The impact of temperature on metal mixture stress: Sublethal effects on the freshwater isopod Asellus aquaticus.

Chemical and natural factors have been demonstrated to interact and potentially change the toxicity of the individual stressors. Yet, while there exists a multitude of papers studying the temperature-dependent toxicity of single chemicals, little research exists on the impact of temperature on chemical mixtures. This paper investigates the effect of temperature on environmentally-relevant mixtures of Cd, Cu and Pb. We linked the effects on respiration, growth, feeding rate and activity of Asellus aquaticus to the free ion activities, as a measure for the bioavailability of the metals, and the body concentrations. We observed interactions of temperature and metal body concentrations on all sublethal endpoints, except activity. Mixture effects on accumulation and feeding rate were observed as well and even an interaction between metal body burden, mixture and temperature treatment was revealed for the feeding rate of Pb exposed isopods. This research adds to a growing body of evidence that the current chemical-based monitoring is insufficient to estimate chemical toxicity in aquatic ecosystems and must, therefore, be complemented with effect-based tools.

The shape of the plasma glucose curve during an oral glucose tolerance test as an indicator of Beta cell function and insulin sensitivity in end-pubertal obese girls.

It is hypothesized that the shape of the glucose curve during an oral glucose tolerance test is an early indicator of the risk for developing type 2 diabetes mellitus. In this study, we aimed to examine the shape of plasma glucose response curves and study their relationship with insulin sensitivity, insulin secretion and components of the metabolic syndrome in end-pubertal obese girls. Eighty-one end-pubertal obese girls [median (range) age: 14.4 (11.2-18.0) years; BMI: 34.6 (25.4-50.8) kg/m(²)] who underwent a 2-h oral glucose tolerance test were classified according to the shape of the glucose curve. Four shape types of the plasma glucose response curve were observed: 28 (34.6%) monophasic, 30 (37.0%) biphasic, 14 (17.3%) triphasic, and 9 (11.1%) unclassified. Patients with a monophasic shape had a higher area under the curve for glucose (p = 0.008), a lower early-phase insulin secretion (p = 0.005), and a poorer beta cell function relative to insulin sensitivity as reflected by the oral disposition index (p = 0.022) compared to the bi- and triphasic shape types. In addition, the triglyceride level and TG/HDL-C ratio was higher in patients with a monophasic shape compared to those with a biphasic shape (p = 0.040 and p = 0.048, respectively). In conclusion, end-pubertal obese girls with a monophasic plasma glucose curve are at increased risk for insulin resistance, which can contribute to the development of type 2 diabetes mellitus and cardiovascular diseases.

Common carp exposed to binary mixtures of Cd(II) and Zn(II): A study on metal bioaccumulation and ion-homeostasis.

The aquatic environment receives a wide variety of contaminants that interact with each other, influencing their mutual toxicity. Therefore, studies of mixtures are needed to fully understand their deleterious effects on aquatic organisms. In the present experiment, we aimed to assess the effects of Cd and Zn mixtures in common carp during a one-week exposure. The used nominal waterborne metal levels were 0.02, 0.05 and 0.10 µM for Cd and 3, 7.5 and 15 µM for Zn. Our results showed on the one hand a fast Cd increase and on the other hand a delayed Zn accumulation. In the mixture scenario an inhibition of Cd accumulation due to Zn was marked in the liver but temporary in the gills. For Zn, the delayed accumulation gives an indication of the efficient homeostasis of this essential metal. Between the different mixtures, a stimulation of Zn accumulation by Cd rather than an inhibition was seen in the highest metal mixtures. However, when compared to an earlier single Zn exposure, a reduced Zn accumulation was observed. Metallothionein gene expression was quickly activated in the analysed tissues suggesting that the organism promptly responded to the stressful situation. Finally, the metal mixture did not alter tissue electrolyte levels.

Physiological performance of common carp (Cyprinus carpio, L., 1758) exposed to a sublethal copper/zinc/cadmium mixture.

