Megacities as sources for pathogenic bacteria in rivers and their fate downstream

Abstract

Poor sanitation, poor treatments of waste water, as well as catastrophic floods introduce pathogenic bacteria into rivers, infecting and killing many people. The goal of clean water for everyone has to be achieved with a still growing human population and their rapid concentration in large cities, often megacities. How long introduced pathogens survive in rivers and what their niches are remain poorly known but essential to control water-borne diseases in megacities. Biofilms are often niches for various pathogens because they possess high resistances against environmental stress. They also facilitate gene transfers of antibiotic resistance genes which become an increasing health problem. Beside biofilms, amoebae are carriers of pathogenic bacteria and niches for their survival. An overview about our current understanding of the fate and niches of pathogens in rivers, the multitude of microbial community interactions, and the impact of severe flooding, a prerequisite to control pathogens in polluted rivers, is given.

Figure 1

Pinheiros River in São Paulo. The Pinheiros River as the Tiete River in Sao Paulo passes through the inner part of the city and is heavily polluted. Pinheiros River is largely anaerobic and heavy methane formation can be observed. In 2008 further down of this place at station PINH 04900 a mean conductivity of 480 μS cm⁻¹, 18.67 mg l⁻¹ ammonium, 55.7 mg l⁻¹ BOD5 and 1,100,000 thermotolerant coliforms per 100 ml have been measured; data taken from the CETESB report 2009 [16].

Figure 2

Annual precipitation 1986 - 2008 in the Metropolitan Region of São Paulo; data taken from the CETESB report 2009 [16]. The mean annual precipitation 1879 - 2008 is 1410 mm a⁻¹. A tendency of decreasing rainfall is evident.

Figure 3

Mean load of thermotolerant coliforms in 2008 along the Tiete River [cfu per 100 mL]. The distance is given in river-km starting from the first sampling site west of Biritiba-Mirim, São Paulo, and the locations of main cities are shown. The onset of input of sewage from the city between km 80 and 120 can clearly be seen in the coliforms load in the river. Downstream from this area the number of coliforms declines considerably but tributaries, for example, Pinheiros River, or cities in the outskirts of São Paulo, for example, Carapicuíba, also dump waste in the river which can be seen by the coliforms number between river-km 130–160. Further down, the number of coliforms declines rapidly but the river is still heavily polluted as judged by the much slower decline in the biochemical oxygen demand (BOD5). As can be seen from the graph, the cities of Salto and Tiete do not contribute significantly to the thermotolerant coliforms load of Rio Tiete. Data taken from the CETESB report 2009 [16].