Assessment of toxicity test endpoints for freshwater mussel larvae (glochidia)

Reduced Freshwater Mussel Juvenile Production as a Result of Agricultural and Urban Contaminant Mixture Exposures

Freshwater mussels provide invaluable ecological services but are threatened by habitat alteration, poor water quality, invasive species, climate change, and contaminants, including contaminants of emerging concern (CECs). Contaminants of emerging concerns are well documented in aquatic environments, including the Great Lakes Basin, but limited information is available on how environmentally relevant mixtures affect freshwater mussel biology throughout their varied life stages. Our main goal was to assess mussels' reproductive output in response to exposure to agricultural and urban CEC mixtures during glochidial development through juvenile transformation and excystment focusing on how exposure duration and treatment affect: (1) the number of glochidia prematurely released by brooding females, (2) glochidial transformation through host-fish excystment, and (3) the number of fully metamorphosed juveniles able to continue the lifecycle. Mussels and host fish were exposed to either a control water (CW), control ethanol (CE), agriculture CEC mixture (AM), or urban CEC mixture (UM) for 40 and 100 days. We found no effect from treatment or exposure duration on the number of glochidia prematurely released. Fewer partially and fully metamorphosed AM juveniles were observed during the 100-day exposure, compared with the 40-day. During the 40-day exposure, CW produced more fully metamorphosed individuals compared with CE and UM, but during the 100-day exposure AM produced more fully metamorphosed individuals compared with the CW. There was reduction in fully metamorphosed juveniles compared with partially metamorphosed for CE and UM during the 40-day exposure, as well as in the CW during the 100-day exposure. These results will be important for understanding how mussel populations are affected by CEC exposure. The experiments also yielded many insights for laboratory toxicology exposure studies. Environ Toxicol Chem 2024;00:1-14. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Major Ion Toxicity to Glochidia of Common and Imperiled Freshwater Mussel Species

Freshwater mussel taxa are severely imperiled and among the most sensitive to several contaminants, including chloride. Relatively little is known of the toxicity of major ions to glochidia (larvae), particularly for rare species, or the effects of hardness on major ion toxicity to glochidia. Therefore, the primary objectives of this work were to: (1) determine the acute toxicity of major ion salts to glochidia, (2) compare chloride sensitivity of glochidia from common and rare species, and (3) evaluate the relationship between water hardness and chloride toxicity to glochidia. We assessed 24 h EC50s for fatmucket (Lampsilis siliquoidea) glochidia exposed to NaCl, KCl, MgCl2, CaCl2, Na2SO4, MgSO4, CaSO4, and NaHCO3 in moderately hard water. We determined NaCl EC50s for four species and KCl EC50s for glochidia of three species. Toxicity of chloride was generally consistent among the various chloride salts except for KCl, which was more toxic than all others by 1–2 orders of magnitude. Our results suggest that commonly tested species may be generally representative of rare species. Water hardness ameliorated the toxicity of chloride for all species to varying degrees. Results of this work indicate that some existing water quality criteria that do not include mussel toxicity data may not be protective of freshwater mussels.

Risk Assessment of Gypsum Amendment on Agricultural Fields: Effects of Sulfate on Riverine Biota

Gypsum (CaSO₄ ∙2H₂ O) amendment is a promising way of decreasing the phosphorus loading of arable lands, and thus preventing aquatic eutrophication. However, in freshwaters with low sulfate concentrations, gypsum-released sulfate may pose a threat to the biota. To assess such risks, we performed a series of sulfate toxicity tests in the laboratory and conducted field surveys. These field surveys were associated with a large-scale pilot exercise involving spreading gypsum on agricultural fields covering 18% of the Savijoki River (Finland) catchment area. The gypsum amendment in such fields resulted in approximately a four-fold increase in the mean sulfate concentration for a 2-month period, and a transient, early peak reaching approximately 220 mg/L. The sulfate concentration gradually decreased almost to the pregypsum level after 3 years. Laboratory experiments with Unio crassus mussels and gypsum-spiked river water showed significant effects on foot movement activity, which was more intense with the highest sulfate concentration (1100 mg/L) than with the control. Survival of the glochidia after 24 and 48 h of exposure was not significantly affected by sulfate concentrations up to 1000 mg/L, nor was the length growth of the moss Fontinalis antipyretica affected. The field studies on benthic algal biomass accrual, mussel and fish density, and Salmo trutta embryo survival did not show gypsum amendment effects. Gypsum treatment did not raise the sulfate concentrations even to a level just close to critical for the biota studied. However, because the effects of sulfate are dependent on both the spatial and the temporal contexts, we advocate water quality and biota monitoring with proper temporal and spatial control in rivers within gypsum treatment areas. Environ Toxicol Chem 2022;41:108-121. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Seawater intrusion: an appraisal of taxa at most risk and safe salinity levels

