The survival of culturable fecal coliforms, fecal streptococci, and Clostridium perfringens spores in freshwater and marine sediments from sites near sewage outfalls was studied. In laboratory studies, the inhibition of protozoan predators with cycloheximide allowed the fecal coliforms to grow in the sediment whereas the presence of predators resulted in a net die-off. C. perfringens spores did not appear either to be affected by predators or to die off throughout the duration of the experiments (28 days). Studies using in situ membrane diffusion chambers showed that, with the exception of C. perfringens, die-off of the test organisms to 10% of their initial numbers occurred in both marine and freshwater sediments within 85 days. The usual exponential decay model could not be applied to the sediment survival data, with the exception of the data for fecal streptococci. It was concluded that application of the usual decay model to the fecal coliform data was confounded by the complex relationship between growth and predation. The survival of seeded Escherichia coli in marine sediment was studied by using an enumeration method which detected viable but nonculturable bacteria. Throughout the duration of the experiment (68 days), the same proportion of E. coli organisms remained culturable, suggesting that sediment provides a favorable, nonstarvation environment for the bacteria.

Escherichia coli and some salmonellas were exposed in seawater and freshwater to natural sunlight, visible light of comparable intensity, and light containing a similar proportion of u.v. as natural sunlight but of a much lower intensity. Direct viable bacterial counts and culturable counts on selective and non-selective media were made at intervals. The rate of decrease in numbers of culturable bacteria was significantly faster in seawater than in freshwater when exposed to natural sunlight. No significant difference was found between the rates of decrease in numbers of culturable bacteria in seawater and those in freshwater when bacteria were exposed to light with a small u.v. component of similar intensity. The effect of salinity no loss of culturability is, therefore, more significant in the presence of u.v. radiation. Direct counts by the acridine orange direct viable count method decreased much more slowly than the culturable counts in seawater but comparably with culturable counts in freshwater in natural sunlight. Direct viable counts and culturable counts decreased at a similar rate in seawater and in freshwater in visible light. This may signify the evolution of enteric bacteria towards a viable but non-culturable form in seawater when exposed to natural sunlight. The presence of humic acids significantly reduced loss of culturability but only in low salinity conditions. Salinity appears to be an important factor influencing culturability in bacteria exposed to sunlight.

No abstract

The dispersion and initial transport of Cryptosporidium oocysts from fecal pats were investigated during artificial rainfall events on intact soil blocks (1,500 by 900 by 300 mm). Rainfall events of 55 mm h ؊1 for 30 min and 25 mm h ؊1 for 180 min were applied to soil plots with artificial fecal pats seeded with approximately 10 7 oocysts. The soil plots were divided in two, with one side devoid of vegetation and the other left with natural vegetation cover. Each combination of event intensity and duration, vegetation status, and degree of slope (5°a nd 10°) was evaluated twice. Generally, a fivefold increase (P < 0.05) in runoff volume was generated on bare soil compared to vegetated soil, and significantly more infiltration, although highly variable, occurred through the vegetated soil blocks (P < 0.05). Runoff volume, event conditions (intensity and duration), vegetation status, degree of slope, and their interactions significantly affected the load of oocysts in the runoff. Surface runoff transported from 10 0.2 oocysts from vegetated loam soil (25-mm h ؊1 , 180-min event on 10°slope) to up to 10 4.5 oocysts from unvegetated soil (55-mm h ؊1 , 30-min event on 10°slope) over a 1-m distance. Surface soil samples downhill of the fecal pat contained significantly higher concentrations of oocysts on devegetated blocks than on vegetated blocks. Based on these results, there is a need to account for surface soil vegetation coverage as well as slope and rainfall runoff in future assessments of Cryptosporidium transport and when managing pathogen loads from stock grazing near streams within drinking water watersheds.

C . M . D A V I E S A N D H . J . B A V O R . 2000.The performances of a constructed wetland and a water pollution control pond were compared in terms of their abilities to reduce stormwater bacterial loads to recreational waters. Concentrations of thermotolerant coliforms, enterococci and heterotrophic bacteria were determined in in¯ow and out¯ow samples collected from each system over a 6-month period. Bacterial removal was signi®cantly less effective in the water pollution control pond than in the constructed wetland. This was attributed to the inability of the pond system to retain the ®ne clay particles (< 2 mm) to which the bacteria were predominantly adsorbed. Sediment microcosm survival studies showed that the persistence of thermotolerant coliforms was greater in the pond sediments than in the wetland sediments, and that predation was a major factor in¯uencing bacterial survival. The key to greater bacterial longevity in the pond sediments appeared to be the adsorption of bacteria to ®ne particles, which protected them from predators. These observations may signi®cantly affect the choice of treatment system for effective stormwater management.

Coxiella burnetii is the causative agent of Q fever, a disease with a spectrum of presentations from the mild to fatal, including chronic sequelae. Since its discovery in 1935, it has been shown to infect a wide range of hosts, including humans. A recent outbreak in Europe reminds us that this is still a significant pathogen of concern, very transmissible and with a very low infectious dose. For these reasons it has also featured regularly on various threat lists, as it may be considered by the unscrupulous for use as a bioweapon. As an intracellular pathogen, it has remained an enigmatic organism due to the inability to culture it on laboratory media. As a result, interactions with the host have been difficult to elucidate and we still have a very limited understanding of the molecular mechanisms of virulence. However, two recent developments will open up our understanding of C. burnetii: the first axenic growth medium capable of supporting cell-free growth, and the production of the first isogenic mutant. We are approaching an exciting time for expanding our knowledge of this organism in the next few years.

No abstract

Although chemical measurement techniques and geochemical speciation modelling may detect and predict the different forms of copper in aquatic systems and hence provide some information about the likely toxicity of the water to aquatic organisms, they do not give direct quantitative data on adverse biological effects. Bioassays or toxicity tests are generic tests that use living organisms as indicators of contaminant bioavailability in aquatic systems. The microbial community, including protozoa, algae, bacteria, and fungi, provides a useful tool for directly assessing the hazard of copper in natural ecosystems. Most of our information on copper toxicity in aquatic systems comes from single-species tests using cultured organisms. However, whole community bioassays with natural phytoplankton and bacterial populations are finding increasing use. Although laboratory toxicity tests using ionic copper spiked into pristine seawater or synthetic softwater provide information on copper toxicity under controlled conditions, their usefulness for estimating bioavailable copper is limited in natural waters, where copper toxicity is ameliorated by complexation and adsorption. Careful selection of appropriately sensitive test species, bioassay endpoints, and test protocols is necessary to ensure the environmental relevance of the bioassays used. An understanding of metal speciation, metal-cell binding, mechanisms of toxicity, and limitations of the bioassays is required to understand copper bioavailability in natural waters and sediments. In this review, the use of bioassays with bacteria and microalgae for assessing copper bioavailability in marine and fresh waters and sediments is discussed, with particular emphasis on the limitations of current techniques. There is an urgent need for more environmentally relevant tests with sufficient sensitivity to detect bioavailable copper at concentrations close to water and sediment quality guideline values. Key words: bioassay, copper, metal, bioavailability, toxicity, bacteria, algae.