If you drink from a plastic water bottle or eat out of a microwave container today, there is a good chance that you are using polypropylene. Polypropylene is considered safe and suitable for various applications – this is why it is the most commonly used plastic in food preparation.
Another place to find polypropylene is in bottles feeding you baby. We generally believe that bottles made of this plastic are hard and stable when they are sterilized with hot water and shaken while preparing the formula.
But in new research, we have shown that preparing infant formula with polypropylene bottles exposes an average of 1 million microplastic particles per day to infants around the world.
This is a surprisingly large increase over previous estimates. Earlier studies suggested that between 74,000 and 211,000 particles were exposed to adults and children throughout the course of the US year, Through the food they eat, the water they drink and the air they breathe.
Microplastic in formula feeding
Like many research projects, our investigation began with a chance observation and interaction. One day a colleague was preparing instant noodles in a plastic container. The container seemed stiff to begin with, but when it poured hot water into it, it became more malleable and soft. We were curious and wondered if the microplastic could continue in the process.
We did a quick test in our lab and found that the container was released into 1 million microplastics per liter of hot water. We started testing other polypropylene containers, such as plastic bottles, with liquids at room temperature and found that very few microplastic particles were released with each liter, ranging from nothing to a few hundred. The heat, it seemed, was the problem.
We wanted to design an experiment that could test how a single polypropylene product reacted to regular heating, and hit on the idea of using feeding bottles. Through survey of bottles in 48 regions and covering 78 percent of the world’s population, we found that polypropylene baby feeding bottles have an 83 percent share in the global market.
We decided to test these bottles by choosing ten polypropylene baby bottles, following the World Health Organization’s 2007 guidelines for preparing bottle feeding formulas at home.
How many microplastics we released following these steps included cleaning, sterilizing, and mixing liquids in every ten bottles, and they found that they were released up to 16 million particles per liter of 70 million C water.
The majority of these microplastics were smaller than 20 micrometers and layer-like with a thick surface, and averaged one-tenth of their width.
When the water temperature had risen from the recommended 70 ° C to 95 ° C – the recently boiled water temperature – the release of microplastics increased from six million particles to 55 million per liter. The sterilization process alone – in which the bottle is disassembled and placed in a pan filled with 95 ° C water – increases microplastic release by at least 35 percent.
We realized that we had a really broad scientific view. We rigorously followed the WHO process, used control tests, repeated the test with different fluids and several times at different temperatures and used statistical analysis to determine if our results were significant.
But we also sent it to an independent laboratory to verify our methodology and sample products. They came back with similar results, and so we can be confident in our conclusions – as shocking as that may sound.
How to reduce exposure
Given how widespread the use of polypropylene bottles is and the large amount of microplastics released in our experiment, we decided to take our research a step further.
We estimated 12-month-old newborns by feeding bottles to the average release rates of microplastics in 48 regions worldwide, market share of plastic bottles, bottle-feeding rates, and how much milk Babies drink daily.
From this, we concluded that infants were likely to consume an average of 1.6 million polypropylene microplastic particles each day.
We do not want to be an alarm. We do not yet fully understand the risks to human health through exposure to these small plastic particles, but this is an area of research that we and other teams are actively pursuing.
Meanwhile, there are ways to reduce a child’s risk for microplastics while feeding formula. We are looking at coatings that can prevent microplastics from being released during use and filters that can prevent microplastics from entering our water supply.
We have also developed a set of procedures for sterilizing bottles and preparing formula feeds to reduce their risk for microplastics from polypropylene bottles. There are four fast and easy steps:
Rinse the sterilized feeding bottles with cool, sterile water.
- Always prepare formulas in a non-plastic container.
- After the formula is cooled to room temperature, transfer it to a cool, sterilized feeding bottle.
- Avoid formulating ready-made formulas in plastic containers, especially with microwave ovens.
Danzhu Li, Research Fellow in Environmental Engineering, Trinity College Dublin and Yunhong Shi, Postdoctoral Researcher in Environmental Engineering, Trinity College Dublin.
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