Cyanotoxins: producing organisms, occurrence, toxicity, mechanism of action and human health toxicological risk evaluation.

Cyanobacteria were present on the earth 3.5 billion years ago; since then they have colonized almost all terrestrial and aquatic ecosystems. They produce a high number of bioactive molecules, among which some are cyanotoxins. Cyanobacterial growth at high densities, forming blooms, is increasing in extension and frequency, following anthropogenic activities and climate changes, giving rise to some concern for human health and animal life exposed to cyanotoxins. Numerous cases of lethal poisonings have been associated with cyanotoxins ingestion in wild animal and livestock. In humans few episodes of lethal or severe human poisonings have been recorded after acute or short-term exposure, but the repeated/chronic exposure to low cyanotoxin levels remains a critical issue. The properties of the most frequently detected cyanotoxins (namely, microcystins, nodularins, cylindrospermopsin and neurotoxins) are here critically reviewed, describing for each toxin the available information on producing organisms, biosynthesis/genetic and occurrence, with a focus on the toxicological profile (including kinetics, acute systemic toxicity, mechanism and mode of action, local effects, repeated toxicity, genotoxicity, carcinogenicity, reproductive toxicity; human health effects and epidemiological studies; animal poisoning) with the derivation of health-based values and considerations on the risks for human health.

In Vitro and In Vivo Biocompatibility Studies on Engineered Fabric with Graphene Nanoplatelets.

To produce clothes made with engineered fabrics to monitor the physiological parameters of workers, strain sensors were produced by depositing two different types of water-based inks (P1 and P2) suitably mixed with graphene nanoplatelets (GNPs) on a fabric. We evaluated the biocompatibility of fabrics with GNPs (GNP fabric) through in vitro and in vivo assays. We investigated the effects induced on human keratinocytes by the eluates extracted from GNP fabrics by the contact of GNP fabrics with cells and by seeding keratinocytes directly onto the GNP fabrics using a cell viability test and morphological analysis. Moreover, we evaluated in vivo possible adverse effects of the GNPs using the model system Caenorhabditis elegans. Cell viability assay, morphological analysis and Caenorhabditis elegans tests performed on smart fabric treated with P2 (P2GNP fabric) did not show significant differences when compared with their respective control samples. Instead, a reduction in cell viability and changes in the membrane microvilli structure were found in cells incubated with smart fabric treated with P1. The results were helpful in determining the non-toxic properties of the P2GNP fabric. In the future, therefore, graphene-based ink integrated into elastic fabric will be developed for piezoresistive sensors.

Cyanobacteria biennal dynamic in a volcanic mesotrophic lake in central Italy: Strategies to prevent dangerous human exposures to cyanotoxins.

Vico Lake, a volcanic meso-eutrophic lake in Central Italy, whose water is used for drinking and recreational activities, experienced the presence of the microcystins (MC) producing cyanobacterium Planktothrix rubescens. In order to assess the human health risks and to provide the local health authorities with a scientific basis for planning tailored monitoring activities, we studied P. rubescens ecology and toxicity for two years. P. rubescens generally dominated the phytoplankton community, alternating with Limnothrix redekei, potentially toxic. P. rubescens was distributed throughout the water column during winter; in summer it produced intense blooms where drinking water is collected (-20 m); here MC were detected all year round (0.5-5 µg/L), with implications for drinking water quality. In surface waters, MC posed no risk for recreational activities in summer, while in winter surface blooms and foams (containing up to 56 µg MC/L) can represent a risk for people and children practicing water sports and for animals consuming raw water. Total phosphorus, phosphate and inorganic nitrogen were not relevant to predict densities nor toxicity; however, a strong correlation between P. rubescens density and aminopeptidase ectoenzymatic activity, an enzyme involved in protein degradation, suggested a role of organic nitrogen for this species. The fraction of potentially toxic population, determined both as mcyB(+)/16SrDNA (10-100%) and as the MC/mcyB(+) cells (0.03-0.79 pg MC/cell), was much more variable than usually observed for P. rubescens. Differently from other Italian and European lakes, the correlation between cell density or the mcyB(+) cells and MC explained only ∼50 and 30% of MC variability, respectively: for Vico Lake, monitoring only cell or the mcyB(+) cell density is not sufficient to predict MC concentrations, and consequently to protect population health. Finally, during a winter bloom one site has been sampled weekly, showing that monthly sampling during such a phase could greatly underestimate the 'hazard'. Our results highlight the need to adopt a stepwise monitoring activity, considering the lake and the cyanobacteria specific features. This activity should be complemented with communication to the public and involvement of stakeholders.

