Control of ammonia toxicity to Hyalella azteca by sodium, potassium and pH

The toxicity of ammonia to Hyalella azteca at constant pH in artificial media was controlled by sodium and potassium, and not by calcium, magnesium, or anions. Small increases in the LC50 for total ammonia (from 0.15 to 0.5 mM) occurred as sodium was increased from 0.1 to 1 mM and above, but major increases in the LC50 (to over 10 mM total ammonia) required the addition of potassium. Potassium was, however, more effective at reducing ammonia toxicity at high (1 mM) sodium than at low (0.1 mM) sodium. Ammonia toxicity was independent of pH at low sodium and potassium concentrations, when ammonia toxicity appeared to be associated primarily with aqueous ammonium ion concentrations. At high sodium and potassium concentrations, the toxicity of ammonia was reduced to the point where un-ionized ammonia concentrations also affected toxicity, and the LC50 became pH dependent. A mathematical model was produced for predicting ammonia toxicity from sodium and potassium concentrations and pH.     

Chronic toxicity of arsenic, cobalt, chromium and manganese to Hyalella azteca in relation to exposure and bioaccumulation

Chronic toxicity of As, Co, Cr and Mn to Hyalella azteca can be described using a saturation-based mortality model relative to total-body or water metal concentration. LBC25s (total-body metal concentrations resulting in 25% mortality in 4 weeks) were 125, 103, 152 and 57,900 nmol g-1 dry weight for As, Co, Cr and Mn respectively. LC50s (metal concentrations in water resulting in 25% mortality in 4 weeks) were 5600, 183, 731, and 197,000 nmol L-1, respectively. A hormesis growth response to As exposure was observed. Growth was a more variable endpoint than mortality for all four toxicants; however, confidence limits based on growth and mortality all overlapped, except Cr which had no effect on growth. Mn toxicity was greater in glass test containers compared to plastic. Bioaccumulation of As, Co, Cr, and Mn was strongly correlated with, and is useful for predicting, chronic mortality.     

Kinetics of uranium uptake in soft water and the effect of body size,bioaccumulation and toxicity to Hyalella azteca

The kinetics of uptake and the effect of body size on uranium (U) bioaccumulation and toxicity to Hyalella azteca exposed to water-only U concentrations in soft water were evaluated. The effect of body size on U bioaccumulation was significant with a slope of ?0.35 between log body concentration and log body mass. A saturation kinetic model was satisfactory to describe the uptake rate, elimination rate and the effect of gut-clearance on size-corrected U bioaccumulation in H. azteca. The one-week lethal water concentrations causing 50% mortality for juvenile and adult H. azteca were 1100 and 4000 nmol U/L, respectively. The one-week lethal body concentration causing 50% mortality was 140 nmol U/g for juvenile H. azteca and 220 nmol U/g for adult H. azteca. One-week bioaccumulation studies that properly account for body-size and gut-clearance times can provide valuable data on U bioavailability and toxicity in the environment.     

Lac Dufault sediment core trace metal distribution, bioavailability and toxicity to Hyalella azteca

To determine changes in metal distribution, bioavailability and toxicity with sediment depth, two 20-cm-long replicate cores were collected from a lake historically subjected to the influence of metal mining and smelting activity. The vertical distribution of Pb, Cd and Cu in sediment was similar for all three metals, with the surface layers showing enrichment and the deeper (pre-industrial) layers showing lower concentrations. Toxicity of each sediment core section was determined in laboratory tests with the freshwater amphipod Hyalella azteca. Bioavailable metal in each sediment slice was estimated from metal concentrations in overlying water in these toxicity tests and, for Cd, also from metal bioaccumulation. The profile for Cd in tissue was comparable to Cd in sediment and overlying water, but relative Cd bioavailability from sediment increased with sediment depth. Survival increased with increasing sediment depth, suggesting that surface sediments were probably less or non-toxic before industrialization.     

