Acute toxicity and n-octanol/water partition coefficients of substituted thiophenols: determination and QSAR analysis.

The acute toxicity (-log EC(50)) to Photobacterium phosphoreum and the n-octanol/water partition coefficient (log K(ow)) of 31 kinds of substituted thiophenols were determined at 298.15K. The -log EC(50) values of studied chemicals are between 4.26 and 5.89. Their log K(ow) values are between 1.34 and 4.02. Comparative molecular field (CoMFA) and comparative molecular similarity index analysis (CoMSIA) models established were successful in predicting -log EC(50) and log K(ow) values of halogenated, methylic, amino and methoxy thiophenols. The size of molecule is the main factor influencing the properties. No correlation was found between the properties and their structural and thermodynamic descriptors from DFT calculation.

Enhancement of odor avoidance regulated by dopamine signaling in Caenorhabditis elegans.

The enhancement of sensory responses after prior exposure to a stimulus is a fundamental mechanism of neural function in animals. Its molecular basis, however, has not been studied in as much depth as the reduction of sensory responses, such as adaptation or habituation. We report here that the avoidance behavior of the nematode Caenorhabditis elegans in response to repellent odors (2-nonanone or 1-octanol) is enhanced rather than reduced after preexposure to the odors. This enhancement effect of preexposure was maintained for at least 1 h after the conditioning. The enhancement of 2-nonanone avoidance was not dependent on the presence or absence of food during conditioning, which generally functions as a strong positive or negative unconditioned stimulus in the animals. These results suggest that the enhancement is acquired as a type of nonassociative learning. In addition, genetic and pharmacological analyses revealed that the enhancement of 2-nonanone avoidance requires dopamine signaling via D(2)-like dopamine receptor DOP-3, which functions in a pair of RIC interneurons to regulate the enhancement. Because dopamine signaling has been tightly linked with food-related information to modulate various behaviors of C. elegans, it may play different role in the regulation of the enhancement of 2-nonanone avoidance. Thus, our data suggest a new genetic and pharmacological paradigm for nonassociative enhancement of neural responses that is regulated by dopamine signaling.

Activated sludge inhibition by chemical stressors--a comprehensive study.

The effects of shock loads of 1-chloro-2,4-dinitrobenzene (CDNB); cadmium; 1-octanol; 2,4-dinitrophenol (DNP); weakly complexed cyanide; pH 5, 9, and 11; and high ammonia levels on activated sludge biomass growth, respiration rate, flocculation, chemical oxygen demand removal, dewaterability, and settleability were studied. For all chemical shocks, except ammonia and pH, concentrations that caused 15, 25, and 50% respiration inhibition were used to provide a single pulse shock to sequencing batch reactor systems containing a nitrifying or non-nitrifying biomass. Cadmium and pH 11 shocks were most detrimental to all processes, followed by CDNB. The DNP and cyanide primarily affected respiration, while pH 5, pH 9, octanol, and ammonia did not affect the treatment process to a significant extent. A chemical source-process effect matrix is provided, which we believe will aid in the development of methods that prevent and/or attenuate the effects of toxic shock loads on activated sludge systems.

A comparison of the lethal and sublethal toxicity of organic chemical mixtures to the fathead minnow (Pimephales promelas).

The joint toxic effects of known binary and multiple organic chemical mixtures to the fathead minnow (Pimephales promelas) were defined at both the 96-h 50% lethal effect concentration (LC50) and sublethal (32-d growth) response levels for toxicants with a narcosis I, narcosis II, or uncoupler of oxidative phosphoralation mode of toxic action. Experiments were designed to define the degree of additive joint toxicity for mixtures of specific xenobiotics that are believed to act through a similar or different primary mode of toxic action. Our results support the general conclusion that concentration addition is expected for the joint toxicity of similarly acting toxicants. When chemicals were thought to act by a dissimilar mechanism, the combined effects we observed at both of the response levels tested were less than predicted by concentration addition, but usually more toxic than that predicted by the independent action/response addition model. It was demonstrated in multichemical mixtures that several toxicants can act together in a nearly additive fashion to produce effects even when they are present at concentrations below their individual no-observed-effect concentration. Concentration-response relationships for test chemicals at both the lethal and sublethal responses were defined for each of the three modes of toxic action studied. When normalized for potency, it was observed that one relationship could be defined to predict lethality to juvenile fathead minnows when exposed to individual chemicals with either a narcosis I, narcosis II, or uncoupler mode of toxic action. These sublethal relationships were similar for the narcosis I and narcosis II test chemicals, but a steeper response was observed for tests conducted with uncouplers.

