Occurrence of toxic cyanobacteria and microcystin toxin in domestic water storage reservoirs, Egypt Zakaria A. Mohamed, Mohamed Ali Deyab, Mohamed I. Abou-Dobara and Wesam M. El-Raghi ABSTRACT Residents in many developing countries store treated drinking water in tanks or reservoirs because of intermittent and infrequent water supplies. Many studies have focused on bacterial contamination of domestic reservoir waters, the cyanobacterial and algal contamination is largely unexplored. Therefore, the present study investigates toxic cyanobacteria and their microcystin (MC) toxins in some domestic water storage reservoirs in Egypt as an example for developing countries. Three phytoplankton groups including cyanobacteria, green algae and diatoms were found in domestic reservoirs. Among these species, the toxic cyanobacterium Microcystis aeruginosa had the highest cell density during warm months (4.2–5.92 cells × 10 6 L –1 ). This cell density increased along the time, indicating that environmental conditions in these reservoirs promoted the proliferation of this species. Intra- and extracellular MCs were also detected in reservoir waters at concentrations of 3.5–40 and 1–7.6 μgL –1 , respectively, exceeding the WHO guideline limit of 1 μgL –1 for these toxins in drinking water. Heterotrophic bacteria were found in association with cyanobacteria in reservoir waters. The study suggests that treated-water storage reservoirs should be monitored for the presence of toxic cyanobacteria to protect the public from exposure to their potent toxins. Zakaria A. Mohamed (corresponding author) Department of Botany and Microbiology, Faculty of Science, Sohag University, Sohag, Egypt E-mail: mzakaria_99@yahoo.com Mohamed Ali Deyab Mohamed I. Abou-Dobara Wesam M. El-Raghi Botany Department, Faculty of Science, Damietta University, Damietta, Egypt Key words | cyanobacteria, domestic reservoirs, drinking water, hygienic risk, microcystins INTRODUCTION In developing countries, the intermittent and infrequent water supply necessitates the need to store water in tanks or reservoirs for drinking and other purposes (Chia et al. ). In Egypt, most of these reservoirs are found above buildings and houses and may therefore be exposed to microbial contamination by receiving contaminated water from drinking water treatment plants or through wind carry- ing the spores and akinetes of microorganisms, which may germinate and grow under suitable conditions (Codony et al. ). However, the latter contamination source is less important as it occurs only when the reservoirs are left open, and this can be easily manipulated and overcome. The breakthrough of microorganisms into storage reservoirs from drinking water treatment plants is of particular concern, as it indicates the ineffectiveness of conventional treatment methods for microbial removal. Cyanobacteria are one of the pathogenic agents recognized in water (WHO ). The presence of cyanobacterial cells in drink- ing water reservoirs is of particular concern for human health, due to the ability of some species to produce taste and odorous substances and potent cyanotoxins including neurotoxins, hepatotoxins and skin irritant toxins (Codd et al. ). Cyanotoxins are produced by both freshwater and marine cyanobacteria (Mohamed & Al-Shehri ). Microcystins (MCs) are the most common cyanobacterial hepatotoxins in freshwaters worldwide with increasing health implications, and hence the World Health Organiz- ation (WHO ) has established a provisional guideline 431 © IWA Publishing 2016 Journal of Water Supply: Research and Technology—AQUA | 65.5 | 2016 doi: 10.2166/aqua.2016.115 Downloaded from https://iwaponline.com/aqua/article-pdf/65/5/431/398463/jws0650431.pdf by guest on 06 June 2020