Influence of bicarbonate and humic acid on effects of chronic waterborne lead exposure to the fathead minnow (Pimephales promelas)

Modulation of Kynurenic Acid Production by N-acetylcysteine Prevents Cognitive Impairment in Adulthood Induced by Lead Exposure during Lactation in Mice

Lead (Pb2+) exposure during early life induces cognitive impairment, which was recently associated with an increase in brain kynurenic acid (KYNA), an antagonist of NMDA and alpha-7 nicotinic receptors. It has been described that N-acetylcysteine (NAC) favors an antioxidant environment and inhibits kynurenine aminotransferase II activity (KAT II, the main enzyme of KYNA production), leading to brain KYNA levels decrease and cognitive improvement. This study aimed to investigate whether the NAC modulation of the brain KYNA levels in mice ameliorated Pb2+-induced cognitive impairment. The dams were divided into four groups: Control, Pb2+, NAC, and Pb2++NAC, which were given drinking water or 500 ppm lead acetate in the drinking water ad libitum, from 0 to 23 postnatal days (PNDs). The NAC and Pb2++NAC groups were simultaneously fed NAC (350 mg/day) in their chow from 0 to 23 PNDs. At PND 60, the effect of the treatment with Pb2+ and in combination with NAC on learning and memory performance was evaluated. Immediately after behavioral evaluation, brain tissues were collected to assess the redox environment; KYNA and glutamate levels; and KAT II activity. The NAC treatment prevented the long-term memory deficit exhibited in the Pb2+ group. As expected, Pb2+ group showed redox environment alterations, fluctuations in glutamate levels, and an increase in KYNA levels, which were partially avoided by NAC co-administration. These results confirmed that the excessive KYNA levels induced by Pb2+ were involved in the onset of cognitive impairment and could be successfully prevented by NAC treatment. NAC could be a tool for testing in scenarios in which KYNA levels are associated with the induction of cognitive impairment.

Bioaccumulation of trace elements in liver and kidney of fish species from three freshwater lakes in the Ethiopian Rift Valley

The objective of the present work was to obtain scientific information on the ecological health of three freshwater lakes (Awassa, Koka, and Ziway) situated in the Ethiopian Rift Valley by investigating possible trace element contamination accumulated in fish. Accordingly, fish liver and kidney samples were collected from three commercially important fish species (Barbus intermedius, Clarias gariepinus, and Oreochromis niloticus) in the lakes to determine the concentrations of chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), selenium (Se), cadmium (Cd), and lead (Pb), using ICP-MS. Trace element concentrations were generally higher in O. niloticus compared with concentrations in B. intermedius and C. gariepinus. Compared to background values of most freshwater fish species, higher liver concentrations of Cu in C. gariepinus and O. niloticus, Mn in O. niloticus, Co in all except B. intermedius, and Zn in C. gariepinus from Lakes Ziway and Awassa were found. Cr, Co, Ni, Cd, and Pb were enriched in kidney, while Mn, Cu, Zn, As, and Se seems retained in the liver tissues. Assessment of transfer factors indicated that bioaccumulation from water and diet occurred, while uptake from sediments was low. Furthermore, the transfer factor values were generally higher for essential elements compared to the non-essential elements. Multivariate statistical analyses showed that the differences between the trace element levels were generally not significant among the lakes (p = 0.672), while significant differences were found between the fish species (p = 0.042), and between accumulation in kidney and liver (p = 0.002).

The influence of salinity and water chemistry on acute toxicity of cadmium to two euryhaline fish species

The euryhaline killifishes, Fundulus heteroclitus and Kryptolebias marmoratus inhabit estuaries that rapidly change salinity. Although cadmium (Cd) toxicity has been well characterized in fish inhabiting freshwaters, fewer studies have examined the toxic effects of Cd in estuarine and saltwater environments. Additionally, current environmental regulations do not account for organism physiology in different salinity waters even though metal sensitivity is likely to change in these environments. In this study, we investigated effects of changing salinity on acute Cd toxicity to larval (7-9 d old) F. heteroclitus and K. marmoratus. Median 96-h lethal concentrations (LC50) for Cd were calculated for both fish species at six different salinities. As salinity increased, metal toxicity decreased in both fish species up to 18 ppt salinity; and F. heteroclitus were more sensitive than K. marmoratus at salinities above 12 ppt. To determine which components of saltwater were protective against Cd toxicity, we investigated the influence of CaSO₄ (100 and 200 mg/L), CaCl₂ (200 mg/L), and MgSO₄ (300 mg/L) on Cd toxicity to K. marmoratus. The results demonstrated that both competition with calcium and complexation with chloride reduced the toxic effects of Cd to K. marmoratus. These findings could be used to improve marine/estuarine biotic ligand models for the determination of site-specific water quality criteria for Cd.

