Developing human noncancer and reproductive/developmental effect factors for Nano- and microplastic exposure in LCA

Background: Nano- and microplastics (NMPs) are ubiquitous in our environment (air, water, food chain) and their presence is believed to be responsible for numerous effects on ecosystems and human health. However, toxicological assessment of potential impacts of NMPs on human health is still lacking in life cycle impact assessment (LCIA), and the detection of these microparticles in human bodies has made it crucial to better understand and characterise such potential impacts. Objective: The aim of this research is to develop human noncancer and reproductive/developmental effect factors for NMPs in LCIA as part of the MarILCA project, based on the study of in vivo animal data and the latest framework in human health impact assessment. Methods: Experimental studies of in vivo mammal toxicity in which a critical effect was observed through daily oral ingestion of pristine NMPs were selected. The obtained curated database was then processed to generate a representative chronic human benchmark dose (BMDh), later extrapolated for LCIA into an effect factor (in DALY/kg or disability-adjusted life years per kg ingested). Results: Preliminary regulatory BMDh of polystyrene NMPs have been identified as 2.63E-3 and 9.33E-3 mg/(kg.d) for general noncancer and reproductive effects, respectively. In terms of effect factors, this would account for 50.2 and 3268 DALY/kg, respectively. Polyethylene NMPs yielded slightly smaller results for BMDh (5.01E-2 and 1.32E-1 mg/(kg.d)) and effect factors (9.3 and 65.1 DALY/kg) for general noncancer and reproductive effects, respectively. Discussion: Polystyrene and polyethylene NMPs have been allegedly found among the top 10% most toxic chemicals, per kg intake, assessed in LCIA. This research calls for a larger discussion and deeper analysis of the obtained results to (in)validate them, as the findings are concerning. Future research into NMPs is needed to improve our understanding of their mode of action and factors affecting their potential effects