Effects of Soil pH and Treatment Level on Persistence and Plant Uptake of 2,4,6-Trinitrotoluene

Abstract

Two studies were conducted to measure uptake of 2,4,6-trinitrotoluene (TNT) by the ubiquitous yellow nutsedge (Cyperus esculentus). The initial study was conducted with three soils treated at low levels of TNT, 20 and 40 μg TNT/g of soil on an oven dry weight (ODW) basis. One of the principal objectives of the initial study was to assess methods for soil treatment, extraction, and analysis. Dry mixing of TNT into the soils resulted in a nonhomogeneous distribution of the compound. Ultrasonic extraction of spiked soils with 200 ml of benzene produced fairly good recoveries of TNT, an average of 80 percent, but coefficients of variation were relatively high. Concentrations of TNT and two of its degradation products, 4-amino-2,6-dinitrotoluene (4ADNT) and 2-amino-4,6-dinitrotoluene (2ADNT), in plants were low. Concentrations of all three compounds were limited to a few micrograms per gram of plant material. The principal objective of the second study was to determine the effects of soil pH on plant uptake of TNT. Plants were grown in two soils at· four pH values (5, 6, 7, and 8) and at four treatment levels (0, 100, 200, and 400 μg TNT/g ODW). Plant uptake of TNT from soils was not statistically significant when compared with controls at any treatment level or pH. Although both 4ADNT and 2ADNT were detected in plants, concentrations of neither were significantly different from controls, except for 4ADNT ·at pH 6 in the US Army Engineer Waterways Experiment Station reference soil (WRS), a Tunica Silt, at the 200-μg/g treatment level. Plant yields tended to decrease as the pH of TNT-treated soils increased. Soil treatment level and soil type exerted a dramatic effect on plant yields. Yields were virtually unaffected by treatment levels in clay. However, in the WRS yields were significantly reduced in the 200-μg TNT/g treatment, and only one of four replicates survived in the 400-μg TNT/g treatment. Results of soil analysis. for TNT, 4ADNT, and 2ADNT at three times during the plant bioassay, i.e. immediately after treatment and 20 days and 65 days after treatment, indicated a rapid decrease in concentrations of TNT in the WRS soil. TNT decreased rapidly from the time of treatment to the first sampling. Some of the loss of TNT is attributable to the production of 4ADNT and 2ADNT, but accumulation of these products did not account for all of the loss. It is likely that volatilization occurred during treatment and for some time after treatment. Between the first and second sampling times, TNT concentrations decreased in the clay as well as in the WRS. Volatilization and soil sorption may account for these results. A decrease was also evident between the second and third sampling times, but it was relatively small and statistically significant in the highest TNT treatments only. Soil concentrations of 4ADNT and 2ADNT rarely exceeded 20 μg/g of soil.