Characterization of soil heavy metal pools in paddy fields in Taiwan: chemical extraction and solid-solution partitioning

Abstract

Background, aim, and scope Ongoing industrialization has resulted in an accumulation of metals like Cd, Cu, Cr, Ni, Zn, and Pb in paddy fields across Southeast Asia. Risks of metals in soils depend on soil properties and the availability of metals in soil. At present, however, limited information is available on how to measure or predict the directly available fraction of metals in paddy soils. Here, the distribution of Cd, Cu, Cr, Ni, Zn, and Pb in 19 paddy fields among the total, reactive, and directly available pools was measured using recently developed concepts for aerated soils. Solid-solution partitioning models have been derived to predict the directly available metal pool. Such models are proven to be useful for risk assessment and to derive soil quality standards for aerated soils. , and directly available metal pools (0.01 M CaCl 2 ) were determined. Solid-solution partitioning models were derived by multiple linear regressions using an extended Freundlich equation using the reactive metal pool, pH, and the cation exchange capacity (CEC). The influence of Zn on metal partitioning and differences between both sampling events (May/November) were evaluated. Results Total metals contents range from background levels to levels in excess of current soil quality standards for arable land. Between 3% (Cr) and 30% (Cd) of all samples exceed present soil quality standards based on extraction with AR. Total metal levels decreased with an increasing distance from the irrigation water inlet. The reactive metal pool relative to the total metal content is increased in the order Cr << Ni = Zn < Pb < Cu < Cd and ranged from less than 10% for Cr to more than 70% for Cd. Despite frequent redox cycles, Cd, Pb, and Cu appear to remain rather reactive. The methods to determine the reactive metal pool in soils yield comparable results, although the 0.43 M HNO 3 extraction is slightly stronger than HCl and EDTA. The close correlation between these methods suggests that they release similar fractions from soils, probably those reversibly sorbed to soil organic matter (SOM) and clay. The average directly available pool ranged from less than 1% for Cu, Pb, and Cr to 10% for Ni, Zn, and Cd when compared to the reactive metal pool. For Cd, Ni, Zn, and to a lesser extent for Cu and Pb, solid-solution partitioning models were able to explain up to 93% (Cd) of the observed variation in the directly available metal pool. CaCl 2 extractable Zn increased the directly available pool for Ni, Cd, and Cu but not that of Pb and Cr. In the polluted soils, the directly available pool was higher in November compared to that in May. Differences in temperature, rainfall, and changes in soil properties such as pH are likely to contribute to the differences observed within the year. The solid-solution partitioning model failed to explain the variation in the directly available Cr pool, probably because Cr is present in precipitates rather than being adsorbed onto SOM and clay. Despite obvious differences in parent material, source of pollu...

Lability, solubility and speciation of Cd, Pb and Zn in alluvial soils of the River Trent catchment UK

“…occluded in Fe oxides. Römkens et al 56 also found that whilst Zn become immobile due to fixation on oxhydroxides, Cd tends to remain 80 potentially available. Other authors have also reported greater fixation of Zn than Cd 25, 57,58 .…”

Toxicity of ZnO Nanoparticles, ZnO Bulk, and ZnCl2 on Earthworms in a Spiked Natural Soil and Toxicological Effects of Leachates on Aquatic Organisms

“…The most active fractions (reactive pools) were sequentially determined in three steps according to the methodology used by Pietrzak and McPhail (2004): F1 = water soluble (WS-Zn) with double-deionized water for 2 h ratio 1:10); and F3 = sorbed (SORB-Zn) with 1 % NaCaHEDTA in 1 M NH 4 OAc for 2 h (using a soil-to-extractant ratio of 1:20). The difference between the total and the reactive pools is considered to be nonreactive or inert (Römkens et al 2009). After each successive extraction, the soil suspension was centrifuged (4,500 rpm, 15 min), and the supernatant obtained was filtered through 0.45-lm cellulose acetate paper and acidified with HNO 3 .…”

Bioaccessibility of heavy metals in soils cannot be predicted by a single model in two adjacent areas

“…The development of predictive models for soil Bio-HMs is an active area of study because of the importance of regulating HM bioavailability. However, universal models for Bio-HMs have not yet been identified (Caboche et al 2010;Römkens et al 2009;Rodrigues et al 2013). Although Baotou and Bayan Obo are geographically quite close, these sites differ in their geological backgrounds.…”

“…In recent studies, stepwise multiple linear regression models have widely been used to create these predictive models (Römkens et al 2009), such as that in Eq. (1):…”

“…Römkens et al (2009) used multiple linear regression to build models to predict available HMs in four sites in Taiwan, China (Römkens et al 2009). Rieuwerts et al (2006) found that pH was a consistent predictor of the extractability of soil metals by reagents (an accepted surrogate for bioavailability) in North Wales (Rieuwerts et al 2006).…”