Comparison of Extractants for Plant‐available Zinc, Cadmium, Nickel, and Copper in Contaminated Soils

Abstract

The objective of this study was to find a suitable extractant(s) for plant‐available metals in metal contaminated soils. Swiss chard (Beta vulgaris L. ‘Fordhook Giant’) was grown in greenhouse pots on 46 Ontario soils varying in degree of contamination with metals. The soils had been contaminated with metals to varying degrees over a period of years. After 40 days, the plants were harvested and Zn, Cd, Ni, and Cu concentrations were measured. Each soil was extracted with nine different extractants: aqua regia, 0.01M EDTA, 0.005M DTPA, 0.02M NTA, 0.5N CH3COOH, 1N CH3COONH4, 0.6N HCl + 0.05N AlCl3, (COOH)2 + (COONH4)2, and H2O. Zinc, cadmium, nickel, and copper concentrations in Swiss chard were correlated with the amounts of soil Zn, Cd, Ni, and Cu removed by each extractant. Of the nine soil extractants, CH3COONH4 was the best predictor of plant‐available Zn if only extractable Zn and soil pH were included as independent variables in a regression equation. Acetic acid was the best extractant for prediction of both plant‐available Cd and Ni when soil pH was included in the equation. Attempts to find a suitable soil extractant for plant‐available Cu were unsuccessful.

Is an adjusted rhizosphere-based method valid for field assessment of metal phytoavailability? Application to non-contaminated soils

“…Availability of metals to plants is complex and affected by several soil properties including soil pH, SOM, FeeMn oxide contents, and CEC (Haq et al, 1980). Thus multiple regression models considering soil characteristics could provide insight into the mechanisms of phytoavailability and improve the predictability of chemical extraction methods (Miner et al, 1997;Brun et al, 2001;Wang et al, 2004).…”

“…Single extraction methods using selective chemical extractants, such as strong chelating agents or mild neutral salts, are commonly used (Beckett, 1989). Among these extractants, EDTA (0.1e1 M) and DTPA (0.005 M), either as sodium or ammonium salts, have been proposed because of their ability to form very stable, water soluble and well-defined complexes with a wide range of metal cations (Haq et al, 1980;Chaignon et al, 2003). A 0.01 M CaCl 2 extractant was also proposed because of the similarity between this extractant and the concentration, composition and pH of soil background electrolytes (Houba et al, 1996).…”

Toxicity thresholds for oat (Avena sativa L.) grown in Ni-impacted agricultural soils near Port Colborne, Ontario, Canada

“…Total Ni concentration in the blended soils was determined as described above. In addition, Ni in each of the blended soils was estimated using ammonium oxalate (for the moderately reducible phase of total soil Ni) (Haq et al 1980) or diethylene triamine pentaacetic acid (DTPA) (for chemical simulation of phytosiderophores) (Lindsay and Norvell 1978) extraction protocols. In brief, the methods for these two extractions are: 0.2 M oxalic acid/ ammonium oxalate (30 mL) is added to 1.5 g of dry soil, which is then shaken for 4 h, and filtered; 5 mM DTPA, 10 mM CaCl 2 and 0.1 M triethanolamine (10 mL of each) added to 5 g of dry soil, which is shaken for 2 h, and filtered.…”

Aplicação de fósforo para imobilização química do cádmio em solo contaminado

“…49 Entretanto, Abreu et al encontraram baixa eficiência dos extratores DTPA e Mehlich-1 em predizer a disponibilidade de Cd em solos não contaminados. 46 As diferenças para os resultados encontrados entre os extratores químicos utilizados podem também estar relacionadas ao pH da solução extratora, uma vez que o extrator DTPA, de caráter quelatizante, tem pH 7,3, enquanto que o Mehlich-1, de caráter ácido, é ao redor de 1,8.…”