Impact of natural organic matter and increased water hardness on DGT prediction of copper bioaccumulation by yellow lampmussel (Lampsilis cariosa) and fathead minnow (Pimephales promelas)

We conducted an exposure experiment with Diffusive Gradients in Thin- Films (DGT), fathead minnow (Pimephales promelas), and yellow lampmussel (Lampsilis cariosa) to estimate bioavailability and bioaccumulation of Cu. We hypothesized that Cu concentrations measured by DGT can be used to predict Cu accumulation in aquatic animals and alterations of water chemistry can affect DGT's predict ability. Three water chemistries (control soft water, hard water, and addition of natural organic matter (NOM)) and three Cu concentrations (0, 30, and 60 μg/L) were selected, so nine Cu-water chemistry combinations were used. NOM addition treatments resulted in decreased concentrations of DGT-measured Cu and free Cu ion predicted by Biotic Ligand Model (BLM). Both hard water and NOM addition treatments had reduced concentrations of Cu ion and Cu-dissolved organic matter complexes compared to other treatments. DGT-measured Cu concentrations were linearly correlated to fish accumulated Cu, but not to mussel accumulated Cu. Concentrations of bioavailable Cu predicted by BLM, the species complexed with biotic ligands of aquatic organisms and, was highly correlated to DGT-measured Cu. In general, DGT-measured Cu fit Cu accumulations in fish, and this passive sampling technique is acceptable at predicting Cu concentrations in fish in waters with low NOM concentrations.

Chronic effects of lead exposure on topsmelt fish (Atherinops affinis): Influence of salinity, organism age, and relative sensitivity to other marine species

The aim of the present study was to determine the influence of salinity and organism age on the chronic toxicity of waterborne lead (Pb) to Atherinops affinis and to compare the relative Pb sensitivity of A. affinis with other marine species. Chronic Pb exposure experiments were conducted in a water flow-through testing system. Survival, standard length, dry weight, and tissue Pb concentration were measured and lethal concentrations (LCs), effect concentrations (ECs), and bioconcentration factors (BCFs) were calculated. In general, increasing salinity and organism age decreased Pb toxicity. The LC50s for larval fish at 14 and 28 ppt salinity were 15.1 and 79.8 μg/L dissolved Pb, respectively; whereas, the LC50 for juvenile fish was 167.6 μg/L dissolved Pb at 28 ppt salinity. Using standard length data, the EC10 values for larval fish were 16.4 and 82.4 μg/L dissolved Pb at 14 and 28 ppt salinity, respectively. The dry weight EC25s for low and high salinity were 15.6 and 61.84 μg/L dissolved Pb, respectively. The BCFs were higher with the lower salinity study (1703) in comparison to the higher salinity study (654). Results of Pb speciation calculation showed higher fraction of Pb²⁺ in water with lower salinity, explaining the higher observed toxicity of Pb in lower salinity water than higher salinity water. Atherinops affinis is more sensitive to Pb than several other marine species. Evidence of abnormal swimming and skeletal deformities were observed in Pb exposure treatments. Results of the present study are useful for marine biotic ligand modeling and support ecological risk assessment and deriving Pb environmental quality criteria for marine environments. Environ Toxicol Chem 2018;37:2705-2713. © 2018 SETAC.

Updated species sensitivity distribution evaluations for acute and chronic lead toxicity to saltwater aquatic life

The US Environmental Protection Agency's (USEPA's) ambient water quality criteria (AWQC) for lead (Pb) in salt water were developed in 1984. The acute and chronic criteria are 210 and 8.1 μg/L dissolved Pb, respectively. Because data were limited in 1984, the chronic criterion was derived using an acute-to-chronic ratio, but there are now sufficient toxicity data such that an acute-to-chronic ratio is no longer needed. Based on the data now available, the proposed updated acute and chronic salt water Pb AWQC (following USEPA methods) are 100 and 10 µg/L, respectively. In the European Union, a chronic salt water predicted no-effect concentration based on the median 5th percentile hazardous concentration (HC5-50) was developed in 2008 for the Registration, Evaluation, Authorisation, and Restriction of Chemicals program, which forms the basis for deriving chronic environmental quality standards for Pb in European marine waters. The salt water HC5-50 previously derived for Pb was 6.1 μg/L, whereas the proposed, updated chronic salt water HC5-50 derived following European Union methods is 11.0 µg/L. Thus, despite differences in derivation methodologies, the proposed AWQC and HC5-50 values are very consistent. Studies evaluating the effect of water quality factors on bioavailability and toxicity of Pb in salt water are limited; the effect of water quality on Pb toxicity in salt water should be considered in future studies. Environ Toxicol Chem 2017;36:2974-2980. © 2017 SETAC.

