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.

Investigating the Effects of Pesticides on Ramshorn Snails (Planorbella [Helisoma] trivolvis) Infected with Echinostoma spp

Globally, parasite-induced diseases in humans and wildlife are on the rise, and pesticide pollution may be a contributing factor. Echinostoma spp. trematode parasites are prominent in North America, and they use ramshorn snails (Planorbella [Helisoma] trivolvis) as intermediate hosts. We investigated the impact of chronic exposure to 1 of 5 pesticide treatments (control, or 50 μg/L of atrazine, glyphosate, carbaryl, or malathion) on uninfected and Echinostoma-infected snails for 41 d in the laboratory. We recorded snail mortality, the number of egg masses laid, change in mass, and behavior. Chronic exposure to atrazine, carbaryl, and malathion significantly decreased snail survival, whereas parasite infection status or exposure to glyphosate did not. Pesticide and parasite treatments did not influence growth or behavior, but parasite infection caused complete reproductive failure in snail hosts. Our results indicated that the direct effects of pesticides could threaten snail populations in natural environments and disrupt host-parasite dynamics.  Environ Toxicol Chem 2021;40:2755-2763. © 2021 SETAC.

A 72-h exposure study with eastern oysters (Crassostrea virginica) and the nanomaterial graphene oxide

Graphene is a 2-dimensional nanomaterial with unique mechanical, thermal, electrical, and optical properties. With increasing applications of graphene-family nanomaterials (GFNs) in electronics, biomedicine, and surface coatings, concern for their impacts on aquatic ecosystems is rising. Current information on the toxicity of GFNs, including graphene oxide, is scarce. Filter-feeding bivalves, such as eastern oysters, are good models for nanomaterial exposure studies. We present results from a 72-h static renewal oyster study using 1 and 10 mg/L graphene oxide, which, to our knowledge, is the first report on in vivo effects of graphene oxide exposures in marine bivalves. Water samples were analyzed for graphene oxide concentration and size assessments. Gill and digestive gland tissues were evaluated for lipid peroxidation and glutathione-S-transferase (GST) activity. In addition, gill sections were fixed for histopathological analyses. Elevated lipid peroxidation was noted in oysters exposed to 10 mg/L graphene oxide. No significant changes in GST activity were observed, but reduced total protein levels were found in digestive gland tissues of exposed oysters at both concentrations. Loss of mucous cells, hemocytic infiltration, and vacuolation were observed in gills of exposed oysters. The results indicate that short-term graphene oxide exposures can induce oxidative stress and epithelial inflammation and adversely affect overall oyster health. Further investigations regarding the fate and sublethal effects of graphene oxide are critical to understanding the risks associated with a rapidly growing graphene consumer market. Environ Toxicol Chem 2019;38:820-830. Published 2019 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.

Toxicity of various road-deicing salts to Asian clams (Corbicula fluminea)

Humans are altering environments by destroying habitats, introducing species, and releasing pollution. One emergent pollutant is the salinization of freshwater habitats from road-deicing salts. Government agencies have set thresholds to protect freshwater ecosystems, yet these values are exceeded in many systems. The present study investigated the tolerance of Asian clams (Corbicula fluminea), a common invasive bivalve, to the common road salt (sodium chloride [NaCl]) and 2 alternatives (magnesium chloride [MgCl₂ ] and calcium chloride [CaCl₂ ]). Experiments conducted at 4 and 8 d revealed that Asian clams are very salt tolerant. The median lethal concentration after 4 d of exposure (LC50_4-d ) estimate was 2162 mg Cl^- /L for MgCl₂ , 3554 mg Cl^- /L for CaCl₂ , and more than 22 581 mg Cl^- /L for NaCl, which were all significantly different from each other (p ≤ 0.05). The LC50_8-d values were significantly different (p ≤ 0.05) from each other and from the LC50_4-d values, and were estimated to be 1769 mg Cl^- /L for MgCl₂ , 2235 Cl^- /L for CaCl₂ , and 10 069 mg Cl^- /L for NaCl. Mortality was determined using 2 methods: either no response after exposure or no response after being in freshwater following exposure. For the majority of the LC50s, these methods were not significantly different (p > 0.05). The high salt tolerance of Asian clams is a concern because of their transportation in ballast water between aquatic ecosystems. Furthermore, salt-tolerant organisms may outcompete sensitive organisms in salinized ecosystems, which may alter ecosystem services. Environ Toxicol Chem 2018;37:1839-1845. © 2018 SETAC.

