ICP-OES assessment of heavy metal contamination in tropical marine sediments: A comparative study of two digestion techniques

Abstract

A closed vessel microwave assisted aqua regia digestion and an alkaline fusion dissolution technique were compared and utilised for heavy metal determination in sediments. Ten metals (Al, As, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn) were analysed by inductively coupled plasma optical emission spectrometry (ICP-OES). The precision and accuracy of the digestion procedures were verified using a reference material (RM) for sediment. The results of the analysis were statistically treated by means of Student's t-test (p<0.05) and regression analysis. A comparison of the two digestion methods showed no statistically significant difference in metal concentrations in the RM except for Al and As. Recovery values for all metals were nearly quantitative (>82%) for both digestion methods, except for Al and As, which were underestimated using the acid digestion (AD) method and the alkaline fusion (AF) method, respectively. The average relative standard deviations for both digestion methods were less than 6%, indicating good method precision. The application of the two methods for the determination of ten heavy metals in ten sediment samples showed significant correlation between results achieved by both digestion methods for all the metals studied except for As. This study has demonstrated that the microwave-assisted aqua regia digestion is more suitable for the determination of minor and volatile elements such as As, while the alkaline fusion technique is more suitable for the determination of silicate bound and refractory metals. Application of the proposed methods to sediments from a coastal environment in Fiji showed that the sediments were highly contaminated with metal levels as much as 345mgkg−1 As, 519mgkg−1 Cr, 530mgkg−1 Cu, 1387mgkg−1 Ni, 800mgkg−1 Pb and 1720mgkg−1 Zn, as a consequence of improper industrial waste management.