Biological responses of maize (Zea mays) plants exposed to chlorobenzenes. Case study of monochloro-, 1,4-dichloro- and 1,2,4-trichloro-benzenes.

A 7-day-exposure time experiment was designed to investigate the phytotoxicity of chlorobenzenes (CBs) on Zea mays seedlings, focusing on the growth and generation of oxidative stress. Significant growth inhibition (based on biomass gain) was observed for exposure to monochlorobenzene (MCB), dichlorobenzene (DCB) and trichlorobenzene (TCB) concentrations higher than 10 mg l(-1). It would seem that CBs inhibit cell division, since the mitotic index decreased for roots exposed to DCB at 80 mg l(-1) dose (8%) and to all the TCB concentrations tested (20% inhibition). CBs exposure resulting in an increase in the oxidative stress response in maize seedlings [reactive oxygen species like H(2)O(2), antioxidant enzymes (POD, GR), lipid peroxidation] correlated to the compound's degree of chlorination, where damage increasing with the number of chlorine atoms (MCB < DCB < TCB). This biological response was also dependent on the dose-exposure. Z. mays exposed to CBs at concentrations <10 mg l(-1) did not induce sufficient oxidative damage to cause root cell death. Therefore, CBs at current environmental concentrations are unlikely to produce evident phytotoxic effects on Z. mays seedlings.

Autochthonous ascomycetes in depollution of polychlorinated biphenyls contaminated soil and sediment.

We investigated the capacity of a consortium of ascomycetous strains, Doratomyces nanus, Doratomyces purpureofuscus, Doratomyces verrucisporus, Myceliophthora thermophila, Phoma eupyrena and Thermoascus crustaceus in the mycoremediation of historically contaminated soil and sediment by polychlorinated biphenyls (PCBs). Analyses of 15 PCB concentrations in three mesocosms containing soil from which the fungal strains had previously been isolated, revealed significant PCB depletions of 16.9% for the 6 indicator PCBs (i-PCBs) and 18.7% for the total 15 PCBs analyzed after 6months treatment. The degradation rate did not statistically vary whether the soil had been treated with non-inoculated straw or colonized straw or without straw and inoculated with the consortium of the six strains. Concerning the sediment, we evidenced significant depletions of 31.8% for the 6 i-PCBs and 33.3% for the 15 PCB congeners. The PCB depletions affected most of the 15 PCBs analyzed without preference for lower chlorinated congeners. Bioaugmented strains were evidenced in different mesocosms, but their reintroduction, after six months treatment, did not improve the rate of PCB degradation, suggesting that the biodegradation could affect the bioavailable PCB fraction. Our results demonstrate that the ascomycetous strains potentially adapted to PCBs may be propitious to the remediation of PCB contaminated sites.

Potential of autochthonous fungal strains isolated from contaminated soils for degradation of polychlorinated biphenyls.

Up to now, most studies on polychlorinated biphenyl (PCB) bioremediation have examined the ability of model fungal strains to biodegrade PCBs. Yet, there is limited information concerning the potential of autochthonous filamentous fungal strains in the biodegradation of PCBs and their possible use in the environmental technologies. In this study, we investigated the capacity of autochthonous fungal strains in the biodegradation of PCBs by isolating 24 taxa from former industrial sites highly contaminated by PCBs. Microscopic and molecular analyses using the internal transcribed spacer (ITS) region revealed that the fungal strains belonged to the phyla Ascomycota (19 strains) and Zygomycota (five strains). The chromatography gas analysis revealed evidence of degradation of seven PCB congeners. With the exception of Circinella muscae which presented no degradation potential, the other fungal strains exhibited a rate of biodegradation ranging from 29 to 85 % after 7 d of incubation in liquid medium. Among these strains, Doratomyces nanus, Doratomyces purpureofuscus, Doratomyces verrucisporus, Myceliophthora thermophila, Phoma eupyrena, and Thermoascus crustaceus showed remarkable degradation ability (>70 %) regardless of the number of chlorine substituents on the biphenyl nucleus and a high tolerance towards PCBs. To our knowledge, this is the first study that demonstrates the ability of PCB degradation by these species and indicates the potential effectiveness of some autochthonous fungal strains in bioremediation systems.

Concentration responses to organochlorines in Phragmites australis.

Phragmites australis shows potential for the phytoremediation of chlorinated chemicals. Also there has been some attempt to determine the phytotoxic effects of organochlorines (OC). This study reports for lindane (HCH), monochlorobenzene (MCB), 1,4-dichlorobenzene (DCB) and 1,2,4-trichlorobenzene (TCB), a no-observed-effect-concentration (NOEC(7d)) that was 1000-300,000 times higher than environmental concentrations. Nevertheless, the combined OC mixture (NOEC(7d) level of each congener) induced a synergistic toxic effect, causing a severe drop (70%) in chlorophyll concentration. The mixture 0.2 mg L(-1) MCB+0.2 mg L(-1) DCB+2.5 mg L(-1) TCB+0.175 mg L(-1) HCH, that was 15 times more concentrated than environmental OC mixture, did not cause phytotoxicity during 21 days. Antioxidant enzymes were affected immediately after the start of exposure (3 days), but the plants showed no signs of stress thereafter. These data suggest that environmental OC mixtures do not pose a significant risk to P. australis.