Heptapeptide toxins contained in natural samples of Microcystis species

Toxins contained in Microcystis species were examined for natural samples of water bloom collected from several lakes in Japan. The toxins were identified as microcystins (cyanoginosins)-LR,-YR, and -RR. The amounts of the three toxins were estimated after adsorption to a C18 cartridge, eluted with methanol, and subjected to high performance liquid chromatography using an octa decylsilanized column. Microcystins-RR and -LR were the main components of the toxins contained in natural samples of Microcystis bloom, while YR was not detected in more than half of the samples analyzed. Six samples were also examined in relation to LD₅₀ values and species composition of Microcystis. The highest total amount of the three toxins was obtained for the sample with the lowest LD₅₀ value and composed mostly of cells of M. aeruginosa. The relation between LD₅₀ values and total contents of the three toxins was well fitted to the formula Y = 1100 × X^?1.079, where Y is the LD₅₀ value and X is the total amount of the three toxins.     

Removal of cyanobacterial toxins in water treatment processes: Laboratory and pilot-scale experiments

The effectiveness of various drinking water treatment processes has been tested in laboratory and pilot scale experiments using neurotoxic and hepatotoxic cyanobacterial blooms and laboratory-grown algal cultures as test material. The species involved belonged to the genera Microcystis, Oscillatoria, and Anabaena. Microcystis and Oscillatoria hepatotoxins were analyzed by high performance liquid chromatography. The Anabaena neurotoxin, anatoxin-a, was determined using gas chromatography/mass spectrometry techniques. Toxicity was tested and verified by mouse bioassay. The laboratory study, made with freeze-dried cyanobacteria, showed that toxins were not removed by conventional flocculation treatment procedures. The simultaneous addition of a small amount of powdered activated carbon with the flocculation chemical did not improve the removal of hepatotoxins significantly. Substantial reduction of toxins was achieved by granulated activated carbon filtration and by ozonization. Pilot plant studies supported the laboratory findings. Results of the slow sand filtration experiments suggested some removal of toxins.     

Production,detection, and quantification of cyanobacterial toxins

Cyanobacterial blooms from several British freshwaters have been toxic by mouse bioassay each year since annual sampling began in 1981. Toxic blooms of Microcystis aeruginosa, Anabaena spp., Gloeotrichia echinulata, Oscillatoria spp., and Aphanizomenon flos-aquae occur, with peptide toxin-producing Microcystis and Anabaena being most often encountered. We are developing a range of detection and quantification methods for cyanobacterial peptide and alkaloid toxins to supplement the standard mouse bioassay. Both types of toxins can be readily assayed by high performance liquid chromatography, and we have developed facile high performance thin layer chromatographic procedures for their detection from natural blooms and laboratory cultures. We have also produced polyclonal and monoclonal antibodies for the assay of Microcystis toxins by enzyme-linked immunosorbent assay and have developed in vitro fibroblast cytotoxicity assays for the toxins of Microcystis and other cyanobacteria.     

Seasonal variations of microcystis species and toxic heptapeptide microcystins in lake suwa

Seasonal changes in species composition of Microcystis and concentrations of toxic heptapeptide microcystins, were investigated in Lake Suwa from June to October in 1991. Microcystins-RR and -LR were the main components of the toxins contained in bloom samples of Microcystis and a very little quantity of - YR was detected through this period. The high amounts of microcystins were estimated during the exponential growth phase of the bloom from June 11 to July 20. The highest concentrations of microcystins-RR and -LR were estimated as 121 and 81.6 μg/100 mg cells on July 20, 1991, respectively. While the higher amounts of the toxins were estimated when M. aeruginosa predominated, the lower amounts were estimated during the predominate period of M. viridis. Since the dissolved inorganic nitrogen (DIN) concentration may well affect the dominance of M. aeruginosa and M. viridis, the production of the toxins by Microcystis may be associated with the DIN concentration. © 1993 John Wiley & Sons, Inc.     

