicator of Tl stress, while QT interval might be used to evaluate DM stress. Pearson correlation analysis indicated that QRS complex and QT interval were significantly associated with Tl stress (r = 0.854, p = 0.0002) and DM stress (r = 0.792, p = 0.001), respectively. QRS complex and QT interval had the highest R², the minimum of SSE and the lowest AIC value in Tl and DM treatments, respectively. Bases on the current experimental results and previous reports, QRS complex and QT interval could be considered as a specific indicator of Tl and DM disturbances in the environment, respectively.

Uniquely high turnover of nickel in contaminated oysters Crassostrea hongkongensis: Biokinetics and subcellular distribution

Despite the environmental concerns regarding nickel (Ni) especially in China, it has received little attention in aquatic animals due to its comparatively weak toxicity. In the present study, we explored the bioaccumulation, biokinetics, and subcellular distribution of Ni in an estuarine oyster Crassostrea hongkongensis. We demonstrated that Ni represented a new pattern of bioaccumulation in oysters characterized by rapid elimination and low dissolved uptake. The waterborne uptake rate constant and dietary assimilation efficiency were 0.036L/g/h and 28%, respectively, and dissolved uptake was the predominant exposure route. The efflux rate constant was positively related to tissue Ni concentration, with the highest efflux of 0.155d^-1. Such high elimination resulted in a high Ni turnover and steady-state condition reached rapidly, as shown with a 4-week waterborne exposure experiment at different Ni concentrations. Ni in oysters was mainly sequestered in metallothionein-like protein (MTLP), metal-rich granule, and cellular debris. MTLP was the most important binding fraction during accumulation and depuration, and played a dynamic role leading to rapid Ni elimination. Pre-exposure to Ni significantly reduced the dissolved uptake, probably accompanied by depressed filtration activity. Overall, the high turnover and regulation of Ni in oysters were achieved by enhanced efflux, suppressed uptake, and sequestration of most Ni into the detoxified pool.

Total and cytosolic concentrations of twenty metals/metalloids in the liver of brown trout Salmo trutta (Linnaeus, 1758) from the karstic Croatian river Krka

Total and cytosolic concentrations of twenty metals/metalloids in the liver of brown trout Salmo trutta (Linnaeus, 1758) were studied in the period from April 2015 to May 2016 at two sampling sites on Croatian river Krka, to establish if river water contamination with metals/metalloids downstream of Knin town has influenced metal bioaccumulation in S. trutta liver. Differences were observed between two sites, with higher concentrations of several elements (Ag, As, Ca, Co, Na, Se, Sr, V) found downstream of Knin town, whereas few others (Cd, Cs, Mo, Tl) were, unexpectedly, increased at the Krka River spring. However, total metal/metalloid concentrations in the liver of S. trutta from both sites of the Krka River were still mainly below previously reported levels for pristine freshwaters worldwide. The analysis of seasonal changes of metal/metalloid concentrations in S. trutta liver and their association with fish sex and size mostly indicated their independence of fish physiology, making them good indicators of water contamination and exposure level. Metal/metalloid concentrations in the metabolically available hepatic cytosolic fractions reported in this study are the first data of that kind for S. trutta liver, and the majority of analyzed elements were present in the cytosol in the quantity higher than 50% of their total concentrations, thus indicating their possible availability for toxic effects. However, the special attention should be directed to As, Cd, Cs, and Tl, which under the conditions of increased exposure tended to accumulate more within the cytosol. Although metal/metalloid concentrations in S. trutta liver were still rather low, monitoring of the Krka River water quality and of the health status of its biota is essential due to a trend of higher metal/metalloid bioaccumulation downstream of Knin town, especially taking into consideration the proximity of National Park Krka and the need for its conservation.

Assessment of biomarkers for contaminants of emerging concern on aquatic organisms downstream of a municipal wastewater discharge

