Responses of zebra and quagga mussels to copper and tribytiltin exposure: Bioconcentration, metabolic and cardiac biomarkers.

One of the top ecological priorities is to find sensitive indicators for pollution monitoring. This study focuses on the bioconcentration and responses (condition index, survival, oxygen consumption, heart rates, and oxidative stress and neurotoxic effect biomarkers) of mussels from the Volga River basin, Dreissena polymorpha and Dreissena bugensis, to long-term exposure to toxic chemicals such as tributyltin (TBT, 25 and 100 ng/L) and copper (Cu, 100 and 1000 µg/L). We found that TBT was present in the tissues of zebra and quagga mussels in comparable amounts, whereas the bioconcentration factor of Cu varied depending on its concentration in water. Differences in responses between the two species were revealed. When exposed to high Cu concentrations or a Cu-TBT mixture, quagga mussels had a lower survival rate and a longer heart rate recovery time than zebra mussels. TBT treatment caused neurotoxicity (decreased acetylcholinesterase activity) and oxidative stress (increased levels of thiobarbituric acid reactive substances) in both species. TBT and Cu levels in mussel tissues correlated positively with the condition index, but correlated with the level of acetylcholinesterase in the mussel gills. The principal component analysis revealed three main components: the first consists of linear combinations of 14 variables reflecting TBT water pollution, TBT and Cu levels in mussel tissues, and biochemical indicators; the second includes Cu water concentration, cardiac tolerance, and mussel size; and the third combines weight, metabolic rate, and heart rates. Quagga mussels are less tolerable to contaminants than zebra mussels, so they may be used as a sensitive indicator.

Seasonal Diet Changes and Trophic Links of Cold-Water Fish (Coregonus albula) within a Northern Lake Ecosystem.

The seasonal feeding patterns of the cold-adapted fish, Coregonus albula, are poorly studied in high-latitude lakes but could provide insight for predicting the effects of global warming. We examined vendace's diet composition, traced the carbon and nitrogen isotope ratios from producers to consumers in the food web, and estimated vendace's trophic position in a subarctic lake (the White Sea basin). Results showed the vendace to be a typical euryphagous fish, but clear seasonal differences were found in the relative importance of plankton and benthos in the diet. The vendace consumed primarily benthic amphipods in the summer, planktonic cladocerans in the autumn, and copepods in the winter-spring (under ice); larvae of aquatic insects were the second-most important food items throughout the year. Because of the substantial proportion of fish embryos in its diet, the vendace had a trophic position similar to that of a predatory fish (perch). The Bayesian food source-mixing model revealed that the majority of vendace energy derives from planktonic copepods. The dominant Cyclops had the lowest carbon isotope values, suggesting a carbon-depleted diet typical for methanotrophic bacteria, as its probable food source was in a lake under ice. Understanding the feeding patterns of vendace provides information to better predict the potential biotic effects of environmental change on lake ecosystems.

Biochemical and respiratory parameters in a gastropod Radix balthica exposed to diclofenac.

Diclofenac, an anti-inflammatory drug, is often detected in natural waters in the ng/L to µg/L range, posing a threat to aquatic organisms. The study focused on the effects of diclofenac in a gastropod mollusk Radix balthica. A 72-h exposure to environmentally relevant concentrations of diclofenac caused deviations from the baseline activities of the studied enzymes in the digestive gland of snails. Acetylcholinesterase activity was induced by the end of exposure, with the most pronounced increase at 3 µg/L. Results on glutathione-S-transferase activity were nonuniform, and no significant variations were observed in thiobarbituric acid reactive substances concentrations, indicating that diclofenac did not cause oxidative stress in the digestive gland of R. balthica at 0.04-4 µg/L range. Diclofenac lowered the oxygen consumption rate in snails in a concentration-dependent manner. At concentrations ≥0.9 µg/L, animals attempted to switch aquatic respiration to breathing air to regulate their metabolic needs. The study showed that diclofenac at environmentally relevant concentrations affected the fitness of R. balthica.

Effects of Diclofenac on the Reproductive Health, Respiratory Rate, Cardiac Activity, and Heat Tolerance of Aquatic Animals.

