Facilitating Effects of Metal Cations on Phenanthrene Sorption in Soils

Abstract

Effects of metal cations (Na + , Ca 2+ , and Al 3+ ) on phenanthrene sorption were investigated using two soils with contrasting organic carbon (OC) contents. The presence of the polyvalent cations (i.e., Ca 2+ or Al 3+ ) at a concentration of 0.01 mol/L significantly increased the capacity and nonlinearity of phenanthrene sorption to soils compared with the monovalent Na + . The effects were governed by the content of soil OC. Rubbery OC (i.e., soft, amorphous OC including dissolved organic carbon (DOC)) tended to become condensed on soil surfaces as evidenced by a decrease in the signals of the 1 H NMR spectra of DOC and an increase in the glass transition temperature (T g ) of the soils when the polyvalent cations were present. Increasing Ca 2+ concentration led initially to an effect similar to that of the polyvalent cations in the low cation concentration range, and the effect was gradually attenuated as Ca 2+ concentration further increased. These findings lead us to propose that the modifications in the physical configuration and chemical characteristics of OC resulting from the presence of metal cations account for the increase in the capacity and nonlinearity of phenanthrene sorption to the soils. This study points to an important role of metal cations in the sorption and fate of phenanthrene in the soil environment.

New Insights into the Influence of Heavy Metals on Phenanthrene Sorption in Soils

“…DOC content and its functional group composition ( 1 H liquid-state NMR spectral analysis), T g analysis, and potential analysis were performed as described previously (6). UV absorbance was measured with a 752-UV/vis spectrophotometer at 254 nm using a quartz cell with a 1-cm path length.…”

“…Phenanthrene (>98%) was purchased from Acros Organics and used as received. Each sorbent sample (0.4000 g) from the original soils, soils incubated with heavy metals, and soils with DOC removed was placed into a PTFE-lined cap glass centrifuge vial of 45 mL capacity, and a 40-mL aliquot of phenanthrene solution of varying concentration (0.02-0.8 mg/L) was added as previously described (6). The solid-to-liquid ratios allowed 30-95% of the sorbate be sorbed at equilibrium.…”

Integrated investigations on the adsorption mechanisms of fulvic and humic acids on three clay minerals

“…ICP-OES analysis indicated that Fe contents were 0.21, 0.30 and 4.29 wt% in kaolinite, smectite and vermiculite, respectively. It is generally believed that trivalent cations can form relatively strong complexes with DOC [17,35,36]. With the presence of Fe 3+ in vermiculite, more carboxyl and hydroxyl functional groups were facilitated for the ligand exchange and cation-bridging on the vermiculite surface, thus improving the adsorption capacities of FA/HA on vermiculite.…”

Effect of phosphate on phenanthrene sorption in soils

“…Previous studies have demonstrated that soil physicochemical properties, particularly of organic carbon (OC), play a dominant role in the sorption reaction [1][2][3][4]. The properties of OC can be readily affected by various coexisting substances [5][6][7] which subsequently influence the sorption characteristics of the compounds in the environment [8][9][10]. For example, Xiao et al [11] observed that coexisting heavy metals modified the hydrophobicity of OC and thus exerted pronounced effects on the sorption of HOCs.…”

“…Yuan and Xing [8] suggested that metal cations could coagulate humic acids from solution and facilitate HOC sorption in humic acids. However, the effects of coexisting substances on the sorption of HOCs in soils have received less attention to date and the exact mechanisms involved still remain obscure [6,12].…”