Abiotic transformation

Although this issue has not been frequently addressed, it is relevant to evaluating bioremediation. Several important issues emerged from a study using a range of three- and four-ring PAHs. 

In contrast to the three-ring compounds, residues of benz[a]anthracene, chrysene, and benzo[fl]pyrene were found after 15 weeks incubation in compost-amended soil. 

Neither dihydrodiols formed by bacterial dioxygenation, nor phenols from fungal monooxygenation followed by rearrangement or hydrolysis and elimination, were found. 

Whereas plausible fungal metabolites from anthracene, acenaphthylene, fluorene, and benz[fl]anthracene—anthracene-9,10-quinone, acenaphthene-9,10-dione, fluorene-9-one, and benz[fl]anthracene-7,12-quinone—were found transiently in compost-amended soil, these were formed even in sterile controls by abiotic reactions (Wischmann and Steinhart 1997). 

These results clearly illustrate the care that must be exercised in interpreting the occurrence of PAH oxidation prodncts in bioremediation experiments as evidence of biological activity. 

---

Chemical, or abiotic, transformations are an important fate of many pesticides. Such transformations are ubiquitous, occurring in either aqueous solution or sorbed to surfaces. Rates can vary dramatically depending on the reaction mechanism, chemical stmcture, and relative concentrations of such catalysts as protons, hydroxyl ions, transition metals, and clay particles. Chemical transformations can be genetically classified as hydrolytic, photolytic, or redox reactions (transfer of electrons). 

Endosulfan in aqueous solutions is also expected to undergo biodegradation. In laboratory tests at pH 7 and 20 , Pseudomonas bacteria degraded endosulfan (isomers not specified) under aerobic conditions with a half-life of about 1 week (Greve and Wit 1971). Biotic and abiotic transformations of endosulfan in seawater/sediment microcosms have been reported (Gotham and Bidleman 1989). In biotic tests, half-lives for the a- and P-isomers in seawater-only microcosms (pH 8) were about 5 and 2 days, respectively. In seawater-only microcosms under sterile conditions at a pH of 8 or higher, the half-life for the a-isomer was 2-3 days, whereas the half-life for the p-isomer was 1-2 days. Half-lives were longer in seawater/sediment microcosms, possibly because of the lower pHs (7.3-7.7) in these test systems half-lives were 22 and 8.3 days for the a- and P-isomers, respectively. Endosulfan diol was the main metabolite identified. 

There is limited information available regarding the abiotic transformation of americium in the atmosphere. Oxidation is the most common reaction that occurs in the atmosphere. This would not be expected for americium compounds, which are generally present in the +3 oxidation date under environmental conditions. 

CN" Metallocomplexes Abiotic transformation in the presence of metals Towilletal. 1978... 

Schanke and Wackett [379] reported TeCA degradation by transition-metal coenzymes. cDCE (53%), tDCE (29%), VC (14%), ethylene (1%), and traces of 1,1,2-TCA were the products from this abiotic transformation with vitamin B12 and titanium(III) citrate. Both dechlorination and dichloroelimination had occurred the major route of degradation was reductive dihaloelimina-tion. 

Kochany, J. Maguire, R.J. 1994, Abiotic transformations of polynuclear aromatic hydrocarbons and polynucleararomaticnitrogenhetrocycles in aquatic environments. 5c . Total Environ. 144 17-31. 

In anoxic hypolimnion samples collected from Lower Mystic Lake, MA, hexachloroethane was abiotically transformed into tetrachloroethylene via reductive elimination and to pentachloro-ethane via hydrogenolysis. Tetrachloroethylene accounted for 70% of hexachloroethane in unaltered lake water and 62% in filter-sterilized water after 10 d. Trichloroethylene and pent-achloroethane accounted for <1 and 2% in unaltered lake water and filter-sterilized water, respectively. Disappearance rate constants for hexachloroethane were 0.33/d for unaltered water and 0.26/d for filter-sterilized water. At least 80% of the hexachloroethane disappearance in unaltered water was abiotic in origin due to the reactions with naturally occurring aqueous polysulfides, H2S and (Miller et al, 1998a). 

