Investigation of mutagenicity of solar disinfected (SODIS) water stored in plastic bottles

Abstract

Waterborne illnesses associated with poor sanitation are a major problem in Africa’s major slum, Kibera. Microbiologically the Solar Disinfected (SODIS) water is safe but the potential mutagenicity of such water is of great concern. When water contained in polyethylene terephthalate bottles is treated using solar, the additives (plasticizers) in the plastic bottle may easily hydrolyze, photochemically degrade and leach into the disinfected water in minute quantities that may be responsible for mutagenicity. In this study, five phthalate esters (dimethyl phthalate, diethyl phthalate, di-n-butyl phthalate, benzyl butyl phthalate and bis-2ethylhexyl phthalate) and bis-2-ethylhexyl adipate residues was liquid- liquid extracted from samples using organic solvents while detection and quantification were done at intervals using a Gas chromatograph mass spectrometer (GC/MS). The study simultaneously evaluated the mutagenicity of the unconcentrated SODIS samples using the Ames Microplate Mutagenicity test with tester strains TA98 and TA100 with and without metabolic activation. A sample was termed mutagenic if it recorded an average mutagenicity ratio ≥ 2.00. Samples were collected and analyzed for total coliform group of bacteria using the Multiple Tube Fermentation Technique. The complete test confirmed presence of fecal coliforms in the samples which upon a six hour exposure to solar reported an 87.37% antibacterial effect. Reported Mutagenicity ratio ranged from undetectable limits to 4.69±0.88 with samples having metabolic activation (72%) generally reporting a higher mutagenicity ratio than the corresponding samples without. Approximately 58% of samples with tester strain TA100 recorded a higher sensitivity to the Ames test than those with TA98. Household water registered the highest levels of both butyl benzyl phthalate (28.27±0.00µg/L) and bis-2ethylhexyl adipate (152.97±0.00µg/L) at the 30th and 60th days respectively. The Most significant Pearson’s correlations (0.99) were reported between levels of toxicity of Kibera house water and bis-2-ethylhexyl adipate at the 90th day. Results of this study reveal that the amount of plasticisers that leak from the PET bottles into SODIS water are generally low and calculated average daily intake of individual analytes are generally lower than reference doses. Hence in isolation, individual phthalate ester or bis-2-ethylhexyl adipate concentration cannot be entirely held responsible for the reported mutagenicity of the water. With respect to mutagenicity SODIS water stored in PET bottles is safe to use up to and including the 30th day after which such bottles should be discarded and replaced with new ones. Sustained monitoring of toxicity levels of drinking water stored in PET bottles between the 30th and the 60thday using automated or robot scoring is recommended to establish the exact day beyond which the bottle is unsafe to use