The significant impacts of laundry wastewater on microplastics: a case study in a residential area

Microplastics (MPs) in urban drainage are a significant source of river pollution. Laundry waste, which can contain high levels of microfibers, is a potential source of MPs in urban drainage. This study investigated the abundance and characteristics of MPs in urban drainage channels in Ketawanggede Village, Malang City, Indonesia. The research involved stages such as inorganic and organic separation using Fe2SO4.7H2O and H2O2, density-based MPs separation, and analysis of abundance, size, color, and polymer through microscopy and FTIR. Statistical testing was performed using the Kruskal-Wallis Test in RStudio. The results showed that the abundance of MPs increased with distance from the river, with the highest abundance found at location 4 (267.44 particles/L). The MPs were dominated by small particles (<1 mm), fibers (58%), and transparent (74.3%) in color. The type of polymer was mostly polypropylene (PP) and nylon. The study also found that the abundance of microfibers was significantly higher at locations 2 and 3 (where laundries were located) compared to location 1. This suggests that laundry waste is a significant source of microfibers in urban drainage.


Introduction
Rivers hold significant importance as vital water resources that demand conservation, as they serve to facilitate various human needs, such as domestic, agricultural, industrial, and livestock-related purposes.Nonetheless, human activities can often be the root cause of river pollution, which, over time, can accumulate and have adverse effects on the health of our oceans.Plastic waste is difficult to decompose in the environment and becoming one of the main pollutants in the ocean.Indonesia is ranked 5th as the country with the highest contribution of plastic waste to the sea [1].Plastic waste which degrades to less than 5 mm in size is called microplastics.Through the food web, the microplastic can be a threat to the biota and also human health.Therefore, the presence of microplastics must be given more attention.
According to a previous study, drainage channels were found to be responsible for a substantial portion of microplastic pollution in rivers, accounting for up to 73% of the total pollution [2].The close relationship between drainage channels and human activities also indicates a relationship between plastic waste and human activities.Additionally, Indonesia ranked fourth in the world's highest 1311 (2024) 012017 IOP Publishing doi:10.1088/1755-1315/1311/1/012017 2 population ranking; and this become a strong indicator of high plastic waste discharge through the ocean from anthropogenic activity [3].
Laundry, as a fundamental human activity, holds a direct and consequential connection to drainage channels, and its impact can potentially lead to substantial environmental hazards [4].Furthermore, it is essential to recognize that laundry practices can exert a far-reaching influence on the environment, particularly in relation to the prevalence of microplastics, notably microfibers.Extensive research has unveiled that these minuscule plastic particles, which are a component of the broader microplastic category, can be directly linked to the laundering process itself [5].
The study was conducted in Ketawanggede Village, Malang City, known for its high population density attributed to the presence of numerous universities that draw students from diverse regions, contributing to the unique demographic characteristics of the area.The study area is surrounded by several large universities which causes an increased demand for housing and consequently the growth of boarding houses.Investors and residents have identified the laundry business as a profitable opportunity in this growing market.However, despite its profit potential, the laundry businesses in Ketawanggede Village have yet to adopt proper waste management practices, raising concerns that the village could become a potential hotspot for microplastic pollution.Therefore, this study aimed to identify the abundance and characteristics of microplastics in urban drainage channels and also identify the impact of laundry waste on microfiber abundance.

Sampling Sites
The research was conducted in Ketawanggede Village, Malang City (Figure 1).The study was conducted in January 2023.The study area was divided into 4 points with respective point codes of 1, 2, 3, and 4. Additionally, for locations 2 and 3, four laundry sampling locations were selected, namely L1, L2, L3, and L4.Sample analysis for this study was conducted at the Soil and Groundwater Laboratory, Department of Irrigation Engineering, Faculty of Engineering, Brawijaya University.
Sampling points 1 and 4 were locations with a percentage of 100% residential.Meanwhile, sampling points 2 and 3 were locations with laundry industries in it.With a buffer of 100 m, at sampling point 2 there are 9 laundry industries, while at sampling point 3 there are 5 laundry industries.The selection of these various locations was carried out to determine the differences in the abundance and characteristics of microplastics produced by locations with the laundry industry compared with other locations.

