Evaluation of Phytoavailability of Heavy Metals to Chinese Cabbage (Brassica chinensisL.) in Rural Soils

This study compared the extractability of Cd, Cu, Ni, Pb, and Zn by 8 extraction protocols for 22 representative rural soils in Taiwan and correlated the extractable amounts of the metals with their uptake by Chinese cabbage for developing an empirical model to predict metal phytoavailability based on soil properties. Chemical agents in these protocols included dilute acids, neutral salts, and chelating agents, in addition to water and the Rhizon soil solution sampler. The highest concentrations of extractable metals were observed in the HCl extraction and the lowest in the Rhizon sampling method. The linear correlation coefficients between extractable metals in soil pools and metals in shoots were higher than those in roots. Correlations between extractable metal concentrations and soil properties were variable; soil pH, clay content, total metal content, and extractable metal concentration were considered together to simulate their combined effects on crop uptake by an empirical model. This combination improved the correlations to different extents for different extraction methods, particularly for Pb, for which the extractable amounts with any extraction protocol did not correlate with crop uptake by simple correlation analysis.

An evaluation of extractants for assessment of metal phytoavailability to guide reclamation practices in acidic soilscapes in northern regions

Abedin, J., Beckett, P. and Spiers, G. 2012. An evaluation of extractants for assessment of metal phytoavailability to guide reclamation practices in acidic soilscapes in northern regions. Can. J. Soil Sci. 92: 253–268. Although soil organic matter and nutrient bioavailability in metal-impacted soilscapes of Sudbury, Ontario, are potentially limiting full ecological recovery, total metal content was used as the critical driver for a 2008 ecological risk assessment. The current greenhouse study evaluated chemical extractants to predict bioavailability of nutrients and contaminant metals to indigenous grasses (Deschampsia). Single extraction methods (0.01 M strontium nitrate, water, 0.01 M calcium chloride, 0.1 M sodium nitrate, 1.0 M ammonium nitrate, 0.1 M lithium nitrate, 1.0 M magnesium chloride, 0.11 M acetic acid, 1.0 M ammonium acetate, 0.05 M ammonium-EDTA, pore water) were examined to assess availability of potentially phytotoxic metals and nutrients in smelter-impacted soils. Extraction procedures to predict phytoavailability were either soil concentration or plant tissue concentration and element dependent. Total and extractable metal concentrations were more correlated for regional contaminant metals (e.g., copper, lead, arsenic, selenium) released by the smelting industry than non-contaminant ones (e.g., iron, calcium, potassium, boron, zinc, molybdenum). The lack of relationship between total and extractable concentrations for most non-contaminant metals suggests total concentration is not a good indicator of phytoavailability for nutrient elements. Stronger correlations between shoot tissue and extractable concentrations were observed for less aggressive extractants (pore water, water, lithium nitrate) reflecting their suitability in predicting phytoavailability over most aggressive ones (except ammonium nitrate).

Heavy metal distribution, bioaccessibility, and phytoavailability in long-term contaminated soils from Lake Macquarie, Australia

This study was conducted to investigate the distribution, bioaccessibility, and phytoavailability of heavy metal(loids) in long-term contaminated soils within the vicinity of a lead (Pb) and zinc (Zn) smelter in Lake Macquarie, NSW, Australia. Thirty-two representative surface (0–100 mm) soils were collected from the region surrounding the smelter. The soils were analysed for aqua regia extractable heavy metals (Cu, Zn, Cd, Pb), bioaccessibility using a simplified physiological-based extraction technique (SBET), and phytoavailability using 1 m NH4NO3 extractions, together with key soil properties known to influence metal speciation and availability. The area was found to be potentially contaminated with heavy metals (Cu, Zn, Cd, Pb) with many soil samples exceeding the Australian Health Investigation Levels for ‘Standard’ residential areas. Lead bioaccessibility ranged from 32 to 100% of the total Pb concentration, with bioaccessibility increasing as metal loading increased. Heavy metal phytoavailability was strongly related to soil pH for Cu (r2 = 0.84, P < 0.001), Pb (r2 = 0.70, P < 0.001), and Cd (r2 = 0.66, P < 0.001), implying that the phytoavailability of these heavy metal was mainly governed by soil acidity. Most significantly, the presence of multiple metals was found to influence metal phytoavailability. For example, the presence of Pb significantly influenced the phytoavailability of Cd (r2 = 0.89, P < 0.001) and Zn (r2 = 0.78, P < 0.001) in mixed heavy metal contaminated soils.

Prediction of Zinc and Cadmium Phytoavailability Within a Contaminated Agricultural Site using DGT

Environmental Context.In some agricultural areas, soils are contaminated by trace elements. This contamination of cultivated soils may constitute a serious problem for human health through the accumulation of metals in the edible parts of crops. In order to assess the risk for human health associated with metal contamination of soil, we need to develop simple tools like Diffusive Gradients in Thin Films (DGT) for predicting crop metal accumulation. The present study focuses on an agricultural site contaminated with fallout from industrial dust and reveals that DGT could be a predictive tool of zinc accumulation in lettuce. Abstract.Risk assessment of metal contamination in cultivated soils needs to address metal phytoavailability. The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal phytoavailability in a wide range of soils. The present study has examined the ability of the DGT method to predict metal phytoavailability within a contaminated agricultural site. Lettuce (Lactuva sativa cv Appia) was grown in nine metal-contaminated soils differing mainly by their pH. Metal concentrations (Zn, Cd) in plant shoots were compared with total soil metal concentrations and free ion metal concentrations in soil pore waters, and effective concentrations, CE, measured by DGT. Plant Zn concentrations were highly related to CE, suggesting DGT can be a sensitive tool able to assess Zn phytoavailability within mildly contaminated agricultural soils. Plant Cd concentrations were less closely related to CE, signifying that processes other than Cd re-supply from the solid phase may occur during soil–plant transfer of Cd.

Biosolids conditioning and the availability of Cu and Zn for rice

Sewage treatment process is a factor to be considered for biosolid use in agriculture. The greatest sewage treatment facility of São Paulo State (Barueri/SP) altered in the year 2000 of its sludge treatment. The addition of ferric chloride and calcium oxide was substituted by the addition of polymers. This change can modify heavy metal phytoavailability. A green house experiment, using 2 soils treated with biosolids (three with and one without polymers with and without polymers) was performed to evaluate Cu and Zn phytoavailability using rice (Oryza sativa L.) as test plant. Three kilograms of two soils (Haphorthox abd Hapludox) were placed in pots and the equivalent to 50 Mg ha-1 (dry basis) of biosolid was added and incorporated. The statistical design adopted was completely randomized experiment, with five treatments (control plus four different biossolids) each soil and four replications. Soil pH before and after harvesting, Cu and Zn concentrations in shoot were evaluated. Tukey (5%) was used to compare the results. DTPA, HCl 0.1 mol L-1 and Mehlich 3 were used to estimate soil available Cu and Zn. Amounts extracted were correlated to those presented in rice shoot, to evaluate the efficiency of predicting Cu and Zn phytoavailabilities. Biosolids with polymers presented higher Cu and Zn phytoavailabilities, possibly due to the lower pH of these residues. In this case soil presented lowest values of pH and plant shoot had highest. All extractants were representative of Cu and Zn availability to rice plants.