Internal Metal Concentrations Research Articles

Polyploidy affects responses to Nickel in Ni-hyperaccumulating plants: Evidence from the model species Odontarrhena bertolonii (Brassicaceae)

Compared with their diploid progenitors, polyploid plants often display enhanced vigor and adaptive ability to extreme conditions. Previous studies investigated polyploid fitness under various forms of environmental stress, but whether the whole-genome duplication can affect growth, accumulation ability and tolerance levels to trace metals in metal-accumulating species remains obscure. We investigated this topic using an experimental approach and Odontarrhena bertolonii as model system. This obligate serpentine endemic includes diploid and tetraploid accessions with allopatric distribution in Tuscany and Liguria. Three diploid (2 n = 2x = 16) and three natural autotetraploid (2 n = 4x = 32) accessions were compared for growth, leaf traits, photosynthetic parameters and metal accumulation after cultivation on natural serpentine soil and in Ni-containing hydroponic solutions. In soil cultivation, shoot Ni concentration was similar in diploid and tetraploid plants, but the metal content per plant was significantly higher in polyploids because of their higher biomass production. The latter was mainly due to the production of larger leaves, coupled to a lower specific leaf area, which pointed to a better adaptation of the tetraploids to serpentine soil. In hydroponics, all the accessions showed an hormetic-like Ni effect, with stimulation of growth and photosynthesis in the low-dose zone. The data fitting to the hormetic model displayed significant differences in some parameters, with the tetraploid plants showing higher maximal length of roots and shoots and higher requirement of both external and internal Ni concentrations for optimal growth, in respect to diploid plants. On the other hand, Ni tolerance to both external and internal metal concentrations was similar in the plants of the two ploidy levels. Our results suggest that whole-genome duplication can affect the potential for growth and Ni-hyperaccumulation in obligate Ni-accumulator plants like O. bertolonii. This points to the opportunity of selecting polyploid instead of diploid accessions for environmental restoration and metal cropping practices, when the candidate species includes both chromosome races.

Toxicokinetics and toxicodynamics of chromium in the soil invertebrate Enchytraeus crypticus (Oligochaeta)

Chromium emissions led to increased concentrations in soil, where it can affect soil organisms to relevant levels. With the aim of better understanding the effects of Cr throughout time, its toxicokinetics-toxicodynamics (TKTD) were evaluated in the soil model organism Enchytraeus crypticus to assess the development of internal concentrations and consequent toxic effects. To achieve this goal, organisms were exposed in LUFA 2.2 soil spiked with increasing CrCl3 concentrations. During the 21-day exposure period, survival, internal concentrations, and reproduction were evaluated at several time points up to 21 days. Uptake and elimination rate constants were 0.0044 kg soil/kg organism/day and 0.023 per day, respectively. Internal Cr concentrations increased with time, generally reaching equilibrium within 14 days with an estimated LC50inter (based on internal metal concentrations) of 57.7 mg Cr/kg body DW. Internal Cr concentrations were regulated by the organisms up to exposure to 360 mg Cr/kg soil DW, where the elimination rate was highest, but at 546 mg Cr/kg soil DW the animals were no longer able to eliminate Cr, and the internal concentrations were well above the estimated LC50inter. At day 21, exposure to 546 mg Cr/kg soil DW significantly reduced survival by 23 %, while reproduction EC50 was 344 mg Cr/kg soil DW. This study highlights the advantages of using a TKTD approach to understand the development of internal metal concentrations in time and relate it to the phenotypical effects observed. Toxicity is better understood when also taking into account time and not just exposure concentration alone.

