molecules

Article Ecotoxicity of the : Influence of the Structure of the Alcohol Substituent

Irina Nikolaevna Vikhareva * , Guliya Karamovna Aminova and Aliya Karamovna Mazitova

Applied and Natural Sciences Department, Ufa State Petroleum Technological University, 450080 Ufa, Russia; [email protected] (G.K.A.); [email protected] (A.K.M.) * Correspondence: [email protected]; Tel.: +7-(347)-242-0370

Abstract: A significant increase in the production of materials and the expansion of their areas of application contributed to the accumulation of a large amount of waste of polymeric materials. Most of the polymer composition is made up of plasticizers. plasticizers have been recognized as potentially hazardous to humans and the environment due to the long period of their biodegradation and the formation of persistent toxic metabolites. It is known that the industrial dioctyl adipate is characterized by reduced toxicity and a short biodegradation period. The paper describes the synthesis of a number of new asymmetric esters based on adipic acid and ethoxylated butanol by azeotropic esterification. The receipt of the products was confirmed by IR spectra. The physicochemical properties of the synthesized compounds were investigated. The glass transition temperatures of PVC composites plasticized with alkyl butoxyethyl were determined using DSC analysis. The ecological safety of esters was assessed by the phytotesting  method. Samples of adipates were tested for fungal resistance, and the process of their biodegradation  in soil was also studied. It is shown that the synthesized esters have good plasticizing properties Citation: Vikhareva, I.N.; Aminova, and are environmentally safe. When utilized under natural conditions, they can serve as a potential G.K.; Mazitova, A.K. Ecotoxicity of source of carbon for soil microorganisms and do not form stable toxic metabolites; therefore, they are the Adipate Plasticizers: Influence of not able to accumulate in nature; when the plasticizers under study are disposed of in the soil, toxic the Structure of the Alcohol substances do not enter. Substituent. Molecules 2021, 26, 4833. https://doi.org/10.3390/ Keywords: adipate plasticizer; biodegradable; environmental damage; esterification; molecules26164833

Academic Editor: Marinella Farré Urgell 1. Introduction

Received: 8 July 2021 Industrial development is inextricably linked with the expansion of the range of Accepted: 6 August 2021 chemicals used. The increase in the volume of chemicals applied is the reason for the steady Published: 10 August 2021 growth of chemical hazards for the environment and humans. A few decades ago, chemical production wastes were simply dumped into the en- Publisher’s Note: MDPI stays neutral vironment. At the same time, it was believed that gaseous substances quickly dissipate with regard to jurisdictional claims in in the atmosphere and liquids partially dissolve in water and are carried away from the published maps and institutional affil- places of release. Although solid products accumulate to a large extent in certain areas, iations. the potential hazard of industrial emissions was considered to be low. In general, the use of chemicals gave an economic effect that many times exceeded the damage caused by toxicants to nature, which, in principle, was not taken into account. However, already in 1962, Rachel Carson in the book “Silent spring” described the Copyright: © 2021 by the authors. influence of anthropogenic factors on living systems, which is not always safe, and progress Licensee MDPI, Basel, Switzerland. is associated with global risks: “No one yet knows what the ultimate consequences may This article is an open access article be” [1,2]. Under public pressure, government legislation has emerged to regulate the distributed under the terms and release of xenobiotics. conditions of the Creative Commons More than 150 million tons of synthetic polymers on a petrochemical basis, charac- Attribution (CC BY) license (https:// terized by a long period of biodegradation, are produced annually all over the world [3]. creativecommons.org/licenses/by/ Most of them are used for the production of disposable consumer products, such as food 4.0/).

Molecules 2021, 26, 4833. https://doi.org/10.3390/molecules26164833 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 4833 2 of 15

packaging. During the operation of plastic products and violation of the rules for their disposal, today about 8.3 million tons of plastic have entered the environment [4]. Environmental pollution by synthetic polymers is considered the most important environmental, economic and social threat. The widespread plastic is found in all environ- ments and affects the biota of the planet. Since most polymeric materials do not decompose when recycled in the environment at the end of their life cycle and are quite resistant to environmental influences, pollution by waste polymeric materials is closely related to other global processes and has long-term consequences [5]. The main amount of plastic enters the soil in a variety of ways: With household waste, when using in agriculture, when irrigating with plastic-contaminated water, during degradation of the road surface, when transferring plastic fragments by air [6–9]. Relatively favorable conditions for the degradation of plastic materials are formed on the soil surface: direct ultraviolet radiation, oxygen availability and relatively high temperatures. In addition, agricultural tillage contributes to the destruction of large fragments to , and soil microorganisms accelerate the biodegradation of [10–13]. Nevertheless, according to researchers’ estimates, the destruction of polymer waste in soil takes a long period of time. The degradation of plastic entering the soil is determined by the ability of the soil environment for self-purification and is carried out mainly by living organisms of the soil biota [14,15]. In this case, soil animals perform the most important functions: Regulation of the activity of microorganisms, mechanical destruction of organic fragments, their movement in the soil profile, and the formation of this profile [16–19]. The degradability of polymeric materials in the environment and their danger to living organisms are determined by the chemical composition, size, shape of particles, the presence of perforation, the degree of porosity, the presence of a filler, etc. [20]. In the literature, a negative impact, lack of influence, and even stimulation of some processes and vital functions of soil-living organisms are noted [21]. Mostly investigated are the health damage or changes in populations due to the physical presence of plastic particles in the environment or food of soil animals. Modern polymeric materials are a complex mixture of polymers, residual monomers and various additives. Of the 50 main types of synthetic polymers, more than 60,000 poly- mer compositions have been created [22], and only about 20 of them have found wide application. The most used plastic polymers are (PP; 16%), low density and linear low density polyethylene (LDPE, LLDPE; 12%), polyvinylchloride (PVC; 11%), high density polyethylene (HDPE; 10%), and polyethylene terephthalate (PET; 5%), which in total account for more than 50% of total plastics usage [4]. Much less is known about the effect on animals of various additives included in the composition of polymeric materials, for example, plasticizers or flame retardants [23,24]. Many additives, for example, , alkylphenols and polybrominated diphenyl ethers, are dangerous for the biota and can cause disruptions in the synthesis and functioning of hormones [25]. In the composition of PVC materials, plasticizers account for up to 50%. These are widely used industrial chemicals that impart elasticity, processability and some specific properties to synthetic polymers. Plasticizers enter the environment during the production, manufacture, use and disposal of polymer products. For this reason, these additives are one of the main potential sources of environmental pollution [26–29]. Phthalates and adipates, the most commonly used plasticizers, are hydrophobic and lipophilic and can accumulate in the soil. In this regard, the need arises for an accurate toxicological assessment of these compounds. There is some analogy between the physiological and toxicological properties of substances similar in chemical nature. In addition, when studying the toxicity of plasticizers, it is necessary to take into account the toxicity of the substances forming them. The type of the forming acid, like the alcohol radical, has an effect on the physiological and toxicological properties of plasticizers. For example, it is known that, in the series of o-phthalic acid esters, an increase in toxicity manifests itself with a decrease in the number of carbon atoms in the alcohol radical [30]: Molecules 2021, 26, x FOR PEER REVIEW 3 of 15