Contaminants of emerging concern (CECs), including pharmaceuticals, personal care products and estrogens, are detected in wastewater treatment plant (WWTP) discharges. However, analytical monitoring of wastewater and surface water does not indicate whether CECs are affecting the organisms downstream. In this study, fathead minnows (Pimephales promelas) and freshwater mussels Pyganodon grandis Say, 1829 (synonym: Anodonta grandis Say, 1829) were caged for 4 weeks in the North Saskatchewan River, upstream and downstream of the discharge from the WWTP that serves the Edmonton, AB, Canada. Passive samplers deployed indicated that concentrations of pharmaceuticals, personal care products, an estrogen (estrone) and an androgen (androstenedione) were elevated at sites downstream of the WWTP discharge. Several biomarkers of exposure were significantly altered in the tissues of caged fathead minnows and freshwater mussels relative to the upstream reference sites. Biomarkers altered in fish included induction of CYP3A metabolism, an increase in vitellogenin (Vtg) gene expression in male minnows, elevated ratios of oxidized to total glutathione (i.e. GSSG/TGSH), and an increase in the activity of antioxidant enzymes (i.e. glutathione reductase, glutathione-S-transferase). In mussels, there were no significant changes in biomarkers of oxidative stress and the levels of Vtg-like proteins were reduced, not elevated, indicating a generalized stress response. Immune function was altered in mussels, as indicated by elevated lysosomal activity per hemocyte in P. grandis caged closest to the wastewater discharge. This immune response may be due to exposure to bacterial pathogens in the wastewater. Multivariate analysis indicated a response to the CECs Carbamazepine (CBZ) and Trimethoprim (TPM). Overall, these data indicate that there is a 1 km zone of impact for aquatic organisms downstream of WWTP discharge. However, multiple stressors in municipal wastewater make measurement and interpretation of impact of CECs difficult since water temperature, conductivity and bacteria are also inducing biomarker responses in both fish and mussels.

Subcellular partitioning of non-essential trace metals (Ag, As, Cd, Ni, Pb, and Tl) in livers of American (Anguilla rostrata) and European (Anguilla anguilla) yellow eels

We determined the intracellular compartmentalization of the trace metals Ag, As, Cd, Ni, Pb, and Tl in the livers of yellow eels collected from the Saint Lawrence River system in Canada (Anguilla rostrata) and in the area of the Gironde estuary in France (Anguilla anguilla). Differential centrifugation, NaOH digestion and thermal shock were used to separate eel livers into putative "sensitive" fractions (heat-denatured proteins, mitochondria and microsomes+lysosomes) and detoxified metal fractions (heat-stable peptides/proteins and granules). The cytosolic heat-stable fraction (HSP) was consistently involved in the detoxification of all trace metals. In addition, granule-like structures played a complementary role in the detoxification of Ni, Pb, and Tl in both eel species. However, these detoxification mechanisms were not completely effective because increasing trace metal concentrations in whole livers were accompanied by significant increases in the concentrations of most trace metals in "sensitive" subcellular fractions, that is, mitochondria, heat-denatured cytosolic proteins and microsomes+lysosomes. Among these "sensitive" fractions, mitochondria were the major binding sites for As, Cd, Pb, and Tl. This accumulation of non-essential metals in "sensitive" fractions likely represents a health risk for eels inhabiting the Saint Lawrence and Gironde environments.

Salinity-dependent nickel accumulation and oxidative stress responses in the euryhaline killifish (Fundulus heteroclitus)

The mechanisms of nickel (Ni) toxicity in marine fish remain unclear, although evidence from freshwater (FW) fish suggests that Ni can act as a pro-oxidant. This study investigated the oxidative stress effects of Ni on the euryhaline killifish (Fundulus heteroclitus) as a function of salinity. Killifish were exposed to sublethal levels (5, 10, and 20 mg L(-1)) of waterborne Ni for 96 h in FW (0 ppt) and 100 % saltwater (SW) (35 ppt). In general, SW was protective against both Ni accumulation and indicators of oxidative stress [protein carbonyl formation and catalase (CAT) activity]. This effect was most pronounced at the highest Ni exposure level. For example, FW intestine showed increased Ni accumulation relative to SW intestine at 20 mg Ni L(-1), and this was accompanied by significantly greater protein carbonylation and CAT activity in this tissue. There were exceptions, however, in that although liver of FW killifish at the highest exposure concentration showed greater Ni accumulation relative to SW liver, levels of CAT activity were greatly decreased. This may relate to tissue- and salinity-specific differences in oxidative stress responses. The results of the present study suggest (1) that there was Ni-induced oxidative stress in killifish, (2) that the effects of salinity depend on differences in the physiology of the fish in FW versus SW, and (3) that increased levels of cations (sodium, calcium, potassium, and magnesium) and anions (SO4 and Cl) in SW are likely protective against Ni accumulation in tissues exposed to the aquatic environment.