The amphipod Parhyale hawaiensis as a promising model in ecotoxicology

Near-shore marine/estuarine environments play an important role in the functioning of the marine ecosystem and are extremely vulnerable to the presence of chemical pollution. The ability to investigate the effects of pollution is limited by a lack of model organisms for which sufficient ecotoxicological information is available, and this is particularly true for tropical regions. The circumtropical marine amphipod Parhyale hawaiensis has become an important model organism in various disciplines, and here we summarize the scientific literature regarding the emergence of this model within ecotoxicology. P. hawaiensis is easily cultured in the laboratory and standardized ecotoxicity protocols have been developed and refined (e.g., miniaturized), and effects of toxicants on acute toxicity (Cd, Cu, Zn, Ag, ammonia, dyes, pesticides, environmental samples), genotoxicity as comet assay/micronuclei, and gene expression (Ag ion and Ag nanoparticles) and regeneration (pesticides) have been published. Methods for determination of internal concentrations of metals (Cu and Ag) and organic substances (synthetic dye) in hemolymph were successfully developed providing sources for the establishment of toxicokinetics models in aquatic amphipods. Protocols to evaluate reproduction and growth, for testing immune responses and DNA damage in germ cells are under way. The sensitivity of P. hawaiensis, measured as 50% lethal concentration (LC50), is in the same range as other amphipods. The combination of feasibility to culture P. hawaiensis in laboratory, the recent protocols for ecotoxicity evaluation and the rapidly expanding knowledge on its biology make it especially attractive as a model organism and promising tool for risk assessment evaluations in tropical environments.

Toxicokinetics and toxicodynamics of copper and cadmium in the soil invertebrate Enchytraeus crypticus (Oligochaeta)

The aim of this study was to evaluate the toxicokinetics-toxicodynamics (TKTD) of Cu and Cd in the soil model organism Enchytraeus crypticus, and assess the development of internal effect concentrations over time. Animals were exposed in LUFA 2.2 soil spiked with increasing concentrations of Cu and Cd. Survival, reproduction and internal metal concentrations in the animals were evaluated at different points in time over a period of 21 days. Internal concentrations increased with time, for Cu reaching a steady state after c. 10 days, except for the highest test concentration, and for Cd continuing to increase after 21 days. Applying a one-compartment model to all data together, estimated uptake and elimination rate constants for Cu and Cd were 0.08 and 0.45 kg soil/kg organism/day and 0.4 and 0.04 per day, respectively. Median lethal concentrations, based on total soil concentrations, decreased with time for Cu and did not reach a steady state level, but they did not change with time for Cd. The LC50inter (based on internal concentrations) was 75 mg Cu/kg body DW and > 800 mg Cd/kg body weight. Animals were able to regulate Cu internal concentrations, keeping them low, while for Cd internal concentrations continued to increase showing lack of regulation and also the importance of exposure time. This study highlights the advantages of using a TKTD approach to understand the relation between organism survival and internal Cu or Cd concentrations over time.

Toxicokinetics of Chromium in Enchytraeus crypticus (Oligochaeta).

Chromium is naturally occurring, but emission from anthropogenic sources can lead to increased soil concentrations. Information on its toxicokinetics is essential in order to understand the time needed to reach toxicity and the mechanisms of uptake/elimination. In this study the toxicokinetics of Cr(III) was evaluated using the soil standard species Enchytraeus crypticus. The animals were exposed to 180 mg Cr/kg dry soil, a sublethal concentration, in LUFA 2.2 natural soil. OECD guideline 317 was followed, with a 14-day uptake phase in spiked soil followed by a 14-day elimination in clean soil. Exposure to Cr led to fast uptake and elimination, with Ku = 0.012 kgsoil/kgorganism/day and Ke = 0.57 day−1. The bioaccumulation factor was 0.022, and DT50 for elimination was 1.2 days. The concentration of Cr reached an internal equilibrium in the animals after 10 days. Transfer to clean soil allowed body Cr concentrations to return to background levels after approximately 7 days. E. crypticus seemed able to efficiently regulate internal Cr concentrations by actively eliminating Cr (an essential element). Although Ku and Ke deviated from the values reported in other studies for other soil invertebrates, the bioaccumulation factors were similar. These findings show the importance of toxicokinetic studies in evaluating toxicity based on internal metal concentrations that can more accurately represent the bioavailable concentration.