Molecules 2021, 26, x FOR PEER REVIEWwhen studying the toxicity of plasticizers, it is necessary to take into account the toxicity3 of 15

of the substances forming them. The type of the forming acid, like the alcohol radical, has an effect on the physiological and toxicological properties of plasticizers. For example, it whenis known studying that, thein the toxicity series of of plasticizers, o-phthalic acid it is esters,necessary an increase to take intoin toxicity account manifests the toxicity itself ofwith the substancesa decrease forming in the number them. The of typecarbon of theatoms forming in the acid, alcohol like the radical alcohol [30]: radical, diisooctyl has anphthalate effect on < the di (2-ethylhexyl)physiological andphthalate toxicologica < dibutyll properties phthalate of < plasticizers.diethyl phthalate For example, < dimethyl it isphthalate. known that, in the series of o-phthalic acid esters, an increase in toxicity manifests itself Molecules 2021, 26, 4833 with aPolyvinyl decrease chloridein the number containing of carbonester plastici atomszers in isthe highly alcohol susceptible radical [30]: to3 microbiolog- of diisooctyl 15 phthalateical attack. < di Microscopic (2-ethylhexyl) fungi phthalate and bacteria < dibutyl us ephthalate similar plasticizers< diethyl phthalate as a carbon < dimethyl source. phthalate.However, it is known that some phthalates, such as diethylhexyl phthalate (DOP), nega- tively affect the reproductive organs by acting as a mimic of the sex hormone estrogen diisooctylPolyvinyl phthalate chloride < di (2-ethylhexyl)containing ester phthalate plastici < dibutylzers is highly phthalate susceptible < diethyl phthalateto microbiolog- ical<[31–33], dimethyl attack. which phthalate.Microscopic has contributed fungi and to the bacteria limited us usee similar of phthalate plasticizers plasticizers. as a carbon Non-toxic, source. bio- However,degradablePolyvinyl it is PVC chlorideknown adipate containingthat plasticizerssome ester phthalates, plasticizers are a suchsafe is highly alternative.as diethylhexyl susceptible Ecotoxicity tophthalate microbiological studies (DOP), of nega-the in- tivelyattack.dustrial affect Microscopic plasticizer the reproductive fungi dioctyl and bacteriaadipate organs use have by similar acconfirmedting plasticizers as a itsmimic safety as a carbonof for the living source.sex hormone organisms However, estrogen [34–36]. [31–33],it is knownIn whichthis that regard, has some contributed we phthalates, obtained to such asymmetricthe as limited diethylhexyl useesters of phthalate phthalateof adipic (DOP), acid plasticizers. and negatively ethoxylated Non-toxic, affect butanol, bio- degradabletheinvestigated reproductive PVC the organs adipate possibility by plasticizers acting of astheir a mimic useare aas of safe PVC the sexalternative. plasticizers, hormone Ecotoxicity estrogen and also [31 – studiedstudies33], which oftheir the envi- in- has contributed to the limited use of phthalate plasticizers. Non-toxic, biodegradable PVC dustrialronmental plasticizer safety. dioctyl adipate have confirmed its safety for living organisms [34–36]. adipate plasticizers are a safe alternative. Ecotoxicity studies of the industrial plasticizer In this regard, we obtained asymmetric esters of adipic acid and ethoxylated butanol, dioctyl2. Results adipate have confirmed its safety for living organisms [34–36]. investigatedIn this regard, the possibility we obtained of their asymmetric use as PVC esters plasticizers, of adipic acid and and also ethoxylated studied their bu- envi- ronmentaltanol,2.1. Synthesis investigated safety. of Butoxyethanol the possibility of their use as PVC plasticizers, and also studied their environmentalEthoxylation safety. of alcohols has been well studied [37,38] (Scheme 1). The synthesis and 2.characteristics Results of the product are described in our previous works [39,40]. 2. Results 2.1.2.1. Synthesis Synthesis ofof ButoxyethanolButoxyethanol EthoxylationEthoxylation of of alcohols alcohols has has been been well well studied studied [37,38 [37,38]] (Scheme (Scheme1). The 1). synthesis The synthesis and and characteristicscharacteristics ofof the the product product are are described described in our in previousour previous works works [39,40 ].[39,40].

Scheme 1. Synthesis of butoxyethanol.

SchemeButoxyethanol 1. Synthesis of butoxyethanol. with a degree of ethoxylation n = 1: density—0.9648, refractive in- Schemedex—1.4267, 1. Synthesis molecular of butoxyethanol. weight (calculated)—1 18, yield—90.5%, reaction time—0.5 h. Butoxyethanol with a degree of ethoxylation n = 1: density—0.9648, refractive index— 1.4267,2.2. ButoxyethanolThe molecular Synthesis weight of withEsters (calculated)—118, a ofdegree Adipic ofAcid ethoxylation yield—90.5%,and Butoxyethanol n reaction= 1: density—0.9648, time—0.5 h. refractive in- dex—1.4267,2.2. TheThe Synthesis synthesis molecular of Esters of unsymmetrical weight of Adipic (calculated)—1 Acid and adipates Butoxyethanol18, of yield—90.5%, butoxyethanol reaction was carried time—0.5 out byh. two- stageThe esterification synthesis of unsymmetricalof adipic acid in adipates one reac oftion butoxyethanol volume (Scheme was carried 2). Initially, out by two- to obtain a 2.2.stagemonoester, The esterification Synthesis a higher of of Esters adipic molecular of acidAdipic in weight oneAcid reaction and alcohol Butoxyethanol volume was (Schemeloaded 2into). Initially, the reaction to obtain mass in an aequimolar monoester,The synthesis ratio a higher of of the molecularunsymmetrical starting weightreagents. adipates alcohol To faci was oflitate loadedbutoxyethanol the into removal the reaction was of the carried massreleased inout an water, by two- the stageequimolarsynthesis esterification ratiowas ofcarried the of starting adipic out in reagents.acid a toluene in one To facilitate reacmedium,tion the volume the removal reaction (Scheme of the mass released 2). wasInitially, water, bubbled to the obtain with aan monoester,synthesisinert gas. was Thea higher carried synthesis outmolecularin time a toluene was weight controlled medium, alcohol the by wasreaction the loaded acid mass number into was the bubbledof reactionthe esterificate. with mass an in Then an inert gas. The synthesis time was controlled by the acid number of the esterificate. Then equimolardiester was ratio obtained. of the starting For this, reagents. another alcoholTo facilitate was loadedthe removal into the of thereactor released in the water, ratio acid:the diesteralcohol was = 1:1.2. obtained. Isolation For this, of target another esters alcohol was was carried loaded out into according the reactor to in the the method ratio acid: described synthesisalcohol = 1:1.2.was Isolationcarried out of target in a esterstoluene was medium, carried out the according reaction to mass the method was bubbled described with an in [41]. Target esters were obtained with a yield of at least 80%. inertin [41 gas.]. Target The esterssynthesis were time obtained was with controlled a yield ofby at the least acid 80%. number of the esterificate. Then diester was obtained. For this, another alcohol was loaded into the reactor in the ratio acid: alcohol = 1:1.2. Isolation of target esters was carried out according to the method described in [41]. Target esters were obtained with a yield of at least 80%.

where R1 = [СН2-СН2-О]-C4H9, R2 = Butyl, Hexyl, Octyl, Decyl.

