Sublethal Toxic Effects and Induction of gGutathione S-transferase by Short-Chain Chlorinated Paraffins (SCCPs) and C-12 alkane (dodecane) in Xenopus laevis Frog Embryos

Short chain chlorinated paraffins (SCCPs) are important industrial chemicals with high persistence in the environment but poorly characterized ecotoxicological effects. We studied embryotoxic effects of commercial mixture of SCCP (carbon length C-12, 56% of chlorine; CP56-12) and non-chlorinated n-alkane (dodecane, C-12) in the 96h Frog Embryo Teratogenesis Assay - Xenopus (FETAX). Only weak lethal effects were observed for both substances (the highest tested concentration 500 mg/L of both chemicals caused up to 11% mortality). On the other hand, we observed developmental malformations and reduced embryo growth at 5 mg/l and higher concentrations. However, the effects were not related to chlorination pattern as both SCCPs and dodecane induced qualitatively similar effects. SCCPs also significantly induced phase II detoxification enzyme glutathione S-transferase (GST) in Xenopus laevis embryos even at 0.5 mg/L, and this biomarker might be used as another early warning of chronic toxic effects. Our results newly indicate significant developmental toxicity of both SCCPs and n-dodecane to aquatic organisms along with inductions of specific biochemical toxicity mechanisms

Markov analysis of stochastic resonance in a periodically driven integrate-fire neuron

We model the dynamics of the leaky integrate-fire neuron under periodic stimulation as a Markov process with respect to the stimulus phase. This avoids the unrealistic assumption of a stimulus reset after each spike made in earlier work and thus solves the long-standing reset problem. The neuron exhibits stochastic resonance, both with respect to input noise intensity and stimulus frequency. The latter resonance arises by matching the stimulus frequency to the refractory time of the neuron. The Markov approach can be generalized to other periodically driven stochastic processes containing a reset mechanism.Comment: 23 pages, 10 figure

Screening assessment of cyanobacterial embryotoxicity to Japanese medaka, Oryzias latipes (Actinopterygii: Beloniformes: Adrianichthyidae)

Background. Fish embryos and larvae are frequently subject to chronic- and damaging exposure of cyanotoxins released by live and decomposing cyanobacteria Whereas the majority of former studies dealt with the embryotoxicological effects of pure toxins and extracts, we focused on the evaluation of toxic effects of crude cyanobacterial biomass in our study. Materials and methods. Samples of crude cyanobacterial biomass—intended for embryotoxicological tests with eggs of Japanese medaka, Oryzias latipes (strain Q2d-rR.YHNI)—were collected from natural bodies of water in the Czech Republic. Those samples consisted predominantly of: Microcystis aeruginosa, M. flos-aquae, Woronichinia naegeliana, Anabaena sigmoidea, and Aphanizomenon flos-aquae. In the preliminary optimization experiments, various numbers of fertilized medaka eggs (from 1 to 6 per one 10-mL well on a six well polypropylene plate) were hatched under standard conditions. Because of the highest hatching rates, 4 eggs per 10 mL well were selected as an optimal treatment. The embryotoxicological tests were performed according to the OECD 212 guideline in two concentrations (extracts of crude cyanobacterial biomass: 40 and 200 mg · L–1dry weight). Fertilized eggs in stage 6 to 8 (some 2–3 h after fertilization) were introduced into test wells, and hatching performance, duration of embryonic development as well as lethal and sublethal effects were monitored. Results. The hatching rates (treatment with 4 eggs per 10 mL well), achieved in the majority of experimental treatments with cyanobacterial biomass, were significantly different from the control group. Also hatching onset was considerably delayed due the presence of cyanobacterial biomass. The embryotoxicological impacts were more pronounced in higher concentrations of cyanobacterial biomass (200 mg · L–1) compared to lower concentrations (40 mg · L–1). Whilst deformities were not recorded in the control, their highest incidence amounted to 11.8% and 40.9% in 40 and 200 mg · L–1 of cyanobacterial biomass, respectively. Conclusion. Cyanotoxicity significantly affected examined parameters (hatching rates, duration of embryonic development, and morphological deformities occurrence) in medaka embryos. The study proved significant embryotoxic effects upon Japanese medaka at environmentally relevant levels of cyanobacteria commonly occurring in surface waters in Europe

Existing and emerging cyanocidal compounds:New perspectives for cyanobacterial bloom mitigation

To help ban the use of general toxic algicides, research efforts are now directed towards the discovery of compounds that are specifically acting as cyanocides. Here, we review the past and look forward into the future, where the less desirable general algicides like copper sulphate, diuron or endothall may become replaced by compounds that show better specificity for cyanobacteria and are biodegradable or transform into non-toxic products after application. For a range of products, we review the activity, the mode of action, effectiveness, durability, toxicity towards non-target species, plus costs involved, and discuss the experience with and prospects for small water volume interventions up to the mitigation of entire lakes; we arrive at recommendations for a series of natural products and extracted organic compounds or derived synthetic homologues with promising cyanocidal properties, and briefly mention emerging nanoparticle applications. Finally, we detail on the recently introduced application of hydrogen peroxide for the selective killing of cyanobacteria in freshwater lakes