Cladoceran Ceriodaphnia Dubia Research Articles

Do short-term, reduced-volume methods accurately reflect chronic toxic effects in the cladoceran Ceriodaphnia dubia? A study with the reference toxicant hexavalent chromium

Cladocerans are frequently used as test organisms in aquatic toxicology studies. For practical reasons (bioethical and economic), efforts are currently made in search of alternative animal models and in defining short-lasting test methods that will allow reliable evaluation of the chronic effect of chemical contaminants. The use of small-sized invertebrates, like the Ceriodaphnia dubia cladoceran, represents a good option and has been included in diverse testing protocols; however, the use of reduced volumes and shortened exposure times, as well as higher temperatures to accelerate their development could influence the results and lead to imprecise conclusions. The present study aimed to evaluate the effects of different test volumes, temperature, and exposure time on the toxicity of hexavalent chrome in C. dubia. In acute and chronic assays, three test volumes (5, 15, and 25 mL) were used. Once the LC50 was determined, four sublethal concentrations (0.01, 0.02, 0.04, and 0.08 mg L−1) of Cr(VI) were applied daily to each of the three test volumes for 21 days, evaluating the progeny and survival of adults. The LC50 values did not differ at 20°C, but at 25°C they were significantly lower in 5 mL. The chronic toxic effects varied depending on the test volume and exposure time. Significant effects were observed on day 7 of exposure (corresponding to the third reproduction) in the accumulated progeny only in the volume of 5 mL. Based on the aforementioned, it is necessary to revise whether the short-term and small-scale methods are not underestimating the detection of chronic effects.

Chronic Toxicity of Iron to Aquatic Organisms under Variable pH, Hardness, and Dissolved Organic Carbon Conditions.

A series of chronic toxicity tests was conducted exposing three aquatic species to iron (Fe) in laboratory freshwaters. The test organisms included the green algae Raphidocelis subcapitata, the cladoceran Ceriodaphnia dubia, and the fathead minnow Pimephales promelas. They were exposed to Fe (as Fe (III) sulfate) in waters under varying pH (5.9-8.5), hardness (10.3-255 mg/L CaCO3 ), and dissolved organic carbon (DOC; 0.3-10.9 mg/L) conditions. Measured total Fe was used for calculations of biological effect concentrations because dissolved Fe was only a fraction of nominal and did not consistently increase as total Fe increased. This was indicative of the high concentrations of Fe required to elicit a biological response and that Fe species that did not pass through a 0.20- or 0.45-µm filter (dissolved fraction) contributed to Fe toxicity. The concentrations frequently exceeded the solubility limits of Fe(III) under circumneutral pH conditions relevant to most natural surface waters. Chronic toxicity endpoints (10% effect concentrations [EC10s]) ranged from 442 to 9607 µg total Fe/L for R. subcapitata growth, from 383 to 15 947 µg total Fe/L for C. dubia reproduction, and from 192 to 58,308 µg total Fe/L for P. promelas growth. Toxicity to R. subcapitata was variably influenced by all three water quality parameters, but especially DOC. Toxicity to C. dubia was influenced by DOC, less so by hardness, but not by pH. Toxicity to P. promelas was variable, but greatest under low hardness, low pH, and low DOC conditions. These data were used to develop an Fe-specific, bioavailability-based multiple linear regression model as part of a companion publication. Environ Toxicol Chem 2023;00:1-15. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Feeding behavior of early life stages of the zebrafish Danio rerio is altered by exposure to glyphosate.

