An Isotopic Study of Bio-accessible Lead in Wheat, Miswak Toothbrush and Miswak Fruit Using the Continuous On-line Leaching Method with Inductively Coupled Plasma Mass Spectrometry

Abstract

In this study, sources of Pb are investigated using the 206Pb/207Pb isotopic ratio measured by inductively coupled plasma quadrupole mass spectrometry in the bio-accessible fractions from wheat, Miswak toothbrush (also used as chewing stick) and Miswak fruit. These samples were obtained for the in vitro batch and on-line leaching methods that mimic the human gastrointestinal tract by sequentially using artificial saliva, gastric juice and intestinal fluid for extraction. The two methods provided similar results according to a Student’s t-test at the 95% confidence level. Significant (p < 0.05) differences in 206Pb/207Pb were noted at the 95% confidence level in different artificial body fluids. Except for unpolluted Miswak toothbrush and Miswak fruit, which only contained geogenic Pb, the samples contained a mixture of geogenic and anthropogenic Pb, with bio-accessible Pb in saliva being mainly from a geogenic source, whereas bio-accessible Pb in the stomach and intestinal fluids was mainly from anthropogenic sources. Despite the fact that leaded petrol was phased out in Saudi Arabia in 2001, a Miswak toothbrush collected on the side of a busy road after exposure for only a few days and Safeer wheat were still being contaminated with Pb and had an isotopic composition matching that of Pb added to petrol. The 208Pb/206Pb isotopic ratio for gastric bio-accessible Pb also matched that reported in tetraethyllead. The 206Pb/207Pb isotopic ratios of intestinal bio-accessible Pb from Qassim wheat and Safeer wheat point to coal combustion as the source. Overall, these results highlight the need for continued Pb monitoring and the value of examining bio-accessible fractions periodically to identify Pb sources.