The effect of environmental stress on absolute and mass-specific scope for growth in Daphnia magna Strauss

Daphnids were reared for 2 weeks in different concentrations of food or cadmium, and growth and reproduction were measured as endpoints. At the end of the 14-day experimental period, scope for growth (SFG) was measured and expressed per individual (mJ/ind/h=absolute SFG) and per mg dry weight (mJ/mg/h=mass-specific SFG). Both food deprivation and cadmium stress decreased body size, and absolute SFG decreased with decreasing body size in both exposure scenarios. Also mass-specific SFG decreased with decreasing body size under cadmium exposure, but an increase in mass-specific SFG was observed in the food ration experiment. This suggested that cadmium stress, apart from decreasing energy assimilation, also disturbs energy metabolism. Changes in both absolute and mass-specific SFG were mainly determined by changes in energy uptake, whereas energy loss varied little in response to both environmental stressors. With the cadmium-stressed daphnids, reproduction correlated positively with both absolute and mass-specific SFG. With the food-stressed daphnids however, reproduction correlated positively with absolute SFG but negatively with mass-specific SFG. Mass-corrected SFG still decreased with increasing cadmium stress, but did not differ between ration groups. Thus, mass-corrected SFG provides an indication of metabolic functioning, but appears less suited as an indicator of reproduction.     

Effects of cadmium exposure on feeding of freshwater planktonic crustaceans

1. Effects of cadmium exposure (0.010-0.100 ppm) on food consumption and assimilation rates of crustacean zooplankton from 2 lakes were studied in laboratory using radioisotope (14C) technique. 2. The inhibiting effects were significant 48 hr after Cd-exposure, but not after 20 hr exposure. 3. Daphnia spp. were the most affected cladocerans; copepods, especially the cyclopoids, appeared less sensitive. 4. The decrease in assimilation rates was much more marked than in the consumption rates. 5. The 14C-technique offers quick and sensitive means of studying the effects of heavy metal toxicity.     

Importance of metallothioneins in the cadmium detoxification process in Daphnia magna

Good knowledge of the relationship between toxic metals and biological systems, particularly the sub-cellular fraction, could be a suitable early indicator of toxic effects. These effects and the sub-cellular behaviour of cadmium were studied with a widely used species in freshwater toxicity bioassays, Daphnia magna. In spite of this very commonplace usage in ecotoxicological studies, very few data are available on its toxicant metabolism and in particular metal homeostasis. Combining multi-tools analysis, a soluble protein was found: it is heat-stable, rich in sulfhydryl groups (differential pulse polarography), characterised by a molecular mass of approximately 6.5 kDa, with a G-75 chromatographic profile corresponding to the rabbit metallothioneins monomer, with few if any aromatic-containing amino acids, it binds metals (e.g. Cd, Cu), and its concentration increases with Cd exposure. This evidence led us to hypothesise that metallothioneins (MTs) are present in D. magna. Up to 75% of the Cd body burden with Cd exposure is bound to the MTs fraction. The increase in the Cd concentration in the surrounding medium and concomitantly in daphnids induces sub-cellular reorganisation of essential metals such as Cu and Zn. The rate of metals in the soluble cellular fraction and associated with MTs increases with the Cd body burden. Monitoring sub-cellular distribution of metals after exposure in the natural environment could be very useful for ecotoxicological assessment.     

Cellular acidosis in rodents exposed to cadmium is caused by adaptation of the tissue rather than an early effect of toxicity

Proton (¹H) Nuclear Magnetic Resonance (NMR) spectroscopy was used to investigate the biochemical response of bank voles and wood mice (two wild rodent species frequently found on metal-contaminated sites) to chronic cadmium (Cd) insult. Similar effects, in terms of both metabolic changes (consistent with cellular acidosis) and induced metallothionin (MT) production were observed in all animals. These changes appeared to be an adaptation of the liver to toxic insult rather than onset of a toxic effect, and, in common with previous studies, were more marked in bank voles than wood mice. This may have reflected the greater Cd intake and assimilation of the former but was not explained by differences in concentrations of free (non MT-bound) Cd; concentrations of which were negligible in both voles and mice. Responses to Cd insult were detected in both species even though their bodies contained cadmium concentrations well below the World Health Organisation critical renal concentration of 200 μg/g dry mass.     

