Concerns about Quadrupole ICP-MS Lead Isotopic Data and Interpretations in the Environment and Health Fields

Abstract

There has been a massive increase in recent years of the use of lead (Pb) isotopes in attempts to better understand sources and pathways of Pb in the environment and in man or experimental animals. Unfortunately, there have been many cases where the quality of the isotopic data, especially that obtained by quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS), are questionable, resulting in questionable identification of potential sources, which, in turn, impacts study interpretation and conclusions. We present several cases where the isotopic data have compromised interpretation because of the use of only the major isotopes 208Pb/206Pb and 207Pb/206Pb, or their graphing in other combinations. We also present some examples comparing high precision data from thermal ionization (TIMS) or multi-collector plasma mass spectrometry (MC-ICP-MS) to illustrate the deficiency in the Q-ICP-MS data. In addition, we present cases where Pb isotopic ratios measured on Q-ICP-MS are virtually impossible for terrestrial samples. We also evaluate the Pb isotopic data for rat studies, which had concluded that Pb isotopic fractionation occurs between different organs and suggest that this notion of biological fractionation of Pb as an explanation for isotopic differences is not valid. Overall, the brief review of these case studies shows that Q-ICP-MS as commonly practiced is not a suitable technique for precise and accurate Pb isotopic analysis in the environment and health fields.

High Frequency of Lead Exposure in the Population of an Endangered Australian Top Predator, the Tasmanian Wedge‐Tailed Eagle (Aquila audax fleayi)

“…Our ability to link the lead exposure detected in the Tasmanian wedge-tailed eagle to lead-based ammunition was limited in 3 ways. First, although recent work has frequently used Q ICP-MS to measure lead 207/206 , there are concerns over the precision of lead 207/206 estimates obtained by this method (Gulson et al 2018). Second, we were unable to directly measure lead isotopes in ammunition available in Tasmania, instead relying on published isotope ratios for ammunition brands currently available in the region.…”

The Isotopic Signature of Lead Emanations during the Fire at Notre Dame Cathedral in Paris, France

“…The fire dust 206 Pb/207 Pb signature was thus assessed as the arithmetic mean of the 206 Pb/207 Pb in dust and was 1.167 ± 0.005. However, it has to be mentioned that the measurement technique has been chosen not for its precision [ 10 ], but for its ability to quickly carry out an isotopic screening on sources and potentially the blood of exposed individuals.…”

Strategies to overcome interferences in elemental and isotopic geochemical analysis by quadrupole inductively coupled plasma mass spectrometry: A critical evaluation of the recent developments

“…Even HR‐ICP‐MS is not an appropriate technique as the removal of 204 Hg isobaric interference on 204 Pb requires a resolution (M/ΔM) of almost 500,000, whereas HR‐ICP‐MS instruments are limited to a resolution of about 10,000 27 . Some authors 168 have incorporated a Hg trap into the Ar gas line to remove Hg in order to obtain very high‐precision and accurate isotopic ratios by HR‐ICP‐MS. However, improved performance was provided by ICP‐MS/MS which resolved difficult polyatomic and isobaric overlaps on lead isotopes 161 .…”