Testing sediment biological effects with the freshwater amphipod Hyalella azteca: the gap between laboratory and nature

The freshwater amphipod, Hyalella azteca, is widely used in laboratory sediment toxicity and bioaccumulation tests. However, its responses in the laboratory are probably very different from those in the field. A review of the literature indicates that in its natural habitat this species complex is primarily epibenthic, derives little nutrition from the sediments, and responds primarily to contaminants in the overlying water column (including water and food), not sediment or porewater. In laboratory sediment toxicity tests H. azteca is deprived of natural food sources such as algal communities on or above the sediments, and is subjected to constant light without any cover except that afforded by burial into the sediments. Under these constraining laboratory conditions, H. azteca has been reported to respond to sediment or porewater contamination. In nature, contamination of overlying water from sediment is less likely than in the laboratory because of the large, generally non-static sink of natural surface water. H. azteca does not appear to be the most appropriate test species for direct assessments of the bioavailability and toxicity of sediment contaminants, though it is probably appropriate for testing the toxicity of surface waters. Toxic and non-toxic responses will be highly conservative, though the latter are probably the most persuasive given the exposure constraints. Thus H. azteca is probably a suitable surrogate species for determining sediments that are likely not toxic to field populations; however, it is not suitable for determining sediments that are likely toxic to field populations.     

Photo-induced toxicity of PAHs to Hyalella azteca and Chironomus tentans: effects of mixtures and behavior

In the aquatic environment, polycyclic aromatic hydrocarbon (PAH) contamination can result from several anthropogenic sources such as petroleum runoff, industrial processes, and petroleum spills. When ultraviolet light (UV) is present at sufficient intensity, the acute toxicity of some PAHs to aquatic biota is greatly enhanced. This photo-induced toxicity of PAHs is directly influenced by the amount of PAH and by the level of UV intensity present in the aquatic environment. Thus, behavioral responses and habits that affect an aquatic organism's exposure to UV as well as exposure to PAHs can influence the extent to which damage due to photo-induced toxicity occurs. Experiments demonstrated the effects of photo-induced toxicity of anthracene and fluoranthene on the survival of two benthic macroinvertebrates, the midge Chironomus tentans and the freshwater amphipod Hyalella azteca. This study further investigated the survival and behavior of the test organisms in different substrates (no substrate, a sand monolayer, leaf discs, and sediment) with and without UV. The free-swimming, epibenthic H. azteca avoided the effects of photo-induced toxicity of PAHs to some extent by hiding in leaves when this substrate was available. Results emphasize the importance of organisms' behavior in affecting the photo-induced toxicity of PAHs in the aquatic environment.     

Decamethylcyclopentasiloxane (D5) spiked sediment: Bioaccumulation and toxicity to the benthic invertebrate Hyalella azteca

Chronic toxicity and bioaccumulation of decamethylcyclopentasiloxane (D5) to Hyalella azteca was examined in a series of spiked sediment exposures. Juvenile H. azteca were exposed for 28 d (chronic) to a concentration series of D5 in two natural sediments of differing organic carbon content (O.C.) and particle size composition. The chronic, LC50s were 191 and 857 μg D5 g⁻¹ dry weight for Lakes Erie (0.5% O.C.) and Restoule (11% O.C.) respectively. Inhibition of growth only occurred with the L. Restoule spiked sediment with a resultant EC25 of 821 μg g⁻¹ dw. Lethality was a more sensitive endpoint than growth inhibition. Biota sediment accumulation factors (BSAFs, 28 d) were <1 indicating that D5 did not bioconcentrate based on lipid normalized tissue concentrations and organic carbon normalized sediment concentrations. Organic carbon (OC) in the sediment appeared to be protective, however normalization to OC did not normalize the toxicity. Normalization of D5 concentrations in the sediments to sand content did normalize the toxicity and LC50 values of 3180 and 3570 μg D5 g⁻¹ sand dw were determined to be statistically the same.     

Screening differentially expressed genes in an amphipod (Hyalella azteca) exposed to fungicide vinclozolin by suppression subtractive hybridization

Vinclozolin, a dicarboximide fungicide, is an endocrine disrupting chemical that competes with an androgenic endocrine disruptor compound. Most research has focused on the epigenetic effect of vinclozolin in humans. In terms of ecotoxicology, understanding the effect of vinclozolin on non-target organisms is important. The expression profile of a comprehensive set of genes in the amphipod Hyalella azteca exposed to vinclozolin was examined. The expressed sequence tags in low-dose vinclozolin-treated and -untreated amphipods were isolated and identified by suppression subtractive hybridization. DNA dot blotting was used to confirm the results and establish a subtracted cDNA library for comparing all differentially expressed sequences with and without vinclozolin treatment. In total, 494 differentially expressed genes, including hemocyanin, heatshock protein, cytochrome, cytochrome oxidase and NADH dehydrogenase were detected. Hemocyanin was the most abundant gene. DNA dot blotting revealed 55 genes with significant differential expression. These genes included larval serum protein 1 alpha, E3 ubiquitin-protein ligase, mitochondrial cytochrome c oxidase, mitochondrial protein, proteasome inhibitor, hemocyanin, zinc-finger–containing protein, mitochondrial NADH-ubiquinone oxidoreductase and epididymal sperm-binding protein. Vinclozolin appears to upregulate stress-related genes and hemocyanin, related to immunity. Moreover, vinclozolin downregulated NADH dehydrogenase, related to respiration. Thus, even a non-lethal concentration of vinclozolin still has an effect at the genetic level in H. azteca and presents a potential risk, especially as it would affect non-target organism hormone metabolism.     