Biochemical biomarkers in chronically metal-stressed daphnids

Biochemical biomarkers are a popular measure of toxic effects on organisms due to their assumed fast response, and are usually assessed after acute exposure of the organism to the stressor. However, increasing interest in the use of biochemical biomarkers in environmental pollution monitoring calls for more laboratory long-term studies of contaminants' effects on biochemical endpoints. In this study, four biochemical biomarkers (protein content, activity of cholinesterase (ChE), catalase (CAT) and glutathione S-transferase (GST), were correlated with standardised reproductive and survival endpoints of water fleas (Daphnia magna) after chronic exposure to Cr (VI) and Cd. No effect on the reproduction and survival was noticed up to the highest tested concentration of Cr (VI) (52.5 microg/L), while the protein content, and the ChE and CAT activity decreased, and GST activity increased. Cd affected reproduction of daphnids above 0.656 microg/L, but the protein content and ChE activity were changed at 0.328 microg/L and 0.082 microg/L of Cd, respectively. Biochemical biomarkers in some cases proved to be equally or more sensitive than reproduction and mortality. We recommend more frequent use of a battery of biochemical biomarkers in combination with other higher-level biomarkers also in chronic studies and not only in the acute ones.     

The effects of cadmium on ALA-D activity, growth and haemoglobin content in the water flea, Daphnia magna

The ALA-D activity, haemoglobin content and growth was studied in the water flea, Daphnia magna, exposed to 0, 0.1, 0.2, 0.4, 0.8 and 1.6 micrograms Cd/l. The ALA-D activity in water fleas exposed to 0.2-1.6 micrograms Cd/l fluctuated around the control value. The activity in animals exposed to 0.1 micrograms Cd/l decreased during the entire experiment. After 16 days exposure to cadmium the haemoglobin content in water fleas ranged between 80 and 31% of control value. In animals exposed to 0.8 and 1.6 micrograms Cd/l the haemoglobin content decreased progressively during the experiment. Growth was not affected by cadmium at these concentrations.     

Time dependent cadmium uptake by fathead minnows (Pimephales promelas) during field and laboratory exposure

Fathead minnows (Pimephales promelas) exposed to 2.5 ppb cadmium in an industrially contaminated lake accumulated whole body burdens of 3.19 ppm Cd in 12 hours, while minnows exposed to 48 ppb Cd in a continuous flow laboratory system did not reach comparable levels until the eighth day of exposure. Significant whole body accumulation of Cd (approximately 9 ppm) peaked within 17–20 days of exposure in the laboratory.     

镉对大型溞摄食能力和相关生理指标的影响

为了探究镉处理对大型溞(Daphnia magna)摄食能力的影响及其机制, 实验设置了3个镉浓度组(0.01、0.05和0.09 mg/L)、1个空白对照和2个处理时间(24h、48h), 研究镉处理对大型溞摄食率与滤水率、体内镉的蓄积量、总抗氧化能力(T-AOC)和脂质过氧化水平(MDA含量)以及乙酰胆碱酯酶(AChE)活性的影响。结果显示, 摄食率和滤水率均随着镉处理浓度的增加而逐渐降低, 当镉浓度为0.09 mg/L, 处理48h时, 摄食率和滤水率均显著或极显著低于对照组(P<0.05,P<0.01), 且摄食率与对照组相比降低了43.89%; 镉在大型溞体内的积累量随镉处理浓度的增加而逐渐升高; T-AOC和MDA含量随着镉浓度的增加而增高, 镉浓度0.09 mg/L时, T-AOC和MDA含量与对照组相比有显著性差异(P<0.05), 且T-AOC与摄食率之间呈负相关性, 相关系数R2分别为0.9521、0.9389; AChE活性随着镉浓度的增加而降低, 镉浓度为0.05、0.09 mg/L时AChE活性显著低于对照组(P<0.05)。这表明镉在体内的蓄积不仅造成了大型溞的氧化损伤, 而且引起了神经系统传导功能的异常, 导致了大型溞摄食能力受到抑制。     

