Enhancement of AhR-mediated activity of selected pollutants and their mixtures after interaction with dissolved organic matter

Dissolved organic matter (DOM) in freshwaters is present at concentrations ranging from 0.5 to 50 mg L?1, and consists of various organic compounds, including humic substances (HS). HS exert a variety of direct and indirect biological effects, including interaction with the aryl hydrocarbon receptor (AhR). AhR is a cytosolic receptor that binds various hydrophobic organic compounds (HOCs) and mediates some of their toxic effects. In vitro effects of binary mixtures of various DOM (mainly HS) with various HOCs on AhR-mediated responses were studied by use of H4IIE-luc cells. Six out of 12 DOM activated the AhR even at environmentally relevant concentrations (17 mg L?1). In simultaneous exposures of H4IIE-luc cells to DOM (17 mg L?1) and each of the model compounds, 2,3,7,8-TCDD, PCB126, PCB169, benzo[a]pyrene, benzo[a]anthracene, dibenz[a,h]anthracene, fluoranthene, a mixture of persistent organic pollutants (POPs), a mixture of polycyclic aromatic hydrocarbons (PAHs), and a mixture of all HOCs, either significant additive or facilitative effects were observed when compared to activities of single HOCs. No significant decrease of effects due to possible sorption of HOCs to DOM was observed, even in subsequent experiments when HOCs+DOM mixtures were preincubated for six days before exposure to H4IIE-luc. Thus, DOM does not seem to protect organisms against AhR-mediated toxic effects of HOCs (as usually predicted due to sorption of HOCs on DOM), but it can actually enhance their potency for AhR-mediated effects in some situations.     

Genotype-specific responses of fluctuating asymmetry and of preadult survival to the effects of lead and temperature stress in Drosophila melanogaster

Although fluctuating asymmetry (FA) increases with exposure to certain types of environmental stressors such as temperature extremes, relatively little is known about the effects of interaction (e.g., synergism) between known sources of environmental stress on FA. Knowledge of such interaction effects, and of the magnitude of genotype-by-environment interaction, are of fundamental importance toward predicting the usefulness of FA as a bioindicator of environmental pollution. We tested for synergistic effects on FA between elevated temperature and exposure to lead, and examined FA responses simultaneously in four genetic strains of Drosophila melanogaster known to differ in their degree of developmental instability, and presumably in their buffering capacity. In the absence of heavy metal, bristle FA increased with temperature, but in the presence of lead, FA at high temperature (30 (degrees)C) was reduced to levels similar, or below, that at lower temperature (25 (degrees)C). This temperature by lead interaction was statistically significant, but paradoxical in that the disruptive effects of temperature appeared to be attenuated in the presence of the heavy metal. In no case was there a significant effect of lead on bristle FAs, despite documented assimilation of heavy metal by flies, and in no case was the genotype by environment interaction significant. Whereas lead treatment did not influence survival, survival was reduced at the high temperature, but significantly so only in one genetic strain (Oregon-R). There was no relationship between survival and FA across stress treatments within lines. Thus, any disproportionate stress-induced mortality in developmentally unstable classes (developmental selection) was unlikely to bias the FA results. Our results underscore the need for independent replication of significant findings before FA-based biomonitoring can be responsibly and effectively implemented. The results call for caution in using FA as a biomarker of stress, because stress factors may interact in complex and unpredictable ways, which could result in erroneous conclusions about real levels of stress present in field populations, under the unduly simplistic assumption that stress factors will act additively to increase FA.     

Dehalogenation potential of municipal waste incineration fly ash

BACKGROUND, AIMS AND SCOPE: It is well known that the fly ash from filters of municipal waste incinerators (MWI-FA) shows dehalogenation properties after heating it to 240-450 degrees C. However, this property is not general, and fly ash samples do not possess dehalogenation ability at all in many cases. Fly ash has a very variable composition, and the state of the fly ash matter therefore plays the decisive role. In the present paper, the function of important components responsible for the dehalogenation activity of MWI-FA is analysed and compared with the model fly ash. METHODS: With the aim of accounting for the dehalogenation activity of MWI-FA, the following studies of hexachlorobenzene (HCB) dechlorination were performed: The role of copper in dehalogenation experiments was evaluated for five types of metallic copper. The gasification of carbon in MWI-FA was studied in the 250-350 degrees C temperature range. Five different kinds of carbon were used, combined with conventional Cu(o) and activated nanosize copper powder. The dechlorination experiments were also carried out with Cu(II) compounds such as CuO, Cu(OH)2, CuCl2 and CuSO4. The results were discussed from the standpoint of thermodynamics of potential reactions. Based on these results, the model of fly ash was proposed, containing silica gel, metallic copper and carbon. The dechlorination ability of MWI-FA and the model fly ash are compared under oxygen-deficient atmosphere. CONCLUSIONS: The results show that, under given experimental conditions, copper acts in the dechlorination as a stoichiometric agent rather than as a catalyst. The increased surface activity of copper enhances its dechlorination activity. It was found further that the presence of copper leads to a decrease in the temperature of carbon gasification. The cyclic valence change from Cu(o) to Cu+ or Cu2+ is a prerequisite for the dehalogenation to take place. RECOMMENDATION AND OUTLOOK: Thermodynamic analysis of the dechlorination effect, as well as the comparison of dechlorination pathways on MWI-FA and model fly ash, can provide a deeper understanding of the studied reaction.