In a natural ecosystem, fish are subjected to a multitude of variable environmental factors. It is important to analyze the impact of combined factors to obtain a realistic understanding of the mixed stress occurring in nature. In this study, the physiological performance of juvenile common carp (Cyprinus carpio) exposed for one week to an environmentally relevant metal mixture (4.8 µg/L of copper; 2.9 µg/L of cadmium and 206.8 µg/L of zinc) and to two temperatures (10 °C and 20 °C), were evaluated. After 1, 3 and 7 days, standard (SMR) and maximum metabolic rate (MMR) were measured and aerobic scope (AS) was calculated. In addition, hematocrit, muscle lactate, histology of the gills and metal accumulation in gills were measured. While SMR, MMR and AS were elevated at the higher temperature, the metal mixture did not have a strong effect on these parameters. At 20 °C, SMR transiently increased, but no significant changes were observed for MMR and AS. During metal exposure, hematocrit levels were elevated in the 20 °C group. The bioaccumulation of Cd in the gills reflected the increased metabolic rate at the higher temperature, with more accumulation at 20 °C than at 10 °C. Anaerobic metabolism was not increased, which corresponds with the lack of significant histopathological damage in the gill tissue. These results show that common carp handled these metal exposures well, although increased temperature led to higher Cd accumulation and necessitated increased hematocrit levels to maintain aerobic performance.

Proximity to roads, but not exposure to metal pollution, is associated with accelerated developmental telomere shortening in nestling great tits.

Comprehensively understanding the factors affecting physiology and fitness in urban wildlife requires concurrently considering multiple stressors. To this end, we simultaneously assessed how metal pollution and proximity to roads affect body condition and telomere shortening between days 8 and 15 of age in nestling great tits (Parus major), a common urban bird. We employed a repeated-measures sampling design to compare telomere shortening and body condition between nestlings from four urban study sites south of Antwerp, Belgium, which are located at different distances from a metal pollution point source. In addition, we explored associations between metal exposure and telomere dynamics on the individual level by measuring blood concentrations of five metals/metalloids, of which lead, copper and zinc were present at concentrations above the limit of detection. To assess whether roadway-associated stressors (e.g. noise and air pollution) might affect nestling condition and telomere shortening, we measured the proximity of nest boxes to roads. Metal exposure was not associated with nestling telomere length or body condition, despite elevated blood lead concentrations close to the metal pollution source (mean ±â€¯SE = 0.270 ±â€¯0.095 µg/g wet weight at the most polluted study site), suggesting that nestlings may have some capacity to detoxify metals. However, nestlings from nest boxes near roads exhibited more telomere shortening between days 8 and 15 of age, and shorter telomeres at day 15. Nestlings in poorer condition also had shorter telomeres, but proximity to the road was unrelated to body condition. Thus, nutritional stress is unlikely to mediate the relationship between proximity to roads and telomere length. Rather, proximity to roads could have affected telomere shortening by exposing nestlings to air or noise pollution. Our study highlights that traffic-related pollution, which is implicated in human health problems, might also affect urban wildlife.

Antagonistic bioaccumulation of waterborne Cu(II) and Cd(II) in common carp (Cyprinus carpio) and effects on ion-homeostasis and defensive mechanisms.

In the aquatic environment, metals are present as mixtures, therefore studies on mixture toxicity are crucial to thoroughly understand their toxic effects on aquatic organisms. Common carp (Cyprinus carpio) were used to assess the effects of short-term Cu(II) and Cd(II) mixtures, using a fixed concentration of one of the metals, representing 25 % of its individual 96h-LC50 (concentration lethal for 50 % of the population) combined with a variable concentration of the other metal corresponding to 10, 25 or 50 % of its 96h-LC50, and vice versa. Our results showed a fast Cu and Cd bioaccumulation, with the percentage of increase in the order gill > liver > carcass. An inhibitory effect of Cu on Cd uptake was observed; higher Cu concentrations at fixed Cd levels resulted in a decreased accumulation of Cd. The presence of the two metal ions resulted in losses of total Na, K and Ca. Fish tried to compensate for the Na loss through the induction of the genes coding for Na+/K+-ATPase and H+-ATPase. Additionally, a counterintuitive induction of the gene encoding the high affinity copper transporter (CTR1) occurred, while a downregulation was expected to prevent further metal ion uptake. An induction of defensive mechanisms, both metal ion binding protein and anti-oxidant defences, was observed. Despite the metal accumulation and electrolyte loss, the low mortality suggest that common carp is able to cope with these metal levels, at least during a one-week exposure.

