Dilution-Extrapolation Hydrometer Method for Easy Determination of API Gravity of Heavily Weathered Hydrocarbons in Petroleum Contaminated Soil

When crude petroleum is spilled onto soil, the oil's properties have a large influence on the toxicity to soil organisms, the biodegradability of the oil, and potential for long term fertility problems in the soil. Furthermore, these properties of environmental concern are related to the crude's density, commonly measured as API gravity. Currently, methods do not exist to determine the API gravity of crude oil in contaminated soil. In this study, a novel method is presented for the determination of API gravity in small volumes of heavy and extra-heavy petroleum from contaminated soil. This paper uses an economical and readily available solvent (diesel + automotive lubricating oil) in a procedure based on the conventional hydrometer method, plus dilution-extrapolation techniques. It was validated with crude petroleum in the 27.1-15.0 API gravity range, obtaining an excellent correlation with the conventional method and an error of less than 0.4% based on specific gravity. Potential applications of this method are discussed for petroleum contaminated soil.