Chronic nickel bioaccumulation and sub-cellular fractionation in two freshwater teleosts, the round goby and the rainbow trout, exposed simultaneously to waterborne and dietborne nickel

Rainbow trout and round goby were exposed for 30 days to waterborne and dietary Ni in combination at two waterborne concentration ranges (6.2-12 μmol/L, 68-86 μmol/L), the lower of which is typical of contaminated environments. The prey (black worms; Lumbriculus variegatus) were exposed for 48 h in the effluent of the fish exposure tanks before being fed to the fish (ration=2% body weight/day). Ni in gills, gut, and prey was fractionated into biologically inactive metal [BIM=metal-rich granules (MRG) and metallothionein-like proteins (MT)] and biologically active metal [BAM=organelles (ORG) and heat-denaturable proteins (HDP)]. Gobies were more sensitive than trout to chronic Ni exposure. Possibly, this greater sensitivity may have been due to the goby's pre-exposure to pollutants at their collection site, as evidenced by ∼2-fold greater initial Ni concentrations in both gills and gut relative to trout. However, this was followed by ∼2-16× larger bioaccumulation in both the gills and the gut during the experimental exposure. On a subcellular level, ∼3-40× more Ni was associated with the BAM fraction of goby in comparison to trout. Comparison of the fractional distribution of Ni in the prey versus the gut tissue of the predators suggested that round goby were more efficient than rainbow trout in detoxifying Ni taken up from the diet. Assessing sub-cellular distribution of Ni in the gills and gut of two fish of different habitat and lifestyles revealed two different strategies of Ni bioaccumulation and sub-cellular distribution. On the one hand, trout exhibited an ability to regulate gill Ni bioaccumulation and maintain the majority of the Ni in the MT fraction of the BIM. In contrast goby exhibited large Ni spillovers to both the HDP and ORG fractions of the BAM in the gill. However, the same trend was not observed in the gut, where the potential acclimation of goby to pollutants from their collection site may have aided their ability to regulate Ni spillover to the BAM more so than in trout. Overall, chronic mortality observed in goby may be associated more with Ni bioaccumulation in gills than in gut; the former at either 4-d or 30-d was predictive of chronic Ni toxicity. BIM and BAM fractions of the goby gills were equally predictive of chronic (30-d) mortality. However, critical body residue (CBR50) values of the BIM fraction were ∼2-4× greater than CBR50 values of the BAM fraction, suggesting that goby are more sensitive to Ni bioaccumulation in the BAM fraction. There was insufficient mortality in trout to assess whether Ni bioaccumulation was predictive of chronic mortality.

Do Cd, Cu, Ni, Pb, and Zn biomagnify in aquatic ecosystems?

In this review, we sought to assess from a study of the literature whether five in organic metals (viz., cadmium, copper, lead, nickel, and zinc) bio magnify in aquatic food webs. We also examined whether accumulated metals were toxic to consumers/predators and whether the essential metals (Cu and Zn and possibly Ni) behaved differently from non-essential ones (Cd and Pb). Biomagnification potential was indexed by the magnitude of single and multiple trophic transfers in food chains. In this analysis, we used three lines of evidence-laboratory empirical, biokinetic modeling, and field studies-to make assessments. Trophic transfer factors, calculatedfrom lab studies, field studies, and biokinetic modeling, were generally congruent.Results indicated that Cd, Cu, Pb, and Zn generally do not biomagnify in food chains consisting of primary producers, macro invertebrate consumers, and fish occupying TL 3 and higher. However, bio magnification of Zn (TTFs of 1-2) is possible for circumstances in which dietary Zn concentrations are below those required for metabolism. Cd, Cu, Ni, and Zn may biomagnify in specific marine food chains consisting of bivalves, herbivorous gastropods, and barnacles at TL2 and carnivorous gastropods at TL3. There was an inverse relationship between TTF and exposure concentration for Cd, Cu, Pb, and Zn, a finding that is consistent with previous reviews of bioconcentration factors and bioaccumulation factors for metals. Our analysis also failed to demonstrate a relationship between the magnitude of TTFsand dietary toxicity to consumer organisms. Consequently, we conclude that TTFs for the metals examined are not an inherently useful predictor of potential hazard(i.e., toxic potential) to aquatic organisms. This review identified several uncertainties or data gaps, such as the relatively limited data available for nickel, reliance upon highly structured food chains in laboratory studies compared to the unstructured food webs found in nature, and variability in TTFs between the organisms found in different habitats, and years sampled.