Sulforaphane prevents microcystin-LR-induced oxidative damage and apoptosis in BALB/c mice

Microcystins (MCs), the products of blooming algae Microcystis, are waterborne environmental toxins that have been implicated in the development of liver cancer, necrosis, and even fatal intrahepatic bleeding. Alternative protective approaches in addition to complete removal of MCs in drinking water are urgently needed. In our previous work, we found that sulforaphane (SFN) protects against microcystin-LR (MC-LR)-induced cytotoxicity by activating the NF-E2-related factor 2 (Nrf2)-mediated defensive response in human hepatoma (HepG2) and NIH 3T3 cells. The purpose of this study was to investigate and confirm efficacy the SFN-induced multi-mechanistic defense system against MC-induced hepatotoxicity in an animal model. We report that SFN protected against MC-LR-induced liver damage and animal death at a nontoxic and physiologically relevant dose in BALB/c mice. The protection by SFN included activities of anti-cytochrome P450 induction, anti-oxidation, anti-inflammation, and anti-apoptosis. Our results suggest that SFN may protect mice against MC-induced hepatotoxicity. This raises the possibility of a similar protective effect in human populations, particularly in developing countries where freshwaters are polluted by blooming algae.     

Persistence and Decomposition of Hepatotoxic Microcystins Produced by Cyanobacteria in Natural Environment

Abstract

Microcystins, the cyclic heptapeptide toxins produced by cyanobacteria such as Microcystis, show tumor-promoting activity through inhibition of protein phosphatases 1 and 2A. They potentially threaten human health and are increasing the worldwide interest in the health risk asSoc. iated with cyanobacterial toxins. Microcystins are normally considered to be confined within cyanobacterial cells and to enter into the surrounding water after lysis and cell death under field conditions. Five pathways may be considered to contribute to natural routes of detoxification of the microcystins: (1) dilution, (2) adsorption, (3) thermal decomposition aided by temperature and pH, (4) photolysis and (5) biological degradation. In this review, we describe the persistence and decomposition of microcystins under the conditions mentioned above and discuss the fate of the toxins in the natural environment.     

Cellular effects of cyanobacterial peptide toxins

Peptide toxins from the cyanobacteria Microcystic aeruginosa, Oscillatoria agardhii, Nodularia spumigena, and Anabaena flos-aquae were isolated. Of these, only the cyclic peptide of Microcystis has been characterized structurally and toxicologically in detail. Preliminary studies of the other peptide toxins have indicated that they may be structurally related to the toxins of Microcystis. The morphological and ultrastructural effects of these toxins were studied using freshly isolated hepatocytes. The toxins caused identical morphological alterations in the hepatocytes. Numerous surface swellings appeared on the cell surface and finally the normal cell morphology was totally disrupted. During this process, however, the viability of the cells was not affected. These results are viewed in the light of recent results showing that these toxins could exhibit a specific interaction with the actin part of the cytoskeleton. The overall results indicate that all four toxins may be toxicologically closely related.     

Occurrence and elimination of cyanobacterial toxins in two Australian drinking water treatment plants.

In Australian freshwaters, Anabaena circinalis, Microcystis spp. and Cylindrospermopsis raciborskii are the dominant toxic cyanobacteria. Many of these surface waters are used as drinking water resources. Therefore, the National Health and Medical Research Council of Australia set a guideline for MC-LR toxicity equivalents of 1.3 microg/l drinking water. However, due to lack of adequate data, no guideline values for paralytic shellfish poisons (PSPs) (e.g. saxitoxins) or cylindrospermopsin (CYN) have been set. In this spot check, the concentration of microcystins (MCs), PSPs and CYN were determined by ADDA-ELISA, cPPA, HPLC-DAD and/or HPLC-MS/MS, respectively, in two water treatment plants in Queensland/Australia and compared to phytoplankton data collected by Queensland Health, Brisbane. Depending on the predominant cyanobacterial species in a bloom, concentrations of up to 8.0, 17.0 and 1.3 microg/l were found for MCs, PSPs and CYN, respectively. However, only traces (<1.0 microg/l) of these toxins were detected in final water (final product of the drinking water treatment plant) and tap water (household sample). Despite the low concentrations of toxins detected in drinking water, a further reduction of cyanobacterial toxins is recommended to guarantee public safety.     

