The objective of this research was to determine the effect of chlorine and other disinfecting agents on Giardia lamblia cyst viability. The agents studied included free residual chlorine and six different methods recommended for emergency disinfection of small quantities of water. The effect of chlorine concentration on Giardia lamblia cyst viability was tested under a variety of conditions. At 25C, 1.5 mg/l chlorine for 10 min killed all cysts at pH 6, 7, and 8. At 15C, 2.5 mg/l for 10 min killed all cysts at pH 6; but at pH 7 and 8, small numbers of viable cysts remained after 30 min, but not after 60 min. At 5C, 1 mg/l chlorine for 60 min failed to kill all cysts at any pH tested. Contact with 2 mg/l chlorine for 60 min killed all cysts at pH 6 and 7, but not at pH 8. A chlorine concentration of 4 mg/l killed all the cysts at all three pH values after 60 min, but not after 30 min. A chlorine dose of 8 mg/l killed all cysts at pH 6 and 7 aftr 10 min contact and at pH 8 after 30 min. The ability of six small-quantity water disinfection methods to destroy Giardia cysts was also studied. Two water qualities (cloudy and clear) and two temperatures (3 and 20C) were tested. At 20C, using cloudy and clear water, all of the methods proved completely effective. But, at 3C in cloudy water, one method (saturated iodine) was not completely effective, and in clear water, four methods (bleach, Globaline, tincture of iodine and saturated iodine) failed to destroy all the cysts. The failure of these methods appeared to be related to either an insufficient halogen residual or contact time.

Caption title. "Sep. 1981." "EPA-600/2-81-174." Microfiche.