Scheme 2. Synthesis of unsymmetrical esters of adipic acid. Scheme 2. Synthesis of unsymmetrical esters of adipic acid. whereThe R1 physicochemical= [СН2-СН2-О]-C4H9, properties R2 = ofButyl, the obtainedHexyl, Octyl, adipates Decyl. are presented in the Table1.

2.3. IR Spectra Scheme 2. Synthesis of unsymmetrical esters of adipic acid. The spectra of the synthesized esters lack an absorption band in the range of 1685–1687 cm−1, which is characteristic of stretching vibrations of the carbonyl group

Molecules 2021, 26, x FOR PEER REVIEW 4 of 15

The physicochemical properties of the obtained adipates are presented in the Table 1.

Table 1. Physicochemical properties of alkyl butoxyethyl adipates. Molecules 2021, 26, 4833 4 of 15 Indicators Ester Molecular Acid Number Ester Number d204 inWeight associates of aliphaticmg КОН carboxylic/g acids. Inmg the synthesizedКОН/g esters, the stretching vibra- BBEA tions302 of the carbonyl group 0.1 are shifted to the high-frequency 369 region and 1.0452 appear as a strong −1 HBEA characteristic330 band corresponding 0.1 to the ester bands 337 in the 1737 cm 1.0636region. There are also absorption bands that refer to the vibrations of the C-O-C ester fragment—1176 cm−1 OBEA for358 butyl butoxyethyl adipate, 0.1 1175 cm−1 for hexyl 311 butoxyethyl adipate, 1.0819 1173 cm−1 for DBEA octyl386 butoxyethyl adipate, 0.1 1173 cm−1 for decyl butoxyethyl 288 adipate. 1.1003

2.3. IR Spectra Table 1. Physicochemical properties of alkyl butoxyethyl adipates. The spectra of the synthesized esters lack an absorptionIndicators band in the range of 1685– −1 1687 cm , which is characteristicEster of stretching vibrationsAcid Number of the carbonylEster group Number in associ- Molecular Weight d20 ates of aliphatic carboxylic acids. In the synthesized esters,mg KOH/g the stretchingmg vibrations KOH/g of the 4 carbonyl group are shiftedBBEA to the high-frequency 302 region and 0.1 appear as a strong 369 character- 1.0452 −1 istic band correspondingHBEA to the ester 330bands in the 1737 cm 0.1 region. There are 337 also absorp- 1.0636 −1 tion bands that referOBEA to the vibrations 358 of the C-O-C ester 0.1 fragment—1176 311cm for butyl 1.0819 butoxyethyl adipate, 1175 cm−1 for hexyl butoxyethyl adipate, 1173 cm−1 for octyl butoxy- DBEA 386 0.1 288 1.1003 ethyl adipate, 1173 cm−1 for decyl butoxyethyl adipate.

2.4. Determination of Glass Transition Temperatures 2.4. Determination of Glass Transition Temperatures A decrease in the glass transition temperature with the introduction of a plasticizer is A decrease inan the important glass transition criterion for temperature assessing the with effectiveness the introduction of its plasticizing of a plasticizer action. is an important criterionThe for glass assessing transition the temperature effectiveness was of determined its plasticizing by DSC action. on a DSC-1 instrument The glass transition(Mettler Toledo)temperature at a heating was ratedetermined of 2 K/min. by TheDSC transition on a DSC-1 of a polymerinstrument from a glassy (Mettler Toledo) toat aa highlyheating elastic rate stateof 2 K/min. is accompanied The transition by an increase of a polymer in the heat from capacity a glassy of theto polymer, a highly elastic statewhich is isaccompanied reflected in the by form an increase of a characteristic in the heat break capacity (step) onof the DSCpolymer, curve. The Tg which is reflectedvalue in the was form found of in a thecharacteristic middle of the break step corresponding(step) on the toDSC this curve. transition. The Tg value was found in theTo middle assess the of effectthe step of plasticizers corresponding on the glassto this transition transition. temperature, plasticized PVC compositions with a plasticizer content of 50 ppm were used for 100 ppm PVC (Figures1 and2 ). To assess the effect of plasticizers on the glass transition temperature, plasticized The DSC thermograms of HBEA and OBEA look similar. PVC compositions withTable a 2plasticizer shows the content glass transition of 50 ppm temperatures were used of PVC for 100 compositions ppm PVC with (Fig- the content ures 1 and 2). Theof DSC the obtained thermograms alkyl butoxyethyl of HBEA and adipates. OBEA look similar.

Figure 1. DSC thermogramFigure of 1. DSCPVC thermogram composition of with PVC compositionBBEA. with BBEA.

2.5. Study of the Environmental Safety of Plasticizers by the Phytotesting Method Within a month, we observed the growth of plants on a control soil sample and on soil samples, into which the obtained plasticizers were introduced in an amount of 1 g/dm3. For

Molecules 2021, 26, 4833 5 of 15

the selected biological objects, morphological parameters were determined and calculations were made for seed germination and germination energy for each phytotest system. Molecules 2021, 26, x FOR PEER REVIEW According to these indicators, the average soil toxicity and the effect5 of of 15 the studied additives on plant growth were evaluated when the samples were kept for one month. The phytotesting results are shown in the Table3.

Figure 2. DSC thermogramFigure of 2. PVCDSC thermogramcomposition of with PVC DBEA. composition with DBEA.

