Since the sixties of the last century the production of plastics has grown almost 9% each year. In 2015, 322 millions of tons were produced according to UN data. Later part of plastic ends in the environment, particularly in the marine environment, around eight million tons per year [1]. The water, microorganisms and sunlight break down the plastic until is reduced to small particles of a few microns in length [2]. Some are so small that they are ingested by marine organisms due to their similar size with microplankton, and microplastics (MPs), also contain attached organic pollutants [3]. MPs are small synthetic particles that come from petroleum derivatives, are difficult to degrade and their origin is in industrial activity and domestic consumption, being present in detergents, toothpastes, salt, in skin products such as exfoliants and sunscreens and even many synthetic fibers from clothing and tires [4]. The problem is that these materials are toxic, abrasive and difficult to treat due to their small size [5]. But the question that science must still answer is from what amount ingested plastic can be a problem for human health. There are two risks, on the one hand the impact of the physical presence of plastic particles and, on the another, the possible toxicity of its chemical components. Studies carried out like “Orb Media”, in collaboration with the Universities of New York and Minnesota, they determined that MPs are omnipresent in the human food chain. According to this study, it was possible to detect the presence of MPs in the feces of people who lives in Europe, Russia and Japan, different types of plastic were found in eight volunteers from this pilot study, presented during a gastroenterology congress in Vienna as a world first [6]. For a week, five women and three men, ages 33 to 65, residing in Finland, Netherlands, Great Britain, Poland, Italy, Russia, Japan, and Austria, wrote down what they ate, the size of the plastic samples found in their stool varies from 50 to 500 micrometers, more or less the thickness of a hair.

Currently assumed they were ingested through seafood that the volunteers consumed, but also from the water in plastic bottles, drinks, or food wrapped in plastic [7]. These products correspond to daily consumption and are in contact with water, the bad disposal of waste also causes large amounts of MPs to be poured into the sewer system [8]. The MPs found in drinking water collection and distribution networks in the city of Riobamba are a constant concern, since the presence of this contaminant in water resources is evident [9]. That is why the concern becomes bigger. In Riobamba city due to the presence of an increasing vehicular flow, the friction between the asphalt in contact with tires of the cars generates the detachment of small residues of it, these residues come to contain an element called plasticizer of di (2-ethylhexyl) phthalate (DEHP) [10], this is a chemical polymer in liquid state derived from petroleum, is commonly added to plastics to make them more flexible, this additive is incorporated in the manufacturing process of the tires and turns out to be very harmful for the ecosystem and for the human being since it is a genotoxic, carcinogenic element [11]. 60% of synthetic rubber and 75% of natural rubber is used in the manufacture of tires and related products [12]. According to data provided by Beliczky and Fajen, the type of rubber used for the manufacture of tires until the year 1993 is natural rubber, however this was modified and currently polymers are used as: Styrene-butadiene (SBR), Polybutadiene (BR), and in very few quantities Polychloroprene (CR), which being modified compounds are more difficult to degrade and whose problem is the chemicals and other elements added as DEHP type plasticizers [13], This additive is compatible with CR, SBR and BR type rubbers, the most widely used rubber families in the tire industry. The friction between the asphalt in contact with the tires of the cars generates the detachment of small residues [14]. Adding of physical factors such as wind [15] and water tend to move into gutters and mix with domestic and industrial wastewater and in the end may appear in the various sewer systems, there is direct contact of these waters with the biological environment becoming a major problem for the habitants of the city [16]. Therefore, the aim is to determine the percentage of source MPs from friction-degraded tires in sewer systems with the city of Riobamba as a case study.

The study area is located in the city of Riobamba, for which it coordinated with the Municipal Company of Potable Water and Sewerage of the city of Riobamba (EP EMAPAR), which provided the respective information of the sewerage networks that exist in the city. There are 41 sewage discharges, however for this investigation 28 discharges are discarded that are purely domestic since they do not have contact with tire waste, resulting in 12 sampling points in which different water samples were taken in order to detect the presence of microplastic from tires in them.

For the investigation we took into account what was indicated by Rojo Nieto & Montoto [19], who establish that the classification of plastic particles according to their size is of a range between 5 mm to 1 μm to denominate it microplastic, it should be taken into account that the analyzed samples are experimental samples that contain elements considered as DEHP type plasticizers from 2 to 6 field units and other polymers such as CR, BR, SBR, for every 250 mL of filtered water as indicated below.

Based on the results obtained in the investigation, after collected and analyzed 30 wastewater samples in different sewage collectors in Riobamba city, is established that in 24 of the samples analyzed there is evidence of the presence of MPs, which represents 80% of the total samples analyzed in the laboratory. Since there are no standardized parameters for the amount of microplastics allowed to be discharged into water bodies, but based on toxicity studies carried out by different organizations, it can be concluded that the amount and type of MPs found in the samples analyzed represent an average risk to the health of animals living in aquatic environments as well as to humans. In addition, the lack of standardized parameters and specific techniques for identifying MPs makes it difficult to establish the chemical and physical properties of the particles found, which is why it was not possible to give a high degree of reliability to the results obtained. Further research should apply other methods for the characterization of microplastics in which the chemical properties of each particle found can be identified. The source of contamination of wastewater with MPs comes from the substitution of natural rubber by synthetic rubber (SBR, CR and BR) in the manufacture of tires as well as the use of different additives such as DEHP type plasticizers, oil-based polymers that are toxic and carcinogenic. It should be noted that the samples that do not present data on the amount of DEHP plasticizer were taken in the morning on days with little rain, which is a possible cause of not finding contaminating elements in these samples, since the residues that are released from the tires tend to remain on the asphalt of the street and others due to density are displaced by the wind, while other less dense elements remain in the asphalt and are transported to the gutters by the action of rain and end up being mixed with wastewater, which is why only residual water discharges - rainwater - were analysed and purely domestic discharges were ruled out. The presence of MPs in the Riobamba sewer system from the friction of the tire with the asphalt is totally evident, which shows the risk that exists when there is no control of them since the different companies that manufacture these tires do not report the content that their products have and the possible risk that can be generated for the environment and living beings.