Abstract

MENDEZ NOVELO, Roger Iván; SAN PEDRO CEDILLO, Liliana; CASTILLO BORGES, Elba René  and  VAZQUEZ BORGES, Elizabeth. Modeling of holding time of water biological samples. Rev. Int. Contam. Ambient [online]. 2010, vol.26, n.4, pp.327-335. ISSN 0188-4999.

According to standard analytical methodologies, in order preserve water samples for microbial determination, they must be maintained under 10 °C for a maximum period of 6 hours for non-drinking water and 30 hours for drinking water. Although there is not an explicit reference to the water organic content, the difference between recommended preservation times could be related with it. Therefore, water samples with low organic content can be preserved for longer periods than those with a higher content. Several samples of water with different organic content (domestic wastewaters, from slaughterhouses and poultry farms, and from shallow wells) were analyzed. Models were developed in order to determine indicator organisms in CFU/100 mL (total and faecal coliforms, and enterococcus) as a function of BOD₅. The assessment was carried out 6 to 48 hours after sampling. It was found that high BOD₅ concentration in water is not a decisive factor when indicator organisms in CFU/100 mL are to be estimated (there is not a significant difference between total or faecal coliforms, neither between enterococcus between 0 and 48 hours). Nevertheless, there is a significant difference between total coliforms in CFU/100 mL when determined at 0 and 6 hours. This contradicts the established in several analytical methods. Samples for faecal coliforms determination can be preserved up to 6 hours, but at 18 hours there is a significant difference for results obtained in CFU/100 mL. For enterococcus, there is no significant difference in preservation between 0 and 48 hours.

Keywords : sample preservation; faecal coliforms; total coliforms; enterococcus; pathogen microorganisms; bacteria.

        · abstract in Spanish     · text in Spanish     · Spanish ( pdf )