Table 2. Glass transition temperatures of PVC compositions containing alkyl butoxyethyl adipates. Table 2 shows the glass transition temperatures of PVC compositions with the con- Glass Transition tent of the obtained alkylPVC butoxyethyl Composition adipates. ∆T, ◦C Temperature, ◦C Table 2. Glass transition temperaturesPVC of PVC compositions containing 87.5 alkyl butoxyethyl – adipates. DOP −37.0 124.5 PVC Composition GlassBBEA Transition Temperature,−48.7 °С ∆Т, °С 136.2 PVC HBEA 87.5 −49.2 – 136.7 DOP OBEA −37.0 −49.7124,5 137.2 BBEA DBEA −48.7 −50.2136.2 137.7 HBEA −49.2 136.7 OBEATable 3. Results of determining the phytotoxicity−49.7 of alkyl butoxyethyl adipates.137.2 DBEA −50.2 Indicators 137.7 Sample Average Length Germination Average Root Seed Average Soil 2.5. Study of the Environmentalof Safety the Ground of Plasticizers by the PhytotestingEnergy Method for ITF Length, cm Germination, % Toxicity Part, cm 5 Days, % Within a month, we observed the growth of plants on a control soil sample and on watercress 1.96 0.51 93 81 1.22 Control soil samples, into which the obtained plasticizers were introduced in an amount of 1 1.29 g/dmradish3. For the selected 14.36 biological 8.32objects, morphological 91 parameters were 77 determined 1.35 and calculationswatercress were2.01 made for seed germination 0.56 and germination 90 energy 76 for each 1.02 phytotest BBEA 1.01 system.radish 14.42 8.64 91 77 1.00 watercressAccording to1.95 these indicators, 0.50 the average soil 87 toxicity and the 72effect of the 0.99 studied HBEA 1.00 additivesradish on plant 14.30 growth were 8.90evaluated when the 90 samples were 73kept for one 1.00 month. The phytotesting results are shown in the Table 3. watercress 1.80 0.38 73 69 0.92 OBEA 0.95 Tableradish 3. Results of 13.90determining the phytotoxicity 8.01 of alkyl 75 butoxyethyl adipates. 64 0.97 watercress 1.62 0.24 65 60 0.83 DBEA 0.84 radish 12.21 7.19Indicators 62 61 0.85 Average Average Length of Germination Average Sample Root Seed Germi- the Energy for 5 ITF Soil Tox- Length, nation, % Ground Days, % icity cm Part, cm watercress 1.96 0.51 93 81 1.22 Control 1.29 radish 14.36 8.32 91 77 1.35 watercress 2.01 0.56 90 76 1.02 BBEA 1.01 radish 14.42 8.64 91 77 1.00 HBEA watercress 1.95 0.50 87 72 0.99 1.00

Molecules 2021, 26, 4833 6 of 15

Radish and watercress were selected as indicator plants. The choice of these crops is due to the rapid germination of their seeds and high germination rate, which is no- ticeably reduced in the presence of pollutants; shoots and roots under the influence of toxic substances undergo morphological changes (growth retardation, curvature of shoots, reduction in root length, etc.). In the control sample, the value of the average soil toxicity is 1.29, which corresponds to the stimulation of the growth and development of rasters. In experimental samples, the value of the test function fluctuates depending on the tested ester and gradually decreases with the elongation of the adipate molecule, that is, the observed toxicity of the soil sample with the ester used increases slightly. However, utilization of even the longest molecule from the entire range, decyl butoxyethyl adipate, does not have an adverse toxic effect on the growth and development of each phytotest system. Thus, the value for BBEA and HBEA corresponds to the norm: The factor does not significantly affect the development of test objects. The magnitude of the test functions is at the control level. The values for OBEA and DBEA correspond to low toxicity: There is a degree of decrease in test function compared to control.

2.6. Study of the Fungal Resistance of Alkyl Butoxyethyl Adipates Table4 shows the results of studies of the obtained alkyl butoxyethyl adipates for fungal resistance.

Table 4. Fungal resistance of alkyl butoxyethyl adipates.

The Degree of Fouling in Points Ester Aspergillus niger Pénicillium funiculosum Trichoderma lignorum BBEA 4 4 4 HBEA 4 4 4 OBEA 3 3 3 DBEA 3 3 3

Analysis of the results showed that all the obtained asymmetric esters of adipic acid and ethoxylated alcohol during the experiment time (28 days) showed the ability to serve as a food source for microscopic fungi: A significant overgrowth of fungal mycelium was observed in all samples. However, the mushroom resistance of OBEA and DBEA esters is slightly higher.

2.7. Biodegradation of Alkyl Butoxyethyl Adipates in Soil Biodegradation of the synthesized esters was tested in soil (Figures3–6). The starting esters under conditions of natural degradation are rapidly hydrolyzed, and monoesters were found only in trace amounts. In the process of decomposition, a gradual accumulation of the corresponding alcohols is observed; however, butoxyethanol completely biodegrades within four days, and the corresponding aliphatic alcohols are oxidized within 5–10 days, depending on the length of the hydrocarbon chain. The fig- ures do not show the alcohols formed during biodegradation, since these compounds are quickly subjected to further attack by microorganisms with the formation of the corre- sponding acids. MoleculesMoleculesMolecules 20212021 2021,, 26,26 26,, x, 4833 xFOR FOR PEER PEER REVIEW REVIEW 77 of 7of of 15 15 15 Molecules 2021, 26, x FOR PEER REVIEW 7 of 15

FigureFigure 3.3. BiodegradationBiodegradation of ofof BBEABBEA inin soil.soil.

Figure 4. Biodegradation of HBEA in soil. FigureFigure 4.4. BiodegradationBiodegradation ofof HBEAHBEA inin soil.soil.

Figure 5. Biodegradation of OBEA in soil. Figure 5. Biodegradation ofof OBEAOBEA inin soil.soil.

MoleculesMolecules 20212021,, 2626,, 4833x FOR PEER REVIEW 88 ofof 1515

Figure 6. Biodegradation of DBEA in soil.