Investigating the effects of a sub-lethal metal mixture of Cu, Zn and Cd on bioaccumulation and ionoregulation in common carp, Cyprinus carpio.

The aquatic environment is continuously under threat because it is the final receptor and sink of waste streams. The development of industry, mining activities and agriculture gave rise to an increase in metal pollution in the aquatic system. Thus a wide occurrence of metal mixtures exists in the aquatic environment. The assessment of mixture stress remains a challenge considering that we can not predict the toxicity of a mixture on the basis of single compounds. Therefore the analysis of the effects of environmentally relevant waterborne mixtures is needed to improve our understanding of the impact of metal pollution in aquatic ecosystems. Our aim was to assess whether 10 % of the concentration of the 96 h LC50 (the concentration that is lethal to 50 % of the population in 96 h) of individual metal exposures can be considered as a "safe" concentration when applied in a trinomial mixture. Therefore, common carp were exposed to a sublethal mixture of Cu 0.07 ±â€¯0.001 µM (4.3 ±â€¯0.6 µg/L), Zn 2.71 ±â€¯0.81 µM (176.9 ±â€¯52.8 µg/L) and Cd 0.03 ±â€¯0.0004 µM (3.0 ±â€¯0.4 µg/L) at 20 °C for a period of one week. Parameters assessed included survival rate, bioaccumulation and physiological biomarkers related to ionoregulation and defensive mechanisms such as MT induction. Our results showed a sharp increase in Cu and Cd concentration in gills within the first day of exposure while Zn levels remained stable. The accumulation of these metals led to a Na drop in gills, liver and muscle as well as a decreased K content in the liver. Biomarkers related to Na uptake were also affected: on the first day gene expression for H+-ATPase was transiently increased while a concomitant decreased gene expression of the Na+/H+ exchanger occurred. A fivefold induction of metallothionein gene expression was reported during the entire duration of the experiment. Despite the adverse effects on ionoregulation all fish survived, indicating that common carp are able to cope with these low metal concentrations, at least during a one week exposure.

Limited oxidative stress in common carp (Cyprinus carpio, L., 1758) exposed to a sublethal tertiary (Cu, Cd and Zn) metal mixture.

Analyzing effects of metal mixtures is important to obtain a realistic understanding of the impact of mixed stress in natural ecosystems. The impact of a one-week exposure to a sublethal metal mixture containing copper (4.8 µg/L), cadmium (2.9 µg/L) and zinc (206.8 µg/L) was evaluated in the common carp (Cyprinus carpio). To explore whether this exposure induced oxidative stress or whether defense mechanisms were sufficiently fitting to prevent oxidative stress, indicators of apoptosis (expression of caspase 9 [CASP] gene) and of oxidative stress (malondialdehyde [MDA] level and xanthine oxidase [XO] activity) were measured in liver and gills, as well as activities and gene expression of enzymes involved in antioxidant defense (superoxide dismutase [SOD], catalase [CAT], glutathione peroxidase [GPx], glutathione reductase [GR] and glutathione-S-transferase [GST]). The total antioxidative capacity (T-AOC) was also quantified. No proof of oxidative stress was found in either tissue but there was indication of apoptosis in the liver. CAT, GPx, GR and GST total activities were reduced after 7 days, suggesting a potential decrease of glutathione levels and risk of increased free radicals if the exposure would have lasted longer. There were no major changes in the total activities of antioxidant enzymes in the gills, but the relative expression of the genes coding for CAT and GR were triggered, suggesting a response at the transcription level. These results indicate that C. carpio is well equipped to handle these levels of metal pollution, at least during short term exposure.

Accumulation and effects of metals in caged carp and resident roach along a metal pollution gradient.

