Escherichia coli Capacity to Repopulate Microcosms Under Osmotic/U.V. Synergic Stress in Tropical Waters.

In both Brazilian and European regulations, the impact assessment of sewage discharges into coastal waters is based on microbiological analyses of fecal indicators such as Escherichia coli, frequently used in prevision hydrodynamic models. However, the decay rates of E. coli vary depending on environmental conditions, and analysis may lead to inaccurate conclusions. This study aimed to analyze the decay of culturable and viable (but not culturable) E. coli in outdoor conditions, by creating microcosms inoculated with pre-treated sewage. The microcosms were filled with 9.88 L of filtered water (0.22 µm membrane), 3.5% salt, 0.1-0.2% BHI, and 1% bacterial suspension obtained by reverse filtration. PMA-qPCR of E. coli uidA gene and Colilert measurements were applied to evaluate population counts after 2 h, 4 h, and 26 h. After nine hours of exposure to solar radiation, the viable cells decreased to 2.76% (interpolated value) of the initial population, and the cultivable fraction of the viable population accounted for 0.50%. In the dark period, the bacteria grew again, and viable cells reached 8.54%, while cultivable cells grew to 48.14% of initial population. This behavior is possibly due to the use of nutrients recycled from dead cells. Likewise, populations of E. coli in sewage outfalls remain viable in the sediments, where resuspension can renew blooming.

Human Heat stress risk prediction in the Brazilian semiarid Region based on the Wet-Bulb Globe Temperature.

OBJECTIVE: the aim of this study is to map thermal stress risks for human health at the São Francisco River Basin (SFRB) in the Semiarid region, for climatic scenarios RCP 4.5 and 8.5. METHODS: The heat stress conditions were defined by the Wet Bulb Globe Temperature (WBGT) indicator and by the average number of annual days in which the WBGT values exceeded the 90th percentile of the reference period. The WBGT was estimated for the climate scenarios RCP 4.5 (intermediate) and 8.5 (pessimistic) for the period 2011-2090 comparing to the period of reference (1961-2005). RESULTS: The projections show that for the pessimistic scenario practically all municipalities of the SFRB region can reach values of WBGT that indicate a high risk for heat stress in the period 2071-2099. For this same scenario and period, the municipalities of the Lower and Under-average regions may present values of WBGT above the 90th percentile of the reference period in more than 90% of the days/year. CONCLUSIONS: These results show that, if the emission of greenhouse gases continues in the present proportions, some municipalities of the SFRB region may present a high risk for heat stress affecting the work capacity and the practice of physical exercises.

Comparative study of fecal bacterial decay models for the simulation of plumes of submarine sewage outfalls.

In the literature, analytical models have been shown to be extremely useful for estimating the decay rates of coliform as fecal indicator microorganisms, providing reliable predictions of bathing conditions in coastal and continental waters. Although a number of different formulations have been developed in the literature, each one may only be suitable for specific environments, and no comparison between these methods has ever been carried out. In the present article, a comparative analysis of bacterial decay models, calculated by eight different formulations, was performed in coastal outfall plumes, considering identical environmental conditions of solar radiation, temperature and salinity. A statistical approach was applied to identify the differences in means and in behaviors of the results obtained in the various simulations. The results indicate good agreement between bacterial decay rates calculated with at least four methods that were considered more reliable, and at least one of the models was shown to be suitable for estimating bacterial decay rates under night-time conditions, considering only the combined influences of temperature and salinity. Moreover, under daytime conditions, it provides consistent decay rates when compared with measurements taken in the field.