The pH dependent toxicity and bioaccumulation of chloroquine tested on S. viminalis (basket willow)

It is known that the uptake and accumulation of electrolytes is very sensitive to pH owing to the slower diffusion of charged compounds across membranes, and other factors such as the Nernst effect and the ion trap effect. However, the significance of pH to the bioaccumulation of electrolytes has only been investigated sparingly in practical laboratory experiments leaving limited data with which to confirm the accuracy of current modeling efforts in the area. The aim of this study was to examine the effects of pH on the the bioaccumulation and toxicity of the malaria drug chloroquine (a divalent weak base) on S. viminalis (basket willow). The transpiration of sprouted S. viminalis cuttings was monitored under the exposure of increasing concentrations (1, 10, 20, and 40 mg/L) of chloroquine at pH levels of 6, 7, 8, and 9. Solutions were buffered with phosphate (pH 6 and 7) and TRIS (hydroxymethyl) – aminomethane (pH 8 and 9). Concentrations were determined with spectrophotometer. Toxicity was derived from calculations of normalized transpiration over time, and RCF (root concentration factor) values were calculated. Increasing BCF values were found for increasing pH levels, and the toxicity was likewise seen to increase with increasing pH. These trends were in good agreement with the expected, and with the findings from other studies where uptake has been examined at various pH.