Fig. 5. (a) Labile Cu pools and (b) Cu sorbed by the resin from the water extract (E_r) as a function of soil pH and treatments. Arrows indicate the control treatment. Error bars represent ±SE of three replicates. RG, red gypsum; RM-H and RM-UK, red mud from Hungary and the United Kingdom, respectively; WTS, water treatment sludge.