Hepatic and renal cadmium accumulation is associated with mass-specific daily metabolic rate in the bank vole (Clethrionomys glareolus)

Previous study has shown that photoperiod and age affect tissue accumulation of cadmium (Cd) in a small rodent, the bank vole. Since the body mass is also influenced by these factors, the present study was designed to determine whether mass-specific daily metabolic rate might be responsible for differential accumulation of Cd in the liver and kidneys of the short- and long-photoperiod bank voles as well as of the young and old animals. One- and five-month old male bank voles were held under short (8 h light/16 h dark) or long (16 h light/8 h dark) photoperiods and exposed to dietary Cd (100 microg/g) for 6 weeks. The bank voles raised under the short photoperiod and those injected subcutaneously with melatonin (7 micromol/kg/day) under the long photoperiod showed significantly higher concentrations of Cd in the liver (43-60%) and kidneys (40-47%) than the age-matched long-photoperiod animals. The old bank voles accumulated significantly less Cd in both organs than the young animals. These differences in Cd accumulation appeared not to be associated with the relative Cd intake. However, the hepatic and renal Cd levels followed a pattern similar to that of the mass-specific daily metabolic rate (or energy expenditure) and energy assimilation efficiency. These data indicate that mass-specific daily metabolic rate and energy assimilation efficiency (an indicative of digestive and absorptive processes) may be responsible for differential tissue Cd accumulation in the bank vole.     

Morphological changes of integumental chloride cells to ambient cadmium during the early development of the teleost, Oreochromis mossambicus

Synopsis Newly-hatched embryos of Oreochromis mossambicus were reared in freshwater and treated with 0 (control), 50 (low level) or 200 (high level) ppb cadmium for 4 days. Changes in the numbers and dimensions of chloride cell apical crypts on the skin of the free embryos were examined daily using scanning electron microscopy. The apical crypts of the chloride cells were rarely observed on the skin of the embryo trunk, and unevenly distributed on the surface of the yolksac. Two days after hatching, the chloride cells of the free embryos exposed to 50 ppb Cd were more active than those of the other two groups. Compared with the control group, the maximum dimensions of the developing apical crypts were stimulated by 50 ppb Cd and inhibited by 200 ppb Cd. The results indicated that the development of chloride cells in tilapia free embryos was provoked by low level Cd exposure and stunted by high level Cd exposure, suggesting the existence of structure/function relationships in which the activation of chloride cells may be related to the ionoregulatory mechanism in adaptation to Cd exposure.     

Interspecific comparisons of relative assimilation efficiencies for zinc and cadmium in an ecological series of talitrid amphipods (Crustacea)

A dual-labelling radioisotope technique has enabled the relative assimilation efficiencies of an essential (Zn) and a non-essential trace metal (Cd) to be determined in an ecological series of talitrid amphipods from low-shore to fully terrestrial habitats. All species exhibited high assimilation efficiencies for zinc and cadmium (within the range 66.7–96.4%). Interspecific differences in assimilation rates showed no trend with increasing terrestriality of the habitat. Elevated dietary zinc concentrations failed to enhance zinc assimilation efficiency. Incorporation of antibiotics into the diet to eliminate gut microflora did not affect zinc assimilation efficiencies. The implications of having high trace-metal assimilation efficiencies are discussed in terms of land invasion by talitrids.     

