A mechanistic model for the uptake of waterborne strontium in the common carp (Cyprinus carpio L.)

Trace Elements and Consequent Ecological Risks in Mining-Influenced Streams of Appalachia

Appalachian (eastern USA) coal surface mines fracture geologic materials, causing release of both major ions and trace elements to water via accelerated weathering. When elevated above natural background, trace elements in streams may produce adverse effects on biota via direct exposure from water and sediment and via dietary exposure in food sources. Other studies have found elevated water concentrations of multiple trace elements in Appalachia's mining-influenced streams. Except for Se, trace-element concentrations in abiotic and biotic media of Appalachian mining-influenced streams are less well known. We analyzed environmental media of headwater streams receiving alkaline waters from Appalachian coal mines for eight trace elements (Al, As, Cd, Cu, Ni, Sr, V, and Zn) and assessed the potential consequent ecological risks. Streamwater, particulate media (sediment, biofilm, leaf detritus), and benthic macroinvertebrates (primary consumers, secondary consumers, crayfish) were sampled from six mining-influenced and three reference streams during low-flow conditions in two seasons. Dissolved Cu, Ni, and Sr were higher in mining-influenced streams than in reference streams; Ni, Sr, and Zn in fine sediments and Ni in macroinvertebrates were also elevated relative to reference-stream levels in samples from mining-influenced streams. Seasonal ratios of mining-influenced stream concentrations to maximum concentrations in reference streams also demonstrated mining-influenced increases for several elements in multiple media. In most media, concentrations of several elements including Ni were correlated positively. All water-column dissolved concentrations were below protective levels, but fine-sediment concentrations of Ni approached or exceeded threshold-effect concentrations in several streams. Further study is warranted for several elements (Cd, Ni, and Zn in biofilms, and V in macroinvertebrates) that approached or exceeded previously established dietary-risk levels. Environ Toxicol Chem 2023;42:2651-2665. © 2023 SETAC.

The Concentration of Radionuclides (Lead-210, Polonium-210, and Cesium-137) in the Muscle of Sardine Fish: a Global Systematic Review, Meta-analysis, and Exposure Assessment

With the increasing use of nuclear technology, concerns about the contamination of water resources with radionuclides and the contamination of seafood are increasing. In the current investigation, a meta-analysis and exposure assessment regarding the concentration of radionuclides, including lead-210 (Pb-210), polonium -210 (Po-210), and cesium-137 (Cs-137) in the muscle of Sardin fish were conducted. In this regard, some databases including Scopus and PubMed were selected to retrieve papers on the concentration of radionuclides in the muscle of Sardin fish from January 2000 to 25 June 2021. The used keywords were polonium-210, natural radioactivity, lead-210, radiocesium, cesium-137, radionuclides, radium-226, seafood, marine foods, fish, sardine fish, sardinella longiceps, and Clupeidae. Also, effective dose (ED) was calculated to estimate carcinogenic risk in Sardine fish consumers. The rank order of radionuclides in the muscle of sardine fish was Po-210 (31.50 Bq/kg) > Pb-210 (3.34 Bq/kg) > Cs-137 (0.48 Bq/kg). Based on level of Pb-210 rank of countries was France (12.00 Bq/kg) > India (4.06 Bq/kg) > Turkey (3.29 Bq/kg) > Spain (1.00 Bq/kg) > Slovenia (0.55 Bq/kg); Po-210 was Turkey (74.96 Bq/kg) > Spain (48.00 Bq/kg) > France (31.500 Bq/kg > India (30.25 Bq/kg) > Slovenia (25.00 Bq/kg) > Kuwait (7.28 Bq/kg) and also, Cs-137 was Japan (1.22 Bq/kg) > Croatia (0.18 Bq/kg) > India (0.23 Bq/kg). The lowest and highest ED of ²¹⁰Po was observed in Kuwait (5.10E-04 msv/y, female) and France (3.14E-01, male); Pb-210, Slovenia (7.24E-05 msv/y, male) and France (1.48E-02 msv/y, female), and Cs-137, Croatia (8.47E-08 msv/y, male) and Japan (2.54E-05 msv/y, female), respectively. The risk assessment shows that the exposed population are at an acceptable range of risk (H < 1 mSv/y).

Clean feed as countermeasure to reduce the 90Sr and 137Cs levels in fish from contaminated lakes

Glubokoye Lake situated within the Chernobyl Exclusion Zone is highly contaminated with respect to radioactive caesium and strontium isotopes, which also is reflected in the contaminated fish. To utilize the fish resources in contaminated lakes, the present work presents for the first time the effectiveness of using clean feed to counteract contamination of radionuclides in fish. The study is based on a series of repeated experiments with Prussian carp (Carassius gibelio (Bloch, 1782)) kept in cages in the contaminated Glubokoye Lake during summer 2018-2021. By the addition of clean feed, the activity concentration of ¹³⁷Cs in fish muscle tissues was lowered with a factor of 2-5 due to biodilution. Surprisingly, additional clean feed did not lead to further decrease in the uptake of ¹³⁷Cs in fish. In contrast to ¹³⁷Cs, the addition of clean feed increased the ⁹⁰Sr activity concentration in fish by a factor of 2-4 compared to fish fed with naturally occurring feed items. Radioactive strontium accumulated mainly in the fish bones and the muscle tissue level was 2 orders of magnitude lower, similar to the distribution observed for stable Sr. By utilizing a new kinetic model describing the dynamics of strontium isotopes in bone tissues of fish, predictions fitted well with site-specific data, taking growth rates and aging into account. Results showed that clean feeding can be used to counteract high activity concentration of ¹³⁷Cs in fish due to biodilution, but cannot counteract bioaccumulation of ⁹⁰Sr. Findings highlighted that it is essential to understand underlying factors influencing the uptake pathways for contaminants, as access to clean feed could increase the growth and thereby reduce the body activity concentration of dietary associated radionuclides such as ¹³⁷Cs (biodilution), as well as increase the transfer of dissolved compounds such as ⁹⁰Sr directly from water to fish.