Metal accumulation and effects on plasma Ca(2+), alanine transaminase (ALT) and fish condition factor were examined in caged carp (Cyprinus carpio) and resident roach (Rutilus rutilus) at four locations along the Grote Nete River system (Belgium). Cadmium and zinc accumulation were found in carp and roach, with highest concentrations at the most contaminated site (dissolved Cd: 1.82 microg/l, Zn: 967 microg/l). On the tissue level, highest cadmium concentrations were measured in kidneys of carp and roach, followed by gills, intestine and liver, while low concentrations were observed in carcass and muscle. For zinc, a similar pattern was observed (intestine>kidney>gills>liver>carcass>muscle). Comparison between species showed higher cadmium concentrations in feral roach, while zinc levels were lower, owing to the high zinc concentrations in control carp. Furthermore, comparison of metal concentrations between two sampling periods (2005 and 2000-2001) revealed a drastic decrease in cadmium concentration in gills, liver and muscle of roach, similar to the reduction in waterborne cadmium concentrations, while differences for zinc were much less pronounced. In addition to metal accumulation, increased metallothionein concentrations (approximately 2x) were found in carp and roach, while no metal-related effects were found on ALT, Ca(2+)or condition factor. However, negative effects on fish community structure, as assessed by the index of biotic integrity (IBI), were found along the pollution gradient and indicated long-term adverse effects of metal pollution.

Influence of tidal regime on the distribution of trace metals in a contaminated tidal freshwater marsh soil colonized with common reed (Phragmites australis).

A historical input of trace metals into tidal marshes fringing the river Scheldt may be a cause for concern. Nevertheless, the specific physicochemical form, rather than the total concentration, determines the ecotoxicological risk of metals in the soil. In this study the effect of tidal regime on the distribution of trace metals in different compartments of the soil was investigated. As, Cd, Cu and Zn concentrations in sediment, pore water and in roots were determined along a depth profile. Total sediment metal concentrations were similar at different sites, reflecting pollution history. Pore water metal concentrations were generally higher under less flooded conditions (mean is (2.32+/-0.08)x10(-3) mg Cd L(-1) and (1.53+/-0.03) x 10(-3) mg Cd L(-1)). Metal concentrations associated with roots (mean is 202.47+/-2.83 mg Cd kg(-1) and 69.39+/-0.99 mg Cd kg(-1)) were up to 10 times higher than sediment (mean is 20.48+/-0.19 mg Cd kg(-1) and 20.42+/-0.21 mg Cd kg(-1)) metal concentrations and higher under dryer conditions. Despite high metal concentrations associated with roots, the major part of the metals in the marsh soil is still associated with the sediment as the overall biomass of roots is small compared to the sediment.

Metal exposure and biological responses in resident and transplanted blue mussels (Mytilus edulis) from the Scheldt estuary.

The Western Scheldt river and estuary is known to be highly polluted as it receives industrial, agricultural and domestic effluents from one of the most populated and industrialised zones in Europe. Aquatic organisms are exposed to pollutants, specifically metals that are present in different environmental phases, e.g. dissolved, suspended material or sediment phases. The objective of this study was to study the relationship that exists between environmental metal levels, the degree of metal uptake by aquatic organisms with the concomitant biological responses. For this purpose the bivalve mollusk, Mytilus edulis, was selected as bioaccumulation indicator organism. Environmental (water and sediment) and mussel samples were collected during the late winter (March 2000) from sampling sites in the Scheldt estuary. Sites were selected to represent a salinity gradient from the mouth of the estuary to the furthest distribution area of mussels upstream in the system. Together with standard water quality parameters (e.g. salinity, dissolved oxygen, dissolved organic carbon, etc.) concentrations of twelve metals were analysed in the water (dissolved and suspended matter) and sediments. Levels of these metals were also measured in the soft tissue of M. edulis, together with concomitant biomarker responses in resident mussel populations at each site. The biomarkers that were included in this study were condition index, scope for growth, survival in air, cell membrane stability, DNA damage, and metallothioneins. Data were subjected to multivariate statistical analysis. The physico-chemical parameters and metals in the environmental samples clustered the sites to reflect the distribution based on the salinity gradient. Bioaccumulation results revealed increased metal uptake along a pollution gradient with the highest metal bioaccumulation occurring at the upstream most sites and therefore closest to the in the industrial activities. However, the biomarker responses clustered the sites in a manner that reflected the influence of combination of internal exposure (bioaccumulation) and external exposure (physico-chemical conditions). These differences in biomarker responses clearly demonstrated were attributed to abiotic factors other than metal pollution alone e.g. localized short-term increases in increased suspended sediment concentrations and decreased dissolved oxygen concentrations.

