Beyond total lead (Pb) content: speciation as a key control on plastic toxicity

Despite recent regulatory efforts, large amounts of legacy plastics containing lead (Pb) additives continue to degrade in the environment. As plastics degrade to micro- and nanoscales, Pb can either be released into the environment or subsequently adsorb onto micro- and nanoplastics. This variability in Pb speciation, with each form displaying distinct leaching behaviour, complicates environmental risk assessment. Here, we compile a dataset of plastic debris collected from beaches worldwide, revealing an average Pb concentration of 110 mg kg^-1, with nearly 15% items exceeding current regulatory limits. A Pb-Cr relationship is observed in nearly half of the samples, which cluster along a Pb/Cr ratio close to 4, suggesting the presence of historical PbCrO₄ pigment and associated with low Pb availability. However, Pb L₃-edge HERFD-XANES spectra indicate significant variability in Pb speciation, pointing to the presence of multiple, previously underrecognized Pb-based additives including organo-Pb compounds. Although these plastics do not contain the highest total Pb concentrations, those containing organic Pb additives exhibit the greatest Pb availability, demonstrating that bulk Pb content alone is a poor predictor of environmental behaviour upon degradation. The high spectral resolution of HERFD-XANES further allows the discrimination of incorporated and adsorbed Pb species, providing direct insights into Pb binding environment, leachability, and potential toxicity. Our results demonstrate that human-health risk assessments should not rely solely on total Pb concentrations, but rather on Pb speciation, which ultimately governs leaching behaviour and bioavailability.