Interactions of waterborne and dietborne Pb in rainbow trout, Oncorhynchus mykiss: Bioaccumulation, physiological responses, and chronic toxicity

In Pb-contaminated environments, simultaneous exposure to both waterborne and dietborne Pb is likely to occur. This study examined the potential interactive effects of these two pathways in juvenile rainbow trout that were exposed to Pb in the water alone, in the diet alone, and in combination for 7 weeks. The highest waterborne Pb concentration tested (110μgL(-1)) was approximately equivalent to the 7-week LC20 (97μgL(-1)) measured in a separate trial, while the lowest was a concentration often measured in contaminated environments (8.5μgL(-1)). The live diet (10% daily ration on a wet mass basis) consisted of oligochaete worms (Lumbriculus variegatus) pre-exposed for 28days to the same waterborne Pb concentration, and the highest dietary dosing rate to the trout was 12.6μg Pb g fish(-1)day(-1). With waterborne exposure, whole body Pb burden increased to a greater extent in the worms than in the fish. Nonetheless, in trout waterborne exposure still resulted in 20-60-fold greater Pb accumulation compared to dietborne Pb exposure. However, combined exposure to both waterborne and dietborne Pb reduced the whole body accumulation extensively at waterborne Pb>50μgL(-1), with similar antagonistic interaction in liver and carcass (but not gill or gut) at a lower threshold of 20μgL(-1). Growth effects in trout were minimal with marginal reductions in the dietborne and combined exposures seen only at 110μgL(-1). Chronic Pb exposure reduced lipid and carbohydrates level in the worms by 50% and 80% respectively, while protein was unchanged, so growth effects in trout may have been of indirect origin. After 7 weeks, Ca(2+) homeostasis in the trout was unaffected, but there were impacts on Na(+). Blood Na(+) was reduced in waterborne and dietborne exposures, while gut Na(+)/K(+) ATPase activities were reduced in waterborne and combined exposures. This study is the first, to our knowledge to examine the interaction of waterborne and dietborne Pb exposure in fish. While physiological impacts of Pb were observed in both worms and fish, higher concentrations of dietborne Pb actually protected fish from waterborne Pb bioaccumulation and these effects. The impacts of metals on diet quality should not be neglected in future dietborne toxicity studies using live prey.

The derivation of effects threshold concentrations of lead for European freshwater ecosystems

The main objective of the present study was to derive ecologically relevant effect threshold concentrations of (dissolved) Pb for selected European Union (EU) freshwater rivers, using the 2008 EU Voluntary Risk Assessment Report as a starting point and more advanced methodologies than those used in the Voluntary Risk Assessment Report. This included 1) implementing more robust quality criteria for selecting chronic toxicity data; 2) the conversion of total to dissolved Pb concentrations using a combination of an empirical equation relating inorganic Pb solubility and geochemical speciation modeling to account for effects of dissolved organic matter; 3) the use of bioavailability models for chronic toxicity for species belonging to 3 different trophic levels; and 4) the use of robust methods for large data set handling (such as species sensitivity distribution [SSD] analysis). The authors used published bioavailability models for an algal species (Pseudokirchneriella subcapitata) and a daphnid (Ceriodaphnia dubia) and developed a new model for the fathead minnow (Pimephales promelas). The research has shown that these models are also useful for, and reasonably accurate in, predicting chronic toxicity to other species, including a snail, a rotifer, midge larvae, and an aquatic plant (read-across). A comprehensive chronic toxicity data set for Pb was compiled, comprising 159 individual high-quality toxicity data for 25 different species. By applying the total dissolved conversion and the bioavailability models, normalized toxicity values were obtained, which were then entered into a SSD analysis. Based on the parametric best-fitting SSDs, the authors calculated that ecological threshold concentrations of Pb protecting 95% of freshwater species for 7 selected European freshwater scenarios were between 6.3 μg dissolved Pb/L and 31.1 μg dissolved Pb/L.