Glyphosate levels and the transfer of glyphosate across trophic levels have rarely been studied in zooplankton. The food preferences of zebrafish during the first-feeding stage (which is critical for the survival of organisms), were analyzed because of the requirement for live food. Larval survival begins to be affected when glyphosate intake exceeds 0.3666µg/larvae/day, in the case that only the food is contaminated; if the medium is also contaminated, the effects on survival start from 0.2456µg/larvae/day. It was shown that glyphosate was more likely to be incorporated through the medium than through the food (zooplankton), which supports the results of previous studies that have ruled out the potential for biomagnification. The bioconcentration factor (BCF) of glyphosate was determined using an ELISA tests specific to measure glyphosate in the fish D. rerio, the rotifers Brachionus calyciflorus and Lecane papuana, and the cladoceran Ceriodaphnia dubia. The experimental design consisted in exposing seven zebrafish adults per replica (four replicates) in three treatments 1, 5, and 10mg/L of glyphosate for 96h to obtain bioconcentration factors in the gills, liver, and muscle. These concentrations were selected as potential glyphosate concentrations right after application as double highest reported concentration. Glyphosate levels in zooplankton can represent up to 6.26% of the total weight of rotifers (BFC = 60.35) and in zebrafish adult organs were less than 8µg/mg of tissue (BCF values < 6). Although glyphosate does not biomagnify, our results suggest that glyphosate affected the dynamics between zooplankton and zebrafish larvae, diminishing survival and feeding rates, given that zooplankton species bioconcentrate glyphosate in large quantities. The BCF values found in this contribution are higher than expected. Glyphosate exposure affected energy metabolism and feeding behavior of zebrafish larvae, which presented high mortality rates at environmentally relevant concentrations.

Stannous chloride as a tool for mercury stripping in contaminated streams: Experimental assessment of toxicity in an invertebrate model species

The chronic toxicity of an innovative Hg water treatment system using tin (Sn) (II) chloride (SnCl2) followed by air stripping was assessed through measurements of survival, growth, and reproduction rate in the freshwater cladoceran Ceriodaphnia dubia, a model species for toxicity testing. We first calculated the concentrations of Hg causing 25% reduction in survival and reproduction (Lethal or Inhibition Concentrations, or LC25 and IC25, for survival and reproduction, respectively) through exposure to aqueous Hg at concentrations ranging from 0 to 25,000 ng L−1. Then, we treated media (DMW and natural stream water) contaminated with Hg at LC25 and IC25 concentrations with SnCl2 at a Sn:Hg stoichiometric ratio of 8:1 and air stripping and exposed C. dubia to this Sn-amended media. Our results showed that Hg significantly affected survival, reproduction rates and impaired growth. SnCl2-treatment removed 100% of the Hg from the media at all concentrations tested with no deleterious effects on survival, growth and reproduction. Our results confirmed the efficacy of SnCl2 in removing aqueous Hg from stream water and showed that the added Sn did not impact C. dubia at the concentrations tested, supporting the suitability of SnCl2-based treatments in appropriate Hg-contaminated environments.

Main drivers in the structure and dynamics of the zooplankton community in a Pampean seepage shallow lake throughout an annual cycle during turbid and clear water regimes

We investigated the composition and dynamics of the zooplankton community in a pampean seepage lake (Buenos Aires, Argentina) under different environmental (rainfall, hydrometric level, conductivity, transparency) and biotic (phytoplankton biomass and presence of submerged macrophytes) conditions. In the annual cycle analyzed, the shallow lake evidenced alternating turbid- and clear-water periods associated with changes in phytoplankton biomass and the extent of colonization by submerged macrophytes. Thirty-five species were identified (21 rotifers, nine cladocerans and five copepods). Only six species were perennial: the rotifers Brachionus caudatus, Keratella tropica; the cladoceran Ceriodaphnia dubia; and the copepods Notodiaptomus incompositus, Metacyclops mendocinus, and Microcyclops dubitabilis. The zooplankton manifested a similar annual-abundance pattern in the three sampling stations established. Density and biomass peaks occurred in autumn during the clear phase without submerged macrophytes, whereas minimum values were obtained during the turbid phase. The presence of submerged macrophytes favored the zooplankton community, as evidenced by an increased abundance (twice that recorded during the turbid period) and species richness (from 20 to 30 species), with both parameters being associated with increased possibilities for zooplankton refuge plus an incorporation of periphytic and benthic species. Rotifers always predominated numerically. The copepod contribution prevailed throughout the annual cycle with respect to biomass except in spring when the cladocerans were more prevalent. These findings demonstrated that the zooplankton community responded positively to the changes that occurred in the environmental conditions of the lake between the turbid- and the clear-water states.

Synergy between glyphosate and cypermethrin formulations on zooplankton: evidences from a single-specie test and a community mesocosm experiment.

