Nowadays, a wide range of polymers with diverse chemical compositions are synthesized [1]: polyethylene (PE), low- and high-density PE (LDPE and HDPE), polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polypropylene (PP), polystyrene (PS), polyamide (PA, Nylon®), aromatic polyamide (Kevlar®), polycarbonate (PC), polyesters: polyethylene terephthalate (PET, trade names such as, e.g. Terylene, Trevira), poly(methyl methacrylate) (PMMA, Plexiglass), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE, Teflon®), polyurethane (PU ), polyisobutylene (PIB), acrylonitrile butadiene styrene (ABS), etc. Depending on the chemical composition of microplastics, they are classified as PE, PP, PET, PS, PVC, PC, PA, PUR, etc. microparticles [10]. The most abundant microplastic particles found in water are based on PP, PE and PS [11], since the most commonly used plastics are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET) and polystyrene (PS). Their chemical structure is stable and resistant to environmental impacts; plastics do not participate in microbial decomposition processes in the environment; they change only slightly due to chemical and physical effects. In principle, microplastic particles can be produced from all types of synthetic polymers. Plastics produced from a mixture of several materials with a composition optimized for use, contain, in addition to the polymer matrix, countless additives, which are already risky during use, let alone as waste, and pose a threat to living organisms.

The properties of plastics are improved and optimized for specific purposes of use with the help of additives. For example, PVC – one of the most widely used polymers in the world – is a naturally brittle, hard and white material, so it contains the greatest number of additives to meet needs for use. Fillers, which increase the volume without changing the main characteristics, are the most used additives. In terms of the quantity used, fillers are followed by plasticizers and pigments. The main functional plastic additives can be classified as:: antioxidants, antistatic agents, chemical foaming agents, flame retardants, heat stabilizers, impact resistance modifiers, light stabilizers, lubricants/slip compounds and plasticizers [21]. In addition, during production, catalysts and technological aids, e.g. lubricants are also used, which can be found in varying amounts – mostly trace amounts – in plastic products, thus also in waste and microplastic particles entering the environment.

The fillers interact with the matrix polymer and change its structure. A wide range of mineral and synthetic fillers is used (CaCO3, talc, ZnO, mica, kaolin, quartz, glass beads, wollastonite, asbestos, etc.). Al(OH)3 and Mg(OH)2 fillers release water when heated, they are also used as flame retardants [1].

Plasticizers are added to polymers to increase their elasticity, softness and pliability. Such substances are phthalates and phthalic acid esters (DPP, DEHA, DOA, DEP, DBP, DEHP, DHA, DCHP, etc.) [22], [23], which are mainly additives for rigid polymers (e.g., PVC) [24]. The main phthalates and phthalic acid esters released from PET bottles have been studied [25]. In mineral waters stored in bottles made only from new PET granules, the concentration of phthalic acid esters is negligible [24]; DiBP, DBP, BBP and DEHP can be detected in the concentration range of < 3.0 μg/dm3 - 0.2 μg/dm3, < 6.6 μg/dm3 - 0.8 μg/dm3, < 6.0 μg dm3-0,1 μg/dm3 and <16,0 ng/dm3 - 1,7 μg/dm3, only in non-carbonated mineral waters stored at different temperatures (22–60 °C) for 90 days. According to the data, the concentration of DEHP is the highest in mineral water samples, but this value does not exceed the limit of 6 μg/dm3 set for food by the European Environmental Protection Agency (EEA) [26]. However, it is interesting how these phthalates get into PET bottled water at all, since plasticizers are not used in PET production. There are many theories about the sources of phthalate contamination in bottled water: technology, especially in the processing of recycled PET; raw materials used to produce the polymer or the quality of the recycled PET; cross-contamination during bottling; and the quality of the caps [24].

Pigments are important components of plastics. Organic and inorganic dyes (e.g. azo compounds, phthalocyanine-based compounds, cobalt and lead compounds) are used for coloring them [22], [23].

Plastics are degraded by heat, mechanical action, oxygen and light. The result of this is the discoloration, wrinkling, and deterioration of the mechanical properties of plastic objects over time. To inhibit degradation, antioxidants (e.g. BHT, BHA, Irganox 1010, BPA Cyanox 2246, 425, TNPP and Irgafos 168) are added during the production process [22], [23]. Primary (alkylphenols, (hydroxyphenyl)propionates, hydroxybenzyl compounds, alkylidene bisphenols, secondary aromatic amines, thiobisphenols, aminophenols) and secondary (thioethers, phosphites, phosphonites, sterically hindered amines) antioxidants are known. To extend the life of plastics, for example, UV light stabilizers (e.g., Tinuvin XT 833 for PVC films, Shelfplus UV 4100 for food packaging, Lowlite 234 for polycarbonates, PETs and polyamides, Univul 3460 for polyurethanes [27]) or heat stabilizers (e.g. Therm-Check 7206, 7209 and 7710, PCP phosphite [27]) are added [22], [23].