Assessing pollution in marine protected areas: the role of a multi-biomarker and multi-organ approach

Marine protected areas (MPAs) are vulnerable to many pressures, including pollution. However, environmental quality monitoring in these areas traditionally relies on only water chemistry and microbiological parameters. The goal of the current study was to investigate the role of a set of biomarkers in different target organs (liver, kidney, and gills) of fish in order to assess the environmental quality of an MPA (MTs, GPx, GST, GSH, DNA damage, LPO, AChE, and condition index). Chemical analyses were also performed on liver and muscle tissues to evaluate metal body burdens, and PAHs were identified in bile. A demersal fish (Cathorops spixii) that is widely consumed by the local population was used as bioindicator species, and the results were integrated using multivariate analysis. The use of the biomarker approach allowed for the identification of both seasonal and spatial variations in pollution sources around the Environmental Protected Area of Cananéia-Iguape-Peruíbe (APA-CIP). Higher metal body burdens associated with biological responses were found in the sites under the influence of urban areas during the dry season, and they were found in the sites under the influence of the Ribeira de Iguape River (RIR) during the rainy season. The liver was found to be more responsive in terms of its antioxidant responses, whereas gills were found to be more responsive to biomarkers of effect. These results show that this set of biomarker analyses in different organs of fish is a useful tool for assessing chemical pollution in an MPA.

The lead accumulation and hematological findings in juvenile rock fish Sebastes schlegelii exposed to the dietary lead (II) concentrations

Juvenile rockfish (mean length 14.2 ± 1.9 cm, and mean weight 57.3 ± 5.2g) were exposed for 4 weeks with the different levels of dietary lead (Pb(2+)) at 0, 30, 60, 120 and 240 mg/L. The exposure concentration and period of Pb have induced significant amount of it the specific tissues of rockfish. The highest Pb accumulation was observed in the kidney tissue by the dietary lead exposure. The growth rate and hepatosomatic index were considerably inhibited over 120 mg/kg. The hematological parameters such as red blood cell (RBC) counts, hematocrit (Ht) value, and hemoglobin (Hb) concentration were significantly decreased over 60 mg/kg Pb concentration. In the inorganic components, the values of calcium and magnesium in plasma were significantly decreased. The glucose and cholesterol values were notably increased, whereas total protein was decreased. The enzyme components, glutamic oxalate transaminase (GOT) and glutamic pyruvate transaminase (GPT), were significantly elevated by the dietary lead exposure, but no change was observed in alkaline phosphatase (ALP).

Cross-species coherence in effects and modes of action in support of causality determinations in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead

The peer-reviewed literature on the health and ecological effects of lead (Pb) indicates common effects and underlying modes of action across multiple organisms for several endpoints. Based on such observations, the United States (U.S.) Environmental Protection Agency (EPA) applied a cross-species approach in the 2013 Integrated Science Assessment (ISA) for Lead for evaluating the causality of relationships between Pb exposure and specific endpoints that are shared by humans, laboratory animals, and ecological receptors (i.e., hematological effects, reproductive and developmental effects, and nervous system effects). Other effects of Pb (i.e., cardiovascular, renal, and inflammatory responses) are less commonly assessed in aquatic and terrestrial wildlife limiting the application of cross-species comparisons. Determinations of causality in ISAs are guided by a framework for classifying the weight of evidence across scientific disciplines and across related effects by considering aspects such as biological plausibility and coherence. As illustrated for effects of Pb where evidence across species exists, the integration of coherent effects and common underlying modes of action can serve as a means to substantiate conclusions regarding the causal nature of the health and ecological effects of environmental toxicants.

Effects of chronic exposure to lead, copper, zinc, and cadmium on biomarkers of the European eel, Anguilla anguilla

Exposure to specific metallic compounds can cause severe deleterious modifications in organisms. Fishes are particularly prone to toxic effects from exposure to metallic compounds via their environment. Species that inhabit estuaries or freshwater environments can be chronically affected by persistent exposure to a large number of metallic compounds, particularly those released by industrial activities. In this study, we exposed yellow eels (European eel, Anguilla anguilla) for 28 days to environmentally relevant concentrations of four specific metals; lead (300, 600, and 1,200 μg/l), copper (40, 120, and 360 μg/l), zinc (30, 60, and 120 μg/l) and cadmium (50, 150, and 450 μg/l). The selected endpoints to assess the toxicological effects were neurotransmission (cholinesterasic activity in nervous tissue), antioxidant defense, and phase II metabolism (glutathione-S-transferase [GST] activity, in both gills and liver tissues), and peroxidative damage. The results showed an overall lack of effects on acetylcholinesterase for all tested metals. Lead, copper, and cadmium exposure caused a significant, dose-dependent, increase in GST activity in gill tissue. However, liver GST only significantly increased following zinc exposure. No statistically significant effects were observed for the thiobarbituric acid reactive substances assay, indicating the absence of peroxidative damage. These findings suggest that, despite the occurrence of an oxidative-based response after exposure to lead, copper, and cadmium, this had no consequence in terms of peroxidative membrane damage; furthermore, cholinergic neurotoxicity caused by lead, copper, and cadmium did not occur. The implications of these results are further discussed.