Toxicokinetics of metals in the soil invertebrate Enchytraeus crypticus exposed to field-contaminated soils from a mining area

Toxicokinetics may help assessing the risk of metal-contaminated soils by quantifying the development of internal metal concentrations in organisms over time. This study assessed the toxicokinetics in Enchytraeus crypticus of non-essential (Pb and Cd) and essential elements (Zn and Cu) in metal-contaminated field soils from a mining area, containing 3.49–24.3 mg Cd/kg dry soil, 433–1416 mg Pb/kg dry soil, 15.7–44.9 mg Cu/kg dry soil and 1718–6050 mg Zn/kg dry soil. Three different uptake-elimination patterns in E. crypticus were found. Both essential elements (Zn and Cu) showed fast increasing internal concentrations reaching equilibrium within 2 d in the uptake phase, without hardly any elimination after transfer to clean soil. The non-essential Cd showed a slow linear accumulation and excretion with body concentrations not reaching steady state within 21 d. Internal Pb concentrations, however, reached equilibrium within 7 d in the uptake phase. Longer exposure times in ecotoxicological tests, therefore, are required for elements like Cd. Porewater pH and dissolved organic carbon (DOC) levels were the dominant factors controlling Cd uptake from the test soils. The 21-d body Cd and Pb concentrations were best explained from 0.01 M CaCl2-extractable soil concentrations. Steady-state Cu and Zn body concentrations were independent of soil exposure concentrations. Bioaccumulation factors (BAF) were low for Pb (<0.1 kgsoil/kgworm), but high for Cd at 1.78–24.3 kgsoil/kgworm, suggesting a potential risk of Cd biomagnification in the terrestrial food chain of the mining area ecosystem.

Dose-dependent effects of lead and cadmium and the influence of soil properties on their uptake by Helix aspersa: an ecotoxicity test approach.

Three soil types with different physicochemical properties were selected to evaluate their effect on lead and cadmium bioavailability and toxicity in the land snail Helix aspersa. In 28-day ecotoxicity tests, H. aspersa juveniles were exposed to increasing concentrations of Pb or Cd. EC50s, concentrations reducing snail growth by 50%, differed between the soils and so did Cd and Pb uptake in the snails. For lead, EC50s were 2397-6357 mg Pb/kg dry soil, while they ranged between 327 and 910 mg Cd/kg dry soil for cadmium. Toxicity and metal uptake were highest on the soil with the lowest pH, organic matter content and Cation Exchange Capacity (CEC). Growth reduction was correlated with metal accumulation levels in the snails' soft body, and differences in toxicity between the soils decreased when EC50s were expressed on the basis of internal metal concentrations in the snails. These results confirm the effect of soil properties; pH, CEC, OM content, on the uptake and growth effect of Pb and Cd in H. aspersa, indicating the importance of properly characterizing soils when assessing the environmental risk of metal contaminated sites.

Feathers and hair as tools for non-destructive pollution exposure assessment in a mining site of the Iberian Pyrite Belt

