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Water Air Soil Pollut (2008) 194:151161 DOI 10.1007/s11270-008-9704-1
An Improved Gravimetric Method to Determine Total Petroleum Hydrocarbons in Contaminated Soils
Mario Villalobos & Ana Paulina Avila-Forcada &
Margarita Eugenia Gutierrez-Ruiz
Received: 26 November 2007 /Accepted: 28 March 2008 /Published online: 25 April 2008 # Springer Science + Business Media B.V. 2008
Abstract A gravimetric method to determine heavy fractions of total petroleum hydrocarbons (TPH) in soils is reported. The method was adapted and calibrated by modifying previous standard methods published, incorporating energy and cost savings where possible. Artificially contaminated soils with different organic matter content, and aged in stationary mode for a period of 8 months were used for calibration. Insufficient solvent evaporation was identified as the most prevalent and largest positive interference in the gravimetric detection. To overcome this, while minimizing the need for heating, a combination of three 10-min rotary evaporator steps and 30 min of vacuum in a desiccator were applied, for a total solvent volume of 60 ml. Hexane was chosen as
the extraction solvent and a 4060 min treatment in an ultrasound bath of 260 W was found suitable to extract 8095% of TPH extracted by the Soxhlet method. Finally, the use of silica gel for cleanup of co-extracted natural organic matter was found unnecessary, because of the low amounts co-extracted for soils with up to 5% organic carbon, and because the chemical nature of the co-extracted organic matter prevents its selective adsorption to silica.
Keywords Contaminated soils . Gravimetric method . Silica gel . Solvent evaporation . Total petroleum hydrocarbons . Ultrasound extraction
1 Introduction
Soil pollution by petroleum hydrocarbons usually originates from spills or leaks of storage tanks during fuel supply and discharge operations. Most petroleum components are hazardous to human health and to the soil biota (MDEP 1994); therefore, measurement of their total concentration (total petroleum hydrocarbons TPH) is the initial and most general indicator of hazard by hydrocarbons for environmental diagnostic purposes.
The US Environmental Protection Agency (USEPA) has published a series of methods for quantifying TPH in solid matrices (including soils; Table 1). The four categories of analytical methods described in Table 1 are based on the final detection method, i.e. gravimetry,
M. Villalobos (*) : M. E. Gutierrez-RuizGrupo de Bio-Geoqumica Ambiental,Laboratorio de FisicoQumica Ambiental...