E-waste disposal effects on the aquatic environment: Accra, Ghana

The volume of e-waste is growing around the world, and, increasingly, it is being disposed of by export from developed to developing countries. This is the situation in Ghana, and, in this paper we address the potential consequences of such e-waste disposal. Herein, we describe how e-waste is processed in Ghana, and what the fate is of e-waste-chemical contaminants during recycling and storage. Finally, to the extent it is known, we address the prospective adverse effects of e-waste-related contaminants on health and aquatic life downstream from a large e-waste disposal facility in Accra, Ghana.In developing countries, including Ghana, e-waste is routinely disassembled by unprotected workers that utilize rudimentary methods and tools. Once disassembled,e-waste components are often stored in large piles outdoors. These processing and storage methods expose workers and local residents to several heavy metals and organic chemicals that exist in e-waste components. The amount of e-waste dumped in Ghana is increasing annually by about 20,000 t. The local aquatic environment is at a potential high risk, because the piles of e-waste components stored outside are routinely drenched or flooded by rainfall, producing run-off from storage sites to local waterways. Both water and sediment samples show that e-waste-related contaminant shave entered Ghana's water ways.The extent of pollution produced in key water bodies of Ghana (Odaw River and the Korle Lagoon) underscores the need for aquatic risk assessments of the many contaminants released during e-waste processing. Notwithstanding the fact that pollutants from other sources reach the water bodies, it is clear that these water bodies are also heavily impacted by contaminants that are found in e-waste. Our concern is that such exposures have limited and will continue to limit the diversity of aquatic organisms.There have also been changes in the abundance and biomass of surviving species and changes in food chains. Therefore, the need for actions to be taken to reduce entry of e-waste pollutants into Ghana's aquatic environment is real and is immediate.Heavy metals (e.g., lead, cadmium, copper and zinc) and organic pollutants (e.g.,PCDD/Fs and PBDEs) have been detected in the sediments of local water bodies in quantities that greatly exceed background levels. This fact alone suggests that aquatic organisms that live in the affected water bodies are highly exposed to these toxic, bio-accumulative, and persistent contaminants. These contaminants have been confirmed to result from the primitive methods used to recycle and process e-waste within the local environment.Only limited local data exist on the threats posed by these e-waste-related contaminants on nearby natural resources, especially aquatic organisms. In this review,we have addressed the potential toxicity of selected heavy metals and organic pollutants on aquatic organisms. Since there are no data on concentrations of contaminants in the water column, we have based our predictions of effects on pollutant release rates from sediments. Pollutants that are attached to sediments are routinely released into the water column from diffusion and advection, the rate of which depends on pH and Eh of the sediments. E-waste contaminants have the potential to produce deleterious effects on the behavior, physiology, metabolism, reproduction,development and growth of many aquatic organisms. Because it is confirmed that both heavy metal and organic contaminants are reaching the biota of Ghana's local waterways, we presume that they are producing adverse effects. Because local data on the aquatic toxicity of these contaminants are as yet unavailable, we strongly recommend that future research be undertaken to examine, on a large scale and long-term basis, both contamination levels in biota, and adverse effects on biota of the nearby water bodies.

Toxic effects of lead on biochemical and histological alterations in green mussel (Perna viridis) induced by environmentally relevant concentrations

Acute and chronic toxicity tests were conducted on green mussel (Perna viridis) to determine the adverse effects of lead (Pb). Exposure of organisms to acute toxicity test for 96 h and lethal concentration (LC(50)) was the endpoint of the test. Acute toxicity for 96-h LC(50) and 95% confidence intervals of P. viridis was 2.62 ± 0.12 (2.62-3.24) mg/L Pb. Chronic toxicity tests revealed that survival of exposed organisms decreased with elevated exposure concentrations. No-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) were calculated based on survival of test organisms. Results of this study demonstrated an increase in toxicity in test organisms with rise in exposure time and concentration. In this study, histology and biochemical enzymes, namely, catalase, reduced glutathione, glutathione S-transferase, and lipid peroxides, were correlated with chronic value and survival endpoints of P. viridis after chronic exposure to Pb. Biochemical and histological responses to different concentrations of Pb were assessed and significant differences were observed between control and increasing exposure concentrations. Biomarker studies in internal organs confirmed that the observed changes are due to adverse effects of Pb. This assessment of toxicity was the first step to determining the seawater quality criteria for marine organisms.

