SHOCK CHLORAMINATION - POTENTIAL TREATMENT FOR CHIRONOMIDAE (DIPTERA)LARVAE NUISANCE ABATEMENT IN WATER-SUPPLY SYSTEMS

In the early 1990s, infestations of midge larvae (Chironomidae, Chiron omus sp,) were discovered in the potable water system of Tel Aviv, Isr ael. Control measures, such as draining and cleaning tanks, spraying w ater into the tank's air space, and electrocution traps of midge adult s, were either inadequate or ineffective. In this system, monochlorami ne concentrations of up to 0.75 mg/liter are used routinely as a secon dary disinfectant. This chemical was tested in the laboratory as a tox icant of midge larvae. The mortality of 4th instar midge larvae after short exposure to high chloramine concentrations (LC50 values of 32 mg /liter for 75 min) suggested the efficacy of instituting a Shock Chlor amination treatment program. Tanks were partially drained until they c ontained only 20 cm of water and were then temporarily disconnected. C hloramine was added to this water to produce a concentration of approx imate to 70 mg/liter for 1-2 h. Subsequently, all dead chironomids wer e flushed out, and the tank was refilled to attain the operational vol ume of water. A 2nd identical treatment of water in the tank was sugge sted 7 d later to kill midges from reproductive adults and egg-masses that survived the Ist treatment. This treatment program was tested in commercial covered tanks and gave complete control of these pests for 6-10 wk. These results suggest that this treatment program may effecti vely prevent midge outbreaks in Israel's drinking water supply system during the height of the summer.