Stability of Lead Immobilized by Apatite in Lead-Containing Rhizosphere Soil of Buckwheat (<i>Fagopyrum esculentum</i>) and Hairy Vetch (<i>Vicia villosa</i>)

<div><p>This study conducted plant growth experiments using a rhizobox system to understand the growth of buckwheat and hairy vetch as well as the stability of lead immobilized by hydroxyapatite (HAP) in the lead-containing rhizosphere soil. The shoot dry weight of buckwheat did not significantly differ between the lead-containing rhizosphere soil with and without HAP, whereas that of hairy vetch with rhizosphere soil without HAP was reduced. Lead was not accumulated from the rhizosphere soil to the shoots of either plant when HAP was added. The percentage of each lead fraction in sequential extraction was approximately the same through the 3 mm of rhizosphere soils from the root surface and non-planted soil, with and without the addition of HAP. For hairy vetch, the amount of water-soluble lead in the HAP-added rhizosphere soil within 3 mm thickness from the root surface did not increase. However, for buckwheat, the amount of water-soluble lead in the HAP-added rhizosphere soil 1 mm from the root surface increased to the same level as that in the non-planted soil without HAP. Our results suggest that when applying phytostabilization combined with apatite to lead-contaminated soil, the plant that cannot re-mobilize lead should be selected.</p></div

Reproducibility of up-flow column percolation tests for contaminated soils

<div><p>Up-flow column percolation tests are used at laboratory scale to assess the leaching behavior of hazardous substance from contaminated soils in a specific condition as a function of time. Monitoring the quality of these test results inter or within laboratory is crucial, especially if used for Environment-related legal policy or for routine testing purposes. We tested three different sandy loam type soils (Soils I, II and III) to determine the reproducibility (variability inter laboratory) of test results and to evaluate the difference in the test results within laboratory. Up-flow column percolation tests were performed following the procedure described in the ISO/TS 21268–3. This procedure consists of percolating solution (calcium chloride 1 mM) from bottom to top at a flow rate of 12 mL/h through softly compacted soil contained in a column of 5 cm diameter and 30 ± 5 cm height. Eluate samples were collected at liquid-to-solid ratio of 0.1, 0.2, 0.5, 1, 2, 5 and 10 L/kg and analyzed for quantification of the target elements (Cu, As, Se, Cl, Ca, F, Mg, DOC and B in this research). For Soil I, 17 institutions in Japan joined this validation test. The up-flow column experiments were conducted in duplicate, after 48 h of equilibration time and at a flow rate of 12 mL/h. Column percolation test results from Soils II and III were used to evaluate the difference in test results from the experiments conducted in duplicate in a single laboratory, after 16 h of equilibration time and at a flow rate of 36 mL/h. Overall results showed good reproducibility (expressed in terms of the coefficient of variation, CV, calculated by dividing the standard deviation by the mean), as the CV was lower than 30% in more than 90% of the test results associated with Soil I. Moreover, low variability (expressed in terms of difference between the two test results divided by the mean) was observed in the test results related to Soils II and III, with a variability lower than 30% in more than 88% of the cases for Soil II and in more than 96% of the cases for Soil III. We also discussed the possible factors that affect the reproducibility and variability in the test results from the up-flow column percolation tests. The low variability inter and within laboratory obtained in this research indicates that the ISO/TS 21268–3 can be successfully upgraded to a fully validated ISO standard.</p></div

Diagram of the up-flow column percolation test (Modified from Naka et al., [16]).

<p>Diagram of the up-flow column percolation test (Modified from Naka et al., [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178979#pone.0178979.ref016" target="_blank">16</a>]).</p

Experimental conditions.

<p>Experimental conditions.</p

Reproducibility of up-flow column percolation tests for contaminated soils - Fig 6

<p>Difference in results within laboratory for Se, As, Cu, Mg, F and DOC (a) concentrations and (b) cumulative releases for Soil II; difference in results within laboratory for Se, As, Cu and B (c) concentrations and (d) cumulative releases for Soil III. The “difference between results” and “difference between cumulative results” corresponds to the difference between concentrations and cumulative releases, divided by their mean and expressed in terms of percentage.</p

Boxplot of parameters: pH, EC, and concentrations of Cu, As, Se, Cl, Ca and F for Soil I.

<p>Whiskers represent mean ± standard deviation values.</p

Difference in results within laboratory for Cu, Se, As and F concentration for Soil I.

<p>The “difference within laboratory” corresponds to the difference between the results obtained in the same laboratory, divided by their mean and expressed in terms of percentage.</p

Boxplot of cumulative releases of Cu, As, Se, Cl, Ca and F for soil I.

<p>Whiskers represent mean ± standard deviation values.</p