Dhaka, May 26 (BDNEWS) – During future episodes of flooding in Bangladesh, resources should not be spent promoting tube well treatment with shock chlorination, an ICDDR,B study suggested.
The study findings demonstrate that chlorine shock treatment of inundated tube wells in Bangladesh three to six weeks after flooding does not improve the bacteriologic quality of tube well water and so would not be expected to improve public health.
"This technique was ineffective probably because the active chlorine did not have sufficient contact with contaminating bacteria. A higher dose of bleach and/or a larger volume of solution possibly with a longer dwell time might improve the efficacy of treatment, but these changes may not make much difference," it said.
The study was conducted in Brahmanbaria sadar upazila, an area heavily affected by the flooding.
In response to severe flooding in July and August 2004, UNICEF collaborated with the Department of Public Health Engineering of Bangladesh government to disinfect flooded tube wells using chlorine shock treatment. ICDDR,B investigated the water quality of the submerged tube wells, and the effect of tube well pumping and shock chlorination on improving bacteriological quality.
A bleach solution poured in the top of a tube well and allowed to sit for 30 minutes would not be expected to diffuse far into the surrounding aquifer that the tube well draws water from.
"Moreover, the source of contamination of these tube wells is unknown. The study team noted that many tube wells were placed within ten meters of a latrine or highly contaminated pond. Even a high dose shock treatment with chlorine would not be expected to effectively treat a tube well drawing water from a sewage-contaminated aquifer," the study said.
"The public health threat represented by submerged tube wells is unclear. Tube well water is not sterile," the study said.
In one study in Matlab, Bangladesh, three of five intensively studied tube wells were contaminated with thermotolerant coliforms. All of the tube wells had multiple other microorganisms present. In a larger study of 105 tube wells in Matlab, 13 (12%) were contaminated with thermotolerant coliforms.
The study was powered to identify an 80% success rate in decontamination with chlorine shock treatment. A 0% success rate was observed, 77% of wells were contaminated before shock treatment and 77% of these wells were contaminated after shock treatment.
It is possible that there is a smaller, but non-zero effectiveness of chlorine shock treatment that this small sample size was insufficient to detect. However, a small effect in improving water quality would be expected to have a small health impact, it opined.
"If tube well submersion is believed to represent a substantial public health threat, then an applied research program to develop and evaluate methods of tube well treatment should be undertaken," the study suggested.
BDNEWS/1524 hrs