Influence of elevated alkalinity and natural organic matter (NOM) on tissue-specific metal accumulation and reproductive performance in fathead minnows during chronic, multi-trophic exposures to a metal mine effluent

Metal bioavailability in aquatic organisms is known to be influenced by various water chemistry parameters. The present study examined the influence of alkalinity and natural organic matter (NOM) on tissue-specific metal accumulation and reproductive performance of fathead minnows (Pimephales promelas) during environmentally relevant chronic exposures to a metal mine effluent (MME). Sodium bicarbonate (NaHCO3) or NOM (as commercial humic acid) were added to a Canadian MME [45 percent process water effluent (PWE)] in order to evaluate whether increases in alkalinity (3-4 fold) or NOM (~1.5-3mg/L dissolved organic carbon) would reduce metal accumulation and mitigate reproductive toxicity in fathead minnows during a 21-day multi-trophic exposure. Eleven metals (barium, boron, cobalt, copper, lithium, manganese, molybdenum, nickel, rubidium, selenium, and strontium) were elevated in the 45 percent PWE relative to the reference water. Exposure to the unmodified 45 percent PWE resulted in a decrease of fathead minnow egg production (~300 fewer eggs/pair) relative to the unmodified reference water, over the 21-day exposure period. Water chemistry modifications produced a modest decrease in free ion activity of some metals (as shown by MINTEQ, Version 3) in the 45 percent PWE exposure water, but did not alter the metal burden in the treatment-matched larval Chironomus dilutus (the food source of fish during exposure). The tissue-specific metal accumulation increased in fish exposed to the 45 percent PWE relative to the reference water, irrespective of water chemistry modifications, and the tissue metal concentrations were found to be similar between fish in the unmodified and modified 45 percent PWE (higher alkalinity or NOM) treatments. Interestingly however, increased alkalinity and NOM markedly improved fish egg production both in the reference water (~500 and ~590 additional eggs/pair, respectively) and 45 percent PWE treatments (~570 and ~260 additional eggs/pair, respectively), although fecundity over 21 day exposure consistently remained lower in the 45 percent PWE treatment groups relative to the treatment-matched reference groups. Collectively, these findings suggest that metal accumulation caused by chronic 45 percent PWE exposure cannot solely explain the reproductive toxicity in fish, and decrease in food availability (decrease in C. dilutus abundance in 45 percent PWE exposures) might have played a role. In addition, it appears that NaHCO3 or humic acid mitigated reproductive toxicity in fish exposed to 45 percent PWE by their direct beneficial effects on the physiological status of fish.

Implications of pH manipulation methods for metal toxicity: not all acidic environments are created equal

The toxicity of many metals is impacted by environmental pH, through both competition and complexation by hydroxide and carbonate ions. To establish safe environmental regulation it is important to properly define the relationship between pH and metal toxicity, a process that involves manipulating the pH of test water in the lab. The current study compares the effects of the three most common pH manipulation methods (carbon dioxide, acid-base addition, and chemical buffers) on acute Pb toxicity of a model fish species, Pimephales promelas. Acidification of test water revealed that the Pb and Pb(2+) LC50 values were impacted by the pH manipulation method, with the following order of effects: HCl<CO2<MOPS. Conversely no differences in toxicity were observed when test pH was alkalinized using MOPS or NaOH. The different impacts of pH manipulation methods on Pb toxicity are likely due to different physiological stresses resulting from the respective methods; the physiological implications of each method are discussed. The results suggest that when studying the impacts of pH on metal toxicity it is important to properly replicate the ambient conditions of interest as artificial buffering using CO2 environments or organic buffers significantly affects the physiology of the test organisms above and beyond what is expected from pH alone. Thus, using CO2 and organic buffers overestimates the impact of acid pH on Pb toxicity.

