Land treatment of oil-based drill cuttings in an agricultural soil

The biodegradation, mobility, and phytotoxity of fuel oil hydrocarbons (HC) contained in drill cuttings (DC) were investigated in a 28-mo field experiment. In an agricultural soil three plots were treated with DC on an extensive basis: 15, 30, and 60 MgDC ha(-1) corresponding to 1.5, 3, and 6 Mg HC ha(-1). Concentration and chemical composition of residual HC in the soil profile (0-80 cm) were periodically determined. The decrease in HC concentration was proportional to the loading rates and mainly due to microbial biodegradation. Gas chromatographic analyses demonstrated the metabolism of n- and branched alkanes and of GC-resolved aromatics. The persistence of some polycyclic saturates and aromatics was shown. At the end of the experiment, 10% of the initial HC amount persisted in the surface soil. A vertical selective migration of the lightest HC was shown during the first days and a low leaching of HC and metabolic byproducts toward the subsurface soil and drainage water occurred. The soil treatment modified the soil fertility: pH and Ca increased due to drill cuttings addition while P2O5 and K2O decreased. Crops (maize [Zea mays L.], wheat [Triticum aestivum L.], pea [Pisum sativum L.]) were successively cultivated and harvested. Phytotoxicity, resulting insignificant reductions of yields was observed on the two first crops on the most heavily treated plots, but no uptake of HC in the seeds was measured.