Subcellular metal partitioning in larvae of the insect Chaoborus collected along an environmental metal exposure gradient (Cd, Cu, Ni and Zn)

Larvae of the phantom midge Chaoborus are common and widespread in lakes contaminated by metals derived from mining and smelting activities. To explore how this insect is able to cope with potentially toxic metals, we determined total metal concentrations and subcellular metal partitioning in final-instar Chaoborus punctipennis larvae collected from 12 lakes situated along gradients in aqueous Cd, Cu, Ni and Zn concentrations. Concentrations of the non-essential metals Cd and Ni were more responsive to aqueous metal gradients than were larval concentrations of the essential metals Cu and Zn; these latter metals were better regulated and exhibited only 2-3-fold increases between the least and the most contaminated lakes. Metal partitioning was determined by homogenization of larvae followed by differential centrifugation, NaOH digestion and heat denaturation steps so as to separate the metals into operationally defined metal-sensitive fractions (heat-denaturable proteins (HDP), mitochondria, and lysosomes/microsomes) and metal-detoxified fractions (heat stable proteins (HSP) and NaOH-resistant or granule-like fractions). Of these five fractions, the HSP fraction was the dominant metal-binding compartment for Cd, Ni and Cu. The proportions and concentrations of these three metals in this fraction increased along the metal bioaccumulation gradient, which suggests that metallothionein-like proteins play an important role in metal tolerance of Chaoborus living in metal-contaminated environments. Likewise, a substantial proportion of larval Zn was in the HSP fraction, but its contribution did not increase progressively along the metal gradient. Despite the increases in Cd, Ni and Cu in the HSP fraction along the metal bioaccumulation gradient, some accumulation of non-essential metals (Cd and Ni) was observed in putative metal-sensitive fractions (e.g., HDP, mitochondria), suggesting that metal detoxification was incomplete. In the case of Cd, there appears to be a threshold body concentration of about 50 nmol Cd g(-1) dry weight, above which Cd detoxification becomes more effective and below which Chaoborus does not "turn on" its detoxification machinery to the fullest extent. We speculate that acclimation or adaptation of Chaoborus to these highly metal-contaminated environments may have resulted in a capacity to tolerate some metal spillover without comprising essential biological functions such as growth and reproduction.

Cadmium exposure route affects antioxidant responses in the mayfly Centroptilum triangulifer

Aquatic organisms accumulate metals directly from water and from their diets. Exposure to metals is known to generate oxidative stress in living organisms and this stress may be ameliorated via activation of antioxidant enzymes and non-enzymatic antioxidants. To determine if antioxidant physiology is dependent on Cd exposure route in the mayfly Centroptilum triangulifer, we exposed larvae to environmentally relevant concentrations of Cd from isolated dissolved or dietary exposure routes to achieve comparable tissue concentrations. Dissolved Cd had no effect on the antioxidant enzymes examined. However, dietary Cd significantly suppressed catalase and superoxide dismutase activities, and decreased concentrations of the reduced (active) form of glutathione in C. triangulifer larvae. These findings suggest that dietary Cd is potentially more toxic than aqueously derived Cd in this mayfly. We further examined the effect of dietary Cd tissue loading rates on antioxidant enzyme suppression and found that absolute tissue load appeared more important than loading rate. These results may help explain why insects are routinely unresponsive to dissolved metal exposures in the laboratory, yet highly responsive to metal pollution in nature.

Assessing abalone growth inhibition risk to cadmium and silver by linking toxicokinetics/toxicodynamics and subcellular partitioning

The purpose of this study was to link toxicokinetics/toxicodynamics and subcellular partitioning for assessing the susceptibility and the growth inhibition risks of abalone Haliotis diversicolor supertexta exposed to waterborne and foodborne cadmium (Cd) and silver (Ag). We reanalyzed published data on growth inhibition and subcellular partitioning associated with the present mechanistic model to explore the correlations among elimination (k (e)), detoxification (k (d)), and recovery (k (r)) rate constants and to assess the growth inhibition risk. We found a positive correlation among k (e), k (d), and k (r) in abalone exposed to Ag. We also employed a life-stage based probabilistic assessment model to estimate the growth inhibition risk of abalone to environmentally relevant Cd (5-995 μg l(-1)) and Ag (0.05-9.95 μg l(-1)) concentrations in Taiwan. The results showed that abalone had a minimum 20% probability of the growth inhibition risk exposed to Cd, whereas Ag exposure was not likely to pose the risk. The maximum biomasses were estimated to be 0.0039 and 0.0038, 61.61 and 43.87, and 98.88 and 62.97 g for larvae, juveniles, and adults of abalone exposed to the same levels of Cd and Ag, respectively. Our study provides a useful tool to detect potential growth biomass of abalone populations subjected to Cd and Ag stresses and mechanistic implications for a long-term ecotoxicological risk assessment in realistic situations.