Assessment of heavy metals in water samples and tissues of edible fish species from Awassa and Koka Rift Valley Lakes, Ethiopia

The Ethiopian Rift Valley Lakes host populations of edible fish species including Oreochromis niloticus, Labeobarbus intermedius and Clarias gariepinus, which are harvested also in other tropical countries. We investigated the occurrence of six heavy metals in tissues of these fish species as well as in the waters of Lake Koka and Lake Awassa. Both lakes are affected by industrial effluents in their catchments, making them ideal study sites. Mercury concentrations were very low in the water samples, but concentrations in the fish samples were relatively high, suggesting a particularly high bioaccumulation tendency as compared with the other investigated metals. Mercury was preferentially accumulated in the fish liver or muscle. It was the only metal with species-specific accumulation with highest levels found in the predatory species L. intermedius. Lower mercury concentrations in O. niloticus could be attributed to the lower trophic level, whereas mercury values in the predatory C. gariepinus were unexpectedly low. This probably relates to the high growth rate of this species resulting in biodilution of mercury. Accumulation of lead, selenium, chromium, arsenic and cadmium did not differ between species, indicating that these elements are not biomagnified in the food chain. Values of cadmium, selenium and arsenic were highest in fish livers, while lead and chromium levels were highest in the gills, which could be related to the uptake pathway. A significant impact of the industrial discharges on the occurrence of metals in the lakes could not be detected, and the respective concentrations in fish do not pose a public health hazard.

Multi-linear regression analysis, preliminary biotic ligand modeling, and cross species comparison of the effects of water chemistry on chronic lead toxicity in invertebrates

The current study examined the chronic toxicity of lead (Pb) to three invertebrate species: the cladoceran Ceriodaphnia dubia, the snail Lymnaea stagnalis and the rotifer Philodina rapida. The test media consisted of natural waters from across North America, varying in pertinent water chemistry parameters including dissolved organic carbon (DOC), calcium, pH and total CO(2). Chronic toxicity was assessed using reproductive endpoints for C. dubia and P. rapida while growth was assessed for L. stagnalis, with chronic toxicity varying markedly according to water chemistry. A multi-linear regression (MLR) approach was used to identify the relative importance of individual water chemistry components in predicting chronic Pb toxicity for each species. DOC was an integral component of MLR models for C. dubia and L. stagnalis, but surprisingly had no predictive impact on chronic Pb toxicity for P. rapida. Furthermore, sodium and total CO(2) were also identified as important factors affecting C. dubia toxicity; no other factors were predictive for L. stagnalis. The Pb toxicity of P. rapida was predicted by calcium and pH. The predictive power of the C. dubia and L. stagnalis MLR models was generally similar to that of the current C. dubia BLM, with R(2) values of 0.55 and 0.82 for the respective MLR models, compared to 0.45 and 0.79 for the respective BLMs. In contrast the BLM poorly predicted P. rapida toxicity (R(2)=0.19), as compared to the MLR (R(2)=0.92). The cross species variability in the effects of water chemistry, especially with respect to rotifers, suggests that cross species modeling of invertebrate chronic Pb toxicity using a C. dubia model may not always be appropriate.

Investigations into the mechanism of lead toxicity to the freshwater pulmonate snail, Lymnaea stagnalis

The freshwater pulmonate snail, Lymnaea stagnalis, is the most sensitive aquatic organism tested to date for Pb with an estimated EC20 for juvenile snail growth of 3 μg l⁻¹. A previous study supported the hypothesis that this hypersensitivity to Pb was due to an extremely high Ca²⁺ uptake rate needed to support shell formation. The current study sought to build upon this working hypothesis and develop a mechanistic predictive model for inhibition of snail growth as a function of Pb exposure. Initial experiments confirmed previous predictions that juvenile snails have net Ca²⁺ uptake rates of 7000-8000 nmol g⁻¹ h⁻¹, approximately 100-fold higher than observed in a typical freshwater fish. However, an initial time course study revealed that the onset of growth inhibition occurs at least 4d prior to inhibition of net Ca²⁺ flux in Pb-exposed snails indicating the latter is not the primary mechanism of action. Qualitative observations during this experiment indicated snail feeding was inhibited in a dose-dependent manner. A subsequent experiment demonstrated that when food is withheld from snails for even 24 h, net Ca²⁺ uptake is significantly (∼50%) reduced. A second time course study demonstrated quantitatively that snail feeding is inhibited by Pb exposure by up to 98% at relatively high Pb concentrations (57 μg l⁻¹) but no inhibition was observed at ≤ 10 μg l⁻¹ Pb indicating feeding inhibition is not causing observed growth effects at concentrations approximating the EC20 of 3 μg l⁻¹ Pb. A final experiment testing whether Pb-induced growth effects are related to inhibition of carbonic anhydrase activity in the snail mantle also failed to demonstrate an effect. We conclude that while both feeding and net Ca²⁺ uptake in snails are affected by Pb exposure, they appear to be secondary effects. The primary mechanism of action explaining L. stagnalis hypersensitivity to Pb remains to be identified.