Combined effects of metal mixtures and predator stress on the freshwater isopod Asellus aquaticus.

Biotic stressors have been demonstrated to change the toxicity of pollutants. While the combined effects of predator cues and pesticides are well documented, the interaction of predator stress with metals is a topic that has remained largely unexplored. In this laboratory experiment, the freshwater isopod Asellus aquaticus is exposed to predator cues and metal mixtures of Cd, Cu and Pb. We examined the effects on growth, respiration and, as behavioral parameters, feeding rate and activity. These were linked to the free ion activities (FIAs) in the water and the metal body concentrations. The findings reveal that Cu accumulation significantly influenced the growth rate, the feeding rate and the activity of isopods exposed to predator stress. Furthermore, we found a concentration-dependent interaction of the Cd + Pb mixtures on the feeding rate and a lower feeding rate for Cd and Pb predator exposed asellids. As several interactions were found between metals and predator stress, it demonstrates the importance of investigating how organisms and whole ecosystems respond to multiple stressors. A better understanding of these interactions will undoubtedly improve risk assessment and management.

Assimilation efficiencies of Cd and Zn in the common carp (Cyprinus carpio): effects of metal concentration, temperature and prey type.

The impact of several factors on the assimilation efficiency (AE) of Cd and Zn from food in the common carp (Cyprinus carpio) was studied. Tested prey species were midge larvae (Chironomus riparius), zebra mussels (Dreissena polymorpha) and oligochaetes (Tubifex tubifex). The Cd load of the larvae did not affect the Cd AE in the carp. The Zn AE however, was negatively related to the Zn load of the prey. Food quantity and starvation of the carp did not significantly affect the Cd AE. For Zn, a significant decrease in AE was found when carp were fed ad libitum. Decreasing the temperature from 25 degrees C to 15 degrees C did not influence the Cd AE, while for Zn a significant decrease of the AE was measured. Carp assimilated Cd from both zebra mussels and oligochaetes with a significantly lower efficiency in comparison to the midge larvae, although Zn AEs was prey independent.

Subcellular distribution of Cd in the aquatic oligochaete Tubifex tubifex, implications for trophic availability and toxicity.

We studied the compartmentalization of cadmium and zinc in the oligochaete Tubifex tubifex. The subcellular distribution was followed over time and levels of metallothionein-like proteins were measured. The impact of the speciation on the trophic transfer was studied by calculating the assimilation efficiencies of metals from Tubificidae fed to carp. It was found that carp were able to assimilate 9.8% of the cadmium. The expected assimilated amount of cadmium, based on the subcellular fractions which are thought to be trophically available, is however 72%. The zinc assimilation results suggest that the debris fraction is at least partially available to predators. Differential centrifugation techniques provide information about the tissue compartmentalization in aquatic organisms but it is not straightforward to directly link internal speciation in prey items to the actual assimilation in the predator. The possible impact that the compartmentalization of cadmium in T. tubifex will have on the toxicity to the organism is also discussed.

Uptake and toxicity of Cd, Cu and Pb mixtures in the isopod Asellus aquaticus from waterborne exposure.