Survival, growth and toxicity of Microcystis aeruginosa PCC 7806 in experimental conditions mimicking some features of the human gastro-intestinal environment.

Cyanotoxins (CTX) are widely produced by several cyanobacteria (CB), increasingly spreading in most water bodies and terrestrial habitats, and represent a risk for human health. CB are prokaryotes, and although mostly autotrophic, several examples of heterotrophy in symbiotic relationship with different organisms have been described. In addition to the known routes of exposure, it has been hypothesized that CB might 'colonize' human intestine with relevant implications for human health. Colonization is a complex process and requires specific features of the possible invaders. Still, a short-term persistence as living and toxin-producing organisms within the intestinal lumen of the host could represent an 'internal' source of exposure to CTX. In this work we ran microcosm experiments (4-18days), looking at Microcystis aeruginosa PCC7806 resistance and cyanotoxin-producing capabilities in darkness, 37°C, pH 2, and subsequent recovery in a rich medium, in darkness, 37°C, in the presence of enteric bacteria, mimicking few important features of the gastrointestinal environment. We measured cyanobacterial populations and growth, microcystin (MC) production and the presence of mcyB gene. M. aeruginosa could grow in the dark at 37°C up to 17days, and survive at pH 2 at a rate between 30% and 70%, depending on the age and toxicity of the starting culture. Cell lysis resulted in a substantial amounts of MC released, not degraded at gastric pH. Following the acidic passage, still in the dark at 37°C, M. aeruginosa restarted to grow within 24h for the next 3-4days, independently on the presence of intestinal bacteria, maintaining the MC cell quota and mcyB gene. Our results show new features of CB: a significant resistance of M. aeruginosa in conditions far from its optimal one, that is an environment mimicking some of the important characteristics of human gastrointestinal tract, suggesting the possibility of an internal source of exposure to CTX, with implications for the risk assessment.

Emerging health issues of cyanobacterial blooms.

This paper describes emerging issue related to cyanobacterial dynamics and toxicity and human health risks. Data show an increasing cyanobacteria expansion and dominance in many environments. However there are still few information on the toxic species fitness, or on the effects of specific drivers on toxin production. Open research fields are related to new exposure scenario (cyanotoxins in water used for haemodialysis and in food supplements); to new patterns of co-exposure between cyanotoxins and algal toxins and/or anthropogenic chemicals; to dynamics affecting toxicity and production of different cyanotoxin variants under environmental stress; to the accumulation of cyanotoxins in the food web. In addition, many data gaps exist in the characterization of the toxicological profiles, especially about long term effects.

Health risk evaluation associated to Planktothrix rubescens: An integrated approach to design tailored monitoring programs for human exposure to cyanotoxins.

Increasing concern for human health related to cyanotoxin exposure imposes the identification of pattern and level of exposure; however, current monitoring programs, based on cyanobacteria cell counts, could be inadequate. An integrated approach has been applied to a small lake in Italy, affected by Planktothrix rubescens blooms, to provide a scientific basis for appropriate monitoring program design. The cyanobacterium dynamic, the lake physicochemical and trophic status, expressed as nutrients concentration and recycling rates due to bacterial activity, the identification/quantification of toxic genotype and cyanotoxin concentration have been studied. Our results indicate that low levels of nutrients are not a marker for low risk of P. rubescens proliferation and confirm that cyanobacterial density solely is not a reliable parameter to assess human exposure. The ratio between toxic/non-toxic cells, and toxin concentrations, which can be better explained by toxic population dynamic, are much more diagnostic, although varying with time and environmental conditions. The toxic fraction within P. rubescens population is generally high (30-100%) and increases with water depth. The ratio toxic/non-toxic cells is lowest during the bloom, suggesting a competitive advantage for non-toxic cells. Therefore, when P. rubescens is the dominant species, it is important to analyze samples below the thermocline, and quantitatively estimate toxic genotype abundance. In addition, the identification of cyanotoxin content and congeners profile, with different toxic potential, are crucial for risk assessment.