Mining is responsible of releasing trace elements to the environment with potential negative effects on wildlife. Traditionally, wildlife exposure assessment has been developed by analyzing mainly environmental compartments or internal tissues. Nowadays, the use of non-destructive matrices such as hair or feathers has increased. Nevertheless, its use in free-living terrestrial mammals or in birds other than raptors or passerines is less frequent. The main objective of our study was to determine the potential for hair and feathers in a rabbit and bird species to be used as non-invasive proxy tissues for assessing internal metal concentrations at polluted sites from mining. We tested whether hair of European rabbit (Oryctolagus cuniculus) and feathers of red-legged partridge (Alectoris rufa) can be used as non-destructive biological monitoring tools of both essential (Cu, Zn) and non-essential (Pb, Cd, As) trace elements in a currently active copper mining site. We found significant different concentrations, particularly in non-essential elements, between reference area and mining site. Non-essential elements Pb and Cd showed higher correlations between tissues and hair/feathers, while few significant patterns were observed for essential elements such as Cu and Zn. Although feathers showed lower levels of correlation with internal tissues than hair, both could be useful as non-destructive biological monitoring tools. Further tissues, and more importantly, hair and feathers allowed discrimination between polluted and reference sites to indicate bioavailability and pollution status. In addition, hair and feathers can be used in monitoring pollution of an active mining site, being specially interesting for biomonitoring a certain period of time in the event of a particular episode of pollution, in addition to the chronic exposure. As occurred with hair in rabbits, feathers seem to be a good compartment to detect differences between a potential polluted area, such the surrounding of an active mine site, and a non-polluted area.

White-tailed eagle (Haliaeetus albicilla) feathers from Norway are suitable for monitoring of legacy, but not emerging contaminants

While feathers have been successfully validated for monitoring of internal concentrations of heavy metals and legacy persistent organic pollutants (POPs), less is known about their suitability for monitoring of emerging contaminants (ECs). Our study presents a broad investigation of both legacy POPs and ECs in non-destructive matrices from a bird of prey. Plasma and feathers were sampled in 2015 and 2016 from 70 whitetailed eagle (Haliaeetus albicilla) nestlings from two archipelagos in Norway. Preen oil was also sampled in 2016. Samples were analysed for POPs (polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorinated pesticides (OCPs)) and ECs (per- and polyfluoroalkyl substances (PFASs), dechlorane plus (DPs), phosphate and novel brominated flame retardants (PFRs and NBFRs)). A total of nine PCBs, three OCPs, one PBDE and one PFAS were detected in over 50% of the plasma and feather samples within each sampling year and location.Significant and positive correlations were found between plasma, feathers and preen oil concentrations of legacy POPs and confirm the findings of previous research on the usefulness of these matrices for non-destructive monitoring. In contrast, the suitability of feathers for ECs seems to be limited. Detection frequencies (DF) of PFASs were higher in plasma (mean DF: 78%) than in feathers (mean DF: 38%). Only perfluoroundecanoic acid could be quantified in over 50% of both plasma and feather samples, yet their correlation was poor and not significant. The detection frequencies of PFRs, NBFRs and DPs were very low in plasma (mean DF: 1–13%), compared to feathers (mean DF: 10–57%). This may suggest external atmospheric deposition, rapid internal biotransformation or excretion of these compounds. Accordingly, we suggest prioritising plasma for PFASs analyses, while the sources of PFRs, NBFRs and DPs in feathers and plasma need further investigation.

Trace element transfer from two contaminated soil series to Medicago sativa and one of its herbivores, Spodoptera exigua

ABSTRACTAlfalfa was cultivated in two potted soil series obtained from two sandy soils contaminated by Cu (SM) and metal(loids)/PAH (CD). Shoot production was monitored for 8 weeks. Then, larvae of Spodoptera exigua were reared on alfalfa of both soil series for eight days. A biotest (using Phaseolus vulgaris) was used to assess the soil phytotoxicity. Increasing soil contamination reduced P. vulgaris growth, but alfalfa growth was only reduced on the SM soil series. Exposure to the SM soil was mirrored by shoot Cu and Cr concentrations of alfalfa (respectively, in mg kg −1 DW, Cu and Cr ranged from 11.9 and 0.4 in the CTRL soil to 98.5 and 1.2 in the SM one). Exposure to the CD soil series was mirrored by shoot Zn concentrations (i.e., 48–91.6 mg kg−1 DW). Internal metal(loid) concentrations of S. exigua remained generally steady across both soil series (respectively Cd 0.05–0.16, Cr 0.5–3.3, Cu 5.8–98.5, Ni 0.6–1.6, Pb 0.4–1.3, and Zn 57–337 mg kg−1 DW), and most of the associated transfer factors were lower than 1. Here, due to the excluder phenotype of alfalfa across our TE contamination gradients, S. exigua could cope with high total metal(loid) concentration in both contaminated soils.