Changes in food quality of the green alga Scenedesmus induced by Daphnia infochemicals: biochemical composition and morphology

1. The effects of Daphnia infochemicals on the morphology and biochemical composition of Scenedesmus were studied and subsequently their influence on Daphnia life history. Three species of Scenedesmus ( S. acutus, S. obliquus and S. subspicatus ) were tested for Daphnia -induced colony formation. Life history experiments were performed with Daphnia cucullata and D. magna feeding on unicellular or colonial S. acutus.
2. Colony formation was promoted when S. acutus and S. obliquus were exposed to filtered water from a D. magna culture. S. subspicatus did not form colonies when exposed to culture water, but showed some colony formation when exposed to live D. magna.
3. No clear differences were found in total lipid, protein or carbohydrate content between the unicellular and colonial ecomorphs of the three Scenedesmus species. However, fatty acid (FA) concentration and composition were changed. Total FA as a percentage of frozen dry weight (DW) were increased in colonies. The ratio of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) and the ratio of ω3 : ω6 fatty acids decreased in colonies.
4. A short-term grazing experiment with three size classes of Scenedesmus revealed lower clearance rates for small Daphnia when feeding on large colonial Scenedesmus.
5. Life history parameters of both Daphnia species were influenced by food type. The intrinsic rate of population increase ( r) was significantly lower for daphnids feeding on colonies.
6. The negative influence of colonial Scenedesmus on population growth of Daphnia seems to be determined by algal morphology rather than biochemical composition.     

Ruditapes decussatus and Ruditapes philippinarum exposed to cadmium: toxicological effects and bioaccumulation patterns

Since differences in metal accumulation may exist between bivalve species, the aim of this study was to assess the impact of cadmium (Cd) on Ruditapes decussatus and Ruditapes philippinarum. For this, the Cd accumulation, mortality rates and biochemical responses were analysed in the two species after 5days of exposure, under laboratory-controlled conditions. The concentration of Cd that caused 50% of mortality on clams was two-times higher in R. decussatus than in R. philippinarum. For both species, higher percentage (84.5-98.2%) of the Cd was in the insoluble fraction, but the Cd concentration in solution was 3 to 8 times higher in R. decussatus. Nevertheless, R. philippinarum presented higher oxidative stress and higher CAT activity. The paradox observed between the two clams can be explained by the higher capacity of R. decussatus to increase the expression of MTs when exposed to Cd.     

Detection of cadmium by a fiber-optic biosensor based on localized surface plasmon resonance

A novel transmission-based localized surface plasmon resonance (LSPR) fiber-optic probe has been developed to determine the heavy metal cadmium ion (Cd(II)) concentration. The LSPR sensor was constructed by immobilizing phytochelatins (PCs), (gammaGlc-Cys)(8)-Gly, onto gold nanoparticle-modified optical fiber (NM(Au)OF). The optimal immobilizing conditions of PCs on to the NM(Au)OF are 71.6mug/ml PCs in pH 7.4 PBS for 2h. The absorbability (change of light absorption) of the PC-functionalized NM(Au)OF sensor increases to 9% upon changing the Cd(II) level from 1 to 8ppb with a sensitivity of 1.24ppb(-1) and a detection limit of 0.16ppb. The sensor retained 85% of its original activity after nine cycles of deactivation and reactivations. In addition, the sensor retains its activity and gives reproducible results after storage in 5% d-(+)-trehalose dehydrate solution at 4 degrees C for 35 days. The dissociation constant (K(d)) of the immobilized PCs with Cd(II) was about 6.77x10(-8)M. In conclusion, the PCs-functionalized NM(Au)OF sensor can be used to determine the concentration of Cd(II) with high sensitivity.     

Accumulation of cadmium and copper by the terrestrial snail Arianta arbustorum L.: kinetics and budgets

Summary Specimens of the terrestrial gastropod Arianta arbustorum were fed on cadmium- or copper-enriched agar plates with the aim of performing an input/output analysis and of studying the distribution of these metals in several organs of the snails. After a feeding period of 20 days about 45% of cadmium were lost. 36% accumulated in the hepatopancreas, where a cadmium concentration of more than 500 g/g was measured. The efficiency of cadmium assimilation decreased from about 90% at the beginning to about 55% after 20 days. Copper was distributed more evenly than cadmium, but the main site of copper storage seemed to be the foot/mantle tissues, where 49% of the ingested copper were found. The efficiency of copper assimilation always exceeded 95%. The patterns of distribution and assimilation of copper and cadmium are discussed in relation to differences in the cytological and biochemical detoxification mechanisms which exist for these metals in molluscs.     