The present study evaluated interactions of waterborne Cd, Cu and Pb mixtures on metal uptake rates in the isopod Asellus aquaticus and related this to mixture effects on toxicity. Secondly, it was assessed whether observed mixture effects were better related to isopod body concentrations compared to exposure concentrations. Isopods were exposed for 10 days to single, binary and tertiary mixtures including five different concentrations of Cd (0.107 to 277 µg L(-1)), Cu (3.35 to 2117 µg L(-1)) and Pb (0.782 to 443 µg L(-1)). Mortality was assessed every day while isopod body concentrations, growth (biomass) and energy reserves (glycogen, lipid and protein reserves) were assessed at the end of the experiment. Synergistic interactions of combined Cd and Pb exposure on Cd and Pb uptake as well as on growth rates and mortality rates were observed. Mixture effects of combined Cd and Pb exposure on toxicity endpoints were directly related to increased Cd uptake in the Cd+Pb treatment. No mixture interactions of Cu on Cd or Pb uptake (and vice versa), nor on toxicity endpoints were observed. All toxicity endpoints were related to body concentrations. However, mixture effects disappeared when growth and mortality rates were expressed on body concentrations instead of exposure concentrations. By combining information of mixture effects on metal uptake with mixture toxicity data, the present study provides more insight in the way metal mixtures interfere with aquatic organisms and how they can induce toxic effects.

Temporal distribution of accumulated metal mixtures in two feral fish species and the relation with condition metrics and community structure.

The present study investigated temporal influences on metal distribution in gudgeon (Gobio gobio) and roach (Rutilus rutilus), and its relation to condition metrics and fish community structure. Fish communities were sampled in two seasons (autumn and spring) during two successive years and the Index of Biotic Integrity (IBI) was calculated. Cadmium, Cu, Pb, Zn and As concentrations were measured in gill, liver, kidney and muscle, and condition factor (CF) and hepatosomatic index (HSI) were measured. Cadmium (max. 39.0 µg g(-1) dw) and Zn (max 2502 µg g(-1) dw) were most strongly stored in kidney and liver and periodical influences on metal accumulation were observed. CF appeared to be a stable metric related to accumulated metal-mixtures and was best related to hepatic levels, while the HSI was less useful. Relations between single metal accumulation and IBI were influenced by sample period, however, when taking into account multiple metals periodical influences disappeared.

Bioavailability of Cd to the common carp, Cyprinus carpio, in the presence of humic acid.

The uptake of cadmium by the common carp, Cyprinus carpio, was studied in chemically defined freshwater in the absence and presence of commercial humic acid. This was done to evaluate whether the cadmium uptake by carp in the presence of humic acid was related to the ambient Cd2+ -ion activity or whether the complexed metal also contributed to the uptake. Uptake of Cd during a 3-h period of exposure was used as a measure of the biological availability of the metal. The uptake rate data for Cd in total fish and gills obtained in the absence (control) and presence (treatment) of humic acid were analyzed using a Michaelis-Menten model for mediated transport. The Michaelis-Menten parameters KM and Vmax obtained in the control and the treatment experiment were compared for each of the two investigated carp compartments (total fish and gills). The model parameter estimates for Cd uptake by total carp in the treatment experiment (KM = 0.41 +/- 0.11 micromol l(-1); Vmax = 0.66 +/- 0.13 micromol kg(-1) h(-1)) were not significantly different from the model parameters in the control experiment (KM = 0.34+/-0.06 micromol l(-1); Vmax = 0.58+/-0.07 micromol kg(-1) h(-1)) on the basis of Welch's approximate t-test. Similarly, the Michaelis-Menten model parameter estimates for Cd uptake by carp gills in the treatment experiment (KM = 0.15 +/- 0.06 micromol l(-1); Vmax = 5.14 +/- 1.07 micromol kg(-1) h(-1)) were not significantly different from the model parameters derived from the control experiment (KM =0.27 +/- 0.09 micromol l(-1); Vmax = 7.63+/-1.38 micromol kg(-1) h(-1)). This indicated that the Cd uptake rate by total carp and in carp gills in the presence of commercial humic acid followed the measured variations in Cd2+ -ion activity as predicted by the control experiment.

In situ and laboratory bioassays to evaluate the impact of effluent discharges on receiving aquatic ecosystems.

