Biological activity of the isotopes of the same element
I would not expect significant differences in the chemical properties (reactivity) of these lead isotopes, the differences in atomic weight being as you point out very small. There are reports  that claim an effect. Ref 1 for instance makes such a claim, but there is no plausible mechanism presented to explain the reported isotopic discrimination. Double check what peer reviewers think (see e.g. the response in Ref 2 to the results presented in Ref 1).
References

Wu J, Liu D, Xie Q, Wang J (2012) Biological Fractionation of Lead Isotopes in Sprague-Dawley Rats Lead Poisoned via the Respiratory Tract. PLOS ONE 7(12): e52462. https://doi.org/10.1371/journal.pone.0052462

Gulson, Brian and Kamenov, George D. and Manton, William and Rabinowitz, Michael (2018) Concerns about Quadrupole ICP-MS Lead Isotopic Data and Interpretations in the Environment and Health Fields. International Journal of Environmental Research and Public Health 15(4): 723. https://doi.org/10.3390/ijerph15040723