Influence of metal-contamination on distribution in subcellular fractions of the earthworm (Metaphire californica) from Hunan Province, China

Earthworms have the ability to accumulate of heavy metals, however, there was few studies that addressed the metals in earthworm at subcellular levels in fields. The distributions of metals (Cd, Cu, Zn, and Pb) in subcellular fractions (cytosol, debris, and granules) of earthworm Metaphire californica were investigated. The relationship between soil metals and earthworms were analyzed to explain its high plasticity to inhabit in situ contaminated soil of Hunan Province, south China. The concentration of Cd in subcellular compartments showed the same pattern as Cu in the order of cytosol > debris > granules. The distribution of Zn and Pb in earthworms indicated a similar propensity for different subcellular fractions that ranked as granules > debris > cytosol for Zn, and granules > cytosol > debris for Pb. The internal metal concentrations in earthworms increased with the soil metals (p<0.05). Significant positive correlations were found between soil Cd and Cd concentrations in cytosol and debris (p<0.01). Moreover, the soil Pb concentration significantly influenced the Pb concentrations in cytosol and debris (p<0.01), similar to that of Cd. The soil Cu concentrations was only associated with the Cu in granules (p<0.05). Soil Zn concentrations correlated with the Zn concentrations in each subcellular fraction (p<0.05). Our results provide insights into the variations of metals partitioning in earthworms at subcellular levels and the relationships of soil metals, which could be one of the detoxification strategies to adapt the long-term contaminated environment.

Chronic and reproductive toxicity of cadmium, zinc, and lead in binary and tertiary mixtures to the earthworm (Eisenia fetida)

The presence of one metal can alter the toxicity of another metal by having an additive, synergistic, or antagonistic impact. Mixed metal pollution has clear ecological consequences. The importance of use of earthworms for ecological health monitoring is recognized widely. This study investigated the effect of binary and tertiary metal mixtures on the toxicity, bioaccumulation, and reproduction of the Eisenia fetida in different South Australian soils. The end points used in this 56-day reproduction study were avoidance behavior, worm mortality, weight loss, reproduction, and metal (Cd, Zn, and Pb) bioaccumulation. The three soils (acidic, neutral, and alkaline) were spiked with selected binary and tertiary concentration mixtures that considered the soil quality guideline values, EC50 and LC50 values for Cd, Zn, and Pb obtained from the previous single metal earthworm experiments done by the authors. In acidic soil, Zn and Cd constituted the most toxic metal combination to earthworms. However, in contrast to this observation, the same metal combination was the least toxic one to earthworms in neutral and alkaline soils. For Zn and Pb spiked soils, relationships between soil and internal metal concentrations were found with R 2 = 0.63, r = 0.8, and R 2 = 0.94, p < 0.01, respectively, for Zn and Pb. This study indicates that earthworms have high tendency to bioaccumulate heavy metals in their tissues and hence serves as ecological indicators of soil heavy metal contamination. The highest bioaccumulation factor (0–9) was evident for Cd in contaminated soils. This study demonstrated the role of soil edaphic factors and metal-metal interactions in the toxicity of metal mixtures to E. fetida. In Zn and Pb binary mixture spiked acidic soil, mortality of 60% was recorded even when the Pb and Zn concentrations were below the Canada and Dutch EIL (ecological investigational levels) values. This indicates the current guideline values are not safe for mixed metal toxicity. Therefore, care must be taken when predicting metal toxicities in mixed metal contaminated soils.

Evaluating blood and excrement as bioindicators for metal accumulation in birds.