Comparative assessment of the specificity of the brine shrimp and microtox assays to hepatotoxic (microcystin-LR-containing) cyanobacteria

Specific, straightforward, and rapid procedures are required for the detection, identification, and quantification of the potent low molecular weight toxins that are produced by blooms and scums of cyanobacteria (blue-green algae) in waterbodies. Use of the Microtox bioluminescence assay and the brine shrimp (Artemia salina) has been advocated for the initial screening of cyanobacterial blooms for microcystin hepatotoxins. Inhibition of bacterial luminescence in the Microtox assay and brine shrimp mortality were determined with microcystin-containing and nonmicrocystin-containing cyanobacteria. Extraction and fractionation of test samples was undertaken to select and isolate microcystincontaining fractions and reduce interference from other fractions. Maximal inhibition of bacterial luminescence in the Microtox assay occurred with fractions from Microcystis strains and an Anabaena bloom that did not contain microcystins. By contrast, the bioassay of fractions using brine shrimps correlated with the distribution of microcystin-LR in the fractionated Microcystis extracts. © 1994 by John Wiley & Sons, Inc..     

Occurrence of microcystin‐producing cyanobacteria in Ugandan freshwater habitats

Microcystins (MCs) are cyclic heptapeptides, which are the most abundant toxins produced by cyanobacteria in freshwater. The phytoplankton of many freshwater lakes in Eastern Africa is dominated by cyanobacteria. Less is known, however, on the occurrence of MC producers and the production of MCs. Twelve Ugandan freshwater habitats ranging from mesotrophic to hypertrophic conditions were sampled in May and June of 2004 and April of 2008 and were analyzed for their physicochemical parameters, phytoplankton composition, and MC concentrations. Among the group of the potential MC‐producing cyanobacteria, Anabaena (0–10⁷ cells ml^?1) and Microcystis (10³–10⁷ cells ml^?1) occurred most frequently and dominated in eutrophic systems. A significant linear relationship (n = 31, r² = 0.38, P < 0.001) between the Microcystis cell numbers and MC concentration (1.3–93 fg of MC cell^?1) was observed. Besides [MeAsp³, Mdha⁷]‐MC‐RR, two new MCs, [Asp³]‐MC‐RY and [MeAsp³]‐MC‐RY, were isolated and their constitution was assigned by LC‐MS². To identify the MC‐producing organism in the water samples, (i) the conserved aminotransferase domain part of the mcyE gene that is indicative of MC production was amplified by general primers and cloned and sequenced, and (ii) genus‐specific primers were used to amplify the mcyE gene of the genera Microcystis, Anabaena, and Planktothrix. Only mcyE genotypes that are indicative of Microcystis sp. were obtained via the environmental cloning approach (337 bp, 96.1–96.7% similarity to the Microcystis aeruginosa strain PCC7806). Accordingly, only the mcyE primers, which are specific for Microcystis, revealed PCR products. We concluded that Microcystis is the major MC‐producer in Ugandan freshwater. © 2009 Wiley Periodicals, Inc. Environ Toxicol 25: 367–380, 2010.     

Dynamics of glutathione-S-transferases in Mytilus galloprovincialis exposed to toxic Microcystis aeruginosa cells, extracts and pure toxins

Molluscs and especially bivalves are able to accumulate dinoflagelates, diatoms and cyanobacteria toxins, and, being vectors for these toxins, transfer them along food chains. The data obtained from laboratory experiments showed that bivalve molluscs are resistant to cyanobacteria toxins. In this work, we wanted to test if Mytilus galloprovincialis organs react to microcystins and other cyanobacteria compounds by inducing or decreasing its GST activity. Acclimated mussels M. galloprovincialis were exposed to the toxic Microcystis aeruginosa M13 strain. Exposure of mussels to toxins was done in three ways: living Microcystis cells, crude Microcystis extracts and pure toxins. The measurement of soluble and microsomal GST activity in the different mussel organs was done by using the substrates 1-chloro-2,4-dinitrobenzene (CDNB) and 2,4-dichloro-1-nitrobenzene (DCNB). Analysis of the GST activity of the control mussels using CDNB as a substrate showed that cytosolic activity is much more significant than microsomal. Intact M. aeruginosa cells did not induce any significant response from the mussels, showing that these animals are quite resistant to the cyanobacteria if they are intact. On the other hand, cell extracts caused an important effect in the gut, in the gills and in the labial palps, although in different ways. There was an increase in GST activity in the gut and gills of mussels exposed to Microcystis extracts, showing a response of this detoxication pathway, but in the labial palps a severe reduction in GST activity occurred. Pure MC LR+YR induced an increase in GST activity in all organs but the labial palps. The results showed that other substances apart from microcystins may cause stress to mussels and affect detoxication enzymes such as GST.     