Re-evaluation of metal bioaccumulation and chronic toxicity in Hyalella azteca using saturation curves and the biotic ligand model

Bioaccumulation by Hyalella of all metals studied so far in our laboratory was re-evaluated to determine if the data could be explained satisfactorily using saturation models. Saturation kinetics are predicted by the biotic ligand model (BLM), now widely used in modelling acute toxicity, and are a pre-requisite if the BLM is to be applied to chronic toxicity. Saturation models provided a good fit to all the data. Since these are mechanistically based, they provide additional insights into metal accumulation mechanisms not immediately apparent when using allometric models. For example, maximum Cd accumulation is dependent on the hardness of the water to which Hyalella are acclimated. The BLM may need to be modified when applied to chronic toxicity. Use of saturation models for bioaccumulation, however, also necessitates the need for using saturation models for dose-response relationships in order to produce unambiguous estimates of LC50 values based on water and body concentrations. This affects predictions of toxicity at very low metal concentrations and results in lower predicted toxicity of mixtures when many metals are present at low concentrations.     

Quantification of bioavailable nickel in sediments and toxic thresholds to Hyalella azteca

Bioaccumulation and chronic toxicity of nickel (Ni) to Hyalella azteca in Ni-spiked sediments was strongly affected by the source of sediment used. The total range in LC50s on a sediment concentration basis ranged over 20 fold. Differences in Ni toxicity generally matched differences in Ni bioaccumulation, and toxicity expressed on a body concentration basis varied less than three fold. Body concentrations, therefore, provide a much more reliable prediction of Ni toxicity in sediments than do concentrations in the sediment. Ni in overlying water was also a reliable predictor of Ni toxicity, but only in tests conducted in Imhoff settling cones with large (67:1) water to sediment ratios. Overlying water LC50s for tests in beakers varied 18 fold. Sediment and body concentrations of Ni tolerated by Hyalella were slightly higher in cones than in beakers. Reproduction was not affected significantly by Ni at concentrations below the LC50 and 10-week EC50s for survival and biomass production (including survival, growth and reproduction) were only marginally lower than 4-week EC50s (survival and growth only).     

Relative contribution of food and water to 27 metals and metalloids accumulated by caged Hyalella azteca in two rivers affected by metal mining

Hyalella were caged at three sites in each of the two rivers for 17 days. Food added to the cages consisted of plant and detrital material collected from the same, or other, sites. Concentrations of some metals in Hyalella (e.g., Cd and Cu), but not others (e.g., Se), appeared to reach steady-state within 5 days in one of the rivers. Metal accumulation was minimal by day 5 in the other river, possibly due to the very low temperatures in this river for the first part of the exposure period. Both analysis of variance and analysis of covariance, using site as a categorical variable and metal in food as either a categorical or continuous variable, indicated that Cd, Cu and Se were the only metals for which concentration in food had a significant effect on concentration in Hyalella. Nevertheless, water was still a major source for these metals as well. Other metals which varied by over fivefold in food but for which concentration in food had no effect on concentration in Hyalella included Ag, As, Bi, Sb, U and Zn. Concentrations of the remaining metals varied less than fourfold in food, making it difficult to determine if these were accumulated from food.     

