Aims. Root elongation tests are sensitive bioassays for testing metal toxicity in nutrient solutions. The metal speciation and, hence, metal exposure conditions are little controlled in the traditional set-up. A resin buffered solution system was developed to overcome this issue.
Methods. Barley (Hordeum vulgare L.) root elongation was tested in aerated 140 mL solution batch systems supplied with 3.3 g Dowex resin for two plants. Copper toxicity was measured in presence or absence of the resin (+R/-R) and in presence or absence of a metal complexing ligand (+NTA; nitrilotriacetic acid/-NTA). In addition, the toxicity in the traditional set without resin and with daily solution replacement was included as a reference.
Results. Metal desorption from the resin is fast in these systems (k= 0.82 h-1). Total dissolved Cu roughly halved during 4 days in –R/-NTA systems due to uptake, while it increased by 30 % in the +R/-NTA, probably due to complexation reactions by root-derived molecules. The toxicity (50 % reduction in root length, EC50) of the initial free Cu2+ was equal in all resin or chelate buffered systems and in the solutions with daily replacement, whereas this threshold was significantly larger in the –R/-NTA due to Cu2+ uptake and complexation reactions.
Conclusion. The resin method is a convenient system for high throughput screening of metal toxicity and avoids uncertainties in metal speciation inherent to chelator buffered systems. Details are given how to prepare the resin to obtain a target metal ion activity.