Oxidative Stress and Histopathological Changes in Gills and Kidneys of Cyprinus carpio following Exposure to Benzethonium Chloride, a Cationic Surfactant

One cationic surfactant with a wide spectrum of microbiocidal activity is benzethonium chloride (BEC). Despite being widely used, the toxicity data on vertebrate organisms are limited. Therefore, we aimed to evaluate within this study the acute toxicity of BEC on the gills and kidneys of Cyprinus carpio (European carp). An alteration of the antioxidant enzymes activities (glutathione reductase, glutathione peroxidase and glutathione S-transferase) was noticed after 96 h of exposure, along with an elevation of lipid peroxidation and decreased concentration of reduced glutathione, which confirmed that BEC was able to induce toxicity to these tissues. These metabolic effects were correlated with unspecific structural changes observed in gills and kidneys, having moderate degree of severity (such as an increase of melanomacrophages aggregation incidence and cytoplasm vacuolation of goblet cells in collecting tubules) and generally being compatible with life for the exposure time studied. The most severe structural effects were observed in gills after 96 h, noticing a lamellar aneurysm, hemorrhages and lamellar epithelium disruption due to the blood vessels and pillar cells damages and increased blood flow inside the lamellae. By our research we can confirm the utility of biochemical and histological analyses in the fish organs as tools for monitoring the water quality and ecotoxicological potential of chemicals.

Seasonal changes in uptake and depuration of 137Cs and 90Sr in silver Prussian carp (Carassius gibelio) and common rudd (Scardinius erythrophthalmus)

Dynamic transfer of radionuclides to fish was studied in a series of experiments under field condition in two lakes within the Chernobyl exclusion zone during 2016-2020. "Clean" common rudd (Scardinius erythrophthalmus) and silver Prussian carp (Carassius gibelio) were transported to the contaminated Glubokoye Lake and kept in cages during several months of exposure, while contaminated Glubokoye fish were kept in cages in the "clean" Starukha Lake. Radiocaesium (¹³⁷Cs) and radiostrontium (⁹⁰Sr) were determined in intestine contents, muscle and bone tissues based on repeated samples during several months of exposure. During summer, the activity concentrations of ¹³⁷Cs and ⁹⁰Sr increased with time of exposure in clean fish caged in the contaminated lake. During autumn and winter, however, minor changes in fish uptake occurred during several weeks of exposure to the contaminated water. Furthermore, depuration in the contaminated fish was significant during summer, while insignificant during winter when exposed in the «clean» water. The rate constant of ¹³⁷Cs uptake in muscle was between 8.0 and 22 day^-1 during summer, while 0.2 to 1.0 day^-1 during autumn-winter. Similarly, the rate constant of ⁹⁰Sr uptake in bone was between 1.4 and 1.6 day^-1, while 0.08-0.52 day^-1 during autumn-winter. Biological half-lives of ¹³⁷Cs in fish muscle tissue in summer were 77 ± 10 days, while exceeded 230 days during seasons at low water temperature. The results demonstrated that the transfer of ¹³⁷Cs and ⁹⁰Sr to fish was highly dependent upon seasons, in particular the water temperature. The transfer data obtained during low water temperature seasons deviated significantly from transfer data in literature and handbooks. Thus, seasonal changes in radionuclide transfer to fish should be taken into account when radiological impact to fish is assessed.

Collation of Strontium Concentration Ratios from Water to Aquatic Biota Species in Freshwater and Marine Environments and Factors Affecting the Ratios

The fate of strontium-90 (⁹⁰Sr) from water to aquatic biota is of concern since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident because of continuous small ⁹⁰Sr releases to the seawater from the FDNPP site. The Japanese diet includes many edible marine and freshwater species, and the environmental parameter, that is, the concentration ratio (CR) from water to biota, is useful to estimate the potential ⁹⁰Sr intake, especially from frequently consumed seafoods. However, widely used CR data for radiation dose assessment only have provided values for biota types such as fish, crustaceans, macroalgae, and so forth, and thus, it is difficult to identify specific data for each species. In this study, therefore, we collated CR data of Sr for aquatic biota by surveying available open data sources from the 1950s to 2019, not only for edible parts but also for whole and inedible parts. In total, we obtained 3800 CR data: 3013 data for marine biota, 28 data for brackish water biota, and 759 data for freshwater biota. The results showed that species-specific CRs may decrease the uncertainties compared to those published in IAEA documents; however, different diets and living areas by species may lead to different uncertainties for different species.