Responses of Hyalella azteca and phytoplankton to a simulated agricultural runoff event in a managed backwater wetland

We assessed the aqueous toxicity mitigation capacity of a hydrologically managed floodplain wetland following a synthetic runoff event amended with a mixture of sediments, nutrients (nitrogen and phosphorus), and pesticides (atrazine, S-metolachlor, and permethrin) using 48-h Hyalella azteca survival and phytoplankton pigment, chlorophyll a. The runoff event simulated a 1 h, 1.27 cm rainfall event from a 16 ha agricultural field. Water (1 L) was collected every 30 min within the first 4 h, every 4 h until 48 h, and on days 5, 7, 14, 21, and 28 post-amendment at distances of 0, 10, 40, 300 and 500 m from the amendment point for chlorophyll a, suspended sediment, nutrient, and pesticide analyses. H. azteca 48-h laboratory survival was assessed in water collected at each site at 0, 4, 24, 48 h, 5 d and 7 d. Greatest sediment, nutrient, and pesticide concentrations occurred within 3 h of amendment at 0 m, 10 m, 40 m, and 300 m downstream. Sediments and nutrients showed little variation at 500 m whereas pesticides peaked within 48 h but at <15% of upstream peak concentrations. After 28 d, all mixture components were near or below pre-amendment concentrations. H. azteca survival significantly decreased within 48 h of amendment up to 300 m in association with permethrin concentrations. Chlorophyll a decreased within the first 24 h of amendment up to 40 m primarily in conjunction with herbicide concentrations. Variations in chlorophyll a at 300 and 500 m were associated with nutrients. Managed floodplain wetlands can rapidly and effectively trap and process agricultural runoff during moderate rainfall events, mitigating impacts to aquatic invertebrates and algae in receiving aquatic systems.     

Saturation models of arsenic, cobalt, chromium and manganese bioaccumulation by Hyalella azteca

Bioaccumulation of As, Co, Cr and Mn by the benthic amphipod Hyalella azteca in Burlington City tap (Lake Ontario) water was measured in 4-week tests. Bioaccumulation increased with exposure concentration and demonstrated an excellent fit to a saturation model (r(2): 0.819, 0.838, 0.895 and 0.964 for As, Co, Cr and Mn, respectively). The proportion of total body Mn eliminated during a 24-h depuration period decreased as Mn body concentration increased, apparently due to a saturation of the elimination rate. The high maximum body concentration of 116,000 nmol g(-1) appears to result from the saturation of the Mn excretion which is slightly greater than the maximum Mn uptake rate. Elimination rates for As, Co and Cr were not dependent on body concentration. The four elements were not physiologically regulated in Hyalella. Their body concentrations should be good indicators of bioavailability and useful for environmental assessment.     

Recolonization of acid-damaged lakes by the benthic invertebrates Stenacron interpunctatum,Stenonema femoratum and Hyalella azteca

The recolonization of acid-damaged lakes in Killarney Park, Canada is described for 3 species of benthic invertebrates; 2 mayflies (Stenonema femoratum, Stenacron interpunctatum) and an amphipod (Hyalella azteca). Synoptic surveys of 119 lakes for amphipods and 77 lakes for mayflies were conducted between 1995 and 1997 and defined pH thresholds of 5.6 for S. femoratum and H. azteca and pH 5.3 for S. interpunctatum. In an intensive study of 2 acid-damaged lakes and 2 reference lakes from 1997 to 2002, reestablishment of S. interpunctatum, S. femoratum and H. azteca occurred, when timing of the events could be estimated, less than 4-8 years after pH thresholds for specific taxa were reached. Dispersal of S. interpunctatum to all habitat patches within a lake was completed 3 years after recolonization was detected in the smallest lake (11 ha). It is anticipated that dispersal throughout the largest lake (189 ha) will take much longer. The time lag from estimated pH recovery to reestablishment and subsequent dispersal of mayflies to all suitable habitats within a lake was as much as 11 to 22+ years. The density of S. interpunctatum increased in the recovering lakes to levels higher than in reference lakes, but stable endpoints have not yet been reached during 6 years of monitoring.     

Toxicity and bioaccumulation of thallium in Hyalella azteca, with comparison to other metals and prediction of environmental impact

Thallium (Tl) is an extremely toxic but little studied metal. For Hyalella azteca exposed in Lake Ontario water, a 25% reduction in survival (the LC25) occurred at about 48 nmol litre(-1) after 4 weeks. Body concentrations of Tl, which were proportional to water concentrations, averaged 290 nmol g(-1) dry mass at the LC25. Growth was reduced at slightly lower concentrations. Concentrations affecting reproduction were variable at < 50% of the LC25. On a water-concentration basis Tl was more toxic than Ni, Cu or Zn, but less toxic than Cd or Hg to Hyalella; toxicity to Pb was similar. On a body-concentration basis, the toxicities of Tl, Cd, Hg and Pb were all similar. Unlike Cd, Tl toxicity and uptake was affected by K concentrations in the water, and not by Ca, Mg, Na or other ions. Toxicity was proportional to uptake, and body concentrations were better predictors of toxicity than water concentrations in media with varying K concentrations. Preliminary measurements of Tl and Cd uptake by Hyalella from Hamilton Harbour and Lake Ontario sediments suggested that total bioavailable metal concentrations were greater in deep-water sediments from Lake Ontario than in sediments from the harbour. The ratio of bioavailable metal to the toxic threshold was slightly higher for Cd than for Tl, but well below 1 for both metals.     