3. DiscussionsThe starting esters under conditions of natural degradation are rapidly hydrolyzed, and monoestersPolymeric materials were found and productsonly in trace made am fromounts. them In arethe widespread.process of decomposition, A large share in a thegradual composition accumulation of PVC of composites the corresponding is occupied alcohols by plasticizers, is observed; the however, characteristics butoxyethanol of which determinecompletely the biodegrades properties within of the composites.four days, and the corresponding aliphatic alcohols are oxidizedThe mostwithin commonly 5–10 days, used depending plasticizer, on the dioctyl length phthalate, of the hydrocarbon has a potentially chain. The hazardous figures environmentaldo not show the impact. alcohols A safe formed alternative during to phthalatesbiodegradation, should since have goodthese plasticizingcompounds prop- are erties,quickly be subjected biodegradable to further upon attack disposal by andmicroorganisms safe during use, with and the also formation not contribute of the tocorre- the accumulationsponding acids. of toxic metabolites that contribute to the disruption of the biosphere balance. Evaluation of the plasticizing properties of the obtained adipate plasticizers was carried3. Discussions out using the glass transition temperature. A decrease in the glass transition temperature due to the introduction of a plasticizer is one of the criteria for assessing the Polymeric materials and products made from them are widespread. A large share in effectiveness of its plasticizing action. A decrease in the glass transition temperature of a the composition of PVC composites is occupied by plasticizers, the characteristics of polymer with the introduction of a plasticizer makes it possible to expand the temperature which determine the properties of the composites. range of its highly elastic state. In addition, as a result, a decrease in the viscosity of The most commonly used plasticizer, dioctyl phthalate, has a potentially hazardous polymer melts makes it possible to significantly facilitate their processing. environmental impact. A safe alternative to phthalates should have good plasticizing Studies have shown that all the obtained alkyl butoxyethyl adipates effectively reduce properties, be biodegradable upon disposal and safe during use, and also not contribute the glass transition temperature of PVC-based composites. Moreover, the lengthening to the accumulation of toxic metabolites that contribute to the disruption of the biosphere of the chain of the alkyl substituent increases the temperature range of the highly elastic statebalance. of the obtained composites. Thus, the long group of the alcohol substituent more effectivelyEvaluation prevents of the the plasticizing interaction properties of the long of chains the obtained of PVC, adipate providing plasticizers greater flexibility was car- andried ductility.out using the glass transition temperature. A decrease in the glass transition temper- atureSince due to adipate the introduction plasticizers of in a PVC plasticizer compositions is one of are the not criteria bonded for to assessing the polymer the effec- by a chemicaltiveness of bond, its plasticizing these additives action. during A decrease operation in the and glass under transition the influence temperature of certain of factors a pol- tendymer to with migrate the introduction from the film. of In a thisplasticizer regard, makes it is important it possible that to the expand developed the temperature plasticizers haverange reduced of its highly toxicity elastic and state. do not In formaddition, toxic as metabolites a result, a indecrease the process in the of viscosity biodegradation. of poly- mer meltsEvaluation makes of it the possible biodegradation to significantly of the facilitate obtained their alkyl processing. butoxyethyl adipates showed that theStudies decomposition have shown path that of all diester the obtained plasticizers alkyl includes butoxyethyl sequential adipates hydrolysis effectively of ester re- bondsduce the through glass transition the formation temperature of a monoester of PVC-based of adipic composites. acid. The Moreover, presence the of lengthen- the latter wasing of observed the chain only of the in alkyl trace substituent amounts. This increa is probablyses the temperature due to the range same of reactivity the highly of bothelas- carboxyltic state of groups the obtained of adipic composites. acid. Determination Thus, the long of thegroup stability of the ofalcohol the monoester substituent in more such experimentseffectively prevents is important, the interaction since it isof believedthe long chains that it isof thePVC, monoester providing of greater the commercial flexibility plasticizerand ductility. DEHP that exhibits toxicity and endocrine activity [42–47]. Scheme3 shows the biodegradationSince adipate pathway plasticizers for butyl in PVC butoxyethyl compositions adipate. are Other not bonded adipates to obtainedthe polymer undergo by a biodegradationchemical bond, these in a similar additives manner during to operatio form then corresponding and under the alcoholsinfluence and of certain acids. factors tend to migrate from the film. In this regard, it is important that the developed plasticizers have reduced toxicity and do not form toxic metabolites in the process of biodegradation. Evaluation of the biodegradation of the obtained alkyl butoxyethyl adipates showed that the decomposition path of diester plasticizers includes sequential hydrolysis of ester

Molecules 2021, 26, x FOR PEER REVIEW 9 of 15

bonds through the formation of a monoester of adipic acid. The presence of the latter was observed only in trace amounts. This is probably due to the same reactivity of both car- boxyl groups of adipic acid. Determination of the stability of the monoester in such exper- iments is important, since it is believed that it is the monoester of the commercial plasti- cizer DEHP that exhibits toxicity and endocrine activity [42–47]. Scheme 3 shows the bio- Molecules 2021, 26, 4833 degradation pathway for butyl butoxyethyl adipate. Other adipates obtained undergo9 bi- of 15 odegradation in a similar manner to form the corresponding alcohols and acids.

SchemeScheme 3. 3.PathPath of of butyl butyl butoxyethyl butoxyethyl adipate adipate biodegradation. biodegradation.

AdipicAdipic acid, acid, butoxyethanol, butoxyethanol, and and the the corre correspondingsponding aliphatic aliphatic al alcohols—butanol,cohols—butanol, hex- hex- anol,anol, octanol, octanol, and and decanol—were decanol—were found found as as further further metabolites metabolites determined determined in in the the course course ofof the the study. study. With With the the lengthening lengthening of of the the chain chain of of the the alcohol alcohol being being formed, formed, the the rate rate of of hydrolysishydrolysis during during biodegradation biodegradation decreased, decreased, and and decanol decanol was was formed formed most most slowly slowly in in the the system.system. Thus, Thus, lengthening lengthening the the chain chain of of the the ester ester molecule molecule limits limits the the rate rate of of degradation. degradation. ThisThis is is probably probably due due to to the the difficulty difficulty of of pene penetrationtration of of the the ester ester molecule molecule through through the the cell cell membrane of microorganisms that carry out the process, that is, shorter molecules are more membrane of microorganisms that carry out the process, that is, shorter molecules are actively processed by organisms present in the soil. more actively processed by organisms present in the soil. On the other hand, the long chain of the alcohol radical inhibits oxidation, which On the other hand, the long chain of the alcohol radical inhibits oxidation, which makes it a poor source of nutrition for microorganisms and leads to the accumulation of makes it a poor source of nutrition for microorganisms and leads to the accumulation of octanoic and decanoic acids. octanoic and decanoic acids. Further, in the studied samples, the corresponding acids were determined as biodegra- Further, in the studied samples, the corresponding acids were determined as biodeg- dation products. radation products. The resulting butoxyethanol also continues to undergo biodegradation to form butanol The resulting butoxyethanol also continues to undergo biodegradation to form buta- and formic acid as metabolites. nol and formic acid as metabolites. The results obtained for the determination of the biodegradation products of the The results obtained for the determination of the biodegradation products of the syn- synthesized esters are in good agreement with the results of the study of the ecotoxicity of thesizedthe products esters formedare in good during agreement the degradation with the ofresults samples of the in study the soil, of whichthe ecotoxicity was carried of the out productsusing the formed biotesting during method. the degradation of samples in the soil, which was carried out using theEcological biotesting and method. toxicological control using biotesting methods makes it possible to assessEcological and predict and thetoxicological impact of control anthropogenic using biotesting load on biologicalmethods makes systems it [possible48,49]. Such to assessan assessment and predict is necessarythe impact to of predict anthropogenic the prospects load of on biodegradable biological systems polymer [48,49]. composites. Such anBiotesting assessment methods is necessary based to on predict the response the prospects of living of biodegradable organisms to thepolymer negative composites. impact of Biotestingpollutants methods are characterized based on bythe efficiency, response speedof living of experiments,organisms to good the negative reproducibility impact andof pollutantsreliability are of results.characterized by efficiency, speed of experiments, good reproducibility and reliabilityPhytotesting of results. was carried out using watercress (Lepidium sativum) and radish (Raphanus sativus)Phytotesting as indicator was plants. carried The out choice using of wate thesercress crops (Lepidium is due to the sativum) rapid germination and radish of (Raphanustheir seeds sativus) and high as indicator germination plants. rate, The which choice is of noticeably these crops reduced is due into thethe presencerapid ger- of minationpollutants; of shootstheir seeds and roots and underhigh germination the influence rate, of toxic which substances is noticeably undergo reduced morphological in the presencechanges of (growth pollutants; retardation, shoots and curvature roots unde of shoots,r the influence reduction of in toxic root length,substances etc.) undergo [50]. morphologicalBased on changes the toxicity (growth rating retardation, scale and thecurvature results of obtained shoots, duringreduction the in disposal root length, of the etc.)studied [50]. plasticizers in the soil, a different picture is observed when using various alcohols as a carbon source to support the growth of soil microorganisms. When utilizing butyl butoxyethyl adipate in the soil, the stimulation of the growth of radish and watercress slightly differs from the control soil sample, the value of the test reaction in the experiment is slightly lower than the control value. With an increase in the length of the ester molecule, the magnitude of the test reaction in the experiment decreases, but the resulting metabolites do not adversely affect the stimulation of growth. Molecules 2021, 26, 4833 10 of 15

Consequently, when the studied plasticizers are utilized in the soil, toxic substances do not enter the soil and the growth of indicator plants is preserved, which confirms their ecotoxicological safety.

