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Adsorption and Reduction in Bioactivity of Polychlorinated Biphenyl (Aroclor 1254) to Redroot Pigweed by Soil Organic Matter and Montmorillonite Clay¹

ABSTRACT

Aroclor 1254 polychlorinated biphenyl (PCB) applied to untreated (1.4% organic matter) and H₂O₂-treated (0.2% organic matter) Lakeland sand at rates of 0, 50, 100, 150, and 200 ppm caused significant reductions in redroot pigweed (Amaranthus retroflexus L.) growth at the high rates of application. Polychlorinated biphenyl decreased plant height in the H₂O₂-treated soil much more than in the untreated soil. A greater decrease in dry weight also resulted in the H₂O₂-treated soil, but only at the 200 ppm rate. In one study, soil was amended with montmorillonite clay and organic matter (peaty muck) at rates of 0, 2.5, 5.0, and 10.0% by weight and treated with 200 ppm PCB. The organic matter proved to be much more effective than montmorillonite in reducing PCB toxicity to pigweed at the lower rates of addition (2.5 and 5.0%), but no differences were noted between the two adsorbents at the 10% rate. Adsorption of ¹⁴C-labeled PCB closely resembling Aroclor 1254 by the untreated and H₂O₂-treated soils, montmorillonite clay, organic matter, and activated carbon was measured. The order of highest to lowest adsorption was as follows: activated carbon >> organic matter > montmorillonite clay > Lakeland sand > H₂O₂-treated Lakeland sand. These experiments suggest that organic matter content of a soil, and clay content to a lesser extent, are involved in reducing the availability of soil-applied PCB to pigweed. Differences in reduction of PCB toxicity to pigweed are explained by differences in adsorption by the adsorbents.

¹ Paper no. 6,874 of the North Carolina Agric. Res. Stn. Jour. Series.

² Graduate Research Assistant, Dep. of Crop Science, and Professor, Dep. of Crop Science and Dep. of Soil Science.

Received for publication March 30, 1981. Accepted for publication November 5, 1981.