硅铝铵离子筛的制备及其对污水中氨氮的脱除性能

通过常温搅拌制备了对污水中NH₄⁺具有高选择性去除的硅铝型弱晶态铵离子筛,其平均孔径介于2倍水合Ca²⁺直径和2倍水合Na⁺直径之间。结果表明,铵离子筛对NH₄⁺具有优良的吸附选择性和可再生性,吸附容量可达到25 mg·g⁻¹。受Na(AlO₄)双位点吸附规则制约,铵离子筛对Ca²⁺、Mg²⁺具有优良的筛截效果,市政污水中质量浓度为70 mg·L⁻¹的Ca²⁺ 不影响铵离子筛对NH₄⁺的吸附性能Na(AlO)。吸附饱和的铵离子筛经0.5 mol·L⁻¹ NaCl溶液多次洗脱和再生之后,仍能将污水中的氨氮质量浓度由40 mg·L⁻¹快速降至1 mg·L⁻¹以下。本研究可为高效去除污水中的氨氮提供一种简单、高效的方法。     

Influence of water hardness on the bioavailability and toxicity of linear alkylbenzene sulphonate (LAS)

In the present work, the influence of Ca²⁺ concentration on the toxicity of single cut linear alkylbenzene sulfonate (LAS) homologues was studied. Precipitation boundary diagrams for each homologue were obtained, indicating turbid and clear zones depending on the LAS and Ca²⁺ concentrations. The separation between transparent and turbid zones is given by the so-called precipitation line. LAS toxicity to Daphnia magna was determined at concentrations close to this precipitation line. It was observed that when Ca(LAS)₂ precipitation progresses, LAS bioavailability decreases for test animals, and the toxicity diminishes even at high nominal LAS concentrations. According to the “free ion activity model” (FIAM), the toxicity of a given chemical compound is mainly due to the ionic species (Ca²⁺–LAS⁻) and not due to the precipitated molecule, Ca(LAS)₂. The significance of the present study is in connection with the assessment of LAS sorption/precipitation studies in soils and sediments, where in situ toxicity is strongly influenced by Ca²⁺/Mg²⁺ ions, according to the results presented in this work.     

Cyst-based toxicity tests XVI--sensitivity comparison of the solid phase Heterocypris incongruens microbiotest with the Hyalella azteca and Chironomus riparius contact assays on freshwater sediments from Peninsula Harbour (Ontario,Canada)

In view of the complexity and costs of "traditional" whole sediment assays, a "culture/maintenance free" direct contact microbiotest has been developed with the freshwater ostracod Heterocypris incongruens. The new Toxkit assay (named Ostracodtoxkit) has been applied to 33 sediment samples from Peninsula Harbour, located in Lake Superior of the Great Lakes water basin in Ontario, Canada. The microbiotest was applied in parallel to direct contact tests with the amphipod Hyalella azteca and the midge larva Chironomus riparius, to compare its relative sensitivity with that of the two "conventional" assays. The study was undertaken in the framework of remediation action plans for specific areas of concern, to enable decision making by the Canadian authorities for the restoration of impacted aquatic environments. Most sediments were found non-toxic (<20% mortality) to both the conventional test species and the ostracod. For the large majority of samples, a very good correspondence was found between the two crustacean test species for the intensity of the toxic signal "mortality", as reflected by a 0.71 (p<0.05) correlation coefficient. Growth inhibition, which is determined in the ostracod microbiotest as a sublethal effect criterion, allowed the earmarking of some sediment samples, which were apparently more toxic for the amphipod than to the ostracod. For 20% of the samples, substantially higher mortality scores were noted with the ostracod assay than with the midge larvae tests and the overall correlation coefficient between these two tests was lower (r=0.60,p<0.05). The results obtained in the present study corroborate those of previous research on sediments collected from various rivers in Flanders, Belgium, and confirm the potential of the new ostracod microbiotest as a reliable and sensitive low cost alternative for traditional whole sediment assays.