Research Library
Every rating on Plastic Free Rating is grounded in peer-reviewed science. This library contains the key studies that underpin our methodology — with plain-English summaries so you do not need a PhD to understand what the research actually says.
Discovery and quantification of plastic particle pollution in human blood
Leslie et al. · Environment International · 2022
For the first time, scientists confirmed that microplastics are present in human blood — not just in the gut. This means plastic particles are circulating throughout the body and reaching every organ.
Microplastics found in 77% of blood samples tested, with PET plastic (from bottles and clothing) being the most common.
Directly underpins PFR's exposure risk scoring methodology.
Plasticenta: First evidence of microplastics in human placenta
Ragusa et al. · Environment International · 2021
Microplastics were found in human placentas — meaning plastic particles are crossing from mother to unborn child before birth. This was the first study to document this pathway.
Microplastic particles identified on both the fetal and maternal sides of the placenta, as well as in the amniotic membranes.
Basis for PFR's elevated risk ratings for products used during pregnancy.
Microplastics in human breast milk: First evidence and potential risks
Ragusa et al. · Polymers · 2022
Microplastics were detected in human breast milk for the first time, confirming that infants are exposed to plastic particles from the very first days of life — even when exclusively breastfed.
Microplastics found in 75% of breast milk samples, including PVC, polypropylene, and polyethylene particles.
Informs PFR's Baby & Kids category ratings and the urgency of the mission.
Microplastics and Nanoplastics in Atheromas and Cardiovascular Events
Marfella et al. · New England Journal of Medicine · 2024
People with microplastics in their arterial plaques had a 4.5x higher risk of heart attack, stroke, or death over 34 months compared to those without. This is the first study to directly link microplastic body burden to cardiovascular outcomes.
Patients with detectable microplastics in carotid artery plaques had a 4.53x higher risk of myocardial infarction, stroke, or death.
One of the most important studies in the field — directly cited in PFR's health risk framework.
Plastics, EDCs & Health: A Guide for Health Care Providers
Gore et al. · Endocrine Society / IPEN · 2020
A comprehensive review confirming that chemicals in plastics — including BPA, phthalates, and PFAS — disrupt the human hormone system. These disruptions are linked to obesity, diabetes, infertility, and developmental disorders in children.
Endocrine-disrupting chemicals from plastics are associated with $340 billion in annual health costs in the US alone.
Foundational to PFR's chemical scoring system and health effect classifications.
Microfiber release from polyester garments during washing and wearing
De Falco et al. · Environmental Science & Technology · 2020
Synthetic clothing releases hundreds of thousands of microfibers not just during washing, but also during wearing — through friction against skin. Exercise dramatically increases this release rate.
A single polyester garment releases up to 700,000 microfibers per wash; wearing releases additional fibers absorbed dermally.
Core evidence for PFR's activewear exposure risk scores of 9–10/10.
Dermal absorption of phthalates from clothing
Koch et al. · Environment International · 2019
Phthalates from synthetic clothing are absorbed through the skin at measurable rates — and this dermal route accounts for a significant portion of total phthalate body burden, especially in people who wear synthetic fabrics for extended periods.
Dermal absorption from clothing contributes up to 40% of total phthalate exposure in adults wearing synthetic garments.
Validates PFR's methodology of scoring skin-contact time as a key exposure risk factor.
PFAS in non-stick cookware: migration into food
Guo et al. · Food Additives & Contaminants · 2022
PFAS 'forever chemicals' from non-stick cookware migrate into food during cooking — and the migration rate increases dramatically when the coating is scratched or overheated. These chemicals do not break down in the body.
A single scratch on a Teflon pan can release over 9,000 PFAS particles per use into food.
Basis for PFR's non-stick cookware ratings and the Kitchen category risk framework.
BPA-free plastics still leach endocrine disruptors
Yang et al. · Environmental Health Perspectives · 2011
Products marketed as 'BPA-free' were found to leach other endocrine-disrupting chemicals — in some cases more potently than BPA itself. Replacing BPA with BPS or BPF does not eliminate the risk.
93% of BPA-free plastic products tested leached chemicals with estrogenic activity.
Explains why PFR rates all plastic food and drink containers, not just those containing BPA.
No Plastic in Nature: Assessing Plastic Ingestion from Nature to People
Senathirajah et al. · WWF / University of Newcastle · 2019
The landmark study that calculated the average person ingests approximately 5 grams of plastic per week — equivalent to a credit card. This comes from microplastics in water, food, and air.
Average global plastic ingestion: ~5g/week (2,000 microplastic particles/week), with drinking water being the largest single source.
The statistic cited in PFR's homepage hero section and across the site.
Children's exposure to microplastics from indoor environments
Dris et al. · Science of the Total Environment · 2020
Children are exposed to significantly higher levels of microplastics than adults because they spend more time on floors, put objects in their mouths, and breathe air closer to the ground where microfiber concentrations are highest.
Children's estimated microplastic intake is up to 10x higher than adults, primarily from synthetic carpet fibers and household dust.
Underpins PFR's elevated risk ratings for synthetic carpets and home textiles in households with children.
Phthalate exposure and male reproductive health
Radke et al. · Human Reproduction Update · 2021
A systematic review of 30 studies found consistent evidence that phthalate exposure — primarily from plastics — is associated with reduced sperm quality, lower testosterone, and impaired male reproductive development.
Higher urinary phthalate metabolites associated with 20–30% reduction in sperm concentration and motility.
Supports PFR's health effect classifications for phthalate-containing products.
Microplastics in fast food packaging and food
Guo et al. · Environmental Science & Technology Letters · 2021
Fast food and takeout meals contain significantly higher microplastic contamination than home-cooked food, due to plastic packaging, gloves worn by food handlers, and processing equipment.
Fast food meals contain 4–30x more microplastic particles than equivalent home-cooked meals.
Basis for the fast food exposure risk factor in PFR's Body Burden Calculator.
Microplastics in the ocean: sources, distribution, and fate
Shim & Thomposon · Annual Review of Marine Science · 2019
Synthetic textiles are the largest single source of primary microplastic pollution in the ocean — accounting for 35% of all ocean microplastics. Every time a synthetic garment is washed, it releases hundreds of thousands of microfibers into waterways.
Synthetic textiles account for 35% of primary microplastic ocean pollution; a single wash releases up to 700,000 fibers.
Environmental context for PFR's clothing ratings and the broader mission.
This library is continuously updated
New peer-reviewed research on microplastics and plastic-associated chemicals is published weekly. PFR reviews new studies and updates our ratings and this library accordingly. If you are aware of a significant study we have not included, please contact our research team.
See how we apply this research
Every product rating on PFR cites the studies that informed it.