“Doubt has been cast on a much-lauded method of disinfecting water using only sunlight, after a study found that it doesn’t reduce diarrhoea among children in families using the technique” SciDev.net reports.
“Solar Water Disinfection (SODIS), a low-cost water purification method that uses only sunlight to disinfect water, is currently used by about three million people in 30 countries, according to the SODIS Reference Centre [at SANDEC] in Switzerland”.
“Laboratory and community studies have shown that the method is effective. But a PLoS Medicine study published [on 18 August 2009] on 22 rural communities in Cochabamba, Bolivia, found no significant reduction in diarrhoea among children aged five and under in families using SODIS”.
“The authors suggest that more research is needed into how the laboratory results can be replicated on the ground and until this is done they say that campaigners should be careful about advocating SODIS”.
“Mercedes Iriarte, co-author of the study and a researcher at the Water and Environmental Sanitation Centre of San Simón University, in Bolivia, told SciDev.Net that in the laboratory there is better control of all factors”.
“Iriarte says that in the laboratory, clean, clear, pH-neutral water is contaminated with known microorganisms to evaluate the method but that in the field researchers should consider other factors such as cloudiness of the water”.
“Margot Franken, a researcher with the environmental quality unit at San Andrés University in Bolivia, told SciDev.Net that low efficacy of the method could also result from inadequate exposure to sunlight”.
Compliance was also low, with only a third of families routinely treating their water in the recommended manner despite 80 per cent claiming to use SODIS at the beginning and end of the study and an intensive promotion campaign.
Link to full article in PLoS Medicine.
See a video about the study on SciVee.
Source: Cristina Pabón, SciDev.net, 31 Aug 2009
Earlier in 2009 Wolf-Peter Schmidt and Sandy Cairncross concluded that the widespread promotion of household water treatment (HWT) is premature given the available evidence. This is echoed by the latest review of impact evaluations examining effectiveness of water, sanitation and hygiene (WSH) interventions by the International Initiative for Impact Evaluation (3ie).
In a comment about the study on its website, the SODIS Reference Centre says that “numerous studies have reported health benefits of SODIS when it is correctly and consistently used”. They cite the example of a study where “the incidence of cholera during an epidemic in Kenya was 88% lower among SODIS than non-users”.
“A well-known weakness of the SODIS process is that it is often not used consistently or is used to treat only a fraction of the drinking water consumed”, the statement continues. “Beneficial health impacts associated with the use of SODIS may also be compromised by poor sanitation and hygiene. Nonetheless, we feel that people should not be discouraged from continuing to use SODIS or from adopting it unless an alternate supply of safe drinking water is available”.
The SODIS Reference Centre/Sandec has also had to respond to “allegations circulating in a number of print media in developing countries on the carcinogenic risk of (re-)using PET bottles”. These “unfounded media reports” are drawn from research that show that antimony and phthalic acid and phthalate esters can leach from PET bottles. Sandec conducts its own study, together with Empa (Swiss Federal Laboratories for Materials Testing and Research) on “the migration of organic compounds – with special focus on plasticisers – into the water contained in PET bottles bottles under typical SODIS conditions”. “According to the results of this study, the risk of negative health effects caused by reused PET bottles for SODIS treatment is negligible”. SANDEC plans to repeat the study in India “to confirm the harmless nature of the technology in a country where media reports on the dangers of PET bottles are particularly widespread”.
Source: Samuel Luzi, Reuse of PET Bottles for SODIS – Blessing or Curse?, Sandec News, no. 10, July 2009
But SODIS is not off the hook yet, as a new danger is looming. In April 2009, scientists at Goethe University found that PET plastics may contain hormone-disrupting chemicals that leach into the water, Discovery News reported. According to researchers, it now appears that some as-yet-unidentified chemicals in PET plastics have the potential to interfere with estrogen and other reproductive hormones in the same manner that bisphenol A (BPA) and phthalates are suspected of doing.