Sample Preparation and Microplastic Identification
The first step involved in this study was sample collection.Sample collection was performed on the surface drainage channels with 3 repetitions for each location [6].Water samples were taken at the centre of the drainage channel with a depth of half of the total channel depth [7].The samples were collected by submerging 1 L glass bottles approximately 20 cm below the water surface, positioned in opposition to the direction of the river flow.Following collection, these samples were filtered using No. 4 (< 4.75 mm) and No. 50 (< 0.30 mm) sieves and subsequently transferred to 250 mL capacity sampler bottles.This method ensured the acquisition of representative samples for our comprehensive analysis.
After sample collection, the samples were further filtered in the laboratory using No. 4 (< 4.75 mm) and No. 50 (< 0.30 mm) sieves, and transferred to beakers for drying in an oven at 60℃.The separation of organic and inorganic materials was carried out using the Wet Peroxide Oxidation (WPO) solution, consisting of 20 mL Fe2SO4.7H2O0.05 M and 20 mL 30% H2O2.A stir bar was placed in the beaker and heated on a hotplate stirrer at 75℃.Then, 6 g of NaCl per 20 mL of solution was added to increase the solution density.The samples were left to settle for 24 hours to separate the microplastic particles from the sedimented particles.Density separation was performed by collecting the floating microplastic particles using a dropper pipette and transferring them to the Whatman filter paper.The samples were then dried again in an oven at 60℃.Microplastics were identified using a binocular microscope at 4x magnification to determine the shape, color, size, and type of microplastics [8].
In this study, blank samples were also collected to determine the possibility of laboratory contamination during the process [9].This was done by placing water inside the laboratory in a 3 L glass jar.From the blank samples, it was found that there was no contamination in the laboratory.
Fourier Transform Infrared (FTIR) spectroscopy was used to elucidate the functional groups found in the materials [10].Attenuated Total Reflectance (ATR) was the method used for FTIR analysis in this research.The device specification of this FTIR is A22415801432, manufactured by Shimadzu in Japan, with a spectral range between 4500 and 500 cm -1 .

Statistical Analysis
The significance test was conducted using the Kruskal-Wallis test method by RStudio software, a widely recognized and powerful statistical tool for analyzing non-parametric data.This method was chosen for its robustness in situations where the assumptions of normal distribution and homogeneity of variances are not met, making it particularly suitable for the analysis of microplastic abundance across various sampled locations.The Kruskal-Wallis test, a non-parametric equivalent of the one-way analysis of variance (ANOVA), was performed to determine whether there were significant differences in the abundance of microplastics among the sampled locations.The significance level (p) was set at 0.05, adhering to the standard threshold for statistical significance, which allows for a rigorous evaluation of the data [11].
To provide a more comprehensive understanding of the data, the Dunn test was conducted following the Kruskal-Wallis test.The Dunn test is a post hoc analysis that allows for multiple pairwise comparisons to be made among the sampled locations.This analysis helps to identify which specific locations exhibit stochastic dominance in terms of microplastic abundance, providing valuable insights into the relative levels of contamination in different areas.By employing both the Kruskal-Wallis and Dunn tests, this study ensured a thorough examination of the data and produced a robust assessment of the significance and dominance of microplastics among the studied groups.

Spatial Distribution of Microplastic Abundance
The presence of microplastic contamination has been ascertained at the designated observation sites.The average abundance of microplastics in the study locations was 169,61 particles/liter.This abundance value increased from point 1, 2, 3, to 4 (Figure 2).The lowest abundance value was 90,44 particles per liter at point 1, while the highest was 267.44 particles/liter at point 4.This observation aligns with earlier research, which suggests that the abundance of microplastics corresponds to the level of population activity [12,13].The statistical test using the Kruskal-Wallis test showed a significant difference in microplastic abundance among the research locations (p-value = 0.02374) Based on the research conducted in the drainage channels, it was found that the abundance of fibertype microplastics increased in locations where laundry industries were located.Subsequently, four samples were taken from the laundry locations with the respective location codes L1, L2, L3, and L4.Based on the research findings, the average abundance of microplastics resulting from laundry waste was 538,25 particles per liter.The lowest abundance was observed at L2 (418.33 particles/liter), while the highest abundance was found at L1 (686.50 particles/liter) (Figure 3).This is consistent with previous research, which stated that densely populated areas can be a significant contributor to the highest levels of microplastic pollution [14].