Agrochemicals can reach freshwater bodies by drift, leaching, or runoff, where they constitute complex mixtures. Given that glyphosate and cypermethrin are within the most worldwide used pesticides, they are likely to co-occur in freshwater bodies. The aim of this study was to analyze the interaction between glyphosate and cypermethrin formulations on the cladoceran Ceriodaphnia dubia (Richard 1894)through an acute toxicity test and on a zooplankton assemblage through a mesocosm (30 L) experiment. The 24-h LC50 of both isolated pesticides and their equitoxic mixture was obtained for C. dubia. The mesocosm was performed by exposing a zooplankton assemblage to both pesticides isolated and in combination. The acute toxicity of the equitoxic mixture in C. dubia was 3 and 4 times higher than the isolated toxicity of glyphosate and cypermethrin, respectively. The total toxic units of the mixture were 0.53, indicating a synergistic interaction. In the mesocosm experiment, both pesticides also interacted causing a synergistic negative effect in Cladocera and Copepoda abundances. No interactions between pesticides were found for Rotifera; therefore, the mixture effect was considered additive. It is suggested to continue analyzing pesticide mixture effects on the basis of complementary scales of analysis to reach more environmentally relevant information.

Changes in life histories of cladocerans (Cladocera) from the rotifer-mediated allelochemicals

ABSTRACT We hypothesised that at higher densities herbivorous rotifers through their allelochemicals affect the survival and reproduction of cladocerans. To test this, we separately cultured three rotifers (Brachionus calyciflorus, Brachionus havanaensis, and Plationus patulus) and three cladocerans (Ceriodaphnia dubia, Daphnia pulex, and Moina macrocopa). Chlorella vulgaris was used as food and reconstituted moderately hard water was used as medium. The conditioned-medium (CM) obtained from each of rotifer species was used to conduct cohort life table tests of cladocerans. SDS PAGE electrophoresis revealed the molecular weights of proteins present in the rotifer conditioned medium were 55–63 kDa. Compared to C. dubia and D. pulex, Moina was more resistant to rotifer-mediated chemicals. Gross reproductive rate of C. dubia was significantly stimulated by the rotifer-CM. However, gross and net reproductive rates of D. pulex were strongly reduced (72–85%) due to P. patulus-CM but not from the other two rotifer species. The rate of population increase of M. macrocopa was significantly reduced by the rotifer CM. Overall, about 46% (adverse effect: 24%; stimulatory impact: 22%) of the life history variables in controls significantly differed from rotifer-CM treatments, thus proving our hypothesis that rotifer-mediated allelochemicals had some effect on the cladoceran life history variables.

Chronic toxicity of major ion salts and their mixtures to Ceriodaphnia dubia.

In previous work we intensively studied the acute responses of the cladoceran Ceriodaphnia dubia to major geochemical ions (Na+ , K+ , Ca2+ , Mg2+ , Cl- , SO42- , and HCO3- /CO32- ), culminating in the development of models to predict acute toxicity from ionic composition. To quantitatively evaluate whether the toxicological behavior of major ions observed for C. dubia extends to chronic toxicity, we conducted 58 chronic toxicity tests with individual major salts and binary mixtures thereof. Chronic responses paralleled those demonstrated previously for acute exposure, specifically 1) similar relative toxicity of individual salts; 2) different Na salts showing similar potency when exposure is expressed as osmolarity; 3) toxicity of Mg, Ca, and K salts related to cation activity; 4) decreased toxicity of Na and Mg salts when Ca activity is increased at less than toxic concentrations; 5) additive behavior for salt mixtures sharing a common cation; and 6) independent behavior for salt mixtures with dissimilar cations, except Mg/Ca mixtures which appeared additive. Acute-to-chronic ratios were fairly consistent among salts, with values of approximately 1.8 for acute 50% lethal concentration (LC50) to chronic 50% effect concentration (EC50) and 2.8 for LC50/EC20 when expressed on an activity basis. Adjusting the previous acute toxicity model for acute-to-chronic ratios yielded chronic models that predict chronic toxicity within the range of intertest variability. Because these models are informed by a wide range of ion mixtures, they should provide robust assessment tools for natural waters enriched with major ions. Environ Toxicol Chem 2019;38:769-783. © Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Chronic toxicity in Ceriodaphnia dubia induced by graphene oxide

