Hydrology and invasive macrophytes may mediate freshwater mussel density and population size structure in a hydropeaking reservoir.

Globally-threatened freshwater mussels belonging to the order Unionida (Bivalvia) may be adversely affected by dense beds of submerged macrophytes that modify habitat at the sediment-water interface. Such effects can be particularly pronounced in modified lentic ecosystems such as reservoirs which are subject to hydrological regimes (e.g., hydropeaking) that can exacerbate macrophyte-mediated impacts, including anoxic or hypoxic conditions, the related release of toxic ions (e.g., ammonia), and silt accumulation that inhibits filter-feeding. Accordingly, we compared how population size-structure and biomass of the New Zealand mussel Echyridella menziesii varied inside and outside of dense beds of invasive macrophytes known to have similar impacts on water chemistry (e.g., anoxia) in two northern New Zealand hydroreservoir locations with contrasting hydrology (lacustrine location dominated by Ceratophyllum demersum; and riverine location dominated by Egeria densa). We found adverse sediment-water interface conditions were not always associated with dense submerged macrophyte beds in littoral zones. Nonetheless, where they occurred, adverse sediment-water interface conditions were related to reduced mussel density and adult skewed size-structure, inferring reduced recruitment. Disentangling direct and indirect effects with structural equation modelling indicated that increased pore-water ammonia did not impact these primarily adult populations of freshwater mussels. Increased sediment organic matter, silt, and previously recorded hypoxia and anoxia were exacerbated in the lacustrine section where variable flows promoting water mixing were not present. High densities of mussels <40 mm in length were associated with favourable sediment-water interface conditions of low silt and sediment organic matter, suggesting that enhanced water exchange in and around macrophyte beds may increase juvenile mussel survival in littoral zones of the riverine lake section. Our findings highlight a potential role for hydropeaking management in mitigating the development of adverse physicochemical conditions, and underscore the context-specific effects that dense non-native macrophyte beds can have on mussel populations.

Investigating the fate of copper in a laboratory-based toxicity test with embryos of Mytilus galloprovincialis: Copper mass balance of a closed bioassay.

The production of accurate and reliable data on metal toxicity during ecotoxicological bioassays is important for credible environmental risk assessments and management in aquatic environments. Actual measurements and reporting of contaminant concentrations in bioassays are, however, often disregarded; and potential contaminant loss attributable to adsorption processes (e.g., wall adsorption) in bioassays is widely omitted, which can have detrimental effects on calculated metal toxicity thresholds. In the present we assessed copper (Cu) mass balance during a standard 48-h bioassay test with blue mussel (Mytilus galloprovincialis) embryos to evaluate effects on calculated toxicity endpoints. We demonstrated that measured Cu concentrations at the test conclusion need to be used to quantify the risk of Cu toxicity because nominal Cu and initial Cu concentrations underestimate overall Cu toxicity by up to 1.5-fold, owing to Cu loss in solution attributable to adsorption and bioaccumulation processes. For the first time we provide evidence that extracellular adsorption to the biological surface of the embryos is the most important sink for total dissolved Cu in a bioassay. We also established that adsorbed extracellular Cu accumulation reduces Cu toxicity to embryos, potentially by inhibiting Cu from entering the cell of the mussel embryo. Environmental factors (e.g., salinity and dissolved organic carbon) did not influence the partitioning of Cu within the laboratory-based bioassay. The present results 1) demonstrate the importance of differentiating extra- and intracellular Cu pools to improve our understanding of Cu toxicity and associated processes, 2) reveal the potential for bias with respect to calculated Cu toxicity thresholds when results are based on nominal and initial Cu concentrations, and 3) point out the need to follow current guidelines for the testing of chemicals to standardize toxicity tests and data reporting. Environ Toxicol Chem 2019;38:561-574. © 2019 SETAC.

Copper toxicity to blue mussel embryos (Mytilus galloprovincialis): The effect of natural dissolved organic matter on copper toxicity in estuarine waters.

