Incidents of odor in selected South African subtropical water bodies, the majority of which are sources of potable water, are presented. The presumed origin, prevalence and frequency of earthy/muddy off-flavors are described. Investigation into odor cases included the following: sensory and instrumental (gas chromatography/mass spectrometry) analyses of odorous water samples, enumeration and identification of cyanobacteria, algae and actinomycetes present in the samples and attempts to establish cultures of responsible microorganisms for confirmation of odor production. The possibility of concomitant production of toxins by odor-forming cyanobacteria is also discussed.
Incidence of off-flavors of 30% was established. All affected reservoirs were dominated by cyanobacteria, mainly Microcystis aeruginosa. Odorous substances detected in water were geosmin and dimethyl trisulphide. Efforts to isolate odor-producing organisms in culture were unsuccessful.
From individual case histories studied it is clear that odor incidents in man-made lakes present a serious problem in South Africa. The warmer climatic conditions and seasonally fluctuating water level create additional factors for odor formation, which are different from those experienced in more temperate regions.
Eighty strains of fungi and heterotrophic bacteria, isolated from natural water sources polluted with heavy metals, were tested for their bioaccumulation abilities. Metal-resistant strains were first selected in a preliminary step. Preselected cultures were then screened for gold, silver, nickel and cadmium uptake capabilities. A collection of bioaccumulating strains, consisting of 39 strains for the recovery of gold, 9 strains for silver, 28 for cadmium and 22 for nickel, has been established. All the strains selected were able to remove metals tested from diluted solutions (ca. 5 mg/l) to levels below 0.5 mg/l. The maximum uptake capacity of strains was determined in concentrated metal solutions (20 - 50 mg/l). Nine of the strains had saturation values of 100 mg/g dry weight or higher. The importance of pH in passive bioaccumulation process is discussed.
Seventy-three bacterial isolates from polluted streams as well as 157 of their heavy metal-tolerant (HM-tolerant) derivatives were tested for their sensitivity to ampicillin, ticarcillin, gentamicin, cephalexin, sulfamethoxazole, tetracycline and colistin. Among the parent strains 19% were sensitive to all antibiotics tested and 70% were multiple resistant. The mean resistance of parent strains was 227 antibiotics per isolate. Mean resistance was increased to 2.82 for silver-, 3.32 for gold-, 3.48 for copper-, 3.78 for nickel-, and 3.79 for cadmium-tolerant subcultures. A statistically significant increase in resistance was demonstrated for tetracycline and sulfamethoxazole in all HM-tolerant subcultures, for cephalexin in gold-, nickel-and cadmium-tolerant strains, for ampicillin in gold-tolerant isolates and for ticarcillin in cadmium-tolerant strains.
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