Naturally occurring soil organic compounds stabilize potentially toxic elements (PTEs) such as Cu, Cd, Pb, and Mn. The hypothesis of this work was that an insoluble glycoprotein, glomalin, produced in copious amounts on hyphae of arbuscular mycorrhizal fungi (AMF) sequesters PTEs. Glomalin can be extracted from laboratory cultures of AMF and from soils. Three different experiments were conducted. Experiment 1 showed that glomalin extracted from two polluted soils contained 1.6-4.3 mg Cu, 0.02-0.08 mg Cd, and 0.62-1.12 mg Pb/g glomalin. Experiment 2 showed that glomalin from hyphae of an isolate of Gigaspora rosea sequestered up to 28 mg Cu/g in vitro. Experiment 3 tested in vivo differences in Cu sequestration by Cu-tolerant and non-tolerant isolates of Glomus mosseae colonizing sorghum. Plants were fed with nutrient solution containing 0.5, 10 or 20 μM of Cu. Although no differences between isolates were detected, mean values for the 20 μM Cu level were 1.6, 0.4, and 0.3 mg Cu/g for glomalin extracted from hyphae, from sand after removal of hyphae and from hyphae attached to roots, respectively. Glomalin should be considered for biostabilization leading to remediation of polluted soils.

Soil solution chemistry is a powerful tool for studying many aspects of soil science. Among several isolation techniques, centrifugation appears most promising as a method of extracting the soil solution in the laboratory. However, some operational conditions must be defined. The present work reports the influence of sample storage on the observed composition of the soil solution of two Brazilian soils submitted to different managements. Since metal speciation in soil solution significantly influences metal bioavailability, a second experiment was conducted to evaluate the effects of storage on Fe, Al, and Mn speciation by size exclusion chromatography (HPLC-SEC). The results showed that the effects of soil handling prior to solution extraction had a significant effect on soil solution composition, mainly when the sample was dried and rewetted. Only the samples that were kept refrigerated (4 °C) for 15 days led to results comparable to those obtained from fresh soils. However, considering the patterns of the UV detection chromatograms and metal distribution, only field moist samples should be used in studies related to Al, Mn, and Fe speciation in the studied soils.