Copper (Cu) is a naturally occurring micronutrient of eco-toxicological concern in aquatic ecosystems. Current knowledge of Cu-speciation and bioavailability in natural saline environments is insufficient to adequately inform environmental protection policy for estuarine systems. We assessed the combined effect of two of the main drivers of metal bioavailability, salinity and natural dissolved organic carbon (DOC), on Cu-speciation and associated Cu-toxicity to blue mussel (Mytilus galloprovincialis) embryos in a standard 48-h bioassay. We placed special emphasis on measurement of Cu-speciation rather than modelling. Cu-toxicity was found to be a function of DOC and salinity. The varying protective effect of different DOC-types suggests that estuarine DOC is more protective against Cu-toxicity than oceanic DOC. Salinity was negatively correlated with [Cu48-h-EC50], indicating a salinity-induced alteration in the physiology of the exposed mussel embryos and/or Cu-DOC-reactivity. These two assumptions were supported by (1) the relative uniformity of bioavailable copper ([Cu']) across similar salinity treatments despite considerable variation in [Cu48-h-EC50] and DOC-concentrations, and (2) the fact that Cu-toxicity and [Cu'] were slightly higher in the 35 salinity treatment compared to the 25 salinity treatment. Stripping voltammetry studies determined the presence of only one strong Cu-binding ligand class (i.e., L1), either actively or passively released by the exposed embryos. [L1] was found to be proportional to the total dissolved Cu-concentration ([CuT]), suggesting a protective effect of Cu-binding-ligands, in addition to the protective effect of DOC. There was also a strong positive correlation between [L1] and [Cu48-h-EC50], implying that electrochemically defined ligand concentrations along with measurements of [Cu'], DOC-quality, and salinity can be used as proxies for 48-h-EC50 Cu-values in estuarine waters, which may result in a significant improvement to risk assessments of Cu in estuarine systems.

Acute toxicity of chlorpyrifos and carbosulfan to glochidia of the freshwater mussel Hyriopsis bialata Simpson, 1900.

The acute toxicity of carbosulfan and chlorpyrifos in formulated pesticides to glochidia (larvae) of the freshwater mussel (Hyriopsis bialata Simpson, 1900) was evaluated under static conditions in moderately hard dechlorinated tap water. Measured pesticide concentrations were 26 to 34% lower than nominal concentrations; therefore, all results are expressed in terms of measured active ingredient. Carbosulfan was relatively non-toxic to the mussel larvae with median effective concentrations (EC50) of carbosulfan at 24 and 48 h greater than 0.10 mg/L. The EC50s of chlorpyrifos at 24 and 48 h were 0.083 and 0.078 mg/L, respectively (measured concentrations). The 48-h EC50 of a combined exposure to a mixture of chlorpyrifos and carbosulfan at a constant ratio of 2.9:1 was 0.0142:0.049 mg CP:CB/L. In a separate experiment, the effect of water hardness on carbosulfan, chlorpyrifos, or a combined exposure was assessed using glochidia exposed to either soft, moderately hard, or hard reconstituted water. There was no effect of water hardness on the survival of glochidia after 24- or 48-h exposure to carbosulfan. The chlorpyrifos 48-h EC50s in soft water, moderately hard water, and hard water were 0.18, 0.11, and 0.16 mg/L, respectively. The data indicate that the lowest water hardness resulted in the highest survival of glochidia, whereas an increase to moderate water hardness resulted in significantly decreased survival of glochidia (F = 15.5, P < 0.05). The EC50s of a combined exposure at 48 h in soft water, moderately hard water, and hard water were 0.124:0.044, 0.132:0.047, and 0.064:0.022 mg CP:CB/L, respectively. The data indicate that the combined toxicity was lowest at low and moderate water hardness, whereas an increase to high water hardness resulted in a significantly decreased survival of glochidia. After 48 h, the toxicity of the combined chlorpyrifos and carbosulfan exposure in soft and hard water was greater than that of chlorpyrifos alone.