4. Materials and Methods 4.1. Materials Adipic acid (purity 99.8%) was purchased from Radici Group, Selbitz-Hochfranken, Bavaria, Germany. Butanol (purity 99.7%), hexanol (purity 98%), octanol (purity 99%) and decanol (purity 99%) were purchased from The Company “Rearus”, (Moskow, Russia). Ethylene oxide is a solid with a purity of 98.2%, was purchased from ECOTECH Chemical Components Plant, Moscow, Russia. Sodium hydroxide was purchased from Joint Stock Company “Caustic,” Sterlitamak, Russia, it is a white solid with a purity of 98.2%. P-toluene sulfonic acid was purchased from Component-Reagent, Moscow, Russia, it is a white solid, with a purity of 95%. Toluene was purchased from Public Joint-Stock Company “Joint-Stock Oil Company Bashneft”, Ufa, Russia. It is a colorless liquid with a characteristic smell and a purity of 99.5%. Polyvinyl chloride (Joint Stock Company “Caustic,” Sterlitamak, Russia): We used industrial samples of suspension polyvinyl chloride PVC 7059M. Suspension polyvinyl chloride made by suspension polymerization, with a K value from 70 to 73, with a bulk density from 0.45 to 0.55 g/cm3, with a residue after sieving on a sieve with a mesh N 0.0063–95%, for the manufacture of plasticized products.

4.2. Synthesis Methods 4.2.1. Synthesis of Ethoxylated Butanol Ethoxylated butanol was obtained by the method described earlier [39]. Briefly, the calculated amount of alcohol and sodium hydroxide catalyst in the flask was heated to 110–120 ◦C, then purged with nitrogen to remove air, then prepared ethylene oxide was gradually introduced. The required temperature of the reaction mixture was maintained within the specified interval for 1 h and then cooled to room temperature. The catalyst was neutralized, the resulting mass was filtered and the light fraction was distilled off from the reaction mixture, boiling up to 50 ◦C at 10 mm Hg. To make sure that the compound was suitable for further work, its density, refractive index and molecular weight were determined. The purity of butoxyethanol was determined by HPLC. Butoxyethanol is a colorless oily liquid soluble in water. The yield was 106.8 g (90.5% of theoretical).

4.2.2. The Synthesis of Esters of Adipic Acid and Ethoxylated Butanol All four unsymmetrical adipates were obtained according to the previously described method [40]. Briefly, 150 mL of toluene, 1 mol of ethoxylated alcohol, 3.0 g (1% by weight) of p-toluene sulfonic acid and 146 g (1 mol) of adipic acid were charged into the reaction flask and the temperature was slowly raised to 90–95 ◦C. Stirring was continued for 1.5 h. The end of the reaction was determined by the acid number of the esterificate. Then was esterified with aliphatic alcohol (1.2 mol). Boiling was continued for 2–3 h. The reaction mixture was cooled and allocated target ester. All obtained adipates were the light clear liquids. The purity of esters was determined by HPLC. The yield of butyl butoxyethyl adipate (BBEA) was 265.8 g (88.0% of theoretical). The yield of hexyl butoxyethyl adipate (HBEA) was 290.7 g (88.1% of theoretical). The yield of octyl butoxyethyl adipate (OBEA) was 318.3 g (88.9% of theoretical). The yield of decyl butoxyethyl adipate (DBEA) was 341.2 g (88.4% of theoretical).

4.3. Methods of Analysis 4.3.1. Analysis of Physicochemical Parameters of Plasticizer The analysis of physicochemical parameters of the compound was carried out in accordance with state standard 8728-88 Plasticizers. Specifications [41]. For this, the Molecules 2021, 26, 4833 11 of 15

following indicators were determined: Acid number, ester number and mass fraction of volatile substances. Determination of plasticizer density according to state standard 18329-2014 Liquid resins and plasticizers. Methods for determination of density [51].

4.3.2. Characterization of Esters of Adipic Acid Samples of the products were analyzed by FTIR spectroscopy (KBr tablets), which were prepared according to a standard procedure. IR absorption spectra were recorded in the range 450–3700 cm−1 using an FTIR-8400S FTIR spectrometer (Shimadzu Corporation, Shimadzu, Japan) at room temperature. Resolution—4 cm−1, number of scans—20.

4.3.3. Determination of Glass Transition Temperature The glass transition temperatures of PVC composites containing the developed plas- ticizers were determined by differential scanning calorimetry using a DSC-1 instrument (Mettler Toledo, Greifensee, Switzerland). The analysis was carried out in the temperature range from −100 to 100 ◦C in air. The measurements were carried out in a dynamic mode at a constant heating rate of 2 deg/min. The mass of the sample taken for measurements was 4–8 mg. For the analysis, aluminum crucibles with a volume of 40 µL were used. A weighed sample was placed in a crucible and sealed with a lid using a press. After quenching at −90 ◦C for 5 min, the sample was heated to 100 ◦C at a rate of 2 ◦C/min. The first heating cycle was used to remove any heat history. The glass transition temperature of the polymer was determined from the DSC curve obtained in the second heating cycle of the sample using the supplied software. Using the tangent method, the middle of the bend (step) on the curve was determined, which was taken as the glass transition temperature.

4.3.4. Study of the Environmental Safety of Plasticizers by the Phytotesting Method The ecotoxicity of the samples was assessed by the phytotesting method (Interstate standard 12038-84) [52]. For this, ester samples were mixed with soil in a ratio of 1 g of ester per 1 kg of soil and their effect on the germination and germination energy of seeds of test objects of radish (Raphanus sativus) and watercress (Lepidium sativum) was determined. The sprouting rate of emergence on the fifth day was calculated by the Formula (1):

B = a/B × 100 (%) (1)

where a—the number of germinated seeds; B—the total number of seeds taken for the experiment. The toxicity index of the evaluated factor (ITF) for each biological test object was calculated by the Formula (2): ITF = TF0/TFK, (2)

where TF0—value of the registered test system in the experiment; TFK—value of the registered test system in control [53].