Effluents are a main source of direct and often continuous input of pollutants into aquatic ecosystems with long-term implications on ecosystem functioning. Therefore, the study of the effects of effluent exposure on organisms, populations or communities within the framework of impact assessment has a high ecological relevance. The aim of this study was to assess the toxicological impact of two effluents, one household wastewater treatment effluent (Effluent 1) and one industrial effluent (Effluent 2), on the receiving aquatic ecosystem using two test species under both in situ and laboratory conditions. Zebra mussel (Dreissena polymorpha) and common carp (Cyprinus carpio) were exposed under laboratory conditions in an online monitoring flow-through system (receiving different concentrations of Effluent 2) and under in situ conditions along the pollution gradient established by these two effluent discharges. Bioassays focussed on growth and condition related endpoints (i.e. condition, growth, lipid budget), since these are key functional processes within organisms and populations. Under laboratory conditions, increasing concentrations of the industrial effluent (Effluent 2) had a negative effect on both zebra mussel and carp energy reserves and condition. Under in situ conditions, the same negative impact of Effluent 2 was observed for zebra mussels, while Effluent 1 had no apparent effect on exposed zebra mussels. Carp growth and condition, on the other hand, were significantly increased at the discharge sites of both effluents when compared to the reference site, probably due to differences in food availability. The results indicate that a combination of in situ and laboratory exposures can illustrate how ecological processes influence bioassay studies. The incorporation of indirect, ecological effects, like changes in food availability, provides considerable benefit in understanding and predicting effects of effluents on selected species under realistic exposure conditions.

Evaluation of effluent toxicity and ambient toxicity in a polluted lowland river.

The impact of an industrial effluent containing high loads of calcium, cadmium, lead chloride and sulphate, on a river ecosystem was assessed using a combination of an effluent toxicity test, an ambient toxicity test and an ecological survey. Only this combination of techniques made it possible to discriminate between the effects of the discharge and those of the background pollution. Each of the individual techniques detected essential effects which the other failed to reveal. With the physical and chemical measurements, important increases of several components were measured at all sampling sites downstream of the discharge. With the ecological survey, however, no large changes in water quality could be determined at the sampling sites, due to the high degree of pollution present upstream of the discharge. Reproduction of Daphnia magna, exposed to sublethal effluent dilutions, was followed over two generations. The offspring of the first generation were shown to have an increased sensitivity to the effluent, compared to the first generation that was born from previously unexposed mothers. Besides the toxicity of the effluent, the acute and chronic toxicity of its main component, CaCl(2), was also determined. The results of the CaCl(2)-tests and toxicity data from literature for the suspected toxicants were transformed to Toxic Units (TU). Using the sum of the TUs we investigated the possibility of predicting effluent toxicity to Daphnia magna. Effluent toxicity was under-estimated by calculating the sum of the TUs of the individual components. Dilution of the effluent to a level at which the measured toxicant concentrations comply with European regulations still showed significant effects on Daphnia reproduction.

Cellular energy allocation in zebra mussels exposed along a pollution gradient: linking cellular effects to higher levels of biological organization.

Organisms exposed to suboptimal environments incur a cost of dealing with stress in terms of metabolic resources. The total amount of energy available for maintenance, growth and reproduction, based on the biochemical analysis of the energy budget, may provide a sensitive measure of stress in an organism. While the concept is clear, linking cellular or biochemical responses to the individual and population or community level remains difficult. The aim of this study was to validate, under field conditions, using cellular energy budgets [i.e. changes in glycogen-, lipid- and protein-content and mitochondrial electron transport system (ETS)] as an ecologically relevant measurement of stress by comparing these responses to physiological and organismal endpoints. Therefore, a 28-day in situ bioassay with zebra mussels (Dreissena polymorpha) was performed in an effluent-dominated stream. Five locations were selected along the pollution gradient and compared with a nearby (reference) site. Cellular Energy Allocation (CEA) served as a biomarker of cellular energetics, while Scope for Growth (SFG) indicated effects on a physiological level and Tissue Condition Index and wet tissue weight/dry tissue weight ratio were used as endpoints of organismal effects. Results indicated that energy budgets at a cellular level of biological organization provided the fastest and most sensitive response and energy budgets are a relevant currency to extrapolate cellular effects to higher levels of biological organization within the exposed mussels.