Introduction

Microplastics (MPs) are plastics with a size smaller than 5 mm (Jiang 2018). They can be either manufactured to have the certain size (primary MPs) or fragmented from larger plastics (secondary MPs). Most common types are polypropylene, polyethylene terephthalate, polymethyl methacrylate, nylon, and polyethylene (Lei et al. 2017). Their abundance and ubiquity are environmental concerns for the aquatic environment. Some milestones in the detection of MPs in various environmental samples are shown in Table 1. There are various studies indicating the existence of MPs found in aquatic systems and related components, such as lakes of India (Sruthy and Ramasamy 2017) and surface waters of China (Wang et al. 2017) and the USA (Eriksen et al. 2013). Additionally, Martin et al. (2017) found that MPs were present in the surface water and sediments (not deeper than 3.5 cm) in Irish continental shelf. Finally, MPs were even found in mineral water (Schymanski et al. 2018; Ossman et al. 2018) and table salts (Gundogdu 2018).

Table 1 Chronological list regarding the occurrence of MPs in various sample types
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In order to evaluate their presence in the environment, their sources must be revealed. Among the main sources of MPs in the environment, one can find personal care and cosmetic products. Many personal care and cosmetic products, such as toothpastes, soaps, and gels, include MPs to enhance scrubbing and to strengthen their cleansing or exfoliating functions. It is estimated that 4360 tons of MPs are used in personal care and cosmetic products as additive agents each year in European Union countries (Lei et al. 2017; Anderson et al. 2016). The occurrence of MPs in cosmetic products has also been frequently reported in the last decade (Fendall and Sewell 2009; Lei et al. 2017; Napper et al. 2015; Godoy et al. 2019; Leslie 2014; Cheung and Fok 2016). It is known that MPs can be added to the formulation to enhance whitening properties and act as smoothing and/or polishing agent (Leslie 2014; Vaz et al. 2018); however, examination of MPs in toothpastes was limited in the literature (Praveena et al. 2018; Hintersteiner et al. 2015).

In this study, we aimed to investigate the presence of MPs in commercially available toothpastes sold in Istanbul, Turkey. For this purpose, toothpastes of various brands were extracted, quantified, and characterized. Based on the data, risk assessment was conducted regarding their daily usage and comprised amounts. To our knowledge, it is the first study to reveal the contribution of toothpastes to MP contamination in Turkey.

Materials and method

Chemicals and instrumentation

Filter papers with particle retention of 4–7 μm were purchased from Macherey-Nagel (Germany). No plastic lab-ware was equipped during extraction, all the flasks and funnels were made of glass, and spatulas used for scraping the dry matters were made of steel.

To characterize and image the MPs, Fourier transform infrared spectrometer (FTIR; Bruker VERTEX 70ATR, Karlsruhe, Germany) and a light microscope with an attached AxioCam ICc 1 camera (Zeiss Scope.A1, Jena, Germany) were used.

Sampling and extraction of MPs

All samples available in different prices and brands were purchased from cosmetic stores and markets in Istanbul, Turkey, and list of samples is given in Table 2.

Table 2 List of samples given with their assertions
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Applied extraction method is summarized in Fig. 1. Ten grams of toothpaste was weighed and mixed with 500 mL deionized water via magnetic stirring while heating. After the entire sample was dissolved, filtration began immediately. Samples were left to be filtrated on their own with the help of gravity. After the filtration was completed, filtrates were dried in an oven at 50 °C for 7–8 h. Once they were cooled down to room temperature, they were weighed and the percentage of undissolved solids in the sample was calculated. Once the filtration was complete, obtained solids were mixed with 50 mL distilled water and present MPs in the structure of polyethylene were expected to float due to its density being lower than water. The mixtures were left to settle for 2 h. After the particles were settled, the liquid part was decanted to flasks made of glass to obtain floated particles and then dried at 75 °C. Weights of the dried solids were recorded. Finally, they were identified by FTIR.

Fig. 1
figure 1

Visual summary of the methods applied for MPs extraction from the toothpaste samples

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Risk assessment

Risk assessment was carried out to find out the contribution of toothpaste to MP pollution in Istanbul, Turkey. For this purpose, findings of this study were utilized to determine the maximum, minimum, and mean values of emission. In order to find out the amount of toothpaste required for a single use, samples from all specimens were weighed and an average value was obtained. For the calculation of the maximum value, it was assumed that toothpastes were used by everyone twice a day, as suggested, and for the minimum value, toothpastes were assumed to be used once a day. The estimated MP emission values are calculated with the following formula, modified from the work of Cheung and Fok (2016) and Praveena et al. (2018):

YME = DU × POPist × TPuse × OR × MP × Ndays

where

YME yearly MP emission

DU number of daily usage

POPist total population of Istanbul

TPuse toothpaste amount required for single use

OR occurrence ratio of MPs in total number of samples

MP MP percentage in samples

Ndays number of days in a year

Results and discussion

In order to detect and quantify the MPs in toothpastes, at first, obtained solid forms after the extraction were calculated as total undissolved solids, floated particles, and their percentage in product. These results are shown in Table 3.

