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Phytoremediation of soils polluted with polycyclic aromatic hydrocarbons (PAHs) has so far neglected the possible role of the ubiquitous symbiotic associations between plant roots and fungi known as arbuscular mycorrhizas. A time course laboratory experiment with clover and ryegrass grown on spiked [500 + 500 + 50 mg kg-1 of anthracene, chrysene and dibenz(a,h)anthracene] soil demonstrated for the first time that dissipation of condensed PAHs may be enhanced in the presence of arbuscular mycorrhiza [66 and 42% reductions in chrysene and dibenz(a,h)anthracene, respectively, versus 56 and 20% reductions in nonmycorrhizal controls]. Addition of a surfactant accelerated initial PAH dissipation but did not attain final PAH concentrations below those obtained with nonmycorrhizal plants. Toxicity tests (earthworm survival and bioluminescence inhibition in Vibrio fischeri) indicated that mycorrhiza reduced the toxicity of PAHs and/or their metabolites and counteracted a temporally enhanced toxicity mediated by surfactant addition. Phospholipid fatty acid profiles demonstrated that the imposed treatments altered the microbial community structure and indicated that the mycorrhiza-associated microflora was responsible for the observed reductions in PAH concentrations in the presence of mycorrhiza.

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Water repellency of volcanic ash soils from the Ecuadorian pa´ramo was studied by a combination of extraction and analysis of water-repellent products, Molarity Ethanol Droplet values, water contactangle measurements by capillary rise, and N 2 adsorption isotherms. The undried samples studied are hydrophilic, but exhibit water repellency after moderate drying (48 hours at 30 C). The advancing water contact-angle measured by capillary rise varies from 78 to 89 . These water contact-angles decrease strongly after extraction of organic materials by an isopropanol-water mixture. Elemental analysis, infrared spectra and gas chromatography-mass spectrometry analyses were used to characterize the extracts. The results show that long-chain fatty acids and more complex non-polar alkyl components (waxes) are the main water-repellent materials. The deposition of such extracted materials onto hydrophilic sand leads to the rapid increase of water contact-angle until values close to those measured on the soil samples are achieved. Assuming a coating of the mineral surface by organic hydrophobic products and using Cassie's law, the water contact-angle of extracted materials was computed. The values ranged from 100 to 157 . Nitrogen specific surface areas of the soils studied were very small, indicating a low adsorbent-adsorbate interaction on hydrophobic surfaces. These results partially validate the hypothesis of water-repellent materials that occur as coatings at least after a drying process.

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Several cyanide-tolerant microorganisms have been selected from alkaline wastes and soils contaminated with cyanide. Among them, a fungus identified as Fusarium solani IHEM 8026 shows a good potential for cyanide biodegradation under alkaline conditions (pH 9.2 to 10.7). Results of K 14 CN biodegradation studies show that fungal metabolism seems to proceed by a two-step hydrolytic mechanism: (i) the first reaction involves the conversion of cyanide to formamide by a cyanide-hydrolyzing enzyme, cyanide hydratase (EC 4.2.1.66); and (ii) the second reaction consists of the conversion of formamide to formate, which is associated with fungal growth. No growth occurred during the first step of cyanide degradation, suggesting that cyanide is toxic to some degree even in cyanide-degrading microorganisms, such as F. solani. The presence of organic nutrients in the medium has a major influence on the occurrence of the second step. Addition of small amounts of yeast extract led to fungal growth, whereas no growth was observed in media containing cyanide as the sole source of carbon and nitrogen. The simple hydrolytic detoxification pathway identified in the present study could be used for the treatment of many industrial alkaline effluents and wastes containing free cyanide without a prior acidification step, thus limiting the risk of cyanhydric acid volatilization; this should be of great interest from an environmental and health point of view.

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