HomePackaging and MOCADishwashers and release of microplastics, the study

Dishwashers and release of microplastics, the study

Pollution from microplastics is ubiquitous and growing, also due to the plastics contained in dishwashers and the plastic objects - plates, glasses, food containers - that are inserted into them.

A recent study (Sol et al., 2023) evaluated the effects of washing, even with an empty load and without detergent, on the release of microplastics in waste water.

The main operational parameters (i.e. time, temperature) and the pre-contamination of the washing water have influenced the release of microplastics which, in any case, is widespread. (1)

1) Microplastics in water

The water it is the first vehicle for the spread of microplastics (MPs) which float everywhere, from bottled mineral waters (2) to an infinite number of products, including foods (3,4). They are formed due to the degradation of the billions of tons of plastic used in every production sector, as well as due to the intentional additions of MPs for technological purposes (i.e. pesticides, cosmetics, etc.). The European snail introduced the first restrictions in this sense, with mild measures applied very slowly. (5)

Primary microplastics (released directly into the environment in the form of small particles) and secondary (resulting from the degradation of larger objects) should be filtered by wastewater treatment plants, in theory, up to 90%. (6) But even if this were the case, the residual 10% would lead to a concentration of up to approximately 300 particles/litre of effluent downstream of each WWTP (Waste Water Treatment Plant), thus releasing millions of particles every day. (7)

Drinking water in turn it contains microplastics - due to the widespread contamination of water basins (8) - and its use, even at domestic level, contributes to increasing the quantity of MPs reintroduced into the cycle. With extreme variability, from 'not determined' to over 6.600 particles/litre. Also having an impact on the waters downstream of the related treatment plants (Sol et al., 2021). (9)

2) Release of microplastics from the dishwasher, the study

The dishwasher it is a household appliance present in many homes, in turn made up of approximately 24% plastic material. In consideration of this the researchers (Sol et al., 2023) first performed empty washing cycles to evaluate the direct release of MPs from the appliance.

The tests – performed with the two programs of pre-wash only (15' at room temperature) and intensive washing (164' at 70° C) – recorded significant releases of microplastics, respectively 230-450 MP/L and 1087-1468 MP/ L. These values ​​also include the pre-contamination levels of the washing water, which were on average approximately 10 times lower than the quantities of MPs released by the dishwasher, also due to the 'solvent' effect in the extraction and conveyance of the microplastics from the household appliance. The first uses seem to bring greater releases, compared to subsequent washes which appear to be more stable.

As for shape, size, color and chemical composition, fragments <60 μm made of polypropylene (PP) dominate (77-250%) compared to fibers (14-36%) of the same material. The greater presence of MPs in purple and gray colors after washing (72-76%), compared to the water used, confirmed the releases from the dishwasher whose components are of that colour.

2.1) Washing plastic food containers

Numerous food contact materials (FCM or MOCA, materials and objects in contact with food) are made of plastic material. The researchers tested two dishwasher cycles with a 6-unit load of polypropylene (PP) lunch boxes to evaluate their impact on the release of MPs.

The number of microplastics, following the two separate washing programs, increased by approximately 14 and 166 MP/L per tub respectively, for an average total of approximately 80 and 996 MP/L. Also in this case, longer times and higher temperatures contributed to a greater release of MPs, mainly made up of fragments (77-90%).

The pressure jet of the dishwasher, in particular, led to greater abrasion of food packaging. Although PP is considered one of the most resistant materials to this phenomenon, compared to other materials such as polystyrene (PS), polyethylene (PET) and polyethylene terephthalate (PET).

2.2) Adding the detergent

The cleaner it was the last component added in the tests. Also in this case the researchers preliminarily measured the MPs present in the detergents of three different 'brands', with variations in the range 0,75 - 3 MP/g of product. Values ​​similar to those of the water used in washing, much lower than those released by dishwashers and plastic trays. Once again the fragments, consisting of 63-87% PP, represented the main form of MPs (57-72%).

The first test was performed with vacuum washing, where the addition of detergent increased the release of MP significantly (35-54%) compared to vacuum washing without detergent with an intensive cycle. PP is in fact very sensitive to the oxidative action caused by detergents and their alkaline pH. It is estimated that each domestic washing machine wash can release approximately 227-321 million MPs, respectively without or with detergent.