Time-dependent accumulation of Cd, Co, Cu, Ni, and Zn in natural communities of mayfly and caddisfly larvae: Metal sensitivity, uptake pathways, and mixture toxicity

Conceptual and quantitative models were developed to assess time-dependent processes in four sequential experimental stream studies that determined abundances of natural communities of mayfly and caddisfly larvae dosed with single metals (Cd, Co, Cu, Ni, Zn) or multiple metals (Cd + Zn, Co + Cu, Cu + Ni, Cu + Zn, Ni + Zn, Cd + Cu + Zn, Co + Cu + Ni, Cu + Ni + Zn). Metal mixtures contained environmentally relevant metal ratios found in mine drainage. Free metal ion concentrations, accumulation of metals by periphyton, and metal uptake by four families of aquatic insect larvae were either measured (Brachycentridae) or predicted (Ephemerellidae, Heptageniidae, Hydropsychidae) using equilibrium and biodynamic models. Toxicity functions, which included metal accumulations by larvae and metal potencies, were linked to abundances of the insect families. Model results indicated that mayflies accumulated more metal than caddisflies and the relative importance of metal uptake by larvae via dissolved or dietary pathways highly depended on metal uptake rate constants for each insect family and concentrations of metals in food and water. For solution compositions in the experimental streams, accumulations of Cd, Cu, and Zn in larvae occurred primarily through dietary uptake, whereas uptake of dissolved metal was more important for Co and Ni accumulations. Cd, Cu, and Ni were major contributors to toxicity in metal mixtures and for metal ratios examined. Our conceptual approach and quantitative results should aid in designing laboratory experiments and field studies that evaluate metal uptake pathways and metal mixture toxicity to aquatic biota.

Exposure of a small Arctic seabird, the little auk (Alle alle) breeding in Svalbard, to selected elements throughout the course of a year

The Arctic marine ecosystem can be altered by processes of natural and anthropogenic origin. Spatio-temporal variation in species exposure to contamination is still poorly understood. Here, we studied elemental concentrations in the non-lethally collected samples from the most numerous seabird in European Arctic, the little auk (Alle alle) nesting in one breeding colony in Svalbard. This seabird spent the breeding season in the high-Arctic zone and the non-breeding period in sub-Arctic areas what may implicate spatio-temporal variation in elements bioaccumulation. We determined concentrations of 19 elements in adults feathers to determine levels of exposure during part of the pre-breeding (n = 74) and post-breeding (n = 74) seasons, feathers from nestlings (n = 18) to determine local contamination, and chick down (n = 16) and post-hatching eggshells (n = 18) to determine maternal input to offspring. During the pre-breeding period adults accumulated in their feathers significantly more Hg (one third of feathers exceeded the established toxicity threshold), Se and Mn compared to the post-breeding period. It reflects a higher exposition of birds to contaminants in pre-breeding moult areas outside the High Arctic compared to the post-breeding moult in the High Arctic. Sex differences in adult feathers representing the post-breeding period were found only for Ca and Zn with higher values in females. Chick down was characterized by high levels of several essential elements, an intermediate level of Hg and Se, and the highest Se:Hg molar ratios of all groups. Chick body feathers had the highest level of Cu and K among all the studied groups. Post-hatching eggshells were characterized by high Sr level (exceeding 2000 μg/g). Concentrations of several non-essential elements (Bi, Cd, Cr, Hg, Ni and Pb) in them were below method detection limits.

Seeking the true time: Exploring otolith chemistry as an age-determination tool

Fish otoliths' chronometric properties make them useful for age and growth rate estimation in fisheries management. For the Eastern Baltic Sea cod stock (Gadus morhua), unclear seasonal growth zones in otoliths have resulted in unreliable age and growth information. Here, a new age estimation method based on seasonal patterns in trace elemental otolith incorporation was tested for the first time and compared with the traditional method of visually counting growth zones, using otoliths from the Baltic and North seas. Various trace elemental ratios, linked to fish metabolic activity (higher in summer) or external environment (migration to colder, deeper habitats with higher salinity in winter), were tested for age estimation based on assessing their seasonal variations in concentration. Mg:Ca and P:Ca, both proxies for growth and metabolic activity, showed greatest seasonality and therefore have the best potential to be used as chemical clocks. Otolith image readability was significantly lower in the Baltic than in the North Sea. The chemical (novel) method had an overall greater precision and percentage agreement among readers (11.2%, 74.0%) than the visual (traditional) method (23.1%, 51.0%). Visual readers generally selected more highly contrasting zones as annuli whereas the chemical readers identified brighter regions within the first two annuli and darker zones thereafter. Visual estimates produced significantly higher, more variable ages than did the chemical ones. Based on the analyses in our study, we suggest that otolith microchemistry is a promising alternative ageing method for fish populations difficult to age, such as the Eastern Baltic cod.

Competitive interactions among H, Cu, and Zn ions moderate aqueous uptake of Cu and Zn by an aquatic insect

The absorption of aqueous copper (Cu) and zinc (Zn) by aquatic insects, a group widely used to assess water quality, is unresolved. This study examined interactions among Cu, Zn, and protons that potentially moderate Cu and Zn uptake by the acid-tolerant stonefly Zapada sp. Saturation uptake kinetics were imposed to identify competitive mechanisms. Decreasing pH reduced the maximum transport capacity, J_max, in both metals, had little effect on the Cu dissociation constant, K_D, and increased the Zn K_D. Partial noncompetitive (Cu) and partial mixed competitive (Zn) inhibitor models most closely tracked the observed Cu and Zn influx rates across pH treatments. The estimated values for acid dissociation constants for the binary (proton-receptor) and ternary (proton-metal-receptor) complexes indicated the strong inhibitory effect of protons on Cu and Zn. In neutral pH water, Cu inhibited Zn influx, but Zn had little effect on Cu influx. The mechanism of Cu-Zn interaction was not identified. Results from separate Zn experiments suggested that the insect's developmental stage may affect the apparent J_max. The study underscores some of the challenges of modeling metal bioaccumulation and informs future research directions.