Flame retardants (e.g. halogenated hydrocarbons [22], [23], PVA, alumina trihydrate and magnesium hydroxide, elemental phosphorus, phosphates, and organophosphorus compounds) are added to polymers used in the construction industry and in the manufacture of electrical and electronic products as fire regulations have become more stringent. The use of flame retardants is quite extensive, represents 10-20% of the plastic weight. The most used flame retardants are based on Br, Cl, P, Al, Mg, N, Sb, Zn, Sn and B. Flame retardants can be additive or reactive depending on their binding to the polymer. The former is not chemically bound to the polymer, they are released more easily due to weaker intermolecular interactions. Gaseous flame retardants released from plastic waste can bind to particulate pollutants in the air and enter the living organisms by inhalation, but they can also be found in drinking water and natural waters [28]. In the past, polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) were widely used for the manufacture of electronic products, but they are no longer used.

Catalysts are used in polymerization reactions. In the production of PET, an antimony compound, Sb(III)oxide, is used as a catalyst for the polycondensation reaction [24]. Directive 98/83/ EC allows a maximum concentration of Sb in drinking water of 5 μg/dm3 (EEA) [29]. According to a limited number of previous measurements in Hungary [30], the concentration of Sb dissolved from PET bottles varied in the range between 0.03 μg/dm3 and 0.8 μg/dm3 in carbonated and non-carbonated mineral waters, so it remained far below the permitted level. The concentration of Sb in carbonated mineral waters was approximately one and a half times higher than in non-carbonated mineral waters of the same quality and stored under the same conditions.

Additional additives are also used. Lubricants (e.g. fatty acid esters, fatty acid amides, metallic stearates, waxes) are used as processing aids [22], [23]. To modify the surface of the fillers, surfactants such as alkylphenols and alkylphenol ethoxylates are used as additives for PVC. Silicone surfactants are used in polyurethane foams. Antistatic agents [22], [23] protect plastic surfaces from electrostatic charging, thus eliminating the undesirable effects of charging (e.g. dust attraction, sparking, adhesion of films and textiles). Traditionally, long-chain alkylphenols, ethoxylated amines and glycerol esters such as glycerol monostearate (GMS), so-called migrating antistatic agents are used. Recently, a phenol- and amine-free antistatic (Maxomer AS -1018/75DC) has also been developed [31]. Subsequent surface treatment is also possible. Currently, permanent antistatic properties of plastics have become necessary, so conductive blocks (e.g. polyether block amides, ethylene ionomers) or interpenetrating networks (e.g. graphite, graphene, carbon nanotube, metal fibers) are created in the polymer matrix that can be used to produce a permanent static dissipation. These are dissipative polymers in their material. Biocides (e.g. triclosan) can also be used [22], [23]. Excipients used in the production of polycarbonate and epoxy resin are bisphenols (BPA). Bisphenols are widely used in the production of plastic tools and bottles. However, since 2011, the use of BPA in the manufacture of baby feeding bottles has been banned in Europe [32]. Due to its widespread use, today, the presence of BPA can be detected in the urine of 93% of the American population [33].

Additives, excipients, and monomers may dissolve in water sold in plastic bottles from the material of the bottle. Oligomers and monomers (e.g. styrene and vinyl chloride) remaining after polymerization [22], [23] are proven to be harmful to health, the latter is a carcinogen (IARC Group 1) [34]. Higher temperatures and UV light promote dissolution, and probably pH also affects the process. During transport, storage, and recycling, the polymer degrades, and BPA leaks out of it even under normal conditions, but the dissolution accelerates as the temperature increases. BPA and phthalates are not chemically but physically bound to the material of the bottles, so they leak more easily [35]. In addition to soluble BPA, water in PC bottles also contains BPS, BPAP and BPAF, while BPA contamination can also be detected in water sold in PET bottles [36]. In a study published in 2018, the phthalate content of bottled water from 21 countries was compared, and extremely high phthalate concentrations were found in the waters of many countries, especially after longer storage. The limits recommended by the World Health Organization (WHO) and the U.S. Food and Drug Administration (FDA) were exceeded by 14% of the tested waters. The authors found that at higher temperatures and longer storage, more phthalates enter the waters from the bottles. Direct sunlight and pH may also play a role in dissolution. Stored under such conditions, it is likely that most water will reach or even exceed the recommended maximum phthalate content within the warranty period [34]. Many additives in plastic manufacturing pose health risks, such as BPA, plasticizers (phthalates, phthalic acid esters) and flame retardants. Phthalates have antiandrogenic, estrogen-like effects and may cause endocrinological disorders, neurodevelopmental disorders, cardiovascular and reproductive disorders or breast cancer [37]. Bisphenols such as BPA (and BPF, BPS) are xenoestrogens, i.e. they have hormone-like effects. They can be classified as EDC (endocrine disrupting compounds, exogenous compounds that affect hormone function) compounds.