The unique physico-chemical properties of nanomaterials have allowed their application in different areas including electronics, energy storage, nanomedicine, environmental remediation and biotechnology. Graphene and its derivatives, in particular, have been commercially available, with prediction for increasing their production in the next years, in a way that their release into aquatic environments is very likely to occur, and the impacts of such situation on organisms are still not completely understood. In this context, we evaluated graphene oxide (GO) effects on the freshwater cladoceran Ceriodaphnia dubia through acute and chronic toxicity, feeding rates, and reactive oxygen species (ROS) generation. The mean effective concentration (EC50) estimated during acute exposure was 1.25 mg L−1 of GO. The chronic exposure resulted in significant decrease in the number of neonates. The feeding rates were also decreased by GO exposure. Sub-lethal concentrations of GO caused an increase in ROS generation in the organisms. Our results indicated that GO cause acute and chronic effects to C. dubia. In the presence of GO there was a shift in the available energy for self-maintenance rather than feeding or reproduction activities. This study provides useful information on GO concentrations that might impair the aquatic biota, and supports regulatory efforts concerning the environmental safety of this product.

Contribution of pharmaceuticals and personal care products (PPCPs) to whole toxicity of water samples collected in effluent-dominated urban streams

Water samples were collected from effluent-dominated urban streams in Tokushima, Kyoto, and Saitama in Japan to roughly determine the contribution of pharmaceuticals and personal care products (PPCPs) and surfactants to whole toxicity of the water. Approximately 100 PPCPs including anionic surfactants such as linear alkylbenzene sulfonate (LAS), were chemically analyzed. Using 14 water samples, chronic or sub-chronic toxicity tests were conducted on three aquatic species, the green alga Raphidocelis subcapitata, the cladoceran Ceriodaphnia dubia, and the zebrafish Danio rerio. Bioassays for the selected individual PPCPs were conducted using the three species. Assuming the concentration addition (CA) model, the contribution of each PPCP to the whole toxicity of the riverwater was estimated based on toxicity unit (TU). The contribution of PPCPs, which primarily consists of a few antibiotic agents such as triclosan and clarithromycin, ranged from 0.9% to 69% of the whole toxicity of the water samples for algae, whereas the selected LAS congeners accounted for at most 5.3%. In contrast, the contribution of LAS ranged from 0.067% to 86% and from 0.021% to 27% of the whole toxicity for cladoceran and zebrafish, respectively, whereas that of PPCPs for these species was at most 2.1% at all sampling points. Our results suggest a limited contribution of PPCPs except for antimicrobial agents and the possible substantial contribution of LAS to toxicity in cladocerans and zebrafish.

Congo red dye affects survival and reproduction in the cladoceran Ceriodaphnia dubia. Effects of direct and dietary exposure.

Nearly 7 00000 tons of dyes are produced annually throughout the world. Azo dyes are widely used in the textile and paper industries due to their low cost and ease of application. Their extensive use results in large volumes of wastewater being discharged into aquatic ecosystems. Large volume discharges constitute a health risk since many of these dyes, such as Congo Red, are elaborated with benzidine, a known carcinogenic compound. Information regarding dye toxicity in aquatic ecosystems is limited. Therefore, the aim of the present study was to evaluate the effect of Congo Red on survival and reproduction of Ceriodaphnia dubia. We determined the 48 h median lethal concentration (LC50) and evaluated the effects of sublethal concentrations in subchronic exposures by using as food either fresh algae or algae previously exposed to the dye. LC50 was 13.58 mg L-1. In subchronic assays, survival was reduced to 80 and 55 %, and fertility to 40 and 70 %, as compared to the control, in C. dubia fed with intoxicated cells or with the mix of intoxicated + fresh algae, respectively, so the quantity and type of food had a significant effect. We determined that Congo Red is highly toxic to C. dubia since it inhibits survival and fertility in concentrations exceeding 3 mg L-1. Our results show that this dye produces negative effects at very low concentrations. Furthermore, our findings warn of the risk associated with discharging dyes into aquatic environments. Lastly, the results emphasize the need to regulate the discharge of effluents containing azo dyes.

Influence of chloride on the chronic toxicity of sodium nitrate to Ceriodaphnia dubia and Hyalella azteca.