4.3.5. Study of Fungal Resistance of Adipates Tests for the ability of adipates to serve as a food source for micromycetes (fungal resistance) were carried out in accordance with Interstate standard 9.049–91. The essence of the method lies in the fact that the sample is infected with mold spores in water. Molds grow only on the nutrients contained in the material. samples of components are taken in 2–3 mL for liquid substances. As test organisms, we used strains of 3 types of microscopic fungi, known as active destructors of various materials: Aspergillus niger, Pénicillium sp., Paecilomyces sp. The fixtures and Petri dishes with the samples were transferred to the box and the surface of the samples was contaminated with a suspension of fungal spores by uniformly applying it with a spray bottle, preventing the droplets from merging. Molecules 2021, 26, 4833 12 of 15

The contaminated samples were kept in a box at a temperature of 25 ± 10 ◦C and a relative humidity of up to 80% until the drops dried, but not more than 60 min. Samples and control Petri dishes were placed in a chamber, at the bottom of which water was poured. The camera was closed. The tests were carried out at a temperature of 29 ± 2 ◦C and a relative humidity of more than 90%. No moisture condensation, forced ventilation or exposure to direct natural or artificial lighting were allowed in the chamber. The duration of tests in assessing the resistance of materials to the degree of development of fungi was 28 days with an intermediate inspection after 14 days. Every 7 days, the lid of the desiccator was slightly opened for 3 min to allow air to flow. During intermediate examinations and at the end of the tests, the samples were removed from the chamber or desiccator, and examined with the naked eye in diffused light at an illumination of 2000–3000 lx and at a magnification of 56–60 times. Fungus resistance was assessed according to the intensity of development of fungi on samples according to a 6-point scale of the standard. To determine the soil toxicity class when disposing of composite samples, the toxicity rating scale was used [54,55].

4.3.6. Study of Biodegradation of Adipates in Soil For testing, the obtained esters were mixed with soil in a ratio of 10 g of ester per 1 kg of soil. At certain intervals, samples of artificially contaminated soil were taken in an amount of 5 g and the content of metabolites in it was determined. For this, extraction was carried out with chloroform 3 times, 20 mL each. The solvent was evaporated. The analysis of the dry residue was determined by the HPLC method.

4.3.7. High Performance Liquid Chromatography The study of the composition of soil samples with utilized adipates was carried out by high performance liquid chromatography (LC-10 from SHIMADZU, Kyoto, Japan) in a reversed-phase mode. The separation of the mixture components was carried out on a column (150 × 4.6 mm) filled with a Separon-C18 sorbent with a particle size of 5 µm in an acetonitrile-water eluent system, taken in a 67/33 volumetric ratio. The eluent flow rate is 0.5 mL/min. A refractometric model detector (RIDK 101, Prague, Czech Republic) was used as a detector. The volume of injected samples was 10 µL. Quantitative analysis was performed using the absolute calibration method. The calibration solutions contained adipic acid, alcohols and esters.

4.4. Preparation of Film Samples The following composition was prepared for testing: One-hundred parts by weight of PVC; 50 parts by weight of the plasticizer; 3 parts by weight of calcium stearate stabilizer. To obtain test samples, all the ingredients of the PVC composition were mixed in a two-stage laboratory mixer for 60 min. To study the PVC composition, samples were obtained in the form of rigid and plasticized films. PVC film samples were obtained by rolling on laboratory rollers at temperatures of 165–175 ◦C for 5 min.

5. Conclusions The analysis of the conducted studies showed that the obtained alkyl butoxyethyl adipates are environmentally friendly plasticizers. All esters showed good plasticizing properties, with an increase in the total molecular length within the investigated range improving the effective effect. From the point of view of biodegradation, the elongation of the molecule of the developed compounds is a factor contributing to a decrease in the rate of hydrolysis of the ester bond and the subsequent oxidation of alcohol. In terms of ecotoxicological assessment, the intermediate monoesters were found to be unstable compounds and were found in trace amounts. Molecules 2021, 26, 4833 13 of 15

Thus, the developed unsymmetrical esters of adipic acid and ethoxylated butanol can serve as a potential source of carbon for soil microorganisms, without being toxicants and without forming persistent toxic metabolites in the process of biodegradation.

Author Contributions: Conceptualization, A.K.M.; methodology, G.K.A.; formal analysis, I.N.V.; investigation, I.N.V.; writing—original draft preparation, I.N.V.; writing—review and editing, A.K.M.; supervision, G.K.A. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding authors. Conflicts of Interest: The authors declare no conflict of interest. Sample Availability: Samples of the compounds butyl butoxyethyl adipate, hexyl butoxyethyl adipate, octyl butoxyethyl adipate and decyl butoxyethyl adipate are available from the authors.

References 1. McLaughlin, D. Fooling with Nature: Silent Spring Revisited. 2010. Available online: https://www.pbs.org/wgbh/pages/ frontline/shows/nature/disrupt/sspring.html (accessed on 8 July 2021). 2. Paull, J. The Rachel Carson Letters and the Making of Silent Spring. Sage Open 2013, 3, 1–12. [CrossRef] 3. Luís, Â.; Ramos, A.; Domingues, F. Pullulan–Apple Fiber Biocomposite Films: Optical, Mechanical, Barrier, Antioxidant and Antibacterial Properties. Polymers 2021, 13, 870. [CrossRef][PubMed] 4. Ryberg, M.W.; Laurent, A.; Hauschild, M. UN Environment. Mapping of Global Plastics Value Chain and Plastics Losses to the Environment (with a Particular Focus on Marine Environment). 2018. Available online: https://backend.orbit.dtu.dk/ws/ portalfiles/portal/163092267/UN_2018_Mapping_of208_global_plastics_value_chain_and_hotspots_final_version.pdf/ (accessed on 2 May 2020). 5. Malizia, A.; Monmany-Garzia, A.C. Terrestrial ecologists should stop ignoring in the Anthropocene time. Sci. Total Environ. 2019, 668, 1025–1029. [CrossRef] 6. Dris, R.; Gasperi, J.; Rocher, V.; Mohamed, S.; Tassin, B. Microplastic contamination in an urban area: A case study in Greater Paris. Environ. Chem. 2015, 12, 592–599. [CrossRef] 7. Bläsing, M.; Amelung, W. Plastics in soil: Analytical methods and possible sources. Sci. Total Environ. 2018, 612, 422–435. [CrossRef] 8. Dris, R.; Gasperi, J.; Mirande, C.; Mandin, C.; Guerrouache, M.; Langlois, V.; Tassin, B. A first overview of textile fibers, including microplastics, in indoor and outdoor environments. Environ. Pollut. 2017, 221, 453–458. [CrossRef][PubMed] 9. Rezaei, M.; Riksen, M.J.; Sirjani, E.; Sameni, A.; Geissen, V. Wind erosion as a driver for transport of light density microplastics. Sci. Total Environ. 2019, 669, 273–281. [CrossRef] 10. He, D.; Luo, Y.; Lu, S.; Liu, M.; Song, Y.; Lei, L. Microplastics in soils: Analytical methods, pollution characteristics and ecological risks. Trends Anal. Chem. 2018, 109, 163–172. [CrossRef] 11. Ali, M.I.; Ahmed, S.; Robson, G.; Javed, I.; Ali, N.; Atiq, N.; Hameed, A. Isolation and molecular characterization of polyvinyl chloride (PVC) plastic degrading fungal isolates. J. Basic Microbiol. 2014, 54, 18–27. [CrossRef] 12. Cosgrove, L.; McGeechan, P.L.; Robson, G.D.; Handley, P.S. Fungal communities associated with degradation of in soil. Appl. Environ. Microbiol. 2007, 73, 5817–5824. [CrossRef] 13. Crabbe, J.R.; Campbell, J.R.; Thompson, L.; Walz, S.L.; Schultz, W.W. Biodegradation of a colloidal ester-based polyurethane by soil fungi. Int. Biodeter. Biodegr. 1994, 33, 103–113. [CrossRef] 14. Kemmitt, S.J.; Lanyon, C.V.; Waite, I.S.; Wen, Q.; Addiscott, T.M.; Bird, N.R.A.; O’Donnell, A.G.; Brookes, P.C. Mineralization of native soil organic matter is not regulated by the size, activity or composition of the soil microbial biomass—A new perspective. Soil Biol. Biochem. 2008, 40, 61–73. [CrossRef] 15. Swift, M.J.; Heal, O.W.; Anderson, J.M. Decomposition in terrestrial ecosystems. Oxf. Blackwell Sci. Publ. 1979, 5, 372. 16. Filser, J.; Faber, J.H.; Tiunov, A.V.; Brussaard, L.; Frouz, J.; De Deyn, G.; Uvarov, A.V.; Berg, M.P.; Lavelle, P.; Loreau, M.; et al. Soil fauna: Key to new carbon models. Soil 2016, 2, 565–582. [CrossRef] 17. Byzov, B.A. Zoomicrobial Interactions in Soil; GEOS: Moscow, Russia, 2005. 18. Striganova, B.R. Locomotor and trophic activity of invertebrates as a factor of soil structure formation. Soil Sci. 2000, 10, 1247–1254. 19. Striganova, B.R. Nutrition of Soil Saprophages; Nauka: Moscow, Russia, 1980. 20. Galloway, T.S.; Cole, M.; Lewis, C. Interactions of microplastic debris throughout the marine ecosystem. Nat. Ecol. Evol. 2017, 1, 0116. [CrossRef] Molecules 2021, 26, 4833 14 of 15