Hepatotoxic microcystins and neurotoxic anatoxin-a in cyanobacterial blooms from Korean lakes

Cyanobacterial bloom samples were collected in the warm season during 1992–1995 from the 12 lakes in Korea. Six species each of Microcystis and Anabaena, and two of Oscillatoria were identified in these lakes. The cyanotoxins of 47 samples collected from the lakes were identified as microcystins-RR, -YR, -LR; desmethyl-7-microcystin-LR (7-DMLR), plus anatoxin-a. Microcystins were the main components of these cyanotoxins, while anatoxin-a was detected in samples from a few lakes. Thirty-four of the 47 samples, included microcystins and the total amounts of microcystin ranged between 20–1500 μg/g freeze-dried bloom material. In four of the 26 samples, the samples contained anatoxin-a, though the amounts varied. The total microcystin concentration in 30 samples from the lakes was equal to the cellular microcystin in these lakes because no extracellular microcystin was detected. All the lakes except for Lakes Younglang and Mijae are a source of drinking water, so the presence of cyanotoxin can be a potential threat and requires more attention to water treatment. © 1998 John Wiley & Sons, Inc. Environ Toxicol Water Qual 13: 225–234, 1998     

Monitoring toxigenic Microcystis strains in the Missisquoi bay,Quebec, by PCR targeting multiple toxic gene loci

The increasing incidence of mixed assemblages of toxic and nontoxic cyanobacterial blooms in Quebec's freshwater bodies over the last decade, coupled with inherent inadequacies of current monitoring approaches, warrants development of sensitive and reliable tools for assessing the toxigenic potential of these water blooms. In this study, we applied three independent polymerase chain reaction (PCR) assays that simultaneously target the microcystin synthetase (mcy) genes A, E, and G to rapidly and reliably detect and quantify potentially toxic Microcystis genotypes in the Missisquoi bay, Quebec, Canada. Linear regressions of quantitative PCR threshold cycles (C_t) against the logarithm of their respective Microcystis cell number equivalents resulted in highly significant linear curves with coefficients of determination (R²) greater than 0.99 (p < 0.0001, n = 6) and reaction efficiencies of 91.0, 95.8, and 92.7%, respectively, for the mcyA, mcyE, and mcyG‐based quantitative real‐time PCR (qPCR) assays. The three assays successfully estimated potential microcystin‐producing Microcystis genotypes from all field samples. The proportions of MicrocystismcyA, mcyE, and mcyG genotypes to total Microcystis cell counts showed substantial spatial variability ranging between 1.7–21.6%, 1.9–11.2%, and 2.2–22.6%, respectively. Correlation of microscopically determined total Microcystis counts to qPCR‐based MicrocystismcyA, mcyE, or mcyG cell number equivalents resulted in highly significant associations with R² > 0.90. Thus, PCR‐based assays targeting the mcyA, mcyG, and/or mcyE genes can serve as powerful screening tools for rapid and sensitive estimation of microcystin‐producing Microcystis genotypes in freshwater water bodies. © 2012 Wiley Periodicals, Inc. Environ Toxicol 29: 440–451, 2014.     

Extended Low‐Dose Exposure to Saxitoxin Inhibits Neurite Outgrowth in Model Neuronal Cells

The potent neurotoxin saxitoxin (STX) belongs to a group of structurally related analogues produced by both marine and freshwater phytoplankton. The toxins act by blocking voltage‐gated sodium channels stopping the inflow of sodium ions and the generation of action potentials. Exposure from marine sources occurs as a result of consuming shellfish which have concentrated the toxins, and freshwater exposure can occur from drinking water although there have been no acute poisonings from the latter source to date. Previously, the majority of research into this group of toxins, collectively known as the paralytic shellfish toxins, has focused on acute exposure resulting in paralytic shellfish poisoning. While acute exposure guidelines exist for both sources, there are no chronic exposure guidelines and there has been minimal research into this pattern of exposure despite the known role of electrical activity in neurogenesis. We aimed to investigate this pattern of exposure and its potential effects on neurodevelopment using model neuronal cells. PC12 and SH‐SY5Y cells were exposed to STX (0.25–3 μg/l) for 7 days, after which time they were stained with TRITC‐Phalloidin, to observe adverse morphological effects. Cells exposed to STX had a significant decrease (18–85%) in long axonlike projections, instead exhibiting a significant increase in shorter projections classified as filopodia (p < 0.05). The results suggest that extended low‐dose exposure to STX can inhibit proper neurite outgrowth at concentrations well below guideline levels for both sources of exposure making it a potential public health concern.     