Birds are widely used to assess metal contamination in the environment and there are different approaches to determine the exposure level in individuals, some being destructive (collection of soft tissues) and some non-destructive (blood, feathers and excrement). The use of blood to detect internal concentrations of metals is an acknowledged method, but to what extent blood can predict the concentrations in soft tissues has been less well evaluated in wild terrestrial birds. The same is true for excrements. This study compares the non-destructive methods using blood and excrement with liver sampling, with respect to exposure and accumulation of the elements arsenic, cadmium, copper, lead and zinc in nestling pied flycatchers (Ficedula hypoleuca). Blood, liver and excrement reflected the environmental exposure of non-essential elements and were independent of nestling sex. There were asymptotic relationships between the concentration of arsenic, cadmium and lead in liver and blood, excrement and liver, and excrement and blood, but none for copper or zinc. Those relationships were generally stronger between liver and blood than between excrements and internal concentrations. Lead had the strongest associations for all matrixes. The conclusion is that blood is an appropriate tool to assess accumulation of arsenic, cadmium and especially lead, but that blood can underestimate the accumulation at highly contaminated sites. Excrement can also give an indication of metal accumulation, but may overestimate internal concentrations at high exposure, and individual variability makes direct comparisons between these matrices less appropriate.

Heavy metal (hyper)accumulation in leaves of Arabidopsis halleri is accompanied by a reduced performance of herbivores and shifts in leaf glucosinolate and element concentrations

Abiotic and biotic factors can significantly influence and modify the chemical composition of a plant. In this study the influences of exposure to cadmium and zinc and of herbivory on plant-insect interactions were investigated. We studied the performance of two herbivore species with different feeding modes (chewing versus sucking) on the metal-hyperaccumulator species Arabidopsis halleri (Brassicaceae) as well as individual glucosinolate (GLS) and element concentrations of young and old leaves in response to different soil and herbivore treatments. The performance of both insect species was reduced on plants grown on metal-amended soil compared to plants grown on unamended soil. This result supports the elemental defense hypothesis, which postulates that high internal metal concentrations can protect plants from herbivores and which was mostly tested with chewing herbivores so far. Alongside higher levels of heavy metals in plants grown on metal-amended soil, GLS and element concentrations were differentially affected in young versus old leaves and responded differently to herbivory. Concentrations of most GLS and elements were higher in young compared to old leaves, which is in line with the optimal defense theory, which predicts a better defense in more valuable tissue. Our results highlight that various organic as well as inorganic compounds in plants can be affected in different directions by the complex interplay between plants, herbivores, and heavy metal contamination of soil.

A structural equation model of soil metal bioavailability to earthworms: confronting causal theory and observations using a laboratory exposure to field-contaminated soils

Structural equation models (SEM) are increasingly used in ecology as multivariate analysis that can represent theoretical variables and address complex sets of hypotheses. Here we demonstrate the interest of SEM in ecotoxicology, more precisely to test the three-step concept of metal bioavailability to earthworms. The SEM modeled the three-step causal chain between environmental availability, environmental bioavailability and toxicological bioavailability. In the model, each step is an unmeasured (latent) variable reflected by several observed variables. In an exposure experiment designed specifically to test this SEM for Cd, Pb and Zn, Aporrectodea caliginosa was exposed to 31 agricultural field-contaminated soils. Chemical and biological measurements used included CaC12-extractable metal concentrations in soils, free ion concentration in soil solution as predicted by a geochemical model, dissolved metal concentration as predicted by a semi-mechanistic model, internal metal concentrations in total earthworms and in subcellular fractions, and several biomarkers. The observations verified the causal definition of Cd and Pb bioavailability in the SEM, but not for Zn. Several indicators consistently reflected the hypothetical causal definition and could thus be pertinent measurements of Cd and Pb bioavailability to earthworm in field-contaminated soils. SEM highlights that the metals present in the soil solution and easily extractable are not the main source of available metals for earthworms. This study further highlights SEM as a powerful tool that can handle natural ecosystem complexity, thus participating to the paradigm change in ecotoxicology from a bottom-up to a top-down approach.