Seawater intrusion into low-lying coastal ecosystems carries environmental risks. Salinity levels at these coastal ecosystems may vary substantially, causing ecological effects from mortality to several sublethal endpoints, such as depression of rates of feeding, somatic growth, or reproduction. This review attempts to establish safe salinity levels for both terrestrial and freshwater temperate ecosystems by integrating data available in the literature. We have four specific objectives: (i) to identify the most sensitive ecological taxa to seawater intrusion; (ii) to establish maximum acceptable concentrations-environmental quality standards (MAC-EQSs) for sea water (SW) from species sensitivity distributions (SSDs); (iii) to compile from the literature examples of saline intrusion [to be used as predicted environmental concentrations (PECs)] and to compute risk quotients for the temperate zone; and (iv) to assess whether sodium chloride (NaCl) is an appropriate surrogate for SW in ecological risk assessments by comparing SSD-derived values for NaCl and SW and by comparing these with field data. Zooplankton, early life stages of amphibians and freshwater mussels were the most sensitive ecological receptors for the freshwater compartment, while soil invertebrates were the most sensitive ecological receptors for the terrestrial compartment. Hazard concentration 5% (HC₅ ) values, defined as the concentration (herein measured as conductivity) that affects (causes lethal or sublethal effects) 5% of the species in a distribution, computed for SW were over 22 and 40 times lower than the conductivity of natural SW (≈ 52 mS/cm) for the freshwater and soil compartment, respectively. This sensitivity of both compartments means that small increments in salinity levels or small SW intrusions might represent severe risks for low-lying coastal ecosystems. Furthermore, the proximity between HC₅ values for the soil and freshwater compartments suggests that salinized soils might represent an additional risk for nearby freshwater systems. This sensitivity was corroborated by the derivation of risk quotients using real saline intrusion examples (PECs) collected from the literature: risk was >1 in 34 out of 37 examples. By contrast, comparisons of HC₅ values obtained from SSDs in field surveys or mesocosm studies suggest that natural communities are more resilient to salinization than expected. Finally, NaCl was found to be slightly more toxic than SW, at both lethal and sublethal levels, and, thus, is suggested to be an acceptable surrogate for use in risk assessment.

Effects of nitrate on freshwater mussel glochidia attachment and metamorphosis success to the juvenile stage

Water quality and contaminants have been frequently identified as critical stressors for freshwater mussels, many species of which are highly imperiled throughout North America and the world. Nutrient pollution, specifically nitrate, has become one of the most prevalent causes of water quality degradation globally, with increasing anthropogenic input from suburban and agricultural runoff, municipal wastewater, and industrial waste. Nitrate acute toxicity is generally low for aquatic species, but the potential effects of nitrate exposure are largely unknown for freshwater mussels, particularly during the parasitic stage of their complex lifecycle. Therefore, this study was designed to determine the effects of short-term nitrate exposure at environmentally relevant concentrations on juvenile production in two freshwater mussel species. Lampsilis siliquoidea and L. fasciola glochidia were exposed to nitrate (0, 11, or 56 mg NO₃-N/L) for 24 h before inoculation on a primary host, Largemouth Bass (Micropterus salmoides). Glochidia attachment, metamorphosis success, and total number of juveniles produced were monitored on individual fish. Exposure of L. siliquoidea glochidia to 56 mg NO₃-N/L nitrate resulted in a significant (p = 0.02) 35% reduction of total juveniles produced, a combined result of moderate decreases in both glochidia attachment and metamorphosis success. A similar trend (28% reduction; p = 0.06) was evident with 11 mg NO₃-N/L. No effects were apparent for L. fasciola, suggesting species-specific differences in responses even among closely related species. These results are the first to suggest that glochidia exposure to nitrate may adversely affect juvenile recruitment in some species. Findings from these studies are important for improving characterization of the hazards of nitrate pollution to aquatic life and this work will help better define the role of water quality in assessing habitat suitability for mussel conservation efforts.

