A novel blood biomarker for plastic ingestion in fledgling procellariiform seabirds.

Plastic ingestion is a well-established threat to wildlife, inducing a series of lethal and sublethal physiological consequences. Yet, in free-living populations, many of these health consequences remain effectively 'invisible' to conventional monitoring, making the development of a minimally invasive biomarker for plastic exposure a longstanding priority. To date, biomarker approaches have focused on detecting exposure (e.g., presence/absence of plastic additives/plasticisers) rather than identifying or classifying biological injury associated with plastic ingestion. Here, we evaluate whether the proteomic signatures previously identified in de Jersey et al. (2025) can be validated and extended across Procellariiform seabirds as a potential biomarker of plastic ingestion. We analysed blood plasma using data-independent mass spectrometry (DIA-MS) from four species during developmental stages including Sable Shearwater (Ardenna carneipes) fledglings, Wedge-tailed Shearwater (Ardenna pacifica) fledglings, Black-winged Petrel (Pterodroma nigripennis) fledglings and Providence Petrel (Pterodroma solandri) chicks with varying levels of plastic ingestion. Using a pathway-level approach that integrates functionally related proteins rather than relying on single-protein markers, we identified a consistent and conserved proteomic signature associated with plastic ingestion across species, achieving 96% classification accuracy. The proposed biomarker includes elevated evidence of cell lysis, compromised stomach permeability and fibrosis, and a decrease in secreted proteins. The detected physiological patterns are aligned with emerging models of plastic-induced pathology and diseases, such as plasticosis. However, as plasma proteomes shift substantially across life stages and retention time of plastic ingestion in adults is unknown, application of the biomarker to adults will require additional targeted validation to associate plastic ingestion to proteomic response. Our findings establish a foundation for a non-lethal, tool capable of diagnosing plastic exposure across seabird taxa, with potential applications in broader ecological monitoring and conservation programs.