Distribution characteristics of cadmium and lead in particle size fractions of farmland soils in a lead–zinc mine area in Southwest China

Abstract

Background: Cd and Pb were the main pollution elements in Pb-Zn mining areas. Several studies have focused on heavy metal pollution and risk assessment in the Huize Pb-Zn mining area. In the present study, the soil aggregate composition, chemical properties, contents and chemical fractions of Cd and Pb were analysed in soils at depths of 0-60 cm in the Huize Pb-Zn mining area. Agricultural soils were sampled at depths of 0-20, 20-40 and 40-60 cm surrounding the Pb-Zn mine. The particle size fractions were determined by the aggregate composition of macroaggregates (0.25-2 mm), micro-aggregates (0.053-0.25 mm), silt (0.002-0.053 mm) and colloid (< 0.002 mm).Results: There was a large proportion of the macro-aggregate (52.4%) and less of the colloid (1.8%). With a decrease in particle size, the pH, organic matter contents, cation exchange capacity, and free iron oxide increased in the soil aggregates. Although the total and available Cd and Pb contents were highest in the colloid, the macro-aggregate maximally contributed to the total Cd (48.18%), total Pb (53.48%) and available Pb (47.42%) content, and the colloid maximally contributed to the available Cd (47.21%) in soils. The Cd and Pb existed primarily as residual fractions, followed by Fe-Mn oxide fraction and the exchangeable fraction in soil aggregates. There were higher distribution factors for the residual and exchangeable fractions of both Cd and Pb in the colloid (DF > 33). Furthermore, there were close correlations between the Cd and Pb fractions and the pH and the phosphorus content and between the exchangeable Pb content and the content of organic matter, cation exchange capacity, and free iron oxide in soil aggregates. Conclusion:Cd and Pb existed mainly in the micro-aggregate and colloid and that their chemical fractions were closely related to the chemical properties in soil aggregates of the polluted farmland.

Soil Lead Concentration and Speciation in Community Farms of Newark, New Jersey, USA

“…Samples HS-2 and 3-UN had Pb-O bond distances of 2.32 Å, which is in between Pb-O distances for birnessite (2.30 Å) and hydroxypyromorphite (2.33 Å), and 1-UN had a Pb-O distance of 2.26 Å consistent with goethite (2.27 Å). This is in agreement with results of the sequential extraction for these samples, which indicates most Pb was present in the reducible fraction (Figure 3a, Particle size distribution is important when studying urban soils as soil components and particle aggregates may control the mobility of heavy metals, with Pb usually associated with micro-aggregates and smaller sized particles [69]. Particle size distribution of Pb was determined by a single-step extraction for samples 1-UN, 3-UN, 3-PL, and HS-2 from Sites 1 and 2 that reported extractable Pb in exceedance of the NJDEP RDCSRS (Figure 4b, Table S8).…”

Arbuscular Mycorrhizal Fungi Are an Influential Factor in Improving the Phytoremediation of Arsenic, Cadmium, Lead, and Chromium

“…In nature, the increase in Cd pollution is mainly due to human activities, including mining, metal smelting processes, Cd-rich phosphate fertilizers, industrial effluents, and fuel production [147,148]; the International Agency for Research on Cancer categorized it as a group 1 carcinogen [149]. Due to the high solubility of Cd, heavy rains, field irrigation, fine soil particles, and preferential flow cause the leaching of Cd from the surface layers of the soil to the subsoil, which is a factor in increasing Cd pollution in groundwater [150][151][152].…”

Organic fermentative‐humic soil subhorizon (Ofh) as a ‘natural sponge’ of selected trace elements: Does this feature make it a potential geoindicator of temperate soil quality?

“…There is no clear answer to the question of the role of SOM in metal retention in soils (Bārdule et al, 2022; Christl et al, 2005; Donisa et al, 2003; Mi et al, 2018; Quenea et al, 2009; X. S. Wang, 2008). Metal depletion of soils with high organic matter content may result from the solubilising effect of SOM, whereas metal accumulation may be due to the strong association of metal and organic matter in solid phase (Staunton, 2002).…”

“…However, regardless of molecular weight, inactive or blocked chelators do not alter the soil's ability to retain elements, even in the presence of significant amounts of SOM (Christl et al, 2001; He et al, 2020; Pandey et al, 2000). The observed discrepancies may also be due to the fact that the above‐mentioned studies refer to soil samples taken from various depths, which may contain different soil horizons characterised by different OM contents, rather than individual soil horizons (Bārdule et al, 2022; Christl et al, 2005; Donisa et al, 2003; Mi et al, 2018; Quenea et al, 2009; X. S. Wang, 2008).…”

“…There is no clear answer to the question of the role of SOM in metal retention in soils (B ardule et al, 2022;Christl et al, 2005;Donisa et al, 2003;Mi et al, 2018;Quenea et al, 2009;X. S. Wang, 2008).…”