Original articleAcute oral toxicity and tissue residues of saxitoxin in the mallard (Anas platyrhynchos)
Introduction
Saxitoxin (STX) is a highly potent algal toxin that occurs in many parts of the world across a wide variety of aquatic habitats, including freshwater, marine, and saline waterbodies, and is known to cause illness in fish, birds, and mammals (Landsberg et al., 2014; Lefebvre et al., 2004; Lefebvre et al., 2005; Wiese et al., 2010). Saxitoxin and its 56 known congeners are a broad group of natural toxins commonly known as paralytic shellfish toxins (PSTs; Hall et al., 1990; Wiese et al., 2010). A single bloom event can harbor more than one PST, and STX, if present, is not always the dominant toxin (Kaas and Henriksen, 2000). These toxins can enter the food web when PST producing dinoflagellates or cyanobacteria are ingested by shellfish, copepods, or other invertebrates and these, in turn, are consumed by larger organisms. Ingestion of PST by mammal and bird species can result in muscular weakness, motor incoordination, respiratory paralysis, and death (Gibble and Hoover, 2018; Landsberg et al., 2014; Shumway et al., 2003).
Saxitoxin has been reported as a cause or suspected cause of death in waterbird and marine mammal mortality events; however, it is often difficult to establish causality among free-ranging populations (Ben-Gigirey et al., 2021; Starr et al., 2017; Van Dolah et al., 2003). Conclusions related to STX intoxication among wildlife are typically based on indirect evidence, including detection of STX in the environment and/or prey species, detection of STX in tissues or gut contents, and the absence of other potential causes of mortality (Armstrong et al., 1978; Coulson et al., 1968; Nisbet, 1983; Shearn-Bochsler et al., 2014; Starr et al., 2017). Recent, widespread seabird mortality events in Alaska, combined with detection of algal toxins in marine wildlife throughout the region prompted investigation of STX as a possible contributing factor (Lefebvre et al., 2016; U.S. Geological Survey, 2020; Van Hemert et al., 2020, 2021). In an assessment of algal toxins associated with a large die-off of common murres (Uria aalge) in the Gulf of Alaska in 2015–2016, STX was detected commonly in beach-cast carcasses as well as in apparently healthy birds, although overall concentrations were higher in samples from birds associated with the mortality event (Van Hemert et al., 2020). In 2017, a multispecies seabird die-off occurred in the Bering and Chukchi Seas during which 88% (14 of 16) of northern fulmars (Fulmarus glacialis) tested had detectable levels of STX in their tissues (Van Hemert et al., 2021). Although emaciation was a common finding, and starvation was identified as a likely cause of death in numerous avian mortality events in Alaskan marine ecosystems since 2015 (U.S. Geological Survey, 2020, Van Hemert et al., 2020, 2021), the frequent detection of STX in carcasses warranted additional investigation. Without knowledge of STX toxicity in birds, or how actual exposure amounts relates to measurable tissue toxin concentrations, the contributions of STX to the cause of these and other recent die-offs remains elusive.
Previous STX dosing studies in birds have been even more limited than field studies. When European starlings (Sturnus vulgaris) were fed clams (Saxidomus gigantea) containing STX, mortality was observed in 1 of 6 birds (Kvitek and Beitler, 1988). No mortality was reported in free-ranging glaucous-winged gulls (Larus glaucescens) after ingesting STX-contaminated shellfish, but regurgitation of the contaminated material and aversion towards future ingestion was noted (Kvitek, 1991).
The primary objective of this study was to evaluate toxicity of STX in birds by estimating the acute oral median lethal dose (LD50) of STX in mallards (Anas platyrhynchos). Secondarily, we evaluated associated tissue pathology, examined distribution and concentration of toxin in tissues, and assessed elimination of STX in fecal material of birds experimentally exposed to STX. These results will be useful for assessing the threat of STX to waterbirds and other wildlife and provide important baseline information for future experimental studies examining the toxicity and pharmacokinetics of STX in seabirds.
Section snippets
Study animals
Fourteen female mallards approximately 10–12 weeks of age were acquired from a commercial vendor in Iowa, United States. Females were used to reduce the potential of introducing another variable (sex) to this study, and females generally have lower LD50 values then males which allows for a more conservative LD50 estimate (reviewed in Bruce, 1985). These birds were hatched and raised indoors for 4 to 6 weeks then moved to outdoor freshwater ponds and provided with supplemental food until
Behavioral observations
Clinical signs of acute toxin ingestion in mallards included head shaking (11/11 mallards), excessive drinking (10/11), and regurgitation (6/11; not recorded in five birds that died acutely). Among survivors (dosed birds that did not die acutely), wing twitching and settling (lifting and dropping wings back into place; 3/5) and tail ‘wagging’ (3/5) behaviors were recorded. None of these behaviors were identified among control birds. Of mallards that died acutely, death occurred between 13 and
Evaluation of LD50
Seabirds and other waterbirds are commonly exposed to STX (Gibble and Hoover 2018; Shumway et al., 2003). Periodically, mortality in birds has been attributed to saxitoxicosis (Shearn-Bochsler et al., 2014; Shumway et al., 2003; Van Hemert et al., 2020), although there had previously been little quantitative information available to interpret findings of STX in birds. In this study, the toxicity of STX was investigated in mallards and the LD50 was estimated to be 167 µg kg−1 (95%
Conclusions
This study demonstrated acute mortality from STX ingestion in mallards and identified potentially greater sensitivity as compared to laboratory mice. Clinical signs of acute toxicity included head shaking, excessive drinking, and regurgitating; among dosed birds that survived, we also observed wing twitching and settling and tail ‘wagging.’ We did not observe gross or histopathological lesions associated with STX toxicity, and detection of STX in tissues other than the gastrointestinal tract
Author declaration
The data contained in this manuscript is original and has not been previously published nor is it being considered for publication elsewhere.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
We thank Dr. E. Falendysz, D. Calhoun, K. Werner, H. Lamb, and the rest of the animal care staff for providing veterinary and daily care of the animals and S. Steinfeldt and D. Johnson for assistance with necropsies and sample processing. Dr. K. Kuletz provided invaluable guidance and support in the conception and development of this project. This work was funded by the USGS Ecosystems Mission Area Biological Threats and Invasive Species Research (Fish and Wildlife Disease and Invasive Species)
References (45)
An up-and-down procedure for acute toxicity testing
Fund. Appl. Toxicol.