While it has been well established that increasing chloride concentration in water reduces the toxicity of nitrite to freshwater species, little work has been done to investigate the effect of chloride on nitrate toxicity. We conducted acute and chronic nitrate (as sodium nitrate) toxicity tests with the cladoceran Ceriodaphnia dubia and the amphipod Hyalella azteca (chronic tests only) over a range of chloride concentrations spanning natural chloride levels found in surface waters representative of watersheds of the Great Lakes Region. Chronic nitrate toxicity test results with both crustaceans were variable, with H. azteca appearing to be one of the more sensitive invertebrate species tested and C. dubia being less sensitive. While the variability in results for H. azteca were to an extent related to chloride concentration in test water that was distinctly not the case for C. dubia. We concluded that the chloride dependent toxicity of nitrate is not universal among freshwater crustaceans. An additional sodium chloride chronic toxicity test with the US Lab strain of H. azteca in the present study suggested that when present as predominantly sodium chloride and with relatively low concentrations of other ions, there is a narrow range of chloride concentrations over which this strain is most fit, and within which toxicity test data are reliable.

Herbivores control effects of algal species richness on community biomass and stability in a laboratory microcosm experiment

Hundreds of studies that have explored how biodiversity affects the productivity and stability of ecosystems have produced a consensus that communities composed of more species tend to have higher biomass that is more stable through time. However, the majority of this work stems from studies performed using highly simplified food webs, often composed of just primary producers competing for inorganic resources in the absence of trophic interactions. When studies have incorporated trophic interactions, diversity‐function relationships have been more variable, leaving open the question of how biodiversity affects the functioning of ecosystems with more trophic levels. Here we report the results of a laboratory experiment that used freshwater microcosms to test for effects of algal diversity (one or four species) on community biomass and temporal variability in the presence and absence of two different herbivore species (cladocerans Ceriodaphnia dubia and Daphnia pulex). When no herbivores were present, we found the classic pattern observed in hundreds of other studies – as species richness of algae increased, algal biomass increased, and the temporal variation in biomass decreased. This pattern was retained when one of the herbivores (C. dubia) was present. Ceriodaphnia dubia exhibited weak and non‐selective grazing on the focal algae, leaving the effect of diversity on biomass and variability essentially intact. In contrast, D. pulex exhibited strong and selective grazing in algal polycultures that qualitatively altered both diversity–function relationships. As algal richness increased, total algal biomass decreased and variation through time increased. These changes were coupled with larger and less variable populations of D. pulex. Our results show that herbivory leads to a richer array of diversity–function relationships than often observed in studies focused on just one trophic level, and suggests trophic interactions should be given more attention in work that seeks to determine how biodiversity impacts the functioning of ecosystems.

Prey C:P ratio and phosphorus recycling by a planktivorous fish: advantages of fish selection towards pelagic cladocerans

AbstractPrey selection by the small planktivore Galaxias maculatus and phosphorus gain depending on diet has been examined related to predator–prey daily distribution. Prey elemental composition (C:P ratio) was analysed as a factor of selectivity. Field experiments were carried out to evaluate the effect of prey on phosphorus recycling. Results revealed that the pelagic cladoceran Ceriodaphnia dubia was a highly selected prey by all fish sizes at dawn and dusk, despite its low abundances in comparison with other zooplankters, while the littoral were ingested only during day. The high selectivity for C. dubia showed that G. maculatus moved to pelagic zone during night to consume this prey but returned to littoral areas during day due to the increase in predation risk. Analysis of elemental composition revealed that P content of C. dubia was significantly higher than other planktonic or littoral prey (Bosmina longirostris, Boeckella gracilipes and chironomids). Phosphorus recycling experiments showed that G. maculatus would transport and supply P in available forms for primary producers. Fish size was observed to influence P recycling as YOY had significant higher mass‐specific P release in the morning and mid‐day when they preyed mainly upon C. dubia. Low prey C:P ratio appears as a factor that would add benefits to the classical visual fish selection towards cladocerans, as this preference would imply a net phosphorus gain for fish.