Acute ammonia toxicity to the larvae (glochidia) of the tropical Australian freshwater mussel Velesunio spp. Using a modified toxicity test protocol

Ammonia is recognized as a major pollutant worldwide, originating from natural and anthropogenic sources. Studies have reported that freshwater mussels are among the most sensitive taxa to ammonia, but few data are available on ammonia toxicity for the early life stages of freshwater mussels from tropical regions. We report on the modification of a 24-h acute toxicity test protocol for tropical freshwater mussels and application of the test using ammonia. Velesunio spp. from 3 different sites were used to assess the toxicity of ammonia at a targeted pH of 6.0 and a water temperature of 27.5 °C, which were the average annual values for some slightly to moderately acidic, soft water (3-6 mg/L as CaCO₃ ) creeks of tropical northern Australia. The valve closure responses of mussel glochidia (larvae) to a sodium chloride solution were used to measure the survival endpoint. Acute toxicity estimates indicate that tropical Velesunio spp. were highly sensitive to ammonia, with 24-h exposures to ammonium sulfate generating median lethal concentration estimates ranging from 6.8 to 14.2 mg/L total ammonia nitrogen, which, when adjusted to pH 7 and 20 °C, were among the highest sensitivities yet reported for any freshwater mussel species, and among the highest in sensitivity for any tropical taxon. These toxicity estimates can contribute to the derivation or refinement of ammonia guideline values for freshwater ecosystems globally. Environ Toxicol Chem 2018;37:2175-2187. © 2018 SETAC.

Sensitivity of the glochidia (larvae) of freshwater mussels (Bivalvia: Unionida: Hyriidae) to cadmium, cobalt, copper, lead, nickel and zinc: Differences between metals, species and exposure time

Freshwater mussels (Bivalvia: Unionida) are among the most threatened freshwater faunal groups worldwide. Metal contamination is one threat that has been linked to declining mussel population distribution and abundance. This study determined the sensitivity (valve closure) of the glochidia (larvae) of six species of Australian freshwater mussels to cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn), key metal contaminants impacting urbanized coastal rivers in south-eastern Australia (home to ~50% of the population), in a soft reconstituted freshwater (hardness 42mgCaCO₃L^-1; alkalinity 22mgCaCO₃L^-1 and pH7.0) over 72h. The sensitivity of each mussel species to each metal increased 2.5-fold with increasing exposure time from 24 to 72h. The most sensitive mussel species (Cucumerunio novaehollandiae), across all metals and exposure times, was ~60% more sensitive than the least sensitive species (Velesunio ambiguus). The relative sensitivity of glochidia to the six selected metals, across all mussel species and exposure times, was: Cu>Cd>Pb>Co=Ni>Zn. Glochidia were most sensitive to Cu and least sensitive to Zn. Quantitatively, the toxicity of Cu was 3-fold more than Cd, 8-fold more than Pb, 14-fold more than Co or Ni and 16-fold more than Zn. The cell surface binding affinities (conditional log K values) of Cd (range 6.65-6.94), Co (6.04-6.29), Cu (7.17-7.46), Ni (6.02-6.29), Pb (6.24-6.53) or Zn (5.96-6.23), pooled for all mussel species after 72h exposure, were positively related to metal sensitivity. The chronic no effect concentrations (NECs) of Cu, Ni and Zn were below (i.e. glochidia were more sensitive than) their national freshwater guideline values, indicating that freshwater mussels may not be adequately protected for these metals in urbanized coastal rivers within south-eastern Australia.

Acute effects of salinity exposure on glochidia viability and host infection of the freshwater mussel Anodonta anatina (Linnaeus, 1758)

Freshwater mussels of the Unionida are globally in decline and knowledge of the sensitivity of their vulnerable life stages to stressors is crucial for their conservation. Increasing salinity, e.g., due to road deicing, has been proposed as an important stressor, but its impact on the complex interaction between mussel larvae and their obligate attachment to fish hosts remains largely unknown. This study tested the acute toxicity effects of environmentally relevant chloride concentrations on larvae of European Anodonta anatina mussel as well as the impacts on attachment rates of the larvae to their fish host. Chloride concentrations above 727 mg⋅L(-1) significantly affected glochidia viability and the 24h EC50 value was determined at 2,505 mg⋅L(-1). Successful attachment of glochidia to the host fish Phoxinus phoxinus was negatively correlated with increasing chloride concentration and became significant at concentrations > 2,909 mg⋅L(-1). Comparable responses could be observed by separately counting fin and gill attached glochidia, while gill attachment showed the highest correlation with overall attachment rates. These results indicate a potential threat from short-term elevated chloride concentrations during runoff events on sensitive life stages of freshwater mussels. Consequently, we propose additional chloride sensitivity tests on other mussel species as well as the reduction of salt peak input loading into freshwater bodies through a 3R-principle (restriction of use, retention of runoff for peak concentration avoidance and replacement by alternatives) in areas where endangered mussels occur.