Diclofenac is an important pharmaceutical present in the water cycle of wastewater treatment and one of the most distributed drugs in aquatic ecosystems. Despite the great interest in the fate of diclofenac in freshwaters, the effects of environmentally relevant concentrations on invertebrates are still unclear. Two species of freshwater invertebrates, the amphipod Gmelinoides fasciatus and the bivalve mollusk Unio pictorum, were exposed to diclofenac concentrations of 0.001-2 µg/L (environmentally relevant levels) for 96 h. A set of biological endpoints (survival, fecundity, embryo abnormalities, respiration and heart rates, heat tolerance, and cardiac stress tolerance) were estimated in exposed invertebrates. Effects of diclofenac on amphipod metabolic rate and reproduction (number and state of embryos) and adaptive capacity (cardiac stress tolerance) in both species were evident. The oxygen consumption of amphipods exposed to diclofenac of 0.1-2 µg/L was 1.5-2 times higher than in the control, indicating increased energy requirements for standard metabolism in the presence of diclofenac (>0.1 µg/L). The heart rate recovery time in mollusks after heating to critical temperature (30 °C) was 1.7 and 9 times greater in mollusks exposed to 0.1 and 0.9 µg/L, respectively, than in the control (24 min). A level of diclofenac >0.9 µg/L adversely affected amphipod embryos, leading to an increase in the number of embryos with impaired development, which subsequently died. Thus, the lowest effective concentration of diclofenac (0.1 µg/L) led to increased energy demands of animals while reducing cardiac stress tolerance, and at a level close to 1 µg/L reproductive disorders (elevated mortality of the embryos) occurred. Environ Toxicol Chem 2022;41:677-686. © 2021 SETAC.

Shifted mineral ions transport in the mollusk Unio pictorum exposed to environmental concentrations of diclofenac.

Previous studies showed that diclofenac (DCF), when released in the environment, can be toxic to aquatic animals (fish and mollusks), affecting gills, which are the main organ of ionic regulation. This study focuses on detecting the effects of relevant environmental concentrations of DCF (0.1-1 µg L-1) on the transport of main mineral cations, i.e. sodium (Na), potassium (K), calcium (Ca), and magnesium (Mg), by widely distributed freshwater bivalve mollusks Unio pictorum. After 96-h exposure to river aerated water at 25 °C with DCF concentrations of 0 (control), 0.1 (treatment I), and 1 µg L-1 (treatment II), the mollusks were transferred to deionized water, and daily (for 7 days) concentrations of these cations in the medium have been measured. Animals exposed to 1 µg L-1 DCF maintained the ionic balance between the organism and the diluted medium at a significantly higher level of Na, K, and Mg ions in water compared to the control and animals exposed to 0.1 µg L-1 DCF. At 0.1 µg L-1 DCF, the greater loss concerning the control (p < 0.05) was found only for Na ion. There were no differences in the dynamics of Ca ions between control and both treatments. This study showed that detectable environmental concentrations of DCF in natural waters can influence the transport of main cations required by freshwater animals to maintain their ionic balance, and the observed effect (elevated ion loss) is ion-specific and also dose-dependent.

Biomarkers in bivalve mollusks and amphipods for assessment of effects linked to cyanobacteria and elodea: Mesocosm study.

The effects of cyanobacteria (Aphanizomenon flos-aquae (90%), Microcystis aeruginosa) and dense Elodea canadensis beds on the health endpoints of the amphipod Gmelinoides fasciatus and bivalve mollusc Unio pictorum were examined in mesocosms with simulated summer conditions (July-August 2018) in the environment of the Rybinsk Reservoir (Volga River Basin, Russia). Four treatments were conducted, including one control and three treatments with influencing factors, cyanobacteria and dense elodea beds (separately and combined). After 20 days of exposure, we evaluated the frequency of malformed and dead embryos in amphipods, heart rate (HR) and its recovery (HRR) after stress tests in molluscs as well as heat tolerance (critical thermal maximum or CTMax) in both amphipods and molluscs. The significant effect, such as elevated number of malformed embryos, was recorded after exposure with cyanobacteria (separately and combined with elodea) and presence of microcystins (MC) in water (0.17 µg/l, 40% of the most toxic MC-LR contribution). This study provided evidence that an elevated number (>5% of the total number per female) of malformed embryos in amphipods showed noticeable toxicity effects in the presence of cyanobacteria. The decreased oxygen under the influence of dense elodea beds led to a decrease in HR (and an increase in HRR) in molluscs. The notable effects on all studied biomarkers, embryo malformation frequency and heat tolerance in the amphipod G. fasciatus, as well as the heat tolerance and heart rate in the mollusc U. pictorum, were found when both factors (elodea and cyanobacteria) were combined. The applied endpoints could be further developed for environmental monitoring, but the obtained results support the importance of the combined use of several biomarkers and species, especially in the case of multi-factor environmental stress.

