chlorophyll-a and anatoxin-a

Chautauqua Lake, New York, is a two-basin lake with a deeper, cooler, and less nutrient-rich Northern Basin, and a warmer, shallower, nutrient-replete Southern Basin. The lake is populated by a complex mixture of cyanobacteria, with toxigenic strains that produce microcystins, anatoxins, and paralytic shellfish poisoning toxins (PSTs). Samples collected from 24 sites were analyzed for these three toxin classes over four years spanning 2014-2017. Concentrations of the three toxin groups varied widely both within and between years. During the study, the mean and median concentrations of microcystins, anatoxin-a, and PSTs were 91 and 4.0 μg/L, 0.62 and 0.33 μg/L, and 32 and 16 μg/L, respectively. Dihydro-anatoxin was only detected once in Chautauqua Lake, while homo-anatoxin was never detected. The Northern Basin had larger basin-wide higher biomass blooms with higher concentrations of toxins relative to the more eutrophied Southern Basin, however blooms in the North Basin were infrequent. Chlorophyll concentrations and toxins in the two basins were correlated with different sets of environmental and physical parameters, suggesting that implementing controls to reduce toxin loads may require applications focused on more than reductions in cyanobacterial bloom density (e.g., reduction of phosphorus inputs), and that lake limnological factors and morphology are important determinants in the selection of an appropriate management strategy. Chautauqua Lake is a drinking water source and is also heavily used for recreation. Drinking water from Chautauqua Lake is unlikely to be a significant source of exposure to cyanotoxins due to the location of the intakes in the deeper North Basin, where there were generally low concentrations of toxins in open water; however, toxin levels in many blooms exceeded the US Environmental Protection Agency's recreational guidelines for exposure to cyanotoxins. Current cyanotoxin monitoring in Chautauqua Lake is focused on microcystins. However, the occurrence of blooms containing neurotoxic cyanotoxins in the absence of the microcystins indicates this restricted monitoring may not be sufficient when aiming to protect against exposure to cyanotoxins. The lake has a large number of tourist visitors; thus, special care should be taken to prevent recreational exposure within this group.

Topics: Animals; Chlorophyll; Cyanobacteria; Cyanobacteria Toxins; Environmental Exposure; Environmental Monitoring; Harmful Algal Bloom; Humans; Lakes; Marine Toxins; Microcystins; Risk Assessment; Shellfish Poisoning; Time Factors; Tropanes; Water Microbiology

Anatoxin-a is one of the common and major cyanobacterial neurotoxins acting as a powerful agonist at nicotinic acetylcholine receptors (nAChR). In recent years, the toxin has become the focus of public attention, due to the mass development of cyanobacteria (cyanobacterial blooms) in freshwater bodies triggered by eutrophication and climate change. Anatoxin-a is suspected to have a distinct toxic mechanism depending on physiological and nervous systems in exposed organisms. The numerous researches have been actively conducted with respect to the toxic effects of anatoxin-a on mammals; however, little research has aimed at its possible effects on aquatic plants, wherein well-structured nervous system is absent with the lack of various components of the acetylcholine mechanism. In this study, submerged macrophyte Ceratophyllum demersum (C. demersum) was adopted to examine the effects of anatoxin-a on morphological (growth), physiological (photosynthetic pigment contents) and biochemical (hydrogen peroxide level, biotransformation and antioxidative enzymes) responses in the aquatic plant at environmentally relevant concentrations (0.005, 0.05, 0.5, 5 and 50 μg/L). The significant elevation of antioxidative enzymes in parallel with increased formation of hydrogen peroxide appeared from 0.5 μg/L of anatoxin-a. In the measurement of photosynthetic pigments, the decrease in chlorophyll a content was detected at 5 and 50 μg/L, whereas the increase in carotenoids/total chlorophyll was observed from 0.05 μg/L. Accordingly, the alteration in growth was manifested in the presence of 5 and 50 μg/L of anatoxin-a. The results clearly indicate that anatoxin-a can disrupt homeostasis of C. demersum through induction of oxidative stress; furthermore this aquatic plant possesses effective defense mechanisms to cope with low concentrations of anatoxin-a.

Topics: Antioxidants; Biotransformation; Chlorophyll; Climate Change; Cyanobacteria; Cyanobacteria Toxins; Eutrophication; Fresh Water; Hydrogen Peroxide; Magnoliopsida; Neurotoxins; Oxidative Stress; Photosynthesis; Tropanes

Recently, aquatic macrophytes have been considered as promising tools for eco-friendly water management with a low running cost. However, only little information is available thus far regarding the metabolic capacity of macrophytes for coping with cyanobacterial toxins (cyanotoxins) in the aquatic environment. Cyanotoxins have become emerging contaminants of great concern due to the high proliferation of cyanobacteria (cyanobacterial bloom) accelerated by eutrophication and climate change. Anatoxin-a, one of the common and major cyanotoxins, is suggested as a high priority water pollutant for regulatory consideration owing to its notoriously rapid mode of action as a neurotoxin. In this study, the time-course metabolic regulation of the submerged macrophyte Ceratophyllum demersum (C. demersum) was investigated during exposure to anatoxin-a at an environmentally relevant concentration (15 μg/L). Biotransformation and antioxidative systems in C. demersum responded positively to anatoxin-a through the promoted synthesis of most of the involved enzymes within 8h. Maximum enzyme activities were exhibited after 24 or 48 h of exposure to anatoxin-a. However, an apparent decline in enzyme activities was also observed at longer exposure duration (168 and 336 h) in company with high steady-state levels of cell internal H₂O₂, which showed its highest level after 48 h. Meanwhile, irreversible inhibitory influence on chlorophyll content (vitality) was noticed, whereas the ratio of carotenoids to total chlorophyll was increased with the increase in exposure duration. Consequently, the reduction in growth (biomass) of C. demersum was observed in sub-chronic exposure to anatoxin-a (8 weeks). Overall results clearly indicate, on the one hand, that anatoxin-a causes negative allelopathic effects on the macrophyte by inducing oxidative stress. On the other hand, the macrophyte might have interactions with anatoxin-a, based on the prompt reaction of its enzymatic defense systems to the toxin. The result obtained from the present study could contribute to the improvement of basic knowledge about the ecological impact of anatoxin-a and the environmental fate of the toxin in the aquatic environment.

Topics: Analysis of Variance; Ascorbate Peroxidases; Biotransformation; Catalase; Chlorophyll; Cyanobacteria Toxins; Fresh Water; Glutathione Reductase; Hydrogen Peroxide; Magnoliopsida; Oxidative Stress; Peroxidase; Reactive Oxygen Species; Superoxide Dismutase; Time Factors; Tropanes