Effect of Temperature and pH on the Toxicity of Monochloramine to the Asiatic Clam

Abstract

The Asiatic clam (Corbicula fluminea) has become a pest to many users of freshwater transmission systems. Monochloramine has been suggested as a biocide because it is effective and the formation of trihalomethanes is low (see the article on page 53 of this issue). Flow‐through aquariums, a laboratory incubator, and a pilot‐scale pipeline were used to show that monochloramine concentrations between 1 and 10 mg/L effectively killed juvenile clams over a wide range of water temperatures, with mortality increasing significantly with temperature. The reduction in clam mortality as water temperature decreases can be overcome by corresponding increases in biocide concentration. An equation is provided that predicts the kill that would be achieved at a given biocide residual and water temperature. The pH did not affect the efficacy of the biocide.

The effect of dissolved oxygen, sediment, and sewage treatment plant discharges upon growth, survival and density of Asiatic clams

“…Less than 5% of the TRC was measured as free residual chlorine (FRC) and the presence of high levels of NH 3 -N would strongly implicate that chloramine species comprised the majority of TRC. Monochloramine is as or more toxic to clams than free chlorine (Cameron et al, 1989b), perhaps because clams are less able to detect chloramine (Sappington, 1987). At sites 5 and 8, TRC was as high as 1.72 mg 1-'.…”

“…Still, secondary effects of temperature in the present study, such as greater sensitivity to chlorine, ammonia, and zinc is likely. These heightened sensitivities would be associated with greater metabolic activity' at higher temperatures (Belanger et al, in review;Cameron et al, 1989b).…”

Minimizing THM Formation During Control of the Asiatic Clam: A Comparison of Biocides

“…Mortality at targets 1 and 5 mg monochloramine/L was significantly lower during winter (17-18°C) and summer (23-28°C) ( Table 2). 36 The LT50s were much lower, on average, than for other biocides, except chlorine dioxide.…”

“…Dye studies demonstrated that 90 percent of the solution in the vials was exchanged within 1 h, ensuring rapid exposure of juvenile clams to biocides. 36 The vials were removed from the aquariums and the number of dead and alive juveniles was counted under a dissecting microscope at 3-, 12-, or 24-h intervals. The surviving clams were identified by presence of foot movement, ciliary action, or heartbeat.…”

“…Target biocide residual concentrations were arbitrarily chosen as 1,2.5, 5, and 10 mg/L; refine ment of the concentration of the selected biocide is reported in the article beginning on page 62 of this issue. 36 Because of various water quality considerations, residual concentrations of biocides > 20 mg/L were not studied.…”