C. I. Mayfield

Measurement of Electron Transport System (ETS) activity in soil.

Electron transport system (ETS) activity was measured in amended and nonamended soil by measuring the reduction of 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (INT) to iodonitrotetrazolium formazan (INT-formazan), which can be easily extracted with methanol without interference from other compounds found in soil. A high correlation between ETS activity and oxygen consumption was observed. This technique allows rapid quantitative measurements of microbial ETS activity in soil.

Microbial and non-biological decomposition of chlorophenols and phenol in soil

The aerobic and anaerobic degradation of phenol and selected chlorophenols was examined in a clay loam soil containing no added nutrients. A simple, efficient procedure based on the high solubility of these compounds in 95% ethanol was developed for extracting phenol and chlorophenol residues from soil. Analysis of soil extracts with UV spectrophotometry showed that phenol,o-chlorophenol,p-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol and 2,4,6-trichlorophenol were rapidly degraded, whilem-chlorophenol, 3,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol were degraded very slowly by microorganisms in aerobically-incubated soil at 23°C. Both 3,4,5-trichlorophenol and 2,3,4,5-tetra chlorophenol appeared to be more resistant to degradation by aerobic soil microorganisms at 23°C. None of the compounds examined were degraded by microorganisms in anaerobically-incubated soil at 23°C. Direct microscopic observation revealed that phenol and selected chlorophenols stimulated aerobic and to a lesser extent, anaerobic microbial growth in soil, and aerobic soil bacteria were responsible for the degradation of 2,4-dichlorophenol in aerobically-incubated soil at 23°C. Phenol,o-chlorophenol,m-chlorophenol,p-chlorophenol and 2,4-dichlorophenol underwent rapid non-biological degradation in sterile silica sand. Non-biological decomposition contributed, perhaps substantially, to the removal of some chlorophenols from sterile aerobically-incubated soil and both sterile and non-sterile anaerobically-incubated soil.

Degradation of chlorophenols in soil, sediment and water at low temperature

Abstract Chlorophenol degradation was studied under aerobic conditions in soil, sediment and water. Ortho -chlorophenol, p -chlorophenol and 2,4-dichlorophenol were degraded by soil and sediment microorganisms at 0°C and 4°C. Metachlorophenol and pentachlorophenol were also degraded, but to a lesser extent. Stream-water microorganisms were only able to degrade 2,4-dichlorophenol at 20°C. None of the other chlorophenols examined were degraded by stream-water microorganisms at 0 or 20°C. The addition of some chlorophenols stimulated aerobic, and to a lesser extent, anaerobic microbial growth in sediment incubated at 0°C. A decrease in the concentration of some chlorophenols was noted in both sterile and non-sterile stream water at 0 and 20°C; which could not be explained by microbial contamination, photodecomposition or volatilization.

Effect of ph on the methylation of mercury and arsenic by sediment microorganisms

Abstract The effect of pH on the methylation of mercury and arsenic in lake sediment amended with nutrients was examined. The formation of methyl mercury from inorganic mercuric chloride occurred only in the pH range of 5.5–6.5. Dimethyl mercury was not produced. Mercury methylation in this narrow pH range was probably the result of a microbial population which had adapted to the in situ pH of 5.8. The levels of methyl mercury were reduced in the presence of sulfuric acid, probably due to sulfide formation. In the arsenic methylation experiments, volatile arsine or methyl arsines were rarely detected. Analysis of the culture fluid revealed that methyl arsonic acid and dimethyl arsinlcacid were formed over the pH range of 3.5 to 7.5. In contrast to the mercury methylation experiments, the arsenic methylating microorganisms were not as sensitive to changes in pH and different microorganisms may have been responsible for methylating arsenic over this pH range.

Impact of volatile aromatic hydrocarbons, alone and in combination, on growth of the freshwater alga Selenastrum capricornutum

Abstract A sealed, air-tight exposure system was employed for toxicity testing of volatile aromatic hydrocarbons. Within the sealed flasks, growth of the representative green alga, Selenastrum capricornutum , was inhibited due to the restriction of gas exchange, but inhibition was overcome by the addition of NaHCO 3 (0.4% w/v) to the growth medium. Toxicity was determined as the concentration required to reduce growth by 50% following an 8-day exposure period (EC 50 ). Relative toxicity of 6 aromatic hydrocarbons was, in order of increasing toxicity, benzene (EC 50 =41.0 mg/l), toluene (9.4 mg/l), ethyl-benzene (4.8 mg/l) and p -, m -, o -xylene (between 3.9–4.4 mg/l). Examination of the toxicity of hydrocarbon mixtures revealed an additive toxicological interaction between benzene, toluene and m -xylene, indicating that the toxicity of a mixture can be predicted from the sum of the toxicities of each component. A synergistic interaction was evident between benzene and toluene at higher concentration levels, but the interpretation of synergism is complicated by a rapid increase in sensitivity of algae to greater toluene concentrations.

