The Vembanad lake has been highly contaminated with faecal waste as a recent international study has recorded E.coli contamination of alarming levels in the waterbody.
The first four months of the 2018 monsoon saw an E.coli count at 16,631 cells in one millilitre of lake water. The World Health Organisation (WHO) guidelines for coastal and freshwater had noted there was a 10% chance of gastrointestinal illness from exposure to water exceeding E. coli abundance of 5 colonies per millilitre.
The study was jointly carried out by the National Institute of Oceanography (NIO), Kochi Regional Centre, Plymouth Marine Laboratory, UK, Nansen Environmental Research Centre India, and the Central Marine Fisheries Research Institute, Kochi. The water quality of the Vembanad lake was monitored for a year prior to the lockdown and immediately after the lockdown, so that the impacts of the 2018 floods and the pandemic-induced lockdown in 2020 on distribution of faecal contaminants in the lake could be assessed.
E. coli counts in the lake are consistently higher than the WHO threshold, irrespective of the season. However, during the lockdown period, there was 99.8% decrease in the average abundance of E. coli, said A. Abdulaziz of NIO, who was the lead author of the scientific paper ‘The distribution of faecal contamination in an urbanised tropical lake and incidence of acute diarrhoeal disease.’
Shubha Sathyendranath, V. Syam Kumar, Nandini Menon, and Grinson George were among the researchers who carried out the year-long analysis
More than 50% of E.coli isolates from the lake showed varying resistance against 12 antibiotics including Erythromycin, Moxifloxacin, Gatifloxacin, Trimethoprim, and Gentamicin, which spoke about the anthropogenic role on the prevalence of faecal contaminants, according to researchers.
Discharge of septage
Direct discharge of septage from commercial and residential buildings and tourist boats and unlawful dumping of toilet waste and solid waste might have contaminated the waterbody. Monsoon showers carried the maximum load of septage to the lake system. Analysis revealed that faecal contamination was prevalent throughout the year, which increased during the southwest monsoon, noted the paper.
Leakage from the sewage treatment systems, including septic tanks, may find its way to the waterbody during the rainfall period. Faecal contamination in the soil could get washed down into the lake during the initial days of rain, the research paper pointed out.
The opening months of the monsoon period also recorded high incidents of Acute Diarrhoeal Diseases (ADD) in Ernakulam, Alappuzha, and Kottayam districts. Around 4,000 cases of ADD were recorded in these districts during the first half of the southwest monsoon season, which coincided with the high levels of faecal pollution in the lake, the researchers noted.
There was not even a single instance during the study period when the abundance of E. coli in the water column of the lake dropped below detectable limits or when no ADDs were reported, noted the paper.
