The Effect of Ambient Concentrations of Chlorate on Survival of Freshwater Aquatic Invertebrates

Abstract

Abstract Chlorate (ClO3-) is present in some pulp and paper mill wastewater as a byproduct of the use of chlorine dioxide in the bleaching processes. Chlorate is harmful to some species of algae and consequently research was undertaken to determine its impact on survival of freshwater aquatic invertebrates. Five species representing four orders of Insecta (Plecoptera: Isoperla transmarina (Newman); Ephemeroptera: Baetis tricaudatus Dodds and Tricorythodes minutus Traver; Hemiptera: Dasycorixa hybrida (Hungerford); and Coleoptera: Haliplus sp.) were exposed to 5.0, 50.0 and 100.0 mg L-1 chlorate for 10 days. The plecopteran Isoperla longiseta Banks was exposed to 0.5, 5.0 and 50.0 mg L-1 chlorate for 10 days. Survival of specimens exposed to chlorate did not differ significantly from that of the controls. The LC50 for Daphnia magna Straus, determined using the 48 h acute lethality test, was estimated at 3,162 mg L-1. Chlorate levels from a bleached kraft pulp mill in northwestern Alberta that employs 100% chlorine dioxide substitution in its bleaching process ranged from nondetectable. (<0.002 mg L-1) to approximately 75 mg L-1 in effluent at the point of entry to the river system. At 25 and 127 km downstream from the mill, highest levels of chlorate in water samples were 3.25 and 1.00 mg L-1, respectively. Comparisons of laboratory results with field measurements suggest that chlorate discharges from this pulp mill would have no adverse effect on the survival of the aquatic insect species evaluated here.