Occurrence and elimination of cyanobacterial toxins in drinking water treatment plants

Toxin-producing cyanobacteria (blue-green algae) are abundant in surface waters used as drinking water resources. The toxicity of one group of these toxins, the microcystins, and their presence in surface waters used for drinking water production has prompted the World Health Organization (WHO) to publish a provisional guideline value of 1.0 mug microcystin (MC)-LR/l drinking water. To verify the efficiency of two different water treatment systems with respect to reduction of cyanobacterial toxins, the concentrations of MC in water samples from surface waters and their associated water treatment plants in Switzerland and Germany were investigated. Toxin concentrations in samples from drinking water treatment plants ranged from below 1.0 microg MC-LR equiv./l to more than 8.0 microg/l in raw water and were distinctly below 1.0 microg/l after treatment. In addition, data to the worldwide occurrence of cyanobacteria in raw and final water of water works and the corresponding guidelines for cyanobacterial toxins in drinking water worldwide are summarized.     

Examination of potential mechanisms of carcinogenicity of 1,4-dioxane in rat nasal epithelial cells and hepatocytes

Several long-term studies with 1,4-dioxane (dioxane) have shown it to induce liver tumors in mice, and nasal and liver tumors in rats when administered in amounts from 0.5 to 1.8% in the drinking water (Argus et al. 1965; Kociba et al. 1974; National Cancer Institute, 1978). In order to examine potential mechanisms of action, chemically-induced DNA repair (as an indicator of DNA reactivity) and cell proliferation (as an indicator of promotional activity) were examined in nasal turbinate epithelial cells and hepatocytes of male Fischer-344 rats treated with dioxane. Neither dioxane nor 1,4-dioxane-2-one, one of the proposed metabolites, exhibited activity in thein vitro primary rat hepatocyte DNA repair assay, even from cells that had been isolated from animals given either 1 or 2% dioxane in the drinking water for 1 week to induce enzymes that might be responsible for producing genotoxic metabolites. No activity was seen in thein vivo hepatocyte DNA repair assay in animals given a single dose of up to 1000 mg/kg dioxane or up to 2% dioxane in the drinking water for 1 week. Treatment of rats with 1.0% dioxane in the drinking water for 5 days yielded no increase in liver/body weight nor induction of palmitoyl CoA oxidase, indicating that dioxane does not fit into the class of peroxisomal proliferating carcinogens. The percentage of cells in DNA synthesis phase (S-phase) was determined by administration of³H-thymidine and subsequent quantitative histoautoradiography. The hepatic labeling index (LI) did not increase at either 24 or 48 h following a single dose of 1000 mg/kg dioxane. The LI did increase approximately two-fold in animals given dioxane in the drinking water for 2 weeks. No DNA repair was seen in either nasoturbinate or maxilloturbinate nasal epithelial cells isolated from animals treated with 1% dioxane in the drinking water for 8 days followed by a single dose of up to 1000 mg/kg dioxane by gavage 12 h before sacrifice. Reexamination of the nasal passages of male rats in archived material from the NTP bioassay (National Cancer Institute 1978), revealed that the primary site of tumor formation was the anterior third of the dorsal meatus. The location of these tumors supports the proposal that inhalation of dioxanecontaining drinking water may account for the site specificity of these nasal lesions.In vivo studies showed no increase relative to controls in cell proliferation at the site of highest tumor formation in the nose in response to 1.0% dioxane in the drinking water for 2 weeks. Thus, repair-inducing DNA adduct formation, peroxisomal proliferation in the liver, and short-term induction of cell proliferation in the nose do not appear to be involved in tumor formation by dioxane. There may be a role of dioxane-induced cell proliferation in the formation of the liver tumors. However, the quantitative relationships between induced cell proliferation and tumorigenic potential have yet to be established.     