Use of reconstituted waters to evaluate effects of elevated major ions associated with mountaintop coal mining on freshwater invertebrates

In previous laboratory chronic 7-d toxicity tests conducted with the cladoceran Ceriodaphnia dubia, surface waters collected from Appalachian sites impacted by coal mining have shown toxic effects associated with elevated total dissolved solids (TDS). The objective of the present study was to evaluate the effects of elevated major ions in chronic laboratory tests with C. dubia (7-d exposure), a unionid mussel (Lampsilis siliquoidea; 28-d exposure), an amphipod (Hyalella azteca; 28-d exposure), and a mayfly (Centroptilum triangulifer; 35-d exposure) in 3 reconstituted waters designed to be representative of 3 Appalachian sites impacted by coal mining. Two of the reconstituted waters had ionic compositions representative of alkaline mine drainage associated with mountaintop removal and valley fill-impacted streams (Winding Shoals and Boardtree, with elevated Mg, Ca, K, SO₄, HCO₃), and a third reconstituted water had an ionic composition representative of neutralized mine drainage (Upper Dempsey, with elevated Na, K, SO₄, and HCO₃). The waters with similar conductivities but, with different ionic compositions had different effects on the test organisms. The Winding Shoals and Boardtree reconstituted waters were consistently toxic to the mussel, the amphipod, and the mayfly. In contrast, the Upper Dempsey reconstituted water was toxic to the mussel, the amphipod, and the cladoceran but was not toxic to the mayfly. These results indicate that, although elevated TDS can be correlated with toxicity, the specific major ion composition of the water is important. Moreover, the choice of test organism is critical, particularly if a test species is to be used as a surrogate for a range of faunal groups.

Behavioural responses of freshwater zooplankton vary according to the different alarm signals of their invertebrate predators

Single behavioural interactions between two freshwater planktonic crustaceans and invertebrate predators from different zones of the common environment were studied. The planktonic prey organisms were the cladoceran Ceriodaphnia dubia and the copepod Notodiaptomus conifer. The three invertebrate predators were the shrimp Macrobrachium borellii, the crab Trichodactylus borellianus and the larva of the dipteran midge Chaoborus. Feeding experiments were first performed to document the effects of exposure time and prey density on predation. All the selected predators fed on C. dubia and N. conifer, and predation rates were dependent on prey density and exposure time. The ability of microcrustaceans to modify their swimming and avoidance behaviour when faced with cues from each predator was then analysed. The cladoceran was more vulnerable to decapod predation, whereas the prey microcrustaceans were taken equally by the dipteran larvae. The analysis showed that the microcrustaceans detected the presence of at least one invertebrate predator through the predator alarm signals. The cladoceran responded to chemical signals from the three predators but copepods modified their behaviour only in the presence of infochemicals of M. borellii. The different outcomes suggest that macrocrustaceans have different vulnerabilities when faced with the same predator and so have evolved specific and different strategies to reduce invertebrate predation.

Chemical repellency and adverse effects of free-floating macrophytes on the cladoceran Ceriodaphnia dubia under two temperature levels

Macrophytes can structure biological assemblages in subtropical lakes. Zooplankton often uses them as a refuge, but in the absence of predators many species frequently avoid them. It is hypothesized that plant exudates can act as “repellent factors” because they can be detrimental to the animals’ life history. This work aimed to test both assumptions: whether exudates of two free-floating species, Eichhornia crassipes and Salvinia biloba, repel the cladoceran Ceriodaphnia dubia and whether they affect its life history. Furthermore, given the possibility that increasing temperatures can modify the observed responses, the experimental research was carried out at two temperature levels: 21 and 25 (±1) °C. First, an avoidance experiment was performed inside narrow aquaria containing the plants, so that repellence was analyzed according to the location of animals after 30, 60 and 90 min. Second, for the life cycle experiments, cladocerans were raised in macrophyte-conditioned water and their lifespan, growth and reproduction were daily monitored. Macrophytes’ exudates effectively repelled C. dubia and affected its life history by decreasing its life expectancy, increasing the age at first reproduction and lowering the number of eggs per female. The magnitude of such effects depended on the treatment, i.e. both plants together caused more negative effects than E. crassipes alone, and this latter was more negative than S. biloba. At higher temperature, the negative effects were intensified but C. dubia maintained the same order of sensitivity to each treatment. This suggests that temperature variations, within a tolerance range, do not alter the allelopathic interactions between the studied species.

