Phytotoxicity and bioavailability of nickel: Chemical speciation and bioaccumulation

Abstract

The effect of pH on the bioaccumulation of nickel (Ni) by plants is opposite when using a nutrient solution or a soil as a growing medium. This paradox can be understood if the pH effect on the bioaccumulation, on the chemical speciation in the soil solution, and on the binding to the soil of Ni are all taken into account. Using simple equations to describe the individual relationships, it is possible to quantify these effects once the relationships have been established. Increased Ni uptake leads to reduced plant dry weight production for a certain growing period. The median effective concentration (EC50) decreased from 23 to 1.7 microM Ni in the nutrient solution for pH 4.0 to 7.0, whereas the EC50 of added Ni in a sandy soil increased from 0.72 to 9.95 mmol Ni/kg soil for pH 4.7 to 6.8. Bioaccumulation, binding to the soil solid phase, and binding to the dissolved organic matter all increase with increasing pH. However, the magnitude of the effect is the least for bioaccumulation as a function of pH, causing the apparent paradox.

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

“…It is notable that the soil Ni EC 25 s suggested by Anderson et al (1973) and Weng et al (2003) are similar to the regulatory criterion for Ni in soil in many jurisdictions, and lower than observed in the present study. The solubility product (an equilibrium constant describing the concentration of ions in a saturated solution of an ionic compound) of Ni hydroxide is 10 (17.2 (Baes and Mesmer 1976), which translates into an equilibrium concentration of Ni, at saturation of solubility, of 0.01 mg L (1 .…”

“…This is perhaps not too surprising, as the exchangeable Ca concentrations in the serpentine soils used in Anderson et al (1973) were low (less than 30% of total CEC), relative to what is common for nonserpentine soils (60Á80% of total CEC), thus potentially posing less competition for Ni uptake by plants ( Kinraide 1998;Parker et al 1998). The data of Weng et al (2003) suggest that the EC 25 for shoot biomass occurred at approximately 4 mmol Ni kg…”

“…(1 presented the possibility that the threshold concentration for phytotoxicity might lie between these two limits, and might be specific to soil type, as has been demonstrated (Weng et al 2003(Weng et al , 2004. Thus, the objective of the present study was to establish phytotoxicity thresholds for oat (Avena sativa L.) in the four soil types found in Port Colborne (till clay, heavy clay, sand and organic muck).…”

Predicting the Phytoextraction Duration to Remediate Heavy Metal Contaminated Soils

“…For plants grown in a system with both soil and roots, pH usually has a negative effect on uptake of HMs (e.g., Smith, 1994). For plants grown in water cultures, however, the opposite has been found (Lexmond & van der Vorm, 1981; (Table 5) and the HM contents in plant shoots and the solubility of HMs (Table 6) Weng et al, 2003). These contrasting effects of pH on plant uptake of HMs may be the result of competition for HM binding by different reactive surfaces, including those of the soil and plant roots (Plette, Nederlof, Temminghoff, & van Riemsdijk, 1999).…”

“…In several pot and field experiments, uptake of HMs was demonstrated to be related to the HM concentration in soil solution (e.g., Hamon, Holm, Lorenz, McGrath, & Christensen, 1999;Chaudri et al, 2001;Weng, Lexmond, Wolthoorn, Temminghoff, & van Riemsdijk, 2003;Song, Zhao, Luo, McGrath, & Zhang, 2004). In the study of Song et al (2004), Cu uptake by roots of Silene vulgaris and Elsholtzia splendens was predicted from regression models relating the Cu content in roots to the Cu concentration in soil solution in combination with pH and dissolved organic carbon (DOC).…”