Assessing the impact of waterborne and dietborne cadmium toxicity on susceptibility risk for rainbow trout

The purpose of this study was to use a risk-based integrated-scale toxicological model to examine the impact of waterborne and dietborne cadmium (Cd) toxicity on rainbow trout (Oncorhynchus mykiss) susceptibility appraised with recent published data. A probabilistic assessment model was performed to estimate Cd susceptibility risk. The dose-response models were constructed based on two endpoints of % Cd in metabolically active pool (MAP) and susceptibility time that causes 50% effect (ST50). We further constructed an elimination-detoxification-recovery scheme to enhance the model predictive ability. We found a 95% probability of % Cd in gill and liver MAP exceeding 47-49% and it was likely (70% probability) to have exceeded 52-55%, but it was unlikely (30% probability) to have exceeded 56-60%. In contrast to gill and liver, gut had a relative lower Cd susceptibility risk (15-17% Cd in MAP) with a longer ST50. We suggested that the proposed probabilistic risk assessment framework can incorporate the elimination-detoxification-recovery scheme to help government based biomonitoring and bioassessment programs to prevent potential aquatic ecosystems and human health consequences.

Trophic transfer of aluminium through an aquatic grazer-omnivore food chain

The potential for trophic transfer of aluminium (Al) was investigated using a grazing detritivore, the freshwater snail Lymnaea stagnalis, and a predator, the signal crayfish Pacifastacus leniusculus. Snails were exposed to either aqueous Al (500 microg l(-1)) in the presence or absence of an inorganic ligand (phosphate (+P); 500 microg l(-1)) for 30 days, or kept as unexposed controls. Subcellular partitioning of Al in the snail tissues was characterised using ultracentrifugation. Al content in the soft tissues and the subcellular fractions was measured using inductively coupled plasma atomic emission spectroscopy. Exposed and control snails were fed to individually housed crayfish (n=6 per group) over 40 days. Water samples, uneaten snail tissue and faeces were collected throughout the experiment in order to assess the fate of Al. Behavioural toxicity to the crayfish was assessed at four time points, and tissue accumulation of Al in soft tissues was measured following a 2-day depuration period. Snails exposed to Al+P accumulated more Al per snail than those exposed to Al only (291 microg vs 206 microg), and also contained a higher proportion of detoxified Al (in inorganic granules and associated with heat stable proteins) (39% vs 26%). There were no significant differences in behavioural activity between the different groups of crayfish at any time point. Crayfish fed snails exposed to only Al accumulated significant levels of Al in their total soft tissues, compared to controls; crayfish fed Al+P-exposed snails did not, even though concentrations of Al in these snails were higher. The highest concentrations of Al were found in the green gland in both crayfish feeding groups, and the gut and hepatopancreas in crayfish fed Al only exposed snails; all of these were significantly higher than in crayfish fed control snails. There was no significant accumulation of Al in the gills or flexor muscle in any group. At least 17% of trophically available Al in the snail tissues was accumulated by the crayfish. This proportion was similar in both feeding groups but, as the proportion of trophically available Al in the snails exposed to Al+P was lower, this led to lower accumulation in the Al+P crayfish feeding group. This study indicates that in comparison to vertebrates, aquatic invertebrates accumulate a higher proportion of Al via oral ingestion but it does not accumulate in tissues that may pose a threat to human consumers.

Accumulation and effects of nickel and thallium in early-life stages of fathead minnows (Pimephales promelas)

Early-life stages of fathead minnows were exposed to environmentally relevant concentrations of aqueous and dietary nickel and thallium and metal accumulation was monitored from the embryo until the larvae reached 21 days after hatching. During and after metal exposure, 6 toxicity endpoints were measured: time to hatch, embryo survival rate, routine metabolic rate and the activity of key enzymes (lactate dehydrogenase, nucleoside diphosphate kinase (NDPK), cytochrome C oxidase (CCO)). Although both Ni and Tl bioaccumulation were significant in embryos and non-feeding larvae, water was the major source of Ni and Tl in feeding larvae. Exposure to aqueous Ni decreased time to hatch and increased aerobic and biosynthetic capacities (as indicated by a higher activity of CCO and NDPK, respectively), suggesting that aqueous Ni exposure stimulates metabolism in early-life stages of fathead minnows.