Vulnerability of Canadian aquatic ecosystems to nuclear accidents

Several cesium and strontium bioaccumulation models are used widely in national and international guidance for ecological and human health risk assessments for radiocesium (¹³⁴Cs and ¹³⁷Cs) and radiostrontium (⁹⁰Sr), but have not been used to make predictions of radiological risk from nuclear accidents under variable environmental conditions on broad geographical scales. In this paper, we first present models for predicting the bioaccumulation of cesium and strontium by aquatic biota based on ambient concentrations of dissolved potassium and calcium, respectively, and then test these models using independent data from aquatic ecosystems at Canadian nuclear sites. Secondly, models yielding the best predictions across a wide range of input parameters were selected to estimate bioaccumulation factors (BAFs) for cesium and strontium in aquatic ecosystems across Canada, using trophic level of organisms and dissolved potassium for cesium and calcium concentrations for strontium as predictor variables, and presented as contour maps of radiological risk. The models show that risk from bioaccumulation of cesium and strontium can vary by several orders of magnitude depending on site-specific environmental conditions and trophic ecology. Overall, our results suggest that single-parameter approaches taken by regulatory standards may either over- or under-predict radiological risk at many locations, and are thus not readily suitable to inform siting decisions for new nuclear developments.

Impact of Environmental Radiation on the Health and Reproductive Status of Fish from Chernobyl

Aquatic organisms at Chernobyl have now been chronically exposed to environmental radiation for three decades. The biological effects of acute exposure to radiation are relatively well documented, but much less is known about the long-term effects of chronic exposure of organisms in their natural environment. Highly exposed fish in freshwater systems at Chernobyl showed morphological changes in their reproductive system in the years after the accident. However, the relatively limited scope of past studies did not allow robust conclusions to be drawn. Moreover, the level of the radiation dose at which significant effects on wildlife occur is still under debate. In the most comprehensive evaluation of the effects of chronic radiation on wild fish populations to date, the present study measures specific activities of ¹³⁷Cs, ⁹⁰Sr, and transuranium elements (²³⁸Pu, ^239,240Pu, and ²⁴¹Am), index conditions, distribution and size of oocytes, as well as environmental and biological confounding factors in two fish species perch ( Perca fluviatilis) and roach ( Rutilus rutilus) from seven lakes. In addition, relative species abundance was examined. The results showed that both fish species are, perhaps surprisingly, in good general physiological and reproductive health. Perch, however, appeared to be more sensitive to radiation than roach: in the most contaminated lakes, a delay of the maturation of the gonads and the presence of several undeveloped phenotypes were evident only for perch and not for roach.

Preferential accumulation of inorganic elements in Amanita muscaria from North-eastern Poland

Concentrations of Al, Ba, Cd, Ca, Co, Cu, Fe, K, Mg, Mn, Hg, Rb, Ag, Na, Sr and Zn were analysed in fruiting bodies of A. muscaria. This mushroom is considered conditionally edible, since parboiling can detoxify its fruiting bodies from the hallucinogens and render it edible. The specific purpose of the research is the little-known phenomenon of the variability of mineral composition of mushrooms for generations harvested in the same forest areas - both in terms of their nutritional value and anthropogenic influences. Fungal materials were digested in nitric acid and analysed by a validated methods using inductively coupled plasma optical emission spectrometer (ICP-OES) and cold - vapor atomic absorption spectroscopy (CV-AAS). A. muscaria collected in the same area over the period of four years showed fluctuations in the concentrations of the essential elements Co, Cu, Fe, K, Mn, Na and Zn (p < 0.05; U Mann-Whitney test), while only Ca and Mg (p > 0.05) levels were similar. In addition, concentrations of Ag, Al, Ba, Cd, Rb and Sr in fruiting bodies fluctuated, while remained at a similar level for Hg. It is important to note that statistically significant variations in levels of several inorganic elements accumulated in A. muscaria would imply a more careful consideration would be required when assessing the nutritional value of mushroom species.

Experimentally derived acute and chronic copper Biotic Ligand Models for rainbow trout

We evaluated the effects of varying water chemistry ([Ca²⁺]=0.2-3mM, [Mg²⁺]=0.05-3mM, dissolved organic matter (DOM, natural, from maple leaves)=0.3-10mg of CL^-1, pH=5.0-8.5) on the acute (96-h, unfed fish) and chronic (30-d, fed fish) toxicity of waterborne Cu to juvenile rainbow trout (Oncorhynchus mykiss) exposed in flow-through conditions. Acute and chronic Biotic Ligand Models (BLMs) were developed from the obtained toxicity data-sets, using the Visual MINTEQ software. Our results indicate that Cu is predominantly an acute toxicant to rainbow trout, as there were no observable growth effects and the 96-h and 30-d LC50 values were similar, with mortality mostly occurring within the first few days of exposure. Calcium and DOM were greatly protective against both acute and chronic Cu toxicity, but Mg seemed to only protect against chronic toxicity. Additional protection by pH 5.0 in acute exposure and by pH 8.5 in chronic exposure occurred. In the range of conditions tested, the observed 96-h LC50 and 30-d LC20 values varied by a factor of 39 and 27 respectively. The newly developed acute and chronic BLMs explained these variations reasonably well (i.e. within a 2-fold error), except at pH≥8 where the high observed acute toxicity could not be explained, even by considering an equal contribution of CuOH⁺ and Cu²⁺ to the overall Cu toxicity. The 96-h LC50 values of 59% of 90 toxicity tests from 19 independent studies in the literature were reasonably well predicted by the new acute BLM. The LC20 predictions from the new chronic BLM were reasonable for 7 out of 14 toxicity tests from 6 independent chronic studies (with variable exposure durations). The observed deviations from BLM predictions may be due to uncertainties in the water chemistry in these literature studies and/or to differences in fish sensitivity. A residual pH effect was also observed for both the acute and the chronic data-sets, as the ratio of predicted vs. observed LC values generally increased with the pH. Additional mechanistic studies are required to understand the influence of pH, Na, and Mg on Cu toxicity to trout. The present study presents the first experimentally developed chronic Cu BLM for the rainbow trout. To the best of our knowledge, it also presents the first acute Cu BLM that is based on a published data-set for trout. These newly developed BLMs should contribute to improving the risk assessment of Cu to fish in freshwater.