Cooper. W.J., Mehran, M., l nsech, D.J., and Joens, J.A. Abiotic transformations of halogenated organics. 1. Elimination reactionof 1,1,2,2-tetrachloroethaneand formation of 1.1.2-trichloroethane. / v7ro/ .5c7 Technol, 21 (11) 1112-1114,1987. Coover, M.P. and Sims, R.C.C. The effects of temperature on polycyclic aromatic hydrocarbon persistence in an unacclimated agricultural soil, Haz. WasteHaz. Mater., 4 69-82, 1987. 

Wolfe. N.L. Abiotic transformations of pesticides in natural waters and sediments, in Fate of Pesticides and Chemicals in the Environment, Schnoor, J.L., Ed. (New York John Wiley Sons, Inc., 1992), pp. 93-104. 

Chapter 14 Abiotic Transformation at the Solid-Liquid Interface.295... 

Genuine hysteresis is considered when contaminant release results only from desorption. Experimental data can be interpreted in terms of genuine desorption only when the system is at equilibrium and released molecules are those adsorbed onto the solid phase surface. Molecules brought back into the solution as result of dissolution, diffusion out of the solid matrix, or biotic/abiotic transformation cannot be considered desorbed molecules. In the subsurface, it is almost impossible to distinguish between desorbed molecules and molecules that were not subjected to adsorption and desorption. 

Abiotic transformation of contaminants in subsurface natural waters result mainly from hydrolysis or redox reactions and, to lesser extent, from photolysis reactions. Complexation with natnral or anthropogenic ligands, as well as differential volatilization of organic compounds from multicomponent hquids or mixing with toxic electrolyte aqueous solutions, may also lead to changes in contaminant properties and their environmental effects. Before presenting an overview of the reactions involved in contaminant transformations, we discuss the main chemical and environmental factors that control these processes. 

Wolfe NL (1989) Abiotic transformation of toxic organic chemicals in liquid phase and sediments. In Gerstl Z, Chen Y, Mingelgrin U, Yaron B (eds) Toxic organic chemicals in porous media. Springer, Heidelberg, pp 136-148... 

Wolfe NL, Mingelgrin U, Miller GC (1990) Abiotic transformation in water, sediments and soils. In Cheng HH (ed) Pesticides in soil environment. Soil Sci Soc Am Book Series no 2, Madison, Wisconsin, pp 104-169... 

Transformation and reactions of contaminants in the subsurface are addressed in Part V. From an environmental point of view, we do not restrict the contaminant transformation to molecular changes we also consider the effects of such changes on contaminant behavior in the subsurface. Abiotic and biologically mediated reactions of contaminants in subsurface water are discussed in Chapter 13. Abiotic transformations of contaminants at the solid-liquid interface are described in Chapter 14, while biologically mediated changes in subsurface contaminants are the subject of Chapter 15. 

No published data were located referencing biotic transformation of thorium in soil. Abiotic transformation processes that can convert immobile thorium in soil into mobile forms through the formation of complexes were discussed in Section 5.3.13. 

Tysklind M, Sellstom U, Soderstrom G, et al. 2001. Abiotic transformation of polybrominated diphenylethers (PBDEs) Photolytic debromination of decambro diphenyl ether. BFR 51-54. 

The hydrolysis half-life of trimethylphosphate (CH30)3P0, TMP) in pure water is 1.2 yr at 25°C and pH 7.0 (Table 13.13). A colleague in oceanography claims that in sterile seawater, he observed a half-life for TMP of only about 80 days at 25°C and pH 7. Is this result reasonable What are the major products of the abiotic transformation of TMP in seawater ... 

Wolfe, N. L., Mingelgrin, U. Miller, G. C. (1990). Abiotic transformations in water, sediments, and soil. In Pesticides in the Soil Environment Processes, Impacts, and Modeling, ed. H. H. Cheng, pp. 103-68. Madison, WI Soil Science Society of America. 

Wolfe, N.L. and Macalady, D.L. New perspectives in aquatic redox chemistry Abiotic transformations of pollutants in groundwater and sediments. J. Contam. Hydrol. 1992, 9, 17-34. 

Zepp, R.G. and N.L. Wolfe. 1987. Abiotic transformation of organic chemicals at the particle-water interface. In W. Stumm, ed., Aquatic Surface Chemistry Chemical Processes at the Particle-Water Interface, pp. 423-455. Wiley, New York. 

---