Events linked to Geosmin and 2-methylisoborneol (2-MIB) in a Water Supply Source in the State of Rio de Janeiro, Brazil: a case study

Abstract

Tastes and odors in tap water are problems faced by water companies all over the world, with complaints from consumers especially during the summer when cyanobacterial blooms occur that produce compounds such as geosmin and 2-methylisoborneol (2-MIB).  We analyzed data on the intensity of taste and odor, and total concentration of the substances geosmin and 2-MIB, present in drinking water and raw water collected by the sanitation company that supplies the metropolitan region of the state of RJ/Brazil, during water crises in the year 2020, and in the new event of 2021, despite the previous warnings made by experts. Statistical and correlation analysis of the public data, and metagenomic analysis of the raw water captured from the Guandu basin in the year 2020 were performed. Organoleptic data allowed us to signal the presence of these compounds in drinking water, the values of the intensity of taste were more times above the MPV of the Brazilian legislation, with the average of the data for 2020 being 37.5 and in the following year this average was 5 times lower, indicating that the measures to remove the compounds were more effective, but did not eliminate the problem. For the year 2020 there was a linear correlation of 0.97 between the taste organoleptic standard and the total concentration of the compounds. The metagenomic data of the raw water of the year 2020, related to the genes mtf, mic and glys indicated that the substance responsible for the taste and odor was 2-MIB, since the read rate for it was higher, both in the first visit and only in the second visit, when there was still perception of intensity of taste and odor. Modifications in the surveillance system of the quality of the water taken and consumed need to be adopted to circumvent the problems of cyanobacterial proliferation in the Guandu basin, since conditions favorable to blooms will occur as long as the sanitation problems in this watershed are not solved.