Modulation of substrate-specific glutathione S-transferase activity in Daphnia magna with concomitant effects on toxicity tolerance

Glutathione S-transferase (GST) activity was measured in Daphnia magna and Ceriodaphnia reticulata using 1-chloro-2,4-dinitrobenzene (CDNB) and ethacrynic acid (EA) as conjugation substrates. Levels of GST activity were comparable between species with CDNB; however, D. magna had nearly twice the GST activity with EA as compared to C. reticulata. GST activity with CDNB was elevated from exposure of daphnids to either CDNB or sodium pentachlorophenate (PCP), but not from exposure to EA. GST activity with EA could not be modulated from exposure to CDNB or EA. GST activity towards CDNB and EA was biochemically separated into different protein fractions suggesting the existence of two distinct isozymes. Preexposure of daphnids to CDNB or PCP increased the organisms' tolerance to the toxic effects of PCP, but not CDNB.     

Feeding in Daphnia galeata on Oscillatoria limnetica and on Detritus Derived from It

Oscillatoria spp. are generally very abundant in many shallow,eutrophic lakes in the Netherlands. However, this is less truefor Daphnia galeata. The main aim of this study was to investigatewhether the edibility of live Oscillatoria limnetica by Daphniagaleata, and of the detritus derived from this filamentous cyanobacterium,was, among others, an important limiting factor for the daphnids.We measured the consumption and assimilation rates of Daphniausing dual-labelling radio-tracer techniques (¹⁴C and ³²P) tolabel separately the live Oscillatoria filaments and detritusprepared from these filaments. The two food types were mixedin different proportions, and both the food ingestion and foodincorporation rates by daphnids were measured. The main findingsof this study were that specific clearance rates of Daphniaon shorter Oscillatoria filaments were significantly higherthan on the longer filaments, in other words the weight-specificingestion rates were higher on the shorter Oscillatoria filamentsthan on the longer filaments from the batch cultures. The longerOscillatoria filaments are more likely to clump and, therefore,are more liable to be rejected by Daphnia during the food collectionand ingestion processes. The shorter filaments, in comparison,are apparently less prone to clumping and, therefore, are clearedby the daphnids at higher rates than the longer filaments. Feedingthe daphnids on double-labelled (¹⁴C and ³²P) shorter filamentsrevealed that the assimilationefficiency of shorter Oscillatoriafilaments was generally higher for P than for C, probably becauseof a high C/P ratio of Oscillatoria. Daphnia (0.75–1.85mm in size) fed significantly better on dead (detritus) Oscillatoriafilaments than on live Oscillatoria filaments, even if the relativeproportion of detritus in the food was only about one-quarterthat of the live filaments. This preference for detritus overlive Oscillatoria, as indicated by Chesson's selectivity coefficienta, was apparently a passive process, rather than a case of activefood selection. This ‘selective’ feeding on detrituswas apparently facilitated by the relatively greater rejectionof the live filaments than the detrital filaments. At very highfood concentrations (15–25 mg C l^–1), with the shareof the live Oscillatoria filaments 2 to 2.5 times greater thanthat of the detritus, the ingestion rates increased proportionallyless with increase in daphnid size than was expected on thebasis of the allometric relationship between the length andweight of these animals. This implies that the larger animalshad greater interfering effects of the Oscillatoria filamentson the food collection and ingestion processes.     