Accumulation of metals relevant for agricultural contamination in gills of European chub (Squalius cephalus)

The study of metal bioaccumulation in the gills of European chub (Squalius cephalus) was conducted in September 2009 at the medium-sized rural river Sutla, characterized by agricultural and municipal type of water contamination. The concentration ranges were established for the first time in the soluble, metabolically available fractions of chub gills for 12 metals, which are environmentally extremely relevant and yet only seldom studied, as follows in a decreasing order: K, 225-895 mg L(-1); Na, 78-366 mg L(-1); Ca, 19-62 mg L(-1); Mg, 13-47 mg L(-1); Rb, 164-1762 μg L(-1); Sr, 24-81 μg L(-1); Ba, 13-67 μg L(-1); Mo, 1.3-16 μg L(-1); Co, 0.7-2.7 μg L(-1); Li, 0.4-2.2 μg L(-1); Cs, 0.2-1.9 μg L(-1); and V, 0.1-1.8 μg L(-1). The concentrations of Fe (1.6-6.4 mg L(-1)) and Mn (16-69 μg L(-1)) were also determined and were in agreement with previous reports. By application of general linear modelling, the influence of different abiotic (metal exposure level) and biotic parameters (fish sex, age, size and condition) on metal bioaccumulation was tested. It was established that bioaccumulation of many metals in fish depended on various physiological conditions, wherein Ba could be singled out as metal exhibiting the strongest association with one of biotic parameters, being significantly higher in smaller fish. However, it was also undoubtedly demonstrated that the concentrations of three metals can be applied as reliable indicators of metal exposure even in the conditions of low or moderate water contamination, such as observed in the Sutla River, and those were nonessential elements Li and Cs and essential element Fe. The results of our study present an important contribution to maintenance of high ecological status of European freshwaters, through enrichment of knowledge on the bioaccumulation of various metals in gills of European chub as frequently applied bioindicator species in monitoring of water pollution.

Linking physiology and biomineralization processes to ecological inferences on the life history of fishes

Biomineral chemistry is frequently used to infer life history events and habitat use in fishes; however, significant gaps remain in our understanding of the underlying mechanisms. Here we have taken a multidisciplinary approach to review the current understanding of element incorporation into biomineralized structures in fishes. Biominerals are primarily composed of calcium-based derivatives such as calcium carbonate found in otoliths and calcium phosphates found in scales, fins and bones. By focusing on non-essential life elements (strontium and barium) and essential life elements (calcium, zinc and magnesium), we attempt to connect several fields of study to synergise how physiology may influence biomineralization and subsequent inference of life history. Data provided in this review indicate that the presence of non-essential elements in biominerals of fish is driven primarily by hypo- and hyper-calcemic environmental conditions. The uptake kinetics between environmental calcium and its competing mimics define what is ultimately incorporated in the biomineral structure. Conversely, circannual hormonally driven variations likely influence essential life elements like zinc that are known to associate with enzyme function. Environmental temperature and pH as well as uptake kinetics for strontium and barium isotopes demonstrate the role of mass fractionation in isotope selection for uptake into fish bony structures. In consideration of calcium mobilisation, the action of osteoclast-like cells on calcium phosphates of scales, fins and bones likely plays a role in fractionation along with transport kinetics. Additional investigations into calcium mobilisation are warranted to understand differing views of strontium, and barium isotope fractionation between calcium phosphates and calcium carbonate structures in fishes.

Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge

Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed.

[Proteases of calpain family in water invertebrates and fish]

The activity of Ca2+-dependent proteases, or calpains (EC 3.4.22.17), in a wide range of aquatic invertebrates (Oligochaeta, Hirudinea, Crustacea, Insecta, Gastropoda, Bivalvia) and vertebrates (Osteichthyes) was estimated. Detected molecular properties ofcalpains from the tissues of different species allow considering the complication of their structural organization and regulatory mechanisms between invertebrates and vertebrates in comparative-evolutionary aspect. Certain conclusions can be drawn about changes in the functional role of this proteolytic system in the cell metabolism.

Utility of tissue residues for predicting effects of metals on aquatic organisms

As part of a SETAC Pellston Workshop, we evaluated the potential use of metal tissue residues for predicting effects in aquatic organisms. This evaluation included consideration of different conceptual models and then development of several case studies on how tissue residues might be applied for metals, assessing the strengths and weaknesses of these different approaches. We further developed a new conceptual model in which metal tissue concentrations from metal-accumulating organisms (principally invertebrates) that are relatively insensitive to metal toxicity could be used as predictors of effects in metal-sensitive taxa that typically do not accumulate metals to a significant degree. Overall, we conclude that the use of tissue residue assessment for metals other than organometals has not led to the development of a generalized approach as in the case of organic substances. Species-specific and site-specific approaches have been developed for one or more metals (e.g., Ni). The use of gill tissue residues within the biotic ligand model is another successful application. Aquatic organisms contain a diverse array of homeostatic mechanisms that are both metal- and species-specific. As a result, use of whole-body measurements (and often specific organs) for metals does not lead to a defensible position regarding risk to the organism. Rather, we suggest that in the short term, with sufficient validation, species- and site-specific approaches for metals can be developed. In the longer term it may be possible to use metal-accumulating species to predict toxicity to metal-sensitive species with appropriate field validation.