A Review of Cyanophage–Host Relationships: Highlighting Cyanophages as a Potential Cyanobacteria Control Strategy

Harmful algal blooms (HABs) are naturally occurring phenomena, and cyanobacteria are the most commonly occurring HABs in freshwater systems. Cyanobacteria HABs (cyanoHABs) negatively affect ecosystems and drinking water resources through the production of potent toxins. Furthermore, the frequency, duration, and distribution of cyanoHABs are increasing, and conditions that favor cyanobacteria growth are predicted to increase in the coming years. Current methods for mitigating cyanoHABs are generally short-lived and resource-intensive, and have negative impacts on non-target species. Cyanophages (viruses that specifically target cyanobacteria) have the potential to provide a highly specific control strategy with minimal impacts on non-target species and propagation in the environment. A detailed review (primarily up to 2020) of cyanophage lifecycle, diversity, and factors influencing infectivity is provided in this paper, along with a discussion of cyanophage and host cyanobacteria relationships for seven prominent cyanoHAB-forming genera in North America, including: Synechococcus, Microcystis, Dolichospermum, Aphanizomenon, Cylindrospermopsis, Planktothrix, and Lyngbya. Lastly, factors affecting the potential application of cyanophages as a cyanoHAB control strategy are discussed, including efficacy considerations, optimization, and scalability for large-scale applications.     

Microcystis toxigenic strains in urban lakes: a case of study in Mexico City

Microcystis is a bloom-forming, common cyanobacterium in urban lakes of Mexico City. To assess the presence of potentially cyanotoxin-producing Microcystis, molecular techniques were applied and acute toxicity bioassays were performed with Daphnia magna neonates exposed to cyanobacterial crude extracts. Toxigenic potential of isolated strains was inferred by amplifying the mcyA-Cd genes and their identity as Microcystis was confirmed through the 16S rDNA and phycocyanin operon amplification. Microcystins synthesized under culture conditions were quantified through ELISA. The acute toxicity bioassays revealed that mortality was independent from the cyanotoxin concentration in some strains; this suggests the presence of other metabolites (different from microcystins) that also exerted an important biological effect. Isolated strains had the mcyA-Cd gene and most of them produced variable amounts of microcystins in the culture conditions used, confirming their toxigenic potential. Results warn about possible toxic effect risks for aquatic biota, neighboring areas, visitors and users of these sites, due to the constant presence of these blooms in the studied water bodies.     

The Dynamics of Microcystis Genotypes and Microcystin Production and Associations with Environmental Factors during Blooms in Lake Chaohu,China

Lake Chaohu, which is a large, shallow, hypertrophic freshwater lake in southeastern China, has been experiencing lake-wide toxic Microcystis blooms in recent decades. To illuminate the relationships between microcystin (MC) production, the genotypic composition of the Microcystis community and environmental factors, water samples and associated environmental data were collected from June to October 2012 within Lake Chaohu. The Microcystis genotypes and MC concentrations were quantified using quantitative real-time PCR (qPCR) and HPLC, respectively. The results showed that the abundances of Microcystis genotypes and MC concentrations varied on spatial and temporal scales. Microcystis exists as a mixed population of toxic and non-toxic genotypes, and the proportion of toxic Microcystis genotypes ranged from 9.43% to 87.98%. Both Pearson correlation and stepwise multiple regressions demonstrated that throughout the entire lake, the abundances of total and toxic Microcystis and MC concentrations showed significant positive correlation with the total phosphorus and water temperature, suggesting that increases in temperature together with the phosphorus concentrations may promote more frequent toxic Microcystis blooms and higher concentrations of MC. Whereas, dissolved inorganic carbon (DIC) was negatively correlated with the abundances of total and toxic Microcystis and MC concentrations, indicating that rising DIC concentrations may suppress toxic Microcystis abundance and reduce the MC concentrations in the future. Therefore, our results highlight the fact that future eutrophication and global climate change can affect the dynamics of toxic Microcystis blooms and hence change the MC levels in freshwater.     

Rapid responses of a melanophore cell line to chemical contaminants in water

We have evaluated a Xenopus cell line as a potential sensor for detecting toxins in water. X. laevis melanophores responded rapidly by dispersing melanosomes following exposure to six (ammonia, arsenic, copper, mercury, pentachlorophenol and phenol) of 12 tested chemicals in the desired sensitivity range. For two additional chemicals (nicotine and paraquat) the melanophore response improved upon the response capabilities of several available toxicity sensors. These results suggest that a melanophore‐based sensor could be useful for the rapid assessment of chemical toxicity in drinking water. Published 2009 by John Wiley and Sons, Ltd.