Multi-linear regression models predict the effects of water chemistry on acute lead toxicity to Ceriodaphnia dubia and Pimephales promelas

The current study examined the acute toxicity of lead (Pb) to Ceriodaphnia dubia and Pimephales promelas in a variety of natural waters. The natural waters were selected to range in pertinent water chemistry parameters such as calcium, pH, total CO(2) and dissolved organic carbon (DOC). Acute toxicity was determined for C. dubia and P. promelas using standard 48h and 96h protocols, respectively. For both organisms acute toxicity varied markedly according to water chemistry, with C. dubia LC50s ranging from 29 to 180μg/L and P. promelas LC50s ranging from 41 to 3598μg/L. Additionally, no Pb toxicity was observed for P. promelas in three alkaline natural waters. With respect to water chemistry parameters, DOC had the strongest protective impact for both organisms. A multi-linear regression (MLR) approach combining previous lab data and the current data was used to identify the relative importance of individual water chemistry components in predicting acute Pb toxicity for both species. As anticipated, the P. promelas best-fit MLR model combined DOC, calcium and pH. Unexpectedly, in the C. dubiaMLR model the importance of pH, TCO(2) and calcium was minimal while DOC and ionic strength were the controlling water quality variables. Adjusted R(2) values of 0.82 and 0.64 for the P. promelas and C. dubia models, respectively, are comparable to previously developed biotic ligand models for other metals.

Effects of acute and chronic waterborne lead exposure on the swimming performance and aerobic scope of fathead minnows (Pimephales promelas)

Fathead minnows were subjected to an incremental velocity test using swim tunnel respirometry for the analysis of aerobic scope and swimming performance, as critical aerobic swim speed (U(crit)), following chronic exposures (33-57 ) to 0.9±0.4, 157±18 or 689±66 nmol L⁻¹ Pb and an acute exposure (24 h) to 672±35 nmol L⁻¹ Pb (mean±SEM). Assessment of Pb-induced anemia and neurological impairment were evaluated by blood hemoglobin (Hb) concentrations and a cost of transport (COT) analysis, respectively. Fish from the acute 672±35 nmol L⁻¹ Pb (24.4±1.2 BL s⁻¹) and chronic 689±66 nmol L⁻¹ Pb (24.6±0.9 BL s⁻¹) treatments exhibited reduced U(crits) compared to control fish (27.6±0.8 BL s⁻¹). Aerobic scope was reduced by acute Pb exposure (8.6±2.6 μmol O₂ g⁻¹ h⁻¹ vs. 22.6±3.8 μmol O₂ g⁻¹ h⁻¹ from controls) owing to a decrease in maximum oxygen consumption rate (38.8±0.8 μmol O₂ g⁻¹ h⁻¹ vs. 54.0±4.2 μmol O₂ g⁻¹ h⁻¹ from controls). However, no effect on aerobic scope was observed with fish chronically exposed to Pb. Significant differences were not observed for Hb concentrations or COT. These findings suggest that the impaired swimming performances arising from acute and chronic Pb exposures reflect different mechanisms of toxicity.

Influences of water chemistry on the acute toxicity of lead to Pimephales promelas and Ceriodaphnia dubia

The acute toxicity of lead (Pb) was examined for fathead minnows (Pimephales promelas; 96-h) and daphnids (Ceriodaphnia dubia; 48-h) in waters modified for hardness (as CaSO₄), dissolved organic carbon (DOC; as Aldrich humic acid) and alkalinity (as NaHCO₃) for parameterization of an acute freshwater biotic ligand model (BLM). Additionally, acute (96-h) and chronic (30-d) bioassays were performed for P. promelas to more clearly define the influence of pH (5.5-8.3) on Pb toxicity as modified by addition of HCl or NaOH using an automated titration system. Results indicate that Ca(2+) is protective against acute Pb toxicity to P. promelas but not C. dubia. Strong protection was afforded by DOC and NaHCO(3) against acute Pb toxicity to P. promelas, whereas milder protection was observed for C. dubia with both parameters. Dissolved Pb LC50s from the P. promelas pH bioassays revealed a complex effect of pH on Pb toxicity, likely explained in part by Pb speciation and the competitive interaction of H(+) with ionic Pb(2+). Chronic pH bioassays also demonstrated that 30-d growth is not impaired in fathead minnows at relevant Pb concentrations. The findings reported herein suggest that development of separate BLMs for P. promelas and C. dubia should be considered.