A review and test of predictive models for the bioaccumulation of radiostrontium in fish

Empirical relations between the (90)Sr concentration factor (CF) and the calcium concentration in freshwater aquatic systems have previously been determined in studies based on data obtained prior to the Chernobyl accident. The purpose of the present research is to review and compare these models, and to test them against a database of post-Chernobyl measurements from rivers and lakes in Ukraine, Russia, Belarus and Finland. It was found that two independently developed models, based on pre-Chernobyl empirical data, are in close agreement with each other, and with empirical data. Testing of both models against new data obtained after the Chernobyl accident confirms the models' predictive ability. An investigation of the influence of fish size on (90)Sr accumulation showed no significant relationship, though the data set was somewhat limited.

pH modulates transport rates of manganese and cadmium in the green alga Chlamydomonas reinhardtii through non-competitive interactions: implications for an algal BLM

The influence of pH on short-term uptake of manganese and cadmium by the green alga Chlamydomonas reinhardtii was studied to better understand the nature of proton interactions with metal membrane transporters. Manganese and cadmium internalization fluxes (J(int)) were measured over a wide range of free metal ion concentrations from 1 x 10(-10) to 4 x 10(-4)M at several pH values (Mn: 5.0, 6.5 and 8.0; Cd: 5.0 and 6.5). For both metals, first-order biological internalization kinetics were observed but the maximum transport flux (J(max)) decreased when pH decreased, in contradiction with the Biotic Ligand Model (BLM). This result suggested a non-competitive inhibition of metal uptake by the H(+)-ion. A Michaelis-Menten type inhibition model considering proton and calcium competition was tested. The metal biotic ligand stability constants and the stability constants for competitive binding of Ca(2+) and H(+) with the metal transporters were calculated: for manganese, K(Mn)=10(4.20) and K(Ca)=10(3.71); for cadmium, K(Cd)=10(4.19) and K(Ca)=10(4.76); for both metal transport systems, K(H) was not a significant parameter. Furthermore, metal uptake was not significantly influenced by the pH of the antecedent growth medium, suggesting that increases in metal fluxes as the pH is raised are caused by conformational changes of the surface transport proteins rather than by the synthesis of additional transport sites. Our results demonstrate that the BLM in its present state does not properly describe the true influence of pH on manganese and cadmium uptake by algae and that a non-competitive inhibition component must be integrated.

Modelling the dispersion of radionuclides following short duration releases to rivers: Part 2. Uptake by fish

This paper evaluates and generalizes state-of-the-art approaches for dynamic modelling of bioaccumulation in fish resulting from short duration liquid discharges of radionuclides ((3)H, (14)C, (60)Co, (134)Cs, (137)Cs, (65)Zn, (89)Sr, (90)Sr, (125)I, (131)I, (241)Am, isotopes of Pu and U) to rivers. Based on a review of model parameter values, predictions are made of maximum and time-integrated activity concentrations in fish. A simplified version of the model was developed and presented as "look-up" graphs. The influence of various environmental parameters on model output was evaluated by sensitivity analysis. Maximum and time-integrated concentrations in fish may be predicted for rivers based on the river volumetric flow rate and water temperature. It is demonstrated that the dynamic model gives lower and more realistic predictions of maximum concentrations in fish than the simpler "Concentration Factor" approach. However, for time-integrated concentration in fish, and estimation of radiation dose to humans from consumption of the fish, the Concentration Factor approach gives similar predictions to the dynamic model.

Mercury and other trace elements in a pelagic Arctic marine food web (Northwater Polynya, Baffin Bay)

Total mercury (THg), methylmercury (MeHg) and 22 other trace elements were measured in ice algae, three species of zooplankton, mixed zooplankton samples, Arctic cod (Boreogadus saida), ringed seals (Phoca hispida) and eight species of seabirds to examine the trophodynamics of these metals in an Arctic marine food web. All samples were collected in 1998 in the Northwater Polynya (NOW) located between Ellesmere Island and Greenland in Baffin Bay. THg and MeHg were found to biomagnify through the NOW food web, based on significant positive relationships between log THg and log MeHg concentrations vs. delta15N muscle and liver . The slope of these relationships for muscle THg and MeHg concentrations (slope=0.197 and 0.223, respectively) were similar to those reported for other aquatic food webs. The food web behavior of THg and delta15N appears constant, regardless of trophic state (eutrophic vs. oligotrophic), latitude (Arctic vs. tropical) or salinity (marine vs. freshwater) of the ecosystem. Rb in both liver and muscle tissue and Zn in muscle tissue were also found to biomagnify through this food web, although at a rate that is approximately 25% of that of THg. A number of elements (Cd, Pb and Ni in muscle tissue and Cd and Li in seabird liver tissue) were found to decrease trophically through the food web, as indicated by significantly negative relationships with tissue-specific delta15N. A diverse group of metals (Ag, Ba, La, Li, Sb, Sr, U and V) were found to have higher concentrations in zooplankton than seabirds or marine mammals due to bioconcentration from seawater. The remaining metals (As, Co, Cu, Ga, Mn, Mo and Se in muscle tissue) showed no relationship with trophic position, as indicated by delta15N values, although As in liver tissue showed significant biomagnification in the seabird portion of the food web.