Concentration dependent toxicokinetics of copper in the red flour beetle Tribolium castaneum (Coleoptera: Tenebrionidae).

To predict internal metal concentrations in animals under specific environmental exposures, the relationship between the exposure concentrations and values of toxicokinetic parameters must be known. At high exposure levels, the availability of carriers transporting metal ions through cellular membranes may become limited, thereby decreasing the assimilation rates (kA). Furthermore, increased metal concentrations in food may result in greater damage to the gut and reduce the assimilation efficiency and/or increase the elimination rate (kE). Therefore, kA should decrease and kE should increase with increasing metal concentrations. In fact, our study on Tribolium castaneum exposed to Cu at 500, 1000, 2000 and 4000 mg kg−1 of dry flour showed that with increasing Cu concentrations, kA decreased from 0.0042 day−1 at 500 mg kg−1 to 0.0026 day−1 at 4000 mg kg−1 in females and from 0.0029 to 0.001 day−1 in males and kE increased from 0.027 to 0.064 day−1 and from 0.018 to 0.04 day−1 in females and males, respectively. Significant differences in kA between the sexes were observed at 2000 and 4000 mg kg−1, whereas significant differences between treatments were found for kA in males. Copper was efficiently regulated by T. castaneum: an eightfold increase in exposure concentrations resulted in only a ca. twofold increase in the internal concentration. No Cu effect on the respiratory metabolism of T. castaneum was found.

Voltammetric characterisation of macroalgae-exuded organic ligands (L) in response to Cu and Zn: a source and stimuli for L

Environmental context Identifying the source and stimuli responsible for organic ligands in seawater is crucial to understanding trace metal availability. Voltammetric techniques were employed to characterise the water chemistry of seaweed cultures exposed to low levels of Cu or Zn over 7 days. The results suggest that seaweeds are a potential source of metal complexing ligands and Cu and Zn appear to stimulate ligand production; further research is required to determine if this is applicable to macroalgae and metals outside this study. Abstract It is widely accepted that organic ligands control metal speciation in seawater, although little is known about their source, stimuli or identity. To gain insight on the possible environmental controls of metal complexing ligands (L), three brown macroalgae common in Irish waters (Ascophyllum nodosum, Fucus vesiculosus and Laminaria hyperborea) were cultured under low levels of Cu (0, 7.86 or 15.7nM) or Zn (0, 15.2 or 91.7nM) exposure. Seaweed chlorophyll-a fluorescence (Fv/Fm), metal speciation (Cu, Zn), complexing ligands (LM), conditional stability constants (logK′LM), glutathione (GSH), cysteine (Cys) and seaweed metal contents were monitored over 7 days. Although there was no effect on the internal seaweed metal concentrations, Cu and Zn additions significantly altered the water chemistry of each culture. Metal additions increased the total dissolved metal concentrations for all three species. Significantly higher [LM] values in cultures with added metals than the relevant controls point to both metals as stimuli of L production. All species released ligands in response to Cu or Zn exposure, indicating each seaweed is a relevant source of L. Comparison of logK′ values to those of previously determined ligands provides little evidence that the ligands reported here belong to the compounds identified as L in the literature.

Low temperatures enhance the toxicity of copper and cadmium toEnchytraeus crypticusthrough different mechanisms

Knowledge about how toxicity changes with temperature is important for determining the extent of safety factors required when extrapolating from standard laboratory conditions to variable field scenarios. In the present study, the authors evaluated the toxicity of Cu and Cd to the potworm Enchytraeus crypticus at 6 temperatures in the range of 11 °C to 25 °C. For both metals, reproductive toxicity decreased approximately 2.5-fold with increasing temperature. This is contrary to what most other studies have found. Measurements of the bioavailable fraction of the metals in the soils and the internal metal concentrations in the worms over time showed that the major cause of change in toxicity with temperature for Cu was the worms' ability to regulate internal concentration at high temperatures. Uptake of Cd increased with time at all temperatures and with higher rates at high temperatures. Hence, the lower toxicity of Cd at high temperatures is proposed to be due to the E. crypticus being more efficient at immobilizing Cd and/or repairing damages at high compared to low temperatures. The present study concludes that no consistent relationship between metal toxicity and temperature across species can be made. The metabolic dependence of the species in terms of regulating metal uptake, excretion, immobilization, damage, and repair processes, will be crucial factors in determining species susceptibility to metals at varying temperatures.

