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Techniques for detecting and quantifying anaerobic transformations of benzene, toluene, ethylbenzene, and xylene (BTEX) are needed to assess the feasibility of using in situ  bioremediation to treat BTEX-contaminated groundwater aquifers.  Deuterated surrogates of toluene (toluene-d8) and xylene (o-xylene-d10) were injected into BTEX-contaminated aquifers during single-well push-pull tests to monitor for the in situ formation of deuterated benzylsuccinic acid (BSA-d8) and o-methyl-BSA-d10. Test solutions (250 L) containing toluene-d8 (4 - 22 M) and o-xylene-d10 (4 - 9 M) along with a conservative bromide tracer (1.3 mM) and nitrate (4 mM) as an electron acceptor were injected into four wells at two sites (Figure 1).  Detection of BSA-d8 and o-methyl-BSA-d10 in groundwater samples collected from the same wells following injection unequivocally demonstrated anaerobic in situ toluene-d8 and o-xylene-d10 transformation with calculated zero-order formation rates ranging from 1.0 to 7.4 nM/day (Figure 2). Concurrent utilization of co-injected nitrate was rapid in all tests at both sites, with zero-order rates ranging from 13 to 39 M/hr. The field tests conducted in this study represent the first reported use of deuterated aromatic hydrocarbons to detect and quantify anaerobic BTEX transformation product formation in the subsurface.

The image contains two line graphs, labeled "a)" and "b)," placed one above the other. Both graphs track changes over time, measured in days, from 0 to 30 on the x-axis.
Graph a) displays "C/C₀" values, ranging from 0.0 to 1.2 on the y-axis. It includes five different data sets, each marked with distinct symbols: filled black circles represent "Br¯," black squares for "Toluene-d₈," filled black triangles for "o-Xylene-d₁₀," inverted open triangles for "Nitrate," and open circles for "Sulfate." The symbols are connected by lines that show a general downward trend, indicating a decrease in concentration over time.
Graph b) illustrates "BSA-d₈, o-Methyl BSA-d₁₀ (nM-dilution adjusted)" on the left y-axis, ranging from 0 to 18, and has dual labeling with "Nitrate (mM-dilution adjusted)" and "Sulfate (mM-dilution adjusted)" on the right y-axis, ranging from 0.0 to 3.0 and 0.0 to 0.20, respectively. Four data sets, indicated by distinct symbols, are plotted: filled black circles for "BSA-d₈," filled black squares for "Methyl BSA-d₁₀," inverted open triangles for "Nitrate," and open circles for "Sulfate." The lines indicate fluctuations with some peaks and valleys.
Both graphs include legends in the upper right, identifying different components associated with the symbols. The x-axis for both graphs is labeled "Time (days)."