The "AQUASCOPE" simplified model for predicting 89,90Sr, 131I, and 134,137Cs in surface waters after a large-scale radioactive fallout

Simplified dynamic models have been developed for predicting the concentrations of radiocesium, radiostrontium, and I in surface waters and freshwater fish following a large-scale radioactive fallout. The models are intended to give averaged estimates for radionuclides in water bodies and in fish for all times after a radioactive fallout event. The models are parameterized using empirical data collected for many lakes and rivers in Belarus, Russia, Ukraine, UK, Finland, Italy, The Netherlands, and Germany. These measurements span a long time period after fallout from atmospheric nuclear weapons testing and following the Chernobyl accident. The models thus developed were tested against independent measurements from the Kiev Reservoir and Chernobyl Cooling Pond (Ukraine) and the Sozh River (Belarus) after the Chernobyl accident, from Lake Uruskul (Russia), following the Kyshtym accident in 1957, and from Haweswater Reservoir (UK), following atmospheric nuclear weapons testing. The AQUASCOPE models (implemented in EXCEL spreadsheets) and model documentation are available free of charge from the corresponding author.

Dynamic model for the accumulation of cadmium and zinc from water and sediment by the aquatic oligochaete, Tubifex tubifex

In aquatic environments, organisms are exposed to and accumulate metals via waterborne and dietary routes including ingested sediment. A key element in understanding metal uptake and accumulation is information concerning the relative importance of the routes of uptake and the kinetics of the processes. In this work the bioaccumulation of the essential element zinc and the nonessential element cadmium were studied from the aqueous and sediment phase, in the cosmopolitan oligochaete Tubifex tubifex, using the radiotracers 109Cd and 65Zn. A compartmental kinetic model was constructed and parametrized by fitting the model to metal body concentrations. Using the pharmacokinetic modeling approach and taking into account the distribution of the metal between water and sediment, the different routes were quantitatively separated. Under the experimental conditions, the sediment phase accounted for 9.8% of the cadmium and 52% of the zinc uptake. These values are based on the uptake of the radiotracers spiked sediments and therefore likely represent maximal values since it was shown that under the specific conditions this was the most mobile metal fraction. This difference was largely explained by the large difference in assimilation efficiency between cadmium and zinc. Simulations of different conditions showed that both dissolved and sediment-associated metal can be important sources of metal exposure for the worms and that the relative importance strongly depends on the metal and exposure conditions including the lability of the metals in the sediment phase.

A protective effect of dietary calcium against acute waterborne cadmium uptake in rainbow trout

The present study examined the interactions between elevated dietary calcium (as ionic Ca2+ in the form of CaCl2 x 2H2O) and acute waterborne Cd exposure (50 microg/l as CdNO3 for 3 h) on whole body uptake and internal distribution of newly accumulated Cd, Ca2+, and Na+ in juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed with three diets 20 (control), 30 and 60 mg Ca2+/g food: for 7 days before fluxes were measured with radiotracers over a 3h period. The two elevated Ca2+ diets reduced the whole body uptake of both Ca2+ and Cd by >50% and similarly reduced the internalization of both newly accumulated metals in most tissues, effects which reflect the shared branchial uptake route for Ca2+ and Cd. As the Ca2+ concentrations of the fluid phases of the stomach and intestinal contents were greatly elevated by the experimental diets, increased gastrointestinal Ca2+ uptake likely caused the down-regulation of the branchial Ca2+ (and Cd) uptake pathway. Waterborne Na+ uptake and internal distribution were not affected. While plasma Ca2+ surged after the first two feedings of the 60 mg Ca2+/g diet, internal homeostasis was quickly restored. Total Ca2+, Na+, and Cl- levels in tissues were not affected by diets. While dietary Ca2+ protected against waterborne Cd uptake, it did not protect against the relative inhibition of waterborne Ca2+ uptake caused by waterborne Cd. Acute exposure to 50 microg/l Cd reduced the uptake and internalization of newly accumulated Ca2+ (but not Na+) by 70% or more, regardless of diet. Since elevated dietary Ca2+ reduces waterborne Cd uptake, fish eating a Ca(2+)-rich invertebrate diet may be more protected against waterborne Cd toxicity in a field situation.

Speciation and Bioavailability of Trace Metals in Water: Progress Since 1982

The advances in studies of trace metal speciation and bioavailability since Mark Florence’s 1982 review of the topic, published in Talanta, have been comprehensively reviewed. While the relative merits of kinetic and equilibrium approaches are still being determined, advances in the applications of stripping voltammetry, including the application of microelectrodes and an appreciation of detection windows in both CSV and ASV, have been matched by the introduction of new dynamic techniques including diffusive gradients in thin films (DGTs), permeation liquid membranes (PLMs), and improved applications of chelating resins. There have also been improvements in equilibrium techniques such as ion-selective electrodes and Donnan dialysis. The ability of geochemical speciation models to predict metal complexation by natural organic matter has greatly improved, yet the models still require validation against field measurements. More reliable and relevant bioassays have been developed using sensitive species such as algae and bacteria, and improved protocols are eliminating uncertainties particularly due to problems with high cell densities, and are allowing more useful comparisons with chemically estimated bioavailability. While the free-ion activity model has provided an improved interpretation of the relative toxicities observed with different metal species, its extension to the biotic ligand model is leading to better predictions of acute effects at least on higher organisms. The extension of such approaches to studies of chronic effects at ‘natural’ concentrations using unicellular organisms remains a challenge, as does the evaluation of whether such approaches are simplified limiting cases of a more dynamic natural situation where chemical reactivity and rates of metal transport could be important.