The second test was created by placing PP lunch trays in the wash. In this case, MP release was not substantially different from vacuum washing without detergent. This effect was associated with the slight difference in the material (PP), which in the dishwasher is reinforced with 20% talc and is therefore more sensitive to the action of the detergent compared to food contact materials.

3) Provisional conclusions

Using the dishwasher is associated with contributors of MP in the environment, to a greater extent if plastic food packaging is used and detergent is added during washing. In all cases, time and temperature contribute to abrasion and dispersion together with the washing water, which is also already 'contaminated'.

The type of containers for foods used (i.e. glass rather than plastic) is fundamental, just as the type of plastic could affect the release of MPs into 'grey water'. Similar effects were observed when washing clothes with synthetic components in the washing machine, with the difference that in this case fibres, rather than fragments, were the most observed forms of microplastic. Once again, with significant impact of time, temperature and detergent factors. (10)

4) Brief notes

Global oat production of plastics records an average annual increase of 4%, with an impact of more than 15% on total greenhouse gas emissions by 2050 (Zheng et al., 2019). Demand is growing and policy-makers have not yet adopted effective policies to reduce it, nor to encourage reuse over recycling, the rates of which are still very low. (11)

The impact of microplastics on the environment, human and animal health - in a 'One Health' logic it is still ignored by governments and authorities responsible for assessing risks, despite the recommendations of WHO (2019) on drinking water. (12) And it is clear, based on the research already published, the need to intervene at the source. When?

Dario Dongo and Andrea Adelmo Della Penna

Footnotes

(1) Sol D. et al. (2023). Contribution of household dishwashing to microplastic pollution. Environmental Science and Pollution Research 30:45140-45150, https://doi.org/10.1007/s11356-023-25433-7

(2) Marta Strinati. Microplastics in mineral water. The French report. GIFT (Great Italian Food Trade).

(3) Marta Strinati. Microplastics in fruit and vegetables. The Italian study. GIFT (Great Italian Food Trade).

(4) Sabrina Bergamini, Dario Dongo. Microplastics on the plate, two new studies and a petition. GIFT (Great Italian Food Trade).

(5) Dario Dongo. Andrea Adelmo Della Penna. Microplastics, the first restrictions in the Old Continent in a mini-reform of the REACH regulation. GIFT (Great Italian Food Trade). 1.10.23

(6) Dario Dongo. Microplastics in water and agriculture, first study in Lombardy. GIFT (Great Italian Food Trade).

(7) Ali I. et al. (2021). Micro- and nanoplastics in wastewater treatment plants: occurrence, removal, fate, impacts and remediation technologies – A critical review. Chem. Eng. J. 423:130205, https://doi.org/10.1016/j.cej.2021.130205

(8) Dario Dongo, Sabrina Bergamini. Microplastics in the water of Italian lakes, the silent emergency. GIFT (Great Italian Food Trade).

(9) Sol D. et al. (2021) Microplastics in wastewater and drinking water treatment plants: occurrence and removal of microfibres. Appl. Sci. 11:10109. https://doi.org/10.3390/app112110109

(10) Napper I.E & Thompson R.C. (2016). Release of synthetic microplastic plastic fibers from domestic washing machines: effects of fabric type and washing conditions. Mar. Pollut. Bull. 112(1–2):39–45,  https://doi.org/10.1016/j.marpolbul.2016.09.025

(11) Dario Dongo, Alessandra Mei. Plastic and greenhouse gas emissions, an emergency to be prevented. Scientific study. GIFT (Great Italian Food Trade).

(12) Marta Strinati. Packaging Regulation (PPWR), the European Parliament approves a softer version. GIFT (Great Italian Food Trade).

(13) Marta Strinati. Microplastics in drinking water, WHO calls for risk assessment. GIFT (Great Italian Food Trade).

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Dario Dongo, lawyer and journalist, PhD in international food law, founder of WIISE (FARE - GIFT - Food Times) and Égalité.

Andrea Adelmo Della Penna
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Graduated in Food Technologies and Biotechnologies, qualified food technologist, he follows the research and development area. With particular regard to European research projects (in Horizon 2020, PRIMA) where the FARE division of WIISE Srl, a benefit company, participates.

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