DETERMINATION OF TOTAL AND PARTIALLY EXTRACTABLE SOLID-BOUND ELEMENT CONCENTRATIONS AND THEIR SIGNIFICANCE IN ENVIRONMENTAL MONITORING STUDIES

Determination of solid-bound element concentrations is an important initial step in environmental studies especially for assessment of contamination, origin and bioavailability. This study revealed that collision/reaction cell inductively coupled plasma-mass spectrometry (CRC ICP-MS) is a potent tool for determining total and partially extractable solid-bound element concentrations (V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As and Pb) in a complex matrix solution containing HF and/or HCl. Six different extraction methods commonly used for environmental monitoring studies were tested for their bias and variability using estuarine and marine standard reference materials. Methods based on concentrated HNO₃±HF±HCl were typically applied for determining pseudo-total or total element concentrations. Dilute-acids (1 M HNO₃, 1M HCl and 0.5 M HCl) were utilized in single-step partial extraction protocols. Except the “dilute acid, cold-extraction” method which was performed at room temperature, other extractions used microwave-digestion. Microwave-assisted extraction methods were easy and effective. However, their application in studies aimed at determining the non-residual, non-specific extractable fractions of elements in samples may result in overestimation, and thus need to be re-examined. We believe that dilute acid, cold extraction methods will play a significant role in future environmental monitoring studies. Nevertheless, the results of partial extraction methods not accompanied with total element concentrations have limited value, as the amount of extraction may vary significantly with the nature (origin) of the elements, and with the types of the samples. Therefore, we suggested combining microwave-assisted total digestion and dilute-acid (0.5 M HCl) cold-extraction methods as a relatively cost- and time-effective, environmentally-sound screening procedure for routine environmental monitoring programs involving a large number of samples from diverse geological and anthropogenic settings. Supported by NOAA-NCDDC and NOAA-NIUST.