Understanding the Effects of Soil Characteristics on Phytotoxicity and Bioavailability of Nickel Using Speciation Models

Abstract

Acidity (pH) has been realized to be the most important soil characteristic that modulates bioavailability of heavy metals by affecting both the chemical speciation of metals in soil and the metal binding to the active sites on biota.In this work, we show that besides soil pH, metal bioavailability also depends to a certain extent on the type of soil. A better understanding of the role of soil type in regulating metal availability can be achieved with the analysis of soil composition and with calculations using chemical speciation models. Results of pot experiments, in which three different soils were spiked with nickel, show that the EC 50 of total nickel in decreasing the biomass production of oats varies widely (0.7-22.5 mmol kg -1 soil, more than 30 times). pH (4.7-7.0) is the most important factor, explaining up to a factor of 14 difference of nickel bioavailability in the soils. The remaining variation is caused by other differences in soil composition (soil type). The bioavailability and toxicity of nickel in the organic matter-rich soil studied is less than half of that in the sandy and clay soil studied at a similar pH. The chemical calculations using a multi-surface speciation model show that soil organic matter binds Ni much stronger than clay silicates and iron (hydr)-oxides within the acidic pH range, which supports the experimental findings. In all three soils, the EC 50 of Ni expressed in terms of Ni in 0.01 M CaCl 2 soil extraction is rather stable (24-58 µM), suggesting the possibility to use this extraction as an estimation of metal availability in soil.

Plasma Membrane Surface Potential: Dual Effects upon Ion Uptake and Toxicity

“…For example, Weng et al (2004) and others have noted significant reductions in metalinduced toxicity with reductions in pH in the 6 to 7 range. Such pH reductions would change c 0 o by less than 1 mV in most media, a change far too small to account for toxicity reductions.…”

“…altered PM surface ion activity and surface-to-surface transmembrane potential difference gradient). This study provides novel insights into the mechanisms of plant-ion interactions and extends current theory to evaluate ion bioavailability and toxicity, indicating its potential utility in risk assessment of metal(loid)s in natural waters and soils.Some solutes in growth media, such as cations and organic matter, influence the bioavailability and toxicity of metals in natural waters and soils (Peijnenburg et al, 1997;Weng et al, 2004;Kopittke et al, 2010). Novel insights into the bioavailability and toxicity of metals have inspired the development of models in order to allow accurate impact assessments of metals emitted into the environment.…”

“…Some solutes in growth media, such as cations and organic matter, influence the bioavailability and toxicity of metals in natural waters and soils (Peijnenburg et al, 1997;Weng et al, 2004;Kopittke et al, 2010). Novel insights into the bioavailability and toxicity of metals have inspired the development of models in order to allow accurate impact assessments of metals emitted into the environment.…”

Biochars Derived from Gasified Feedstocks Increase the Growth and Improve Nutrient Acquisition of Triticum aestivum (L.) Grown in Agricultural Alfisols

“…These results mirrored those observed for Al, again indicating that declining concentrations of Ni are likely due to a combination of increasing pH and other soil or biochar properties. Previous studies have indicated that Ni bioavailability is dependent on soil organic matter [18] and on biochar particle size [19]. Overall, the combinatorial effects of an in increase in pH and intrinsic biochar properties likely led to most of the source-specific elemental changes we observed, including decreased Fe concentrations in roots grown with KB-sourced amendments and increased Zn concentrations in shoots grown in wood-sourced biochar.…”

Toxicidade do níquel em plantas de feijão e efeitos sobre a microbiota do solo

“…Isto era esperado porque a disponibilidade deste elemento é maior em valores de pH mais baixos (Uren, 1992;Weng et al, 2004). É interessante observar que, na dose correspondente a 10,5 mg kg -1 , as plantas não apresentaram diferença no teor de Ni nas folhas, independentemente da presença ou não de calcário.…”