Environmental toxicity and radioactivity assessment of a titanium‐processing residue with potential for environmental use

Thorough examination of the physicochemical characteristics of a Ti-processing residue was undertaken, including mineralogical, geochemical, and radiochemical characterization, and an investigation of the environmental toxicity of soft-water leachate generated from the residue. Concentrations of most metals measured in the leachate were low; thus, the residue is unlikely to leach high levels of potentially toxic elements on exposure to low-ionic strength natural waters. Relative to stringent ecosystem health-based guidelines, only chromium concentrations in the leachate exceeded guideline concentrations for 95% species protection; however, sulfate was present at concentrations known to cause toxicity. It is likely that the high concentration of calcium and extreme water hardness of the leachate reduced the bioavailability of some elements. Geochemical modeling of the leachate indicated that calcium and sulfate concentrations were largely controlled by gypsum mineral dissolution. The leachate was not toxic to the microalga Chlorella sp., the cladoceran Ceriodaphnia dubia, or the estuarine bacterium Vibrio fischeri. The Ti-processing residue exhibited an absorbed dose rate of 186 nGy/h, equivalent to an annual dose of 1.63 mGy and an annual effective dose of 0.326 mGy. In summary, the results indicate that the Ti-processing residue examined is suitable for productive use as an environmental amendment following 10 to 100 times dilution to ameliorate potential toxic effects due to chromium or sulfate.

Functional responses and feeding rates of Mesocyclops pehpeiensis Hu (Copepoda) fed different diets (rotifers, cladocerans, alga and cyanobacteria)

The feeding rates and functional responses of the copepod Mesocyclops pehpeiensis (adult females) were quantified using rotifers (Brachionus rubens, Brachionus havanaensis and Plationus patulus), cladocerans (Moina macrocopa, Ceriodaphnia dubia and Alona glabra), the green alga Chlorella vulgaris and the cyanobacterium Anabaena sp. as food. Mesocyclops pehpeiensis showed preferences for B. havanaensis, B. rubens and M. macrocopa when offered mixed rotifer and cladoceran species. Functional response curves showed increased consumption with increasing density of B. rubens in the medium until about 160 ind. 40 ml−1 of prey, and thereafter reached an asymptote. In general, regardless of water temperature, prey consumption was higher in the absence of algae in the medium. Consumption was highest at 35°C and declined with decreasing temperatures. Ingestion rates of the alga and cyanobacterium showed maxima at 25°C. Our results also indicated that M. pehpeiensis is an omnivore, consuming phytoplankton and zooplankton.

Productive use of steelmaking by-product in environmental applications – II: Leachate geochemistry, ecotoxicity and environmental radioactivity

Detailed laboratory studies have indicated that the HIsmelt steelmaking by-product has the ability to neutralise acidity and hence, may have potential application as an environmental amendment. Prior to widespread environmental use, however, an ecotoxicological characterisation of the by-product leachate and an environmental radioactivity risk assessment are required. Ecotoxicity testing indicated that the HIsmelt steelmaking by-product softwater leachate, adjusted from its natural pH of 10.6–8.0 prior to use, was of low toxicity to Chlorella algae and the marine bacterium Vibrio fischeri, and not toxic to the cladoceran Ceriodaphnia dubia. Leachate metal concentrations in HIsmelt by-product were low. Relative to stringent health-based guidelines for Australian drinking water, the HIsmelt softwater leachate only exceeds the pH guideline of 6.5–8.5. The acidic toxicity characteristic leaching procedure (TCLP) HIsmelt leachate compares favourably with TCLP leachates from international steel-making by-products with low trace element concentrations reflecting low solid-phase concentrations. The HIsmelt steelmaking by-product exhibited low to moderate U and Th decay chain radionuclide activities with an absorbed dose rate of 65nGy/h. Given the low ecotoxicity, low leachate trace elements concentrations and acceptable radioactivity, the HIsmelt steelmaking by-product has potential applications as a construction material or as a soil amendment to ameliorate acidity. However, based on the results of the synthetic softwater leachate tests, it is likely that the HIsmelt steelmaking by-product will require mixing with other materials to reduce leachate pH prior to use as an environmental amendment.