Impact of the exodermis on infection of roots by Fusarium culmorum

Patterns of infection withFusarium culmorum (W G Smith) Saccardo were observed in seedling roots of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), maize (Zea mays L.) and asparagus (Asparagus officinalis L). Apical regions of the main roots were not infected. Since penetration into the root occurred several days after inoculation and the roots were growing during the experiment, these regions had apparently not been in existence long enough to be infected. In older regions of barley, wheat and asparagus, hyphae entered through the tips of lateral roots. In barley and wheat, which had not developed any suberin lamellae in their subepidermal layer, infection occurred randomly over the remainder of the root. In maize, the fungus penetrated the epidermis at many sites but did not breach the exodermis in which all cells possessed both Casparian bands and suberin lamellae. Maize roots, therefore, sustained only minimal infections. In asparagus, the fungus grew through the short (passage) cells but never the long cells of the exodermis. In doing so, it penetrated cells possessing Casparian bands but lacking suberin lamellae. The results support the hypothesis that suberin lamellae provide effective barriers to the growth ofF. culmorum hyphae.

THE RELATIONSHIP BETWEEN TOXICITY AND BIOCONCENTRATION OF VOLATILE AROMATIC HYDROCARBONS BY THE ALGA SELENASTRUM CAPRICORNUTUM

Abstract Bioconcentration potentials determined for benzene, toluene, ethylbenzene and 3 xylene isomers (para, meta and ortho) using the alga Selenastrum capricornutum were found to range from 1.63 [log=μg/kg/μg/L] for benzene to 2.41 for p -xylene. A strong linear correlation was evident between bioconcentration and the octanol/water partition coefficient (Kow), as well as between bioconcentration and toxicity. Two intracellular components (cell wall and microsome) were isolated and examined for their ability to bioconcentrate aromatic hydrocarbons. The microsome component was found to bioconcentrate aromatic hydrocarbons to the same degree as the whole cell, while the cell wall component showed a more limited capacity for bioconcentration.

Microbial responses to salt-induced osmotic stress

SummaryThe construction and assembly of a model root region is described. The model was used to manipulate the soil matrix, soil microorganisms, and to simulate release of root exudates. The design of the apparatus facilitated long-term, direct microscopic observations of microbial activity in soil and on artificial roots. Preliminary studies indicate that microbial responses to osmotic stress and to changes in components of exudate solutions are easily monitored.

New role for community networks

OMMUNITY INFORMATION COVERS A WIDE RANGE OF SOURCES. IT ALSO serves many users, encompassing government, health and public safety organizations, businesses of all types, service organizations, tourist attractions , historical societies, and members of the public. In fact, communities are repositories of large amounts of heterogeneous information that need to be searched, read, explored, acted upon, updated, and that offer opportunities for collaboration and other forms of two-way communication. In the absence of digital library technology, most of this information is not easily accessible to members of the community or to those making inquiries from outside. Thus, the ability to browse, search, and acquire data is essential for the establishment of community networks. Within Canadas Technology Triangle (CTT) we are creating a community-based digital library called the CTT Community Network. The region of Waterloo (including the cities of Kitchener, Waterloo, and Cambridge), and the city of Guelph comprise the CTT; so named because of its con-Communities as very large repositories of information are digital libraries with some unique browsing and data acquisition characteristics.

Endotoxin Inactivation in Water by Using Medium-Pressure UV Lamps

ABSTRACT Deionized water was spiked with various concentrations of endotoxin and exposed to UV irradiation from medium-pressure UV lamps to assess endotoxin inactivation. It was found that endotoxin inactivation was proportional to the UV dose under the conditions examined. The inactivation rate was determined to be ∼0.55 endotoxin unit/ml per mJ/cm2 of irradiation delivered.