Table 3 Characterization and percentages of the particles obtained from toothpaste samples. NI, not identified; PE, polyethylene
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To characterize the solid forms obtained from toothpaste extraction, FTIR and microscopic analysis were applied. It is known that MPs can be characterized by the presence of polypropylene, polyethylene terephthalate, polymethyl methacrylate, nylon, or polyethylene (Lei et al. 2017). In the FTIR analysis, polyethylene gives characteristic signals at 2915, 2848, 1460, and 716 cm−1 (Cheung and Fok 2016; Jung et al. 2018). According to the FTIR spectrums, four samples contained polyethylene which are 2, 3, 12, and 20 (Fig. 2). The samples including MPs by the occurrence of polyethylene had 0.039, 0.10, 0.043, and 0.064 g of floated particles in 10 g of samples 2, 3, 12, and 20, respectively. As shown in Table 3, solids obtained from other samples were also characterized by FTIR and contained various types of additives such as mica, CaCO3, and Ca3(PO4)2. These Ca-containing additives are generally added to the formula for polishing and whitening purposes (Carretero and Pozo 2010), whereas mica is often used for enhanced scrubbing effect. Solids obtained from samples 5, 6, 10, and 14 could not be identified.

Fig. 2
figure 2

FTIR results of particles extracted from samples a 2, b 3, c 12, and d 20. Characteristic peaks of PE are marked with grey arrows

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In addition to FTIR characterization, the samples which included polyethylene were viewed under a microscope. Analysis by microscopy reveals that they have mostly irregular shapes with opaque appearance, as can be seen in Fig. 3. On the other hand, samples 3, 12, and 20 had also transparent/colorless objects that have square-like shapes. The images showed that particle sizes are smaller than 20 μm. Overall, particle sizes can be measured between 4 and 20 μm, because filter papers used for extraction were able to collect particles larger than 4 μm. Parallel to our study, Praveena et al. (2018) examined particle sizes of MPs in toothpaste and found the size in range of 3–145 μm.

Fig. 3
figure 3

Microscopic views of extracted MPs in samples of a 2, b 3, c 12, and d 20 under × 40 magnification. “i” represents opaque particles and “ii” represents transparent particles. Scale bar (black line): 20 μm

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To understand the contribution of a single source to MP contamination, occurrence of MPs should be determined in the representative samples of that source and emission rate should be calculated considering the population and usage frequency. In our study, we found that 4 out of 20 samples contained polyethylene as MPs and their concentrations varied between 0.4 and 1.0%. Furthermore, Hintersteiner et al. (2015) tested only one sample of toothpaste and found that 0.17% of the sample contained polyethylene-type MPs. In the study of Praveena et al. (2018), low-density polyethylene was found in one of the most popular toothpaste brands in Malaysia with less than 7% concentration. Brate et al. (2018) extracted approximately 100 mg of polyethylene from a 100-mL tube of a popular toothpaste brand with 50 μm size. Contrarily, Lei et al. (2017) reported that none of the toothpastes in their samples contained MPs.

To examine the risk of MPs release from toothpaste, we conducted an assessment using the data obtained in this study and consumption estimations for the residents of Istanbul. There are a limited number of studies in the literature evaluating the risks of contamination from different sources (Cheung and Fok 2016; Praveena et al. 2018). Cheung and Fok (2016) conducted a risk assessment and estimated that yearly, 342.2 billion microbeads were released to the environment from solely facial scrubs in Hong Kong. Praveena et al. (2018) reported the total emission of microbeads from personal care products (five facial cleansers and five toothpastes) as 0.199 trillion per year. However, there were some limitations such as examining mixed sample types and restrictions on age and population. Thus, to make an accurate estimation, it is important to calculate the contribution of a single source to environmental contamination. For this purpose, we conducted a modified risk assessment based on the works of Cheung and Fok (2016) and Praveena et al. (2018). As can be seen in Table 4, the risk assessment showed that emission of MPs from toothpaste usage in Istanbul can cause the release of yearly 220 million–3 billion g (average 871 million g) of MPs by the joining domestic wastewater stream and draining to seas or rivers. However, information on the escape rate of MPs from wastewater treatment plants of Istanbul Water and Sewerage Administration (ISKI) is unknown; escape rates are mainly determined by the technology used in treatment plants, and it was reported that current wastewater treatment plants have the inability to capture MPs efficiently (Roex et al. 2013; Kay et al. 2018).

Table 4 Yearly emissions of MPs caused by the MPs in toothpaste for the city of Istanbul, Turkey
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Conclusion

In this study, 20 different toothpaste samples were examined to detect and quantify MPs. Four samples were found to have polyethylene in varying amounts. Considering the data obtained from the study, yearly 871 million g of MPs on average is estimated to be emitted from toothpastes in Istanbul, Turkey. To our knowledge, this is the first study to thoroughly investigate toothpastes for MPs and calculate the yearly emissions in Istanbul. The concerns for possible threats of MP contamination in aquatic life continue to rise due to unavoidable usage and accumulation of those particles in the environment with increasing population. Further studies are needed to understand the fate and impact of MPs in aquatic environment.