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Soil Chemistry

Exchangeable Cation Hydration Properties Strongly Influence Soil Sorption of Nitroaromatic Compounds

^a Dep. of Crop and Soil Sciences, and Environmental Science and Policy Program, Michigan State Univ., East Lansing, MI 48824
^b USDA-ARS, National Soil Tilth Lab., Ames, IA 50011

^* Corresponding author (boyds{at}msu.edu)

Nitroaromatic compounds (NACs) are commonly found as soil contaminants in military training sites and manufacturing facilities, and may adversely affect human and ecosystem health. Exchangeable cation effects on p-nitrocyanobenzene (p-NCB) and 1,4-dinitrobenzene (1,4-DNB) sorption by the Webster (fine loamy, mixed, mesic Typic Haplaquoll) soil series A (WA) and B (WB) horizons were determined from batch sorption experiments. Smectite is the most abundant mineral in the horizons of this soil. Soil organic matter (SOM) removal increased p-NCB sorption to the WA and WB horizons by 1.5 times, and increased 1,4-DNB sorption to the A and B horizons by 1.2 to 2.2 times, respectively. Greater sorption of NACs by whole soils after SOM removal suggests that SOM suppresses p-NCB and 1,4-DNB sorption by soil mineral components. Clay (<2-µm fraction) removal decreased p-NCB sorption to the WA and WB horizons by 8 and 11 times, respectively; clay removal decreased 1,4-DNB sorption to the WA and WB horizons by 4.8 and 6.7 times, respectively. Nitroaromatic compound sorption to different soil fractions was measured to identify the independent effects of soil components and exchangeable cations on sorption. For this purpose, 1,2,4-trichlorobenzene (1,2,4-TCB) and 1,4-DNB sorption to two organic soils and a soil devoid of smectites, and p-NCB sorption to whole soil and the soil clay-sized fraction were determined. Exchangeable cation type was found to minimally affect sorption of 1,2,4-TCB, p-NCB, and 1,4-DNB by SOM. Sorption of p-NCB to homoionic soil clay-sized fractions was generally greater for clays saturated with monovalent cations than clays saturated with divalent cations. Greater p-NCB sorption followed decreases in cation hydration energy in the order Na⁺ < Li⁺ < < K⁺ < Cs⁺ and Ca²⁺ < Ba²⁺ < Mg²⁺. Similar trends were observed for whole-soil samples exchanged with these cations. This indicates that differences in nitroaromatic sorption are due to exchangeable cation effects on the clay mineral fraction.

Abbreviations: 1,2,4-TCB, 1,2,4-trichlorobenzene • 1,3,5-TNB, 1,3,5-trinitrobenzene • 1,4-DNB, 1,4-dinitrobenzene • BL, Brookston loam • C_e, equilibrium solute concentration • CEC, cation exchange capacity • C_i, initial solute concentration • DNOC, 4,6-dinitro-o-cresol • FeOx, iron oxides • HM, Houghton muck • HPLC, high-performance liquid chromatography • MSU, Michigan State University • NAC, nitroaromatic compound • NOCs, neutral organic contaminants • SOM, soil organic matter • p-NCB, 1-nitro-4-cyanobenzene • PP, Pahokee peat • WA, The Webster soil series horizon A • WB, The Webster soil series horizon B • XRD, x-ray diffraction

This article has been cited by other articles:

				S. M. Charles, B. J. Teppen, H. Li, and S. A. Boyd Fractional Availability of Smectite Surfaces in Soils for Adsorption of Nitroaromatic Compounds in Relation to Soil and Solute Properties Soil Sci. Soc. Am. J., May 1, 2008; 72(3): 586 - 594. [Abstract] [Full Text] [PDF]