Validation of a new method for monitoring trace elements in Mediterranean cereal soils

ABSTRACT

In the Mediterranean region, agricultural soils are seriously polluted with toxic trace elements (TEs) which could enter the food chain via the soil-plant trophic chain. For food safety reasons, the monitoring of TE concentrations in these agricultural soils is thus imperative. The most powerful monitoring method for TE measurements is based on perchloric acid (HClO₄) and hydrofluoric acid (HF) digestion, commonly used as reference total digestion (RTD) method, with consequent use of inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). Unfortunately, HF and HClO₄ manipulations are highly dangerous and ICP-OES and ICP-MS apparatus are very expensive, thus they are unaffordable, notably in developing countries. In this paper, an alternative, microwave sulphuric digestion (MSD) method, combined with atomic absorption spectroscopy (AAS) is proposed. First, the suggested method was validated on a soil certified reference material, for the determination of 7 TEs (As, Cd, Co, Cr, Cu, Ni and Pb). Second, the MSD method was applied on agricultural soil samples situated in the Bekaa valley, East Lebanon and results were compared to those of RTD method. The MSD method, coupled to AAS, offers a promising and feasible alternative to HF, as well as, aqua regia based methods.

KEYWORDS:

• Method validation
• trace elements
• soil
• microwave digestion
• atomic absorption spectroscopy
• Bekaa
• East Mediterranean

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Funding

This research was funded by the project PHC-Cèdre (bilateral French–Lebanese funding program) and the Lebanese Agricultural Research Institute (LARI).