Occurrence of Merismopedia minima in a Drinking Water Treatment Plant in Sohag City and Removal of Their Microcystins by Sediments

Abstract

C YANOBACTERIA in drinking water are a major problem that threatens humans, animals and plants, especially if they produce toxins.This study aimed to remove cyanobacterial species, especially Merismopedia mianima and their microcystins (MCs) during the treatment process of drinking water. Water samples were collected from raw water, after each process and from the final treated water including coagulation, sedimentation, filtration and disinfection as well as from the final treated during the study period (May-December 2019). In all of these samples, M. minima was detected with an average cell count of 80-2200 cells/ mL.This increase in algal count may be due to the warm season when the temperature was favorable for cyanobacterial growth (blooming). Results also showed that traditional treatment methods could remove some cyanobacterial species but are ineffective in for completely removing MCs produced by M. minima, which was isolated even from the final stage of drinking water treatment. Furthermore, MCs were determined by High-Performance Liquid Chromatography (HPLC) analysis and the particulate MCs concentration of M. minima was found to record 500μg MCs/L (2.27pg/cell). Extracellularly released MCs were also not completely removed and remained at high concentrations of 0.74-1.47μg/L which exceeded the limit proposed by the World Health Organization (WHO= 1µg/L).The toxin concentration was mitigated to levels less than WHO limits when water sediments were used to remove MCs. Therefore, this study recommends using sediments to remove cyanobacteria and their cyanotoxins from water plants, which is an inexpensive method especially for the developing countries.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

“…Although it can also be found in wet soil and other moist habitats, Merismopedia is primarily found in oceans, seas, and other aquatic environments. Additionally, Merismopedia is frequently linked to cyanobacterial mats because of its ability to adapt to different light, temperature, and salt concentrations [ 71 , 72 ].…”

“…It can grow rather quickly under ideal circumstances, such as temperatures between 25 and 35 °C and pH levels between 6 and 8.1. It is crucial to understand where Merismopedia is typically located and how to recognize it because this tiny but mighty genus of cyanobacteria can create toxins that can be dangerous to people if swallowed or even inhaled [ 71 , 72 , 73 ].…”

Chroococcus minutus Growth and Toxicity Inhibition Using Extremely Low-frequency Electromagnetic Fields

“…Multiple species of cyanobacteria produce potent toxins that pose a threat to humans and aquatic organisms (Neilan, 2013). According to a previous study, the toxic cyanobacterium Merismopedia minima in in drinking water was not eliminated by conventional water treatment methods and poses a threat to humans, animals and plants, particularly if they produce toxins (Bakr, 2022). Chroococcus minutus (Kützing) Nägeli is a unicellular cyanobacterium that produces microcystin (MCs) (Mohamed, 2016b;Mohamed et al 2022).…”