Acute toxicity of copper, zinc, and ammonia to larvae (Glochidia) of a native freshwater mussel Echyridella menziesii in New Zealand.

Adult New Zealand freshwater mussel Echyridella menziesii were collected from three locations in the North Island of New Zealand. In a series of tests that followed standard test guidance, glochidia were exposed to either dissolved copper (Cu), zinc (Zn), or total ammonia nitrogen (TAN) for 6, 24, or 48 h (20 °C, pH 7.8, water hardness 30 mg L(-1) as CaCO3, dissolved organic carbon [DOC] 2.0-2.9 mg L(-1)). Of the three contaminants and tests that met control survival criteria, mussel larvae (glochidia) were most sensitive to Cu exposure (48-h EC50 = 1.7-3.4 µg L(-1), 48-h no observed effect concentrations (NOEC) of 1.3-2.6 µg L(-1)). The Zn 48-h EC50 concentrations were 229-337 µg L(-1) and the 48-h NOEC values were 128-240 µg L(-1). Compared with other native New Zealand species, glochidia were also relatively sensitive to TAN exposure (48-h EC50 12-15 mg TAN L(-1) [pH 7.8], 48-h NOEC 8-10 mg TAN L(-1)). Comparison of our data with those of previous studies on North American freshwater mussels indicates that (1) E. menziesii are among those aquatic species most sensitive to acute Cu or TAN exposure; and (2) E. menziesii juveniles would not be adequately protected by current ANZECC water quality guidelines for TAN or Cu. Inclusion of North American juvenile mussel data in a revision of the current ANZECC water-quality guideline (95th percentile) for chronic ammonia exposure results in a decrease from 0.9 mg to 0.2 mg TAN L(-1) (pH 8).

Pulse-dose application of chelated copper to a river for Didymosphenia geminata control: effects on macroinvertebrates and fish.

A 1-h pulse-dose of a chelated Cu formulation (Gemex™; New Zealand) was applied to a river to test efficacy against the invasive mat-forming diatom Didymosphenia geminata (didymo) and to provide information on nontarget species effects that could not be adequately predicted from laboratory and experimental mesocosm studies. Intensive sampling allowed characterization of doses achieved at multiple downstream locations, and concurrent application of rhodamine dye allowed quantification of dispersion, adsorption, and dilution processes. The target dose of 10 to 20 mg Cu/L for 60 min was achieved at least 0.9 km downstream at sites with contrasting levels of didymo mat development. Adsorptive losses of Gemex were 12%/km where didymo was mostly nonvisible and approximately 36%/km where substantial didymo mats were present. At 0.9 km downstream, Cu concentrations peaked at 12 mg/L, and didymo was <5% viable (down from 65-72%) for ≥21 d posttreatment. Viability data indicate that elimination of nonvisible infestations is possible and that suppression of early-stage infestations (≤40% cover, ≤4.5 mm thick) could be achieved after repeated applications. After a single Gemex application, no significant accumulation of Cu was noted in the sediments six weeks posttreatment, but Cu concentrations remained high in algal mats (109-367 mg/kg dry wt). Long-term effects on the nontarget algal, invertebrate, or fish communities were minimal, although significant localized trout mortalities, not predicted by prior laboratory exposures, occurred on the treatment day. Extended Gemex exposure in low-hardness waters might have caused the mortalities, although changes in chelated Cu speciation also possibly contributed. The present study integrates effects on resident biota with dosage data, including changes in pH, in a natural waterway.

Survival of Lost River suckers (Deltistes luxatus) challenged with Flavobacterium columnare during exposure to sublethal ammonia concentrations at ph 9.5.