Toxicokinetics of tilapia following high exposure to waterborne and dietary copper and implications for coping mechanisms

One of the major challenges in assessing the potential metal stress to aquatic organisms is explicitly predicting the internal dose in target organs. We aimed to understand the main sources of copper (Cu) accumulation in target organs of tilapia (Oreochromis mossambicus) and to investigate how the fish alter the process of Cu uptake, depuration, and accumulation (toxicokinetics (TK)) under prolonged conditions. We measured the temporal Cu profiles in selected organs after single and combined exposure to waterborne and dietary Cu for 14 days. Quantitative relations between different sources and levels of Cu, duration of treatment, and organ-specific Cu concentrations were established using TK modeling approaches. We show that water was the main source of Cu in the gills (>94 %), liver (>89 %), and alimentary canal (>86 %); the major source of Cu in the muscle (>51 %) was food. Cu uptake and depuration in tilapia organs were mediated under prolonged exposure conditions. In general, the uptake rate, depuration rate, and net bioaccumulation ability in all selected organs decreased with increasing waterborne Cu levels and duration of exposure. Muscle played a key role in accounting for the rapid Cu accumulation in the first period after exposure. Conversely, the liver acted as a terminal Cu storage site when exposure was extended. The TK processes of Cu in tilapia were highly changed under higher exposure conditions. The commonly used bioaccumulation model might lead to overestimations of the internal metal concentration with the basic assumption of constant TK processes.

Behavioural and physiological responses of Gammarus pulex exposed to cadmium and arsenate at three temperatures: individual and combined effects.

This study aimed at investigating both the individual and combined effects of cadmium (Cd) and arsenate (AsV) on the physiology and behaviour of the Crustacean Gammarus pulex at three temperatures (5, 10 and15°C). G. pulex was exposed during 96 h to (i) two [Cd] alone, (ii) two [AsV] alone, and (iii) four combinations of [Cd] and [AsV] to obtain a complete factorial plane. After exposure, survival, [AsV] or [Cd] in body tissues, behavioural (ventilatory and locomotor activities) and physiological responses (iono-regulation of [Na+] and [Cl−] in haemolymph) were examined. The interactive effects (antagonistic, additive or synergistic) of binary mixtures were evaluated for each tested temperature using a predictive model for the theoretically expected interactive effect of chemicals. In single metal exposure, both the internal metal concentration in body tissues and the mortality rate increased along metallic gradient concentration. Cd alone significantly impaired both [Na+] and [Cl−] while AsV alone had a weak impact only on [Cl−]. The behavioural responses of G. pulex declined with increasing metal concentration suggesting a reallocation of energy from behavioural responses to maintenance functions. The interaction between AsV and Cd was considered as ‘additive’ for all the tested binary mixtures and temperatures (except for the lowest combination at 10°C considered as “antagonistic”). In binary mixtures, the decrease in both ventilatory and locomotor activities and the decline in haemolymphatic [Cl−] were amplified when respectively compared to those observed with the same concentrations of AsV or Cd alone. However, the presence of AsV decreased the haemolymphatic [Na+] loss when G. pulex was exposed to the lowest Cd concentration. Finally, the observed physiological and behavioural effects (except ventilation) in G. pulex exposed to AsV and/or Cd were exacerbated under the highest temperature. The discussion encompasses both the toxicity mechanisms of these metals and their interaction with rising temperature.