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Carbon Tetrachloride Retention by Modern and Buried Soil A Horizons

Department of Agronomy, Univ. of Nebraska-Lincoln, Lincoln, NE 68583-0915.

^* Corresponding author (agro026{at}unlvm.unl.edu).

ABSTRACT

Carbon tetrachloride (CCl₄) was commonly used as a fumigant for stored corn (Zea mays L.) and other grains. This practice and other industrial uses have resulted in instances of soil and groundwater contamination. To better understand the potential for downward CCl₄ movement, retention by a buried soil A horizon was compared with that of the modern A horizon in that same location and its loess C parent material. Batch equilibration was used to determine sorption coefficients (K_d) to compare retention among horizons. Mean K_d values were 0.83 (standard deviation [SD] = 0.18) for the modern A, 0.36 (SD = 0.10) for the loess C and 0.41 (SD = 0.07) for the buried A. Mean organic carbon (OC) contents were 14.9 g kg^–1 (SD = 2.6) for the modern A, 1.3 g kg^–1 (SD = 0.50) for the loess C, and 5.3 g kg^–1 (SD = 0.60) for the buried A. Sorption coefficients were most strongly related to percent OC (R = 0.91 across all soils). Log OC coefficients (log K_oc) were 1.74 (SD = 0.04) for the modern A, 2.43 (SD = 0.18) for the loess C, and 1.89 (SD = 0.10) for the buried A. The OC coefficient varied with OC content of the horizons. This variation may be attributed to qualitative chemical differences in the organic matter fractions. This may also be caused by the increased importance of the clay mineral fraction at low OC contents, leading to falsely high K_oc values. The presence of a buried A horizon may help retard movement of CCl₄ to groundwater.

Journal Series no. 11608, Agricultural Research Division, Univ. of Nebraska-Lincoln.

Received for publication August 7, 1996.