Presence Established, Quantity Disputed, Harm Unknown: Micro- and Nanoplastics and Endocrine-Disrupting Chemicals in the Human Body

Micro- and nanoplastics (MNPs) have been detected in human blood, placenta, lung, heart, testes,
and brain. The brain finding dominates public attention: a 2025 Nature Medicine study reported
brain concentrations 7–30 times higher than liver or kidney, rising ~50% between 2016 and 2024.
A 2026 Nature Health dataset of 191 brain samples confirmed near-universal presence at
concentrations roughly two orders of magnitude lower. This review compiles the primary
literature on both sides of that dispute, the formal methodological challenges to the field's
dominant measurement technique, the exposure inventory (with heat identified as the master
variable of chemical and particle migration), the separate but entangled literature on endocrinedisrupting plastic additives — bisphenols, phthalates, thermal-paper developers — and the
current state of institutional response and removal claims. Its synthesis is three clauses: presence
is established; quantity is disputed; harm in humans is unknown. The paper closes with the
author's precautionary argument: for hormonally active exposures deployed at population scale
with multi-decade latencies and no unexposed control population, the absence of proof of harm
is a property of the experimental design, not of the substances.