Methods and implications of lead variability within Pacific oyster shells
Motivation and Project Description:
Lead (Pb) concentrations and isotopic compositions of environmental samples can provide important information about Pb sources, sinks, pathways, and distributions o in the environment. However, due to the low Pb levels found in many environmental samples Pb isotopic
measurements are often challenging. Here we present a study of the use of LA-ICP-MS with collisional focusing coupled with an Aerosol Rapid Introduction System (ARIS) for measuring Pb isotopes in reference glasses with variable Pb concentrations (X–Y ppm Pb) and real samples (i.e., Pacific oyster (Crassostrea gigas) shells) with relatively low Pb concentrations (~ ppm Pb). The accuracy and precision of this method were evaluated using three glass reference materials (USGS basaltic BCR-2G and BHVO-2G, and MPI-DING komatiite GOR128-G). Lead isotopic results for 206Pb/207Pb and 208Pb/206Pb ratios were within 0.2% and 0.7% of reported values for all three reference materials. External precision on repeated analyses of reference materials was between 0.4% and 2.1% (RSD) for 206Pb/207Pb, with highest values observed for GOR128-G run using a 25 μm spot size. External precision on repeated analyses of the same Pacific oyster sample was similar at ~ 0.5 % for 206Pb/207Pb. Internal precision on Pb isotopic analyses were generally better for
homogeneous glass reference materials [~0.6% (2RSE)] as compared to heterogenous samples (~ 2.5%). Results indicate that low count rates resulting from either small spot size or low sample Pb levels contribute to poor precision. For example, GOR128-G analyses using a 25 μm spot had comparable uncertainties to samples (~ 2% RSE), indicating a significant influence from low Pb concentrations within the shell. Lead isotopic measurements showed good repeatability across parallel transects of the same shell (r = 0.70). High measurement uncertainties (RSD > 0.5%), however, makes fingerprinting of Pb sources in the natural samples impossible. In approaching new studies with the methods presented here, researchers will need to determine if the uncertainties associated with their sample Pb levels are sufficient to obtain precision needed in their application.
See Chapter 3 of my dissertation
This work was funded by Oregon Sea Grant (Grant ID: R/SAQ-21-Shiel).