Deflocculation effects due to chemical perturbations in sequencing batch reactors.

Toxic shock-induced deflocculation was examined for activated sludge exposed to six different classes of industrially relevant chemical toxins: an electrophilic solvent (1-chloro-2,4-dinitrobenzene, CDNB), a heavy metal (cadmium), a hydrophobic chemical (1-octanol), an uncoupling agent (2,4-dinitrophenol, DNP), alkaline pH, and weakly complexed cyanide. The concentrations required to inhibit respiration by 50% were used to shock sequencing batch reactors (SBRs) containing a nitrifying (10-day solids retention time (SRT)) and a non-nitrifying (2-day SRT) biomass. Effluent total suspended solids (TSS) and soluble potassium were monitored to examine deflocculation caused by a bacterial stress response mechanism called glutathione-gated potassium efflux (GGKE). Reactors were monitored for recovery over a period of 3 SRTs or less. At the concentrations tested, CDNB, cadmium and pH 11 were found to cause significant increases in effluent TSS concentrations and showed elevated levels of potassium. In contrast, octanol, DNP and cyanide did not induce severe deflocculation and showed moderate increases in effluent potassium levels. Recovery of effluent TSS and potassium concentrations to control levels generally did not correlate, supporting the hypothesis that reflocculation requires regrowth of biomass. These results suggest that different chemicals induce deflocculation in SBRs, but deflocculation is not necessarily caused by the GGKE mechanism in all cases.

Resazurin metabolism assay is a new sensitive alternative test in isolated pig cornea.

The main object of our study was to investigate whether the resazurin metabolism assay is a sensitive surfactant and alcohol toxicity test in isolated pig cornea and to compare this recently developed fluorometric assay with the data collected in the eye irritation reference chemical data bank. Resazurin is a substrate that changes color in response to metabolic activity. Isolated pig corneas were immersed for 10 min in surfactants and alcohol irritant solutions. After incubation, resorufin fluorescence was read and corneal viability was assessed. This corneal viability was compared with the maximal modified average score published in the report of ECETOC. This assay highlighted different concentration-dependent irritation potentials of the three surfactants tested, and the same results were obtained with corneas treated with the alcohols. We observed that the degree of surfactant- and alcohol-induced decrease in corneal viability, using the resazurin reduction test, was correlated with the in vivo irritancy measurements as determined by the Draize test and scored with the Modified Maximum Average Score (MMAS). This assay allowed us to classify the ocular irritancy of the tested surfactants and alcohols in the same ranking order as the Draize classification. Corneal viability measurement can be used as a potential alternative for the toxicological assessment of surfactants and alcohols. The nontoxic, nonradioactive resazurin metabolism assay allows rapid assessment of many samples with simple equipment and at reduced cost for continuous monitoring of corneal viability. This assay seems to be suitable as a toxicological screening test for eye irritation determination.

Progress in an ecotoxicological standard protocol with protozoa: results from a pilot ring test with Tetrahymena pyriformis.

The aim of this project was to develop a standardized multigeneration growth inhibition test protocol to assess the sublethal effects of industrial chemicals and pesticides on protozoans. The inclusion of a test with protozoa would be an ecologically relevant supplement to the existing basic set in aquatic toxicity testing. The different aspects evaluated in the pilot ring study include: two media, two volumes, two end points and two different methods to measure the cell density. Taking into account the aim to develop a simple, sensitive, reproducible and cost effective test, recommendations are made for a standardized protocol.