Sampling, Identification and Characterization of Microplastics Release from Polypropylene Baby Feeding Bottle during Daily Use

Summary

This study detailed a reliable and cost-effective protocol for microplastics collection and detection from the daily use of plastic products.

Abstract

Microplastics (MPs) are becoming a global concern due to the potential risk to human health. Case studies of plastic products (i.e., plastic single-use cups and kettles) indicate that MP release during daily use can be extremely high. Precisely determining the MP release level is a crucial step to identify and quantify the exposure source and assess/control the corresponding risks stemming from this exposure. Though protocols for measuring MP levels in marine or freshwater has been well developed, the conditions experienced by household plastic products can vary widely. Many plastic products are exposed to frequent high temperatures (up to 100 °C) and are cooled back to room temperature during daily use. It is therefore crucial to develop a sampling protocol that mimics the actual daily-use scenario for each particular product. This study focused on widely used polypropylene-based baby feeding bottles to develop a cost-effective protocol for MP release studies of many plastic products. The protocol developed here enables: 1) prevention of the potential contamination during sampling and detection; 2) realistic implementation of daily-use scenarios and accurate collection of the MPs released from baby feeding bottles based on WHO guidelines; and 3) cost-effective chemical determination and physical topography mapping of MPs released from baby feeding bottles. Based on this protocol, the recovery percentage using standard polystyrene MP (diameter of 2 µm) was 92.4-101.2% while the detected size was around 102.2% of the designed size. The protocol detailed here provides a reliable and cost-effective method for MP sample preparation and detection, which can substantially benefit future studies of MP release from plastic products.

Introduction

Most types of plastics are non-biodegradable but can break down into small pieces due to chemical and physical processes such as oxidation and mechanical friction^1,2. Plastic pieces smaller than 5 mm are classified as microplastics (MPs). MPs are ubiquitous and found in almost every corner in the world. They have become a global concern due to the potential risk to humans and wildlife^3,4. To date, significant accumulations of MPs have been found in fish, birds, insects^5,6 as well as mammals (mo....

Protocol

1. Hot water preparation

1. For all hardware that comes into contact with the samples, use clean glass made of borosilicate 3.3 to prevent any potential contamination. Thoroughly clean all the glassware.
   Caution: Pre-existing scratches or imperfection spots on glassware can release particles during the heating and shaking process. We suggest that users check the glassware and avoid the use of the scratched glassware. Our comparison of glassware made of different glasses (such as soda-lime and borosilicate) showed that borosilicate 3.3 releases the lowest quantity of glass particles (can be screened for by Raman spectroscopy), and we re....

Results

To validate this protocol, the water sample was prepared by adding standard polystyrene microplastic spheres (a diameter of 2.0 ± 0.1 µm) to DI water. The MP quantity added corresponded to 4,500,000 particles/L, which is similar to the MP release level from BFBs. Following protocol sections 2-3, the MPs were successfully collected (Figure 4A) and the recovery rate was 92.4-101.2%. This recovery rate is comparable to a previous study on MPs²³. Using ImageJ, t.......

Discussion

Though the study of MPs in marine and freshwater has been widely reported and the relevant standard protocol has been developed¹⁷, the study of daily-use plastic products is an important emerging research area. The different environmental conditions experienced by household plastic products means that extra care and efforts are needed to obtain reliable results. The study protocol must be consistent with the real daily use scenarios. For example, sonication is widely used in lab-tests to clean sam.......

Materials

Name	Company	Catalog Number	Comments
AFM cantilever	NANOSENSORS	PPP-NCSTAuD-10	To obtain three-dimensional topography of PP MPs
Atomic force microscope	Nova	NT-MDT	To obtain three-dimensional topography of PP MPs
Detergent	Fairy Original	1015054	To clean the brand-new product
Gold-coated polycarbonate-PC membrane filter-0.8 um	APC, Germany	0.8um25mmGold	To collect microplastics in water and benefit for Raman test
Gwyddion software	Gwyddion	Gwyddion2.54	To determine MPs topography
ImageJ software	US National Institutes of Health	No, free for use	To determine MPs size
Microwave oven	De'longhi, Italy	815/1195	Hot water preparation
Optical microscope, x100	Mitutoyo, Japan	46-147	To find and observe the small MPs
Raman spectroscopy	Renishaw	InVia confocal Raman system	To checmically determine the PP-MPs
Shaking bed-SSL2	Stuart, UK	51900-64	To mimic the mixing process during sample preparaton
Standard polystyrene microplastic spheres	Polysciences, Europe	64050-15	To validate the robusty of current protocol
Tansfer pipette with glass tip	Macro, Brand	26200	To transfer water sample to glass filter
Ultrasonic cleaner	Witeg, Germany	DH.WUC.D06H	To clean the glassware
Vacuum pump	ILMVAC GmbH	105697	To filter the water sample