(1985)- et al.
Saxitoxins (PSP toxins) in Danish lakes
Water Res.
(2000) The anatomy, physiology, and diseases of the avian proventriculus and ventriculus
Vet. Clin. Exot. Anim.
(2003)- et al.
Morphological abnormalities and sensorimotor deficits in larval fish exposed to dissolved saxitoxin
Aquat. Toxicol.
(2004) - et al.
Prevalence of algal toxins in Alaskan marine mammals foraging in a changing arctic and subarctic environment
Harmful Algae
(2016) - et al.
Acute toxicities of saxitoxin, neosaxitoxin, dicarbamoyl saxitoxin, and gonyautoxins 1&4 and 2&3 to mice by various routes of administration
Toxicon
(2013) - et al.
Marine birds and harmful algal blooms: sporadic victims or under-reported events?
Harmful Algae
(2003) - et al.
Enzymatic transformation of PSP toxins in the littleneck clam (Protothaca staminea)
Biochem. Biophys. Res. Commun.
(1983) - et al.
Algal toxins in Alaskan seabirds: evaluating the role of saxitoxin and domoic acid in a large-scale die-off of common murres
Harmful Algae
(2020) - et al.
Further mass seabird deaths from paralytic shellfish poisoning
Br. Birds
(1978)
Problems of toxicants in marine food products
Bull. World Health Organ.
Paralytic and amnesic shellfish toxins impacts on seabirds, analyses and management
Toxins
Saxitoxin increases phocine distemper virus replication upon in-vitro infection in harbor seal immune cells
Harmful Algae
Accumulation of PSP toxins in Atlantic mackerel: seasonal and ontogenetic variations
J. Fish Biol.
Exceptional mortality of shags and other seabirds caused by paralytic shellfish poison
Br. Birds
Forensic Pathology
Dataset: acute oral toxicity and tissue residues of saxitoxin in the mallard (Anas platyrhynchos)
U.S. Geol. Surv. Data Release
Interactions between seabirds and harmful algal blooms
Vulnerability of coastal ecosystems to changes in harmful algal bloom distribution in response to climate change: projections based on model analysis
Glob. Change Biol.
Ocean warming since 1982 has expanded the niche of toxic algal blooms in the North Atlantic and North Pacific Oceans
Proc. Natl. Acad. Sci. NAS
Toxins and Toxicity of Protogonyaulax from the Northeast Pacific
The saxitoxins: sources, chemistry, and pharmacology
Cited by (6)
A review on aquatic toxins - Do we really know it all regarding the environmental risk posed by phytoplankton neurotoxins?
2023, Journal of Environmental ManagementReview of harmful algal bloom effects on birds with implications for avian wildlife in the Chesapeake Bay region
2022, Harmful AlgaeCitation Excerpt :This is not the case for algal toxins and wildlife, and in fact results from older studies may be compromised by questionable toxin purity. While this situation would seemingly be resolved by additional large-scale dose-response studies with captive birds (waterfowl as model species), there is an ongoing movement away from traditional wildlife testing through the 3Rs (i.e., reduction in animal use, refine test protocols to minimize pain and distress, replace animals altogether with in vitro tests and in silico approaches, e.g., Lillicrap et al., 2016) as reflected in recent studies with aetokthonotoxin and saxitoxin (Breinlinger et al., 2021; Dusek et al., 2021). As data on comparative toxicity of algal toxins among wildlife species is limited, use of mammalian toxicity data and thresholds in assessing mortality events in wildlife is commonplace, and likely will remain so into the future.
Paralytic shellfish toxins associated with Arctic Tern mortalities in Alaska
2022, Harmful AlgaeCitation Excerpt :We detected PSTs in four Arctic Tern carcasses found dead at colony sites. Although quantitative data describing the correlation between toxicity and specific tissue concentrations are not yet available for seabirds, results from the lower gastrointestinal tract of the single adult specimen (51.2 µg 100g−1 STX-eq; Table 3) were comparable to those measured in Mallards that died acutely from oral STX administration in experimental trials (Dusek et al., 2021). Concentrations of STX in tern nestlings at the Mendenhall Lake colony (Tables 1, 3) also overlapped those reported in an incident of saxitoxicosis involving Kittlitz's Murrelet chicks near Kodiak Island AK in 2012, with STX liver concentrations of 5.6 to 10.6 µg 100g−1 and upper gastrointestinal content concentrations ranging from 5.2 to 21.6 µg 100g−1 (Shearn-Bochsler et al., 2014).
Current Trends and New Challenges in Marine Phycotoxins
2022, Marine Drugs