The Lost River sucker (Deltistes luxatus) is a federally listed, endangered species inhabiting the hypereutrophic waters of Upper Klamath Lake in southern Oregon, USA. High pH (> or =10) and elevated ammonia concentrations (> or =1 mg NH(3)-N/L) often occur during blooms of cyanobacteria (Aphanizomenon flos-aquae) in the lake, with major fish kills sometimes following a mid- or late-summer "crash" of the cyanobacterial population. Previous histopathology analyses and bacterial sampling indicated that infections of the pathogenic bacterium Flavobacterium columnare might contribute to the fish kills. We hypothesized that prior exposure to adverse water quality conditions increases the susceptibility of Lost River suckers to F. columnare infections. To test this, we exposed juvenile Lost River suckers to four sublethal ammonia concentrations at pH 9.4 for 62 d. On day 31, fish in half of the aquaria were exposed to F. columnare. As expected, survival of the Lost River suckers decreased in aquaria inoculated with F. columnare. Ninety-four percent of the fish that died were infected by F. columnare in the gills, kidney, or skin, whereas none of the survivors or unexposed control fish was infected. However, contrary to our hypothesis, survival of the fish exposed to F. columnare increased significantly (p < 0.05) as unionized ammonia concentrations increased. Our results suggest that complex interactions can complicate prediction of the responses of fish to concurrent chemical stressors and bacterial pathogens.

Bioavailability and toxicity of dietborne copper and zinc to fish.

To date, most researchers have used dietborne metal concentrations rather than daily doses to define metal exposure and this has resulted in contradictory data within and between fish species. It has also resulted in the impression that high concentrations of dietborne Cu and Zn (e.g. > 900 mg kg(-1) dry diet) are relatively non-toxic to fish. We re-analyzed existing data using rations and dietborne metal concentrations and used daily dose, species and life stage to define the toxicity of dietborne Cu and Zn to fish. Partly because of insufficient information we were unable to find consistent relationships between metal toxicity in laboratory-prepared diets and any other factor including, supplemented metal compound (e.g. CuSO(4) or CuCl(2)), duration of metal exposure, diet type (i.e. practical, purified or live diets), or water quality (flow rates, temperature, hardness, pH, alkalinity). For laboratory-prepared diets, dietborne Cu toxicity occurred at daily doses of > 1 mg kg(-1) body weight d(-1) for channel catfish (Ictalurus punctatus), 1-15 mg kg(-1) body weight d(-1) (depending on life stage) for Atlantic salmon (Salmo salar) and 35-45 mg kg(-1) body weight d(-1) for rainbow trout (Oncorhynchus mykiss). We found that dietborne Zn toxicity has not yet been demonstrated in rainbow trout or turbot (Scophthalmus maximus) probably because these species have been exposed to relatively low doses of metal ( < 90 mg kg(-1) body weight d(-1)) and effects on growth and reproduction have not been analyzed. However, daily doses of 9-12 mg Zn kg(-1) body weight d(-1) in laboratory-prepared diets were toxic to three other species, carp Cyprinus carpio, Nile tilapia Oreochromis niloticus, and guppy Poecilia reticulata. Limited research indicates that biological incorporation of Cu or Zn into a natural diet can either increase or decrease metal bioavailability, and the relationship between bioavailability and toxicity remains unclear. We have resolved the contradictory data surrounding the effect of organic chelation on metal bioavailability. Increased bioavailability of dietborne Cu and Zn is detectable when the metal is both organically chelated and provided in very low daily doses. We have summarized the information available on the effect of phosphates, phytate and calcium on dietborne Zn bioavailability. We also explored a rationale to understand the relative importance of exposure to waterborne or dietborne Cu and Zn with a view to finding an approach useful to regulatory agencies. Contrary to popular belief, the relative efficiency of Cu uptake from water and diet is very similar when daily doses are compared rather than Cu concentrations in each media. The ratio of dietborne dose:waterborne dose is a good discriminator of the relative importance of exposure to dietborne or waterborne Zn. We discuss gaps in existing data, suggest improvements for experimental design, and indicate directions for future research.