CAPSULE

Freshwater mussels of the Unionoida are globally in decline and knowledge on the sensitivity of the most vulnerable larval stages to salinity is crucial for their conservation.

Metabolomic, behavioral, and reproductive effects of the aromatase inhibitor fadrozole hydrochloride on the unionid mussel Lampsilis fasciola

Androgen-induced masculinization of female aquatic biota poses concerns for natural population stability. This research evaluated the effects of a twelve day exposure of fadrozole hydrochloride on the metabolism and reproductive status of the unionid mussel Lampsilis fasciola. Although this compound is not considered to be widespread in the aquatic environment, it was selected as a model aromatase (enzyme that converts testosterone to estradiol) inhibitor. Adult mussels were exposed to a control and 3 concentrations of fadrozole (2μg/L, 20μg/L, and 50μg/L), and samples of gill tissue were taken on days 4 and 12 for metabolomics analysis. Gills were used because of the variety of critical processes they mediate, such as feeding, ion exchange, and siphoning. Daily observed mussel behavior included female mantle display, foot protrusion, siphoning, and larval (glochidia) releases. Glochidia mortality was significantly higher in the 20μg/L treatment. Fewer conglutinate (packets of glochidia) releases were observed in the 50μg/L treatment, and mortality was highly correlated to release numbers. Foot protrusion was significantly higher in females in nearly all treatments, including the control, during the first 4days of observations. However, this sex difference was observed only in the 50μg/L treatment during the last 8days. Generally, metabolites were significantly altered in female gill tissue in the 2μg/L treatment whereas males were mostly affected only at the highest (50μg/L) treatment. Both sexes also revealed significant reductions in fadrozole-induced metabolic effects in gill tissue sampled after 12days compared to tissue sampled after 4days, indicating time-dependent mechanisms of disruptions in metabolic pathways and homeostatic processes to compensate for such disruptions.

Metabolomic, behavioral, and reproductive effects of the synthetic estrogen 17 α-ethinylestradiol on the unionid mussel Lampsilis fasciola

The endocrine disrupting effects of estrogenic compounds in surface waters on fish, such as feminization of males and altered sex ratios, may also occur in aquatic invertebrates. However, the underlying mechanisms of action and toxicity, especially in native freshwater mussels (Order Unionoida), remain undefined. This study evaluated the effects of a 12-day exposure of 17 α-ethinylestradiol (EE2), a synthetic estrogen in oral contraceptives commonly found in surface waters, on the behavior, condition, metabolism, and reproductive status of Lampsilis fasciola. Adult mussels of both sexes were exposed to a control and two concentrations of EE2 (0 ng/L, 5 ng/L considered to be environmentally relevant, and 1,000 ng/L designed to provide a positive metabolic response), and samples of gill tissue were taken on days 4 and 12; gills were used because of the variety of critical processes they mediate, such as feeding, ion exchange, and siphoning. Observations of mussel behavior (mantle display, siphoning, and foot movement) were made daily, and condition of conglutinates (packets of eggs and/or glochidia) released by females was examined. No significant effects of EE2 on glochidia mortality, conglutinate condition, female marsupial gill condition, or mussel foot extension were observed. However, exposure to both concentrations of EE2 significantly reduced male siphoning and mantle display behavior of females. Metabolomics analyses identified 207 known biochemicals in mussel gill tissue and showed that environmentally relevant EE2 concentrations led to decreases in glycogen metabolism end products, glucose, and several essential fatty acids in females after 12 days, indicating reductions in energy reserves that could otherwise be used for growth or reproduction. Moreover, males and females showed significant alterations in metabolites involved in signal transduction, immune response, and neuromodulation. Most of these changes were apparent at 1,000 ng/L EE2, but similar metabolites and pathways were also affected at 5 ng/L EE2. Components of the extracellular matrix of gill tissue were also altered. These results demonstrate the utility of metabolomics when used in conjunction with traditional physiological and behavioral toxicity test endpoints and establish the usefulness of this approach in determining possible underlying toxicological mechanisms of EE2 in exposed freshwater mussels.