Resumo

RIVERA-VAZQUEZ, Ricardo et al. Coliforms and helminthes pollution in the Texcoco, Chapingo and San Bernardino Rivers at the east Part of the Mexican Valley watershed. Rev. Int. Contam. Ambient [online]. 2007, vol.23, n.2, pp.69-77. ISSN 0188-4999.

The Texcoco zone, located at the east of the Mexican Basin, presents serious contamination of its rivers caused by discharges of raw wastewater. Until this research, there were not available records about the contamination sources and the pollutants discharge. The aim of this research was to identify the effluent discharges to the river and their degree of pollution. From May 2004 to April 2005, water samples were collected ten times from 28 wastewater discharges to the rivers. Chemical (methylene blue active substances, trace elements, N, P and EC) and biological (total coliform bacteria content (TBC), fecal bacteria coliform (FBC) and helminth ova) contaminant contents were analyzed, according to the Mexican regulation. The TBC (as the most probable number MPN) ranged from 1.6 x 10⁴ MPN 100 mL^-1 to 2.4 x 10⁷ MPN 100 mL^-1, the FBC ranged from 1 x 10⁴ to 2.4 x 10⁷ and helminth ova ranged from 0.38 to 6.78 eggs L^-1. These amounts exceeded the permissible limits established by the Mexican guideline NOM-001-SEMARNAT (1000 NMP of FBC per 100 mL and 5 helminth ova as monthly average in water used for not restricted irrigation). A fraction of the wastewater discharge into streams and rivers is used for irrigation of agricultural lands, while other is lixiviated to subsoil and could eventually polluted groundwater. The waste water treatment before its discharge to the rivers is recommended.

Palavras-chave : wastewater; biological pollution; urban effluents.