Chronic exposure of a freshwater mussel to elevated pCO2 : Effects on the control of biomineralization and ion-regulatory responses

Freshwater mussels may be exposed to elevations in mean partial pressure of carbon dioxide (pCO₂ ) caused by both natural and anthropogenic factors. The goal of the present study was to assess the effects of a 28-d elevation in pCO₂ at 15 000 and 50 000 μatm on processes associated with biomineralization, ion regulation, and cellular stress in adult Lampsilis siliquoidea (Barnes, 1823). In addition, the capacity for mussels to compensate for acid-base disturbances experienced after exposure to elevated pCO₂ was assessed over a 14-d recovery period. Overall, exposure to 50 000 μatm pCO₂ had more pronounced physiological consequences compared with 15 000 μatm pCO₂ . Over the first 7 d of exposure to 50 000 μatm pCO₂ , the mRNA abundance of chitin synthase (cs), calmodulin (cam), and calmodulin-like protein (calp) were significantly affected, suggesting that shell formation and integrity may be altered during pCO₂ exposure. After the removal of the pCO₂ treatment, mussels may compensate for the acid-base and ion disturbances experienced during pCO₂ exposure, and transcript levels of some regulators of biomineralization (carbonic anhydrase [ca], cs, cam, calp) as well as ion regulation (na⁺ -k⁺ -ATPase [nka]) were modulated. Effects of elevated pCO₂ on heat shock protein 70 (hsp70) were limited in the present study. Overall, adult L. siliquoidea appeared to regulate factors associated with the control of biomineralization and ion regulation during and/or after the removal of pCO₂ exposure. Environ Toxicol Chem 2018;37:538-550. © 2017 SETAC.

Effects of carbon dioxide on juveniles of the freshwater mussel (Lampsilis siliquoidea [Unionidae])

Carbon dioxide (CO₂ ) has shown promise as a tool to control movements of invasive Asian carp, but its effects on native freshwater biota have not been well studied. The authors evaluated lethal and sublethal responses of juvenile fatmucket (Lampsilis siliquoidea) mussels to CO₂ at levels (43-269 mg/L, mean concentration) that bracket concentrations effective for deterring carp movement. The 28-d lethal concentration to 50% of the mussels was 87.0 mg/L (95% confidence interval [CI] 78.4-95.9) and at 16-d postexposure, 76.0 mg/L (95% CI 62.9-90.3). A proportional hazards regression model predicted that juveniles could not survive CO₂ concentrations >160 mg/L for more than 2 wk or >100 mg/L CO₂ for more than 30 d. Mean shell growth was significantly lower for mussels that survived CO₂ treatments. Growth during the postexposure period did not differ among treatments, indicating recovery of the mussels. Also, CO₂ caused shell pitting and erosion. Behavioral effects of CO₂ included movement of mussels to the substrate surface and narcotization at the highest concentrations. Mussels in the 110 mg/L mean CO₂ treatment had the most movements in the first 3 d of exposure. If CO₂ is infused continuously as a fish deterrent, concentrations <76 mg/L are recommended to prevent juvenile mussel mortality and shell damage. Mussels may survive and recover from brief exposure to higher concentrations. Environ Toxicol Chem 2017;36:671-681. Published 2016 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.

Salinity and dissolved organic carbon both affect copper toxicity in mussel larvae: Copper speciation or competition cannot explain everything

Predicting copper (Cu) toxicity in marine and estuarine environments is challenging because of the influence of anions on Cu speciation, competition between Cu(2+) and other cations at the biotic ligand and the effect of salinity on the physiology of the organism. In the present study the combined effect of salinity and dissolved organic carbon (DOC) on Cu toxicity to larvae of Mytilus galloprovincialis was assessed. Two statistical models were developed and used to elucidate the relationship between Cu toxicity, salinity, and DOC. All models based on dissolved Cu indicate a decrease in Cu toxicity with increasing DOC concentrations, which can partly be explained by complexation of Cu(2+) ions with DOC. These models also indicate an increase in Cu toxicity (modeled with dissolved Cu or Cu(2+) activity) with increasing salinity, suggesting a salinity-induced alteration in the physiology of the mussel larvae. When based on Cu body burdens, neither of the models indicates an effect of salinity or DOC. This shows that the Cu body burden is a more constant predictor of Cu toxicity, regardless of the water chemistry influencing Cu speciation or competition and possible physiological alterations or changes in Cu speciation or competition.