Use of solar radiation in disinfecting contaminated drinking water with cysts of Giardia lamblia

Abstract number: 1733_22

Zinyowera S., Midzi N., Muchaneta-Kubara C., Simbini T., Mduluza T., Robertson V.


1. To determine whether solar radiation is capable of inactivating cysts of Giardia lamblia.

2. To analyse use of different types of containers.

Methods: This is an experimental study. One hundred stool specimens for the isolation of G. lamblia cysts were collected from pupils of grades one to five from a rural primary school in Zimbabwe. Permission to conduct the study and collect specimens from students was granted including consent from the participants themselves. Specimens were screened for the presence of G. lamblia. They were concentrated using sheaters solution and purified using the discontinuos percoll gradient centrifugation method. Protozoan parasites were then preserved in distilled water, quantified using a hemocytometer, then stored at 4°C.

Empty 2L polyethelyne terephthalate (PET) plastic containers were painted black on one side including a 2L high density polypropelene plastic containers. One thousand eight hundred millilitres of tap water were placed in the 2L containers. Initial temperature of each container was measured. One milliliter of the parasite suspension was added to each bottle. The containers were shaken to aerate the water. These were then placed outside on a black surface with the clear side facing the sun.

Temperatures were recorded hourly and at each hour, water in a PET bottle painted black on one side would be spun at 500 g for 3 minutes using 50 ml VWR centrifuge tubes. One ml of the pooled sediment was stained with the vital dyes 0.4% trypan blue, 0.3% Congo red and the flourogenic dyes propidium iodide (PI) and 4,6 diamidino-2-phenylindole dihydrochloride (DAPI) were also used.

Results: When there was full sunshine 95% of parasites would be dead after 3 hours at temperatures of 46°C, and after 4 hours when the temperature was above 50°C, 100% of G. lamblia cysts were non-viable. During cloudy conditions when the water temperature was 38°C, 26% of parasites were non-viable. PET bottles painted black on one side absorbed more heat than those not painted including the high density polypropelene plastic containers. The open PET bottles did not kill parasites completely as the water temperature did not rise rapidly.

Conclusion: Solar radiation is effective in killing G. lamblia cysts. More assays need to be carried out to find out if it is the UVA produced by the sun or the heat from the sun that is capable of disinfecting these parasites.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
Back to top