Bioavailability of waterborne strontium to the common carp, Cyprinus carpio, in complexing environments

The uptake of strontium (Sr) and calcium (Ca) in the common carp, Cyprinus carpio, was studied in chemically defined freshwater in the presence of the complexing ligands, ethylenediaminetetraacetic acid (EDTA), and nitrilotriacetic acid (NTA). The uptake rates were measured in the whole body, gills, and blood of the fish after an exposure period of 3 h. The uptake rates were determined by using the radiotracers (85)Sr and (45)Ca, and analyzed as a function of the free-ion activity of Sr and Ca in water. Although Sr(2+) activity decreased, the uptake of Sr showed an increase at relatively low concentrations of EDTA and NTA, and a decrease at relatively high concentrations. This can be explained by the decreased competition between Sr(2+) and Ca(2+) at the gill uptake sites due to approximately 30-140-fold higher affinity of EDTA and NTA for Ca(2+) than Sr(2+). With decreasing Ca(2+) activity, Ca uptake rates decreased in the presence of EDTA and NTA, but the effect of NTA was less pronounced. A Michaelis-Menten type competitive inhibition model was derived that could predict the whole-body Sr and Ca uptake rates, taking into account the ambient Sr(2+) and Ca(2+) activities in the presence of EDTA. In case of NTA, the uptake rates were found to be 1.5-3.2 times higher than what was predicted by the model. When the fish were exposed to complexing environments in the complete absence of Ca, an increased uptake of Sr was still observed in case of NTA, but not EDTA. The increased uptake in the presence of NTA is attributed to the direct uptake of SrNTA(-) and CaNTA(-) complexes from water. The results reveal that the uptake of Sr and Ca in carp is not merely a function of the free metal-ion activity but that certain complex species may contribute significantly to overall uptake.

Metal speciation dynamics and bioavailability: Zn(II) and Cd(II) uptake by mussel (Mytilus edulis) and carp (Cyprinus carpio)

In the analysis of metal biouptake from complexing environments, both chemical speciation and biological uptake characteristics have to be taken into account. The commonly used free ion activity model is based on equilibrium speciation and implies that diffusion of the bioactive free metal toward the organism is not rate-limiting. In the presence of complexes, however, sufficiently labile species might contribute to the biouptake via preceding dissociation. Coupling of the ensuing diffusional mass transfer flux of metal with the biouptake flux of free metal, the supposedly bioactive species, shows under which conditions labile metal complexes can contribute to the uptake. The goal of the present paper is to apply this type of analysis to experimental data on metal uptake by mussel (Mytilus edulis) and carp (Cyprinus carpio) in complexing environments. These biosystems have fairly well-characterized uptake parameters, but the uptake fluxes cannot be fully explained by considering equilibrium speciation only. For Zn(II) uptake by mussel, evidence was found for diffusional limitation at low concentrations, whereas for Cd(III) uptake by carp, diffusion is not limiting at all. The analysis provides an example of how a more comprehensive treatment of complex systems can be applied to real experimental data.

Effect of temperature on the uptake of waterborne strontium in the common carp, Cyprinus carpio (L.)

The effect of temperature on the uptake kinetics of strontium (Sr) in the common carp (Cyprinus carpio) was studied in vivo, exposing pre-acclimated fish to a wide range of Sr concentrations in water (Sr(total)=0.2-10,000 microM; Ca(total)=348 microM) at 10, 20, 25 and 30 degrees C. Sr uptake rates were determined in the whole body, gills and blood of the fish after an exposure period of 3 h and were analyzed as a function of the free-ion activity of Sr and Ca in water. The uptake of Sr(2+) by the whole body, gills and blood increased with temperature and showed saturation kinetics with the increase of Sr(2+) activity. Analyzing the observed uptake rates with a Michaelis-Menten type model showed that the kinetic parameters (J(max), K(m) and K(i)) for both Sr(2+) and its analogue Ca(2+) are temperature dependent. Thermodynamic analysis of the temperature effects indicates that the Arrhenius activation energies (E(a)) required for Sr(2+) uptake (91.9 kJ mol(-1)) and Ca(2+) uptake (105.9 kJ mol(-1)) in the whole body of carp were constant over the temperature range 10-25 degrees C and showed a break in the Arrhenius plots above this temperature. The Arrhenius plot for the Sr(2+) uptake in blood was similar to that for the whole body uptake with an E(a) of 98.1 kJ mol(-1). However, the E(a) for Sr(2+) uptake in gills was much smaller and constant (58.1 kJ mol(-1)) over the temperature range of 10-30 degrees C. For a temperature change from 10 to 25 degrees C, the Q(10) for Sr(2+) uptake in whole fish, gills and blood were 3.71, 2.29 and 4.05, respectively. Compared with Ca(2+) uptake, Sr(2+) uptake appears to require a lower activation energy for transport across the solution body interface in carp. The similar pattern of Arrhenius plots and magnitude of activation energies for Sr(2+) uptake both in blood and whole fish suggest that the uptake into the blood across the basolateral membrane is the rate-limiting energy barrier and hence dictates the overall uptake rate of Sr(2+) in whole fish.