HEALTH EFFECTS OF MICROPLASTICS.

Over the past 5 years  an increasing number of studies have reported the presence of micro- and nanoplastics in drinking water, air, food and soil. This raises questions and concerns about the impact of microplastics debris on human health, and had recently also been the driver behind the European Plastic Pact. Nanoconsult has been contracted by ICCA to compose a white paper on the human health effects of microplastics by inhalation and oral intake. The white paper indicate how read-across from other particle domains such as PSLT and ambient PM may help to advance decision making and learning in this phase.

DRAFT REPORT SUMMARY

As many answers will remain open for the next 5-10 years, the white paper uses the paradigms developed in other domains of particle toxicology as a starting platform, and explores the question whether these could serve as guidance and database for read-across or harmonization of approaches. The scientific principles that have been developed in domains including Poorly Soluble Low Toxicity (PSLT) particles, ambient particulate matter (PM), synthetic fibres and nanomaterials are interrogated with respect to potential use in the context of MPs. The analysis starts with an overview of available particle properties and those that may be relevant for biological effective dose, such bio-persistence, validated in PSLT, fibres and nanomaterials. The evaluation of exposure and intake data for the inhalation route reviews of  exposure studies, and focusses in detail on 3 studies from Europe (London, Hamburg, Aarhus) showing mainly deposition of fibrous fragments a limited group of synthetic (4-72  %) and non-synthetic (cellulose, protein) materials. It is also noted that atmospheric deposition of MPs is the standard method used revealing MP numbers between 100 and 1000 N/m2.day, but such data cannot be used for human exposure estimation. Best calculated dose in 3 studies ranges between 160 and 43,234 particles/day for human inhalation, noting that most particles are not in the respirable (< 10 µm) range.

In reviewing studies evaluating potential hazards it is noted that most hazards for inhalation are based on studies using a few model nanoparticles, not identified in real-life, at exposures that are many orders magnitude higher than encountered in ambient atmosphere. Oral intake studies have applied appropriate particle sizes but also particle numbers (107– 108 particles/day) and doses that exceed normal human dietary intake (10 2– 103 /kg. day) by far. Hazard studies from pharma were excluded from survey as the materials are highly specific and not adequate to describe environmental MPs.

Finally, using read-across as an approach to apply existing know-how to the  particle domains PSLT, ambient PM and organic fibres, has both fundamental and practical limitations. First of all, read-across has barely been explored to the level of groups of (particle) substances, and secondly the data gaps between particle domains are too large for validating an overarching hypothesis such as inflammatory response in the lung characterizes all particle domains. The best candidate for read-across emerging from this effort, is provided by the robust worldwide dataset of ambient PM, and the missing links regarding exposure measurements and hazard testing at relevant levels will be able to close the current data-gap. New emerging data on MP content in PM10 samples (first estimate: 2502/m3) will help in the next years to fill the first data gap for using PM data in MP health impact assessment.

Finally, the paper provides a number of recommendations that have emerged from the gap analysis including accurate estimation of both oral and inhalation intake and uptake of MP.  The major challenge for this field and the regulatory bodies is in hazard identification, considering the low, chronic exposure to relevant model or real-life particles.. New models retaining anatomical integrity along with maintenance over longer periods, such as organoids may provide new approaches to consider long-term exposure to low concentrations of MPs.

LITERATURE.

WHO report Microplastics in drinking-water. Geneva, World Health Organization (2019) ISBN 978-92-4-151619-8

SAPEA, Science Advice for Policy by European Academies. (2019). A Scientific Perspective on Microplastics in Nature and Society.  Berlin: SAPEA. https://doi.org/10.26356/microplastics

Bucci K, Tulio M, Rochman CM (2019) What is known and unknown about the effects of plastic pollution: A meta-analysis and systematic review. Ecol Appl. 2019 Nov 23:e02044. doi: 10.1002/eap.2044.

Ogonowksi M, Gerdes Z, Gorokhova E (2018) What we know and what we think we know about microplastic effects- a critical perspective. Current opinion in Environmental Science & Health 1: 41-46.

Gouin T, Becker RA, Collot A-G et al (2019) Toward the development and application of an environmental risk assessment framework for Microplastic. Environ Toxicol & Chemistry 38: 2087- 2100.