The protective nature of Chironomus luridus larval tubes against copper sulfate.

The objective of this study was to determine whether the tubes in which Chironomus larvae dwell protect them against chemical toxicants. A laboratory culture of an Israeli benthic midge, Chironomus luridus, was exposed to copper sulfate. Two conditions were tested in bioassay experiments: larvae within silt tubes and larvae without tubes. The non toxic, anionic, fluorescent dye, fluorescein, was used to examine the effect of sub-lethal copper sulfate concentrations on the permeability of cuticular, gill and gut epithelia of the chironomids. Increased cell permeability, which is the cause of cell damage, was reflected by an increase in fluorescence intensity. Following exposure to copper sulfate, higher fluorescence was found in different body compartments: midgut, hindgut, tracheal gills, fat body and muscles, and the Malpighian tubules. The effect was significantly higher in tube-free larvae when compared to silt tube dwelling larvae. We conclude that in addition to its other functions in feeding, respiration, and anti-predation shelter, the Chironomus luridus tube protects its inhabitant from toxins such as copper sulfate.

Chloramine and copper sulfate as control agents of planktonic larvae of Chironomus luridus in water supply systems.

The latest approach to control of midge larvae in drinking-water supplies is suppression of the planktonic 1st-stage larvae, by using 2 disinfectants, chloramine and copper sulfate. The median lethal concentration for 24-h exposure of the 1st-stage larvae of Chironomus luridus to chloramine and copper sulfate individually was 0.51 and 0.38 mg/liter, respectively. The increase of copper sulfate to 0.5 mg of copper per liter to water containing chloramine (0.5 mg/liter) created a synergistic reaction that resulted in 96% (+/-8% SD) mortality of the planktonic larvae. This treatment may serve as an effective control of 1st-stage larvae in municipal drinking-water supplies.

Shock chloramination: potential treatment for Chironomidae (Diptera) larvae nuisance abatement in water supply systems.

In the early 1990s, infestations of midge larvae (Chironomidae, Chironomus sp.) were discovered in the potable water system of Tel Aviv, Israel. Control measures, such as draining and cleaning tanks, spraying water into the tank's air space, and electrocution traps of midge adults, were either inadequate or ineffective. In this system, monochloramine concentrations of up to 0.75 mg/liter are used routinely as a secondary disinfectant. This chemical was tested in the laboratory as a toxicant 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 Chloramination treatment program. Tanks were partially drained until they contained only 20 cm of water and were then temporarily disconnected. Chloramine was added to this water to produce a concentration of approximately 70 mg/liter for 1-2 h. Subsequently, all dead chironomids were flushed out, and the tank was refilled to attain the operational volume of water. A 2nd identical treatment of water in the tank was suggested 7 d later to kill midges from reproductive adults and egg-masses that survived the 1st 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 effectively prevent midge outbreaks in Israel's drinking water supply system during the height of the summer.

Metabolism of parathion and brain cholinesterase inhibition in aroclor 1254-treated and untreated Caspian terrapin (Mauremys caspica rivulata, Emydidae, Chelonia) in comparison with two species of wild birds.

The mean level of PCB residues in the liver of the Caspian turtle collected in nature was 23 ppm, or approximately 20-fold greater than that detected in the two bird species tested. Treatment of the turtles with aroclor 1254 resulted in a 30-fold increase in the level of PCB residues in the liver but did not cause any increase in the content of cytochrome P-450 and the desulfurase activity of this hemoprotein. The Ki value for acetylcholinesterase inhibition by paraoxon in brain homogenate of the Caspain terrapin was 3 and 2 orders of magnitude higher than that found in the African bulbul and the barn owl, respectively.

Pesticide residues in fish and aquatic invertebrates.

Over the past 6 years a great number of fish and aquatic invertebrates from experimental and commercial fishponds have been analyzed for the presence of organochlorine insecticides and polychlorinated biphenyls (PCBs). Invariably, all specimens contained DDE and PCBs and in many instances also DDT, DDD and BHC isomers. A study of the kinetics of the organophosphorus compound parathion in an experimental fishpond ecosystem revealed a rapid bioconcentration of the chemical in algae, zooplankton, aquatic invertebrates and fish. The time-course of parathion disappearance showed an exponential type decline of the chemical over a period of three weeks.