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Persistence of Aerially Applied Hexachlorobenzene on Grass and Soil¹

ABSTRACT

The persistence of aerially applied hexachlorobenzene (HCB, C₆Cl₆) (equivalent to 10 ppm in the top 5 cm of soil) in "simulated" pasture was followed for 19 months in the greenhouse. The hypothesis that burning off the grass canopy would decrease the persistence of HCB in soil was also tested. Gas-liquid chromatographic analysis revealed no degradation products of HCB in plant or soil samples and that burning off the grass had no significant effect on subsequent persistence of HCB in soil. On day 1 (20 hours after application) the top 2 cm of soil contained 5.60 ppm HCB. Concentrations (air-dry basis) found after 0.5, 1, 6.5, 12, and 19 months were 45.2%, 24.4%, 7.9%, 4.7%, and 3.4% of day 1, respectively. Concentration in the 2- to 4-cm layer averaged 0.11 ppm with no significant change over the 19 months. Day 1 grass samples contained 1,060 ppm HCB, but after 2 weeks only 15.6 ppm (1.5% of day 1) were found. Concentrations after 1, 6.5, 12, and 19 months were 0.66%, 0.06%, 0.01%, and < 0.01% of day 1, respectively. HCB appears to volatilize rapidly from plant and soil surfaces but could be persistent within the soil.

Key Words: HCB residues • pesticide dissipation • environmental pollution

¹ Contribution of the USDA, ARS, Agric. Environ. Qual. Inst., Beltsville, MD 20705.

² Plant Physiologist.

Received for publication October 1, 1975.