Binding of 2,4,6-Trinitrotoluene and its Degradation Products in a Soil Organic Matter Two-Phase System J. Eriksson* and U. Skyllberg ABSTRACT mands strictly anaerobic conditions (McCormick et al., 1976; Rieger and Knackmuss, 1995). Intermediates in The widely used explosive 2,4,6-trinitrotoluene (TNT) and its deg- this degradation pathway, such as nitroso and hydrox- radation products are of large environmental concern because of their toxic properties and high concentrations encountered in contaminated ylamino derivatives and the azoxy products, are very soils. Batch experiments were used to study TNT* (the sum of TNT reactive and have recently been shown to bind to soil and its degradation products) bonding to dissolved (DOM) and partic- organic matter (SOM) within hours or days (Achtnich ulate (POM) soil organic matter. Reversed-phase high performance et al., 1999a). Trinitrotoluene, as well as other nitroaro- liquid chromatography (RP-HPLC) was used as a separation tech- matic compounds (NAC), are also known to bind to nique in combination with 14 C-labeled TNT to determine free TNT negatively charged 2:1 phyllosilicates (Haderlein et al., and TNT* bound to DOM. By use of dialysis we showed that DOM 1996), possibly via an electron donor–acceptor complex did not interfere with the HPLC analysis of free TNT. Depending (EDA) involving an electron excessive clay surface and on pH and total TNT concentration, the relative distribution of TNT* the electron deficient NAC (Haderlein and Schwarzen- among water, POM, and DOM varied between 60 to 90, 10 to 30, bach, 1993; Weissmahr et al., 1997). Thus, retention and and 0.5 to 6%, respectively, after 22 h of equilibration. The association of TNT* to DOM was strongly pH dependent and followed a nonlinear mobility of TNT and its degradation products in soil Langmuir isotherm. The association of TNT* to POM was less pH are highly dependent on the availability of 2:1 phyllosili- dependent and data were equally well fitted by linear and nonlinear cates and SOM. Water-soluble organic matter is of spe- isotherms. Particulate organic matter had 6.4 (pH 6.2) to 22 (pH 5.2) cial interest if it associates with TNT and its degradation times greater capacity to bind TNT* than DOM, but the binding products, possibly enhancing their mobility. strength (the slope of the isotherm) was greater for DOM. The TNT Soil organic matter may be separated into dissolved degradation was enhanced with increasing concentration of soil or- (DOM) and particulate (POM) organic matter. Dissolved ganic matter, resulting in a stronger bonding of TNT* to DOM and organic matter comprises a complex mixture of organic POM. Based on our results, combined with other recent findings, we substances with sizes between 200 and 100 000 Da. A suggest that it is mainly the degradation products of TNT that associate variable but dominant portion of the organic substances with DOM and POM, and that the association with DOM is mainly of ionic character involving specific DOM sites. The greater binding in soil can be described as humic substances (i.e., unde- capacity and a weaker, linear type of isotherm suggests a nonspecific fined macromolecules largely built up of aromatic and type of partitioning in POM, possibly of hydrophobic character. aliphatic moieties) (Stevenson, 1994). An obvious dif- ference between DOM and POM is the size of the or- ganic molecules, being smaller for the former. Otherwise, T rinitrotoluene, a widely used explosive, and its little is known about chemical and structural differences degradation products have toxic and mutagenic ef- between DOM and POM. Important for the bonding fects on several organisms, including humans (Kaplan of organic chemicals to SOM is the composition and and Kaplan, 1982). In Sweden, ammunition found in density of reactive organic groups and hydrophobic moi- areas used for incineration and dumping is considered eties in DOM and POM (Engebretson and von Wan- an environmental threat and since 1995 has been the druszka, 1997, 1998). The strong tendency of nonpolar subject of investigation by the Defence Research Estab- organic chemicals to associate with SOM through hy- lishment (FOA). Risk assessments are focused on the drophobic partition is well known (Hassett et al., 1983; transportation of TNT and its degradation products in Chiou, 1989), whereas possible specific bonding involv- soils and how these products may reach and affect bio- ing functional groups of SOM is less studied and not logical systems. In order to understand how these sub- well understood. stances are retained or transported in soils we need to The limited knowledge about the binding of TNT and study in detail their affinity for mobile and nonmobile its degradation products to SOM is largely based on soil constituents. Of special importance is the bonding of studies of extracted humic acids (HA). Li et al. (1997) TNT and its degradation products to dissolved (mobile) reported a strong binding of TNT, aminodinitrotoluene and particulate (mostly nonmobile) soil organic matter. (ADNT), and diaminonitrotoluene (DANT) to Aldrich Trinitrotolune degrades by a stepwise reduction of (Milwaukee, WI) humic acid after 48 h of equilibration its three nitro groups to corresponding amino groups. during nonsterile conditions, while Held et al. (1997) The first nitro group is reduced even during aerobic found no significant association of TNT to HA under conditions while reduction of the last nitro group de- sterile conditions. This indicates that it is the reduced Abbreviations: ADNT, aminodinitrotoluene; DANT, diaminonitroto- J. Eriksson and U. Skyllberg, Dep. of Forest Ecology, Swedish Univ. luene; DOM, dissolved soil organic matter; FA, fulvic acid; HA, humic of Agriculture, SLU, S-901 83 Umea˚ , Sweden. J. Eriksson, Defence acid; HPLC, high performance liquid chromatography; POM, particu- Research Establishment, FOA, S-901 82 Umea˚ , Sweden. Received late soil organic matter; RP, reversed phase; SOM, soil organic matter; 22 Jan. 2001. *Corresponding author (Johan.Eriksson@sek.slu.se). TNT, trinitrotoluene; TNT*, sum of trinitrotoluene and its degrada- tion products. Published in J. Environ. Qual. 30:2053–2061 (2001). 2053 Published November, 2001