Coupled Application of Antioxidant Defense Response and Embryo Development in Amphipod Crustaceans in the Assessment of Sediment Toxicity.

Survival rate, frequency of malformed embryos, and antioxidant defense system responses in the benthic amphipod Gmelinoides fasciatus from the Baltic Sea were measured to examine the effects of toxic sediments, and to assess the usefulness of these endpoints in sediment toxicity biotesting. A highly contaminated sediment sample from the Baltic Sea was diluted with sediment from a clean site to come up with a series of 5 test sediments with dilutions from 1:32 to 1:1024, and the reference sediment. The 1:32 dilution of the test sediment was analyzed for organotins (2862 µg tin [Sn] kg dry wt -1 ), polycyclic aromatic hydrocarbons (6064 µg kg dry wt -1 ), and selected trace metals (e.g., copper 352 mg kg dry wt -1 ). The survival rate of G. fasciatus (10-d toxicity test) was 100% in the reference and 1:1024 treatments, and began to decline from the 1:256 dilution onward. In a 28-d experiment, various types of morphological malformations were observed in 11 to 80% of the amphipod embryos in the 1:64, 1:128, and 1:256 dilutions, with only <5% in the reference treatment. Also, elevated activities in the antioxidant defense system enzymes glutathione S-transferase and catalase were observed in amphipods exposed to the contaminated sediments compared with the reference treatment, with responses at lower contamination levels compared with the appearance of malformations in the embryos. The results obtained illustrate the effectiveness of the combined application of embryonic malformations and antioxidant defense system biomarkers in amphipods in the assessment of sediment toxicity, and potentially also of sublethal effects of chemical contamination in aquatic ecosystems. Environ Toxicol Chem 2019;38:2020-2031. © 2019 SETAC.

A relative contribution of carbon from green tide algae Cladophora glomerata and Ulva intestinalis in the coastal food webs in the Neva Estuary (Baltic Sea).

We analyzed stable isotope composition of carbon and nitrogen of suspended organic matter (seston) and tissues of macroalgae, macroinvertebrates and fish from the coastal area of the highly eutrophic Neva Estuary to test a hypothesis that organic carbon of macroalgae Cladophora glomerata and Ulva intestinalis produced during green tides may be among primary sources supporting coastal food webs. The Stable Isotope Bayesian mixing model (SIAR) showed that consumers poorly use organic carbon produced by macroalgae. According to the results of SIAR modeling, benthic macroinvertebrates and fish mostly rely on pelagic derived carbon as a basal resource for their production. Only some species of macroinvertebrates consumed macroalgae. Fish used this resource directly consuming zooplankton or indirectly via benthic macroinvertebrates. This was consistent with the results of the gut content analysis, which revealed a high proportion of zooplankton in the guts of non-predatory fish.

The causes and consequences of algal blooms: the Cladophora glomerata bloom and the Neva Estuary (eastern Baltic Sea).

The biomass dynamics of the green alga Cladophora glomerata was studied in the shallow-water littoral zone of the Neva estuary during May-October of 2003-2005. Additionally, the average production rate of C. glomerata, the biomass of drifting algae and oxygen depletion were examined during period of algae decomposition. Two peaks in C. glomerata biomass, in July and in September, were observed during all years studied, reaching a maximum 300+/-100 g DW m(-2). The primary production of C. glomerata varied from 3.6 to 7.9 g C m(-2) contributing to around 90% of the total primary production in this habitat. From the middle of July to late August the biomass of drifting C. glomerata exceeded the biomass of the attached algae, accounting for 62% of the total algal biomass in shallow areas (0-1m). The hypoxia (a minimum oxygen level of 5% or 0.62 mg dm(-3)) in the water was recorded near shore (to 20-m distance from the shore), negatively influencing the quality of shallow-water habitats.