The Characteristics of Microplastics
In the study area (Figure 4), Small Microplastics (SMP) were found to dominate at each drainage sampling point.The highest SMP abundance was observed at point 1 (95.69%).And then, Large Microplastics (LMP) were most dominant at point 4 (22.16%).The average values for SMP and LMP were 433.08 particles/liter and 75.5 particles/liter, respectively.Consistent with the preceding discussion, on a laundry sampling point, SMP (Small Microplastics) is also the dominant type of microplastic (>70% for each sampling location) (Figure 5).Based on these results, it was found that fiber-type microplastics were the most dominant type among the four laundry locations.This further strengthens the evidence that laundry activities contribute to the abundance of microplastics in the drainage channels.Based on previous research, it has been revealed that the smaller the size of microplastic particles, the higher the ecological risk as well.This phenomenon is attributed to the heightened potential of smaller particles to attract diverse pollutants from the surrounding environment [15].In connection with this matter, it is projected that there will be adverse effects on other organisms that inhabit the same environment [16].The analysis of microplastics within the drainage sampling points revealed a diverse array of microplastic types, encompassing fragments, fibers, films, pellets, and foam, as visually depicted in Figure 6(a).Among these distinct microplastic categories, fragments emerged as the predominant type at points 1 and 2, accounting for a substantial proportion of 65.07% and 66.66%, respectively.This high prevalence of microplastic fragments is of considerable interest, as it signifies a potential link to the breakdown of larger plastic materials [17].Such a phenomenon can be attributed to various sources, including the degradation of plastic waste within the local environment.This is consistent with the location of the study, which is in an area with a relatively high population density.On the other hand, fiber-type microplastics were found to dominate at points 3 and 4 (72.65% and 74.99%).The dominance of fiber-type microplastics is related to the presence of several laundry industries in the study area.At the specific laundry sampling points within our study, an insightful breakdown of microplastic types was observed, with fibers comprising the majority at a noteworthy 56% of the total microplastics detected.In addition to fibers, fragments accounted for a substantial 32%, while films constituted 7%, pellets 11%, and foams 3% of the microplastic composition, as visually represented in Figure 7.This distinctive profile of microplastic types merits in-depth consideration, as it resonates with prior research findings that consistently point to the prevalence of fiber-type microplastics across diverse land-use scenarios, particularly in regions characterized by high population density [18].The predominance of fiber-type microplastics at our laundry sampling points hints at a compelling connection between clothing laundering processes and microplastic contamination, which is further corroborated by the presence of multiple laundries in the vicinity of our study site [19].The role of laundry operations in releasing microplastics into the local environment needs more investigation.This emphasizes our research's importance in confirming the significance of fiber-type microplastics and the necessity for sustainable practices in the laundry industry to reduce their environmental impact.Our study aims to offer insights into microplastic pollution from human activities and assist in developing policies to address this environmental issue.
Moreover, by using the Kruskal-Wallis method for significance testing, a notable significance value was detected at a laundry sampling point of different microplastic type (p-value < 0.05).Post hoc analysis using the Dunn test unveiled a substantial variance in the abundance of fiber and fragment-type microplastics compared to film, pellet, and foam forms.Based on the above results, the fibers detected can originate from textile fibers and ropes [20].On the other hand, the fragments detected may have originated from PVC pipes used in laundry wastewater disposal [21].
Regarding their color, on the drainage sampling point, transparent microplastics were the most dominant (74.3%).Other colors found in the study area included black (12.8%), red (11.6%), blue (1.2%), and green (0.1%) (Figure 6(b)).This is consistent with previous research conducted in Vietnam, which demonstrated that transparent color is the predominant microplastic color found in drainage channels [22].Based on FTIR with the ATR method, it was found that the type of polymer identified at locations 1 and 2 is Polypropylene (PP), while at locations 3 and 4, it is nylon.Polypropylene (PP) is commonly used for bottle caps, straws, food containers, and diapers [23].Previous research states that PP, PE, PVC, LDPE, and HDPE are some of the polymer types commonly encountered in household items [22].This aligns with the polymer types found at the study site, specifically PP, considering the study site's densely populated residential.
On the other hand, nylon is used in various applications such as clothing, ropes, and fishing lines [24].Nylon is one of the polymer types frequently employed in garment production [25].The increased presence of fiber-type microplastics at this particular point can stem from the clothing-washing process, subsequently entering water channels [26].In studies previously conducted, it has been demonstrated that approximately 35% of microplastics in aquatic environments can originate from fibers formed during textile washing processes [27].This is consistent with the possibility that the microplastics found are a result of anthropogenic activities, considering that the study area is densely populated.
The study was conducted in a specific location, so the results may not be generalizable to other areas.The study only looked at a small number of laundry industries, so it is possible that the results would be different if a larger number of industries were studied.The study did not look at the impact of different types of laundry detergents on the release of microplastics.It is important to do more research on the impact of industrial laundry effluents on microplastic pollution.This research could help us to develop better ways to reduce the release of microplastics into the environment.

Conclusion
This study investigated the impact of industrial laundry effluents on the prevalence and types of microplastics in drainage systems.The results showed that small microplastics (SMPs) were the most common type of microplastic in both laundry sampling points and drainage channels.Fibers were the most abundant SMP type, accounting for 56% of the total SMPs identified in drainage channels and 58% of the SMPs identified at laundry sampling points.Fragments were the second most abundant SMP type, followed by films, foams, and pellets.The Kruskal-Wallis test showed that there were statistically significant differences in the types of SMPs found in laundry sampling points and drainage channels.This suggests that the presence of laundry industries can change the composition of SMPs in drainage systems.This means that industrial laundries release a lot of small plastic fibers into the water.These fibers can end up in drainage systems and eventually in the environment, where they can harm wildlife and pollute our oceans.The study was conducted in a specific location, so the results may not be generalizable to other areas.However, the findings of this study suggest that industrial laundry effluents are a significant source of microplastic pollution and that more research is needed to understand the full extent of the problem.This research could help us to develop better ways to reduce the release of microplastics into the environment.

Figure 2 .
Figure 2. The abundance of microplastics at the research location.

Figure 3 .
Figure 3.The abundance of microplastics in the laundry study area.

Figure 4 .
Figure 4. Analyzing the presence of small microplastic particles (SMP) versus large microplastic particles (LMP) in the study area.

Figure 5 .
Figure 5.Comparison of the abundance of small microplastic particles (SMP) and large microplastic particles (LMP) in the laundry study area.

Figure 6 .
Figure 6.Microplastic characterization in drainage sampling point based on shape (a) and color (b).

Figure 7 .
Figure 7. Microplastic characterization in the laundry study area based on shape.