Growth response of four species of soil algae to monocrotophos and quinalphos

Abstract

Scenedesmus bijugatus, a green alaga, and three blue-green algae (Cyanobacteria)—Synechococcus elongatus, Nostoc linckia and Phormidium tenue—all isolated from a black soil, were tested for their growth response to monocrotophos and quinalphos, using either cell number or chlorophyll a as toxicity criteria. Monocrotophos was significantly toxic above 20 μg ml⁻¹ to S. bijugatus, but enhanced the growth of S. elongatus, at all concentrations (5 to 100 μg ml⁻¹) tested. At 100 μg ml⁻¹, monocrotophos was toxic to N. linckia and, at 50 and 100 μg ml⁻¹, to P. tenue, but lower concentrations increased the growth of these two algae significantly. Quinalphos above 5 or 10 μg ml⁻¹ exhibited an algistatic effect S. bijugatus, S. elongatus and N. linckia and was algicidal to them at the higher concentrations. Quinalphos, however, resulted in a significant enhancement in the growth of P. tenue at all concentrations.