Date of Award

1988

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Oceanography and Coastal Sciences

First Advisor

William H. Patrick, Jr

Abstract

Potential environmental hazards are posed by the presence of 2,4,6-Trinitrotoluene (TNT) contamination in soils of US Army Ammunition Plants (AAPs). Adsorption and desorption studies were conducted on soil samples collected from 13 AAPs. Soils were found to be primarily silt loams, low in organic carbon. TNT reached a steady state of adsorption with test soils within 2 hrs of contact. Desorption also reached steady state within 2 hrs with more than half of the adsorbed TNT being removed. Batch adsorption isotherms were best fit by the Langmuir adsorption model. Average adsorption coefficients (soil concentration to solution concentration), or K$\sb{\rm d}$, was 4.0. However, K$\sb{\rm d}$ varied with soil type. TNT adsorption correlated most highly with cation exchange capacity, extractable iron, clay content, and percent organic carbon. Sequential desorption indicated that almost all of the adsorbed TNT was desorbed after three sequential desorption cycles. Therefore, soil sorption will not effectively prevent mobility of TNT in the environment unless adsorption increases over extended periods of time, or more strongly adsorbing decomposition products are formed. Redox potential and pH exerted no measurable effects on adsorption and desorption. Microbial degradation appeared to be greater in reduced than in oxidized soils, but differences were not significant. Plant uptake of TNT and two of its principal degradation products, 4-amino-2,6-dinitrotoluene (4ADNT) and 2-amino-4,6-dinitrotoluene (2ADNT), was also investigated. Results indicated that little TNT and 4ADNT, and no 2ADNT was absorbed by leafy portions of the test plant, yellow nutsedge (Cyperus esculentus). Plant uptake was greatest from 4ADNT-treated silt, an indication that 4ADNT is more readily mobilized into the plant than TNT or 2ADNT. Greater plant uptake from silt than from clay indicated that bioavailability is reduced in the clay. The reduction in bioavailability may be due to an increase in soil sorption of TNT and its degradation products over time. Results of the study suggest that plant uptake from soils contaminated with 80 ug of the respective treatment compound per g will not be environmentally significant.

Pages

172

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