Prostate Tissue Metal Levels and Prostate Cancer Recurrence in Smokers

Although smoking is not associated with prostate cancer risk overall, smoking is associated with prostate cancer recurrence and mortality. Increased cadmium (Cd) exposure from smoking may play a role in progression of the disease. In this study, inductively coupled plasma mass spectrometry was used to determine Cd, arsenic (As), lead (Pb), and zinc (Zn) levels in formalin-fixed paraffin embedded tumor and tumor-adjacent non-neoplastic tissue of never- and ever-smokers with prostate cancer. In smokers, metal levels were also evaluated with regard to biochemical and distant recurrence of disease. Smokers (N?=?25) had significantly higher Cd (median ppb, p?=?0.03) and lower Zn (p?=?0.002) in non-neoplastic tissue than never-smokers (N?=?21). Metal levels were not significantly different in tumor tissue of smokers and non-smokers. Among smokers, Cd level did not differ by recurrence status. However, the ratio of Cd ppb to Pb ppb was significantly higher in both tumor and adjacent tissue of cases with distant recurrence when compared with cases without distant recurrence (tumor tissue Cd/Pb, 6.36 vs. 1.19, p?=?0.009, adjacent non-neoplastic tissue Cd/Pb, 6.36 vs. 1.02, p?=?0.038). Tissue Zn levels were also higher in smokers with distant recurrence (tumor, p?=?0.039 and adjacent non-neoplastic, p?=?0.028). These initial findings suggest that prostate tissue metal levels may differ in smokers with and without recurrence. If these findings are confirmed in larger studies, additional work will be needed to determine whether variations in metal levels are drivers of disease progression or are simply passengers of the disease process.     

Periphyton as alternative food source for the filter-feeding cladoceran Daphnia magna

1.  Daphnia magna , a well-studied primary consumer, is mainly known as a filter feeder. In this study, we investigated the ability of D. magna to use periphyton as an alternative food source to phytoplankton. We examined the development of laboratory populations fed with different food sources ( Desmodesmus subspicatus and/or periphyton or neither) over a period of 42 days, and observed the behaviour of the daphnids.
2.  The addition of periphyton to phytoplankton food led to an increase of daphnid population biomass. When fed with periphyton as the only food source, a small but stable D. magna population developed.
3.  The behaviour of daphnids fed with both food sources revealed a preference for feeding on D. subspicatus . Only below a concentration of D. subspicatus of approximately 0.05 mg C L⁻¹ (0.4 × 10⁷ cells L⁻¹) did D. magna use periphyton as an alternative food source.
4.  Periphyton showed distinct reactions to grazing by D. magna . The thickness of the periphyton layer was reduced from about 4 to 1 mm and we observed a change in species composition due to grazing.
5.  The ability of D. magna to graze on periphyton could serve to stabilize its population density and reinforce its competitive advantage over other cladocerans. By switching between food sources, D. magna can act as a coupler between pelagic and benthic habitats and food webs.     

Acute dietary pre-exposure and trace metal bioavailability to the barnacle Balanus amphitrite

Rates of uptake from solution and assimilation efficiencies of the trace metals Ag, Cd and Zn were investigated in the barnacle Balanus amphitrite after exposure in the laboratory for 19 days to low and high doses of added Ag and Cd in a diatom (Thalassiosira weissflogii) diet, the major route of metal uptake in barnacles. The hypothesis under test was that acute metal pre-exposure would affect the assimilation efficiency (AE) of that and other metals and their rate of uptake from solution. It was found that pre-exposure of the barnacles to atypically high dietary challenges of Cd and Ag did not cause changes in the rates of uptake of Cd, Ag or Zn from solution. Similarly, there was no clear consistent effect of dietary pre-exposure to Cd or Ag on the assimilation efficiency of Cd, Ag or Zn. The efflux rates of the metals were also comparable following the acute dietary exposure. Subcellular fractionation data indicated that the majority of the three metals were partitioned in the insoluble fraction, with very little in the soluble fraction consisting of metallothionein-like proteins and other (heat-sensitive) proteins. The lack of induction of increased Cd or Ag AE after pre-exposure in barnacles contrasts with results for mussels; this inconsistency is interpreted to result from differences in physiological accumulation patterns, the barnacles relying to an extreme extent on insoluble detoxification.