21. Chae, Y.; An, Y.-J. Current research trends on plastic pollution and ecological impacts on the soil ecosystem: A review. Environ. Pollut. 2018, 240, 387–395. [CrossRef] 22. Yvonne, S. Conservation of Plastics: Materials Science, Degradation and Preservation; Butterworth Heinemann: Oxford, UK, 2008; p. 286. 23. Babi´c,S.; Bariši´c,J.; Bielen, A.; Bošnjak, I.; Klobuˇcar, R.S.; Ujevi´c,I.; Strunjak-perovi´c,I.; Popovi´c,N.T.; Což-rakovac,ˇ R. Multilevel ecotoxicity assessment of environmentally relevant concentrations using the soil invertebrate Eisenia fetida. J. Hazard. Mater. 2016, 318, 477–486. [CrossRef] 24. Gaylor, M.O.; Harvey, E.; Hale, R.C. Polybrominated diphenyl ether (PBDE) accumulation by earthworms (Eisenia fetida) exposed to biosolids-, polyurethane foam microparticle-, and penta-BDE-amended soils. Environ. Sci. Technol. 2013, 47, 13831–13839. [CrossRef] 25. Avio, C.G.; Gorbi, S.; Regoli, F. Plastics and microplastics in the oceans: From emerging pollutants to emerged threat. Mar. Environ. Res. 2017, 128, 2–11. [CrossRef] 26. Staples, C.A.; Peterson, D.R.; Parkerton, T.F.; Adams, W.J. The environmental fate of phthalate esters: A literature review. Chemosphere 1997, 35, 667. [CrossRef] 27. Fromme, H.; Kücher, T.; Otto, T.; Pilz, K.; Müller, J.; Wenzel, A. Occurrence of phthalates and bisphenol A and F in the environment. Water Res. 2002, 36, 1429. [CrossRef] 28. Fernandez, M.P.; Ikonomou, M.G.; Buchanan, I. An assessment of estrogenic organic contaminants in Canadian wastewaters. Sci. Total Environ. 2007, 373, 250. [CrossRef] 29. Zeng, F.; Cui, K.; Xie, Z.; Wu, L.; Luo, D.; Chen, L.; Lin, Y.; Liu, M.; Sun, G. Distribution of phthalate esters in urban soils of subtropical city, Guangzhou (China). J. Hazard. Mater. 2009, 164, 1171–1178. [CrossRef][PubMed] 30. Lazarev, N.; Levina, E. Harmful Substances in Industry: Handbook for Chemists, Engineers and Doctors; Chemistry Publ.: Leningrad, Russia, 1976. 31. Harris, C.A.; Henttu, P.; Parker, M.G. The estrogenic activity of phthalate esters in vitro. Environ. Health Perspect. 1997, 105, 802. [CrossRef][PubMed] 32. Paganeto, G.O.; Campi, F.; Varani, K. Endocrinedisrupting agents on health human tissues. Pharm. Toxicol. 2000, 86, 24. [CrossRef] [PubMed] 33. Petrovic, M.; Barceló, D. Determination of anionic and non ionic surfactants, their degradation products, and endocrine-disrupting compounds on sewage sludge by liquid chromatography/mass spectrometry. Anal. Chem. 2000, 72, 4560. [CrossRef] 34. Felder, J.D.; Adams, W.J.; Saege, V.W. Assessment of the safety of dioctyl adipate in freshwater environments. Environ. Toxicol. Chem. 1986, 5, 777–784. [CrossRef] 35. Webb, J.S.; Nixon, M.; Eastwood, I.M.; Greenhalgh, M.; Robson, G.D.; Handley, A.S. Fungal Colonization and Biodeterioration of Plasticized Polyvinyl Chloride. Appl. Environ. Microbiol. 2000, 66, 3194–3200. [CrossRef] 36. Yabannavar, A.V.; Barth, R. Methods for Assessment of Biodegradability of Plastic Films in Soil. Appl. Environ. Microbiol. 1994, 60, 3608–3614. [CrossRef][PubMed] 37. Miller, S.A.; Bann, B.; Thrower, R.D. The reaction between phenol and ethylene oxide. J. Chem. Soc. 1950, 1, 3623–3628. [CrossRef] 38. Staude, F. The lithium phenoxide Catalyzed Addition of propylene oxide to phenol. Polym. J. 1971, 2, 468–474. [CrossRef] 39. Mazitova, A.K.; Vikhareva, I.N.; Aminova, G.K.; Savicheva, J.N. Application of Zinc Oxide to Obtain and Modify Properties of Adipate Plasticizer of Polyvinyl Chloride. Polymers 2020, 12, 1728. [CrossRef] 40. Vikhareva, I.N.; Aminova, G.K.; Buylova, E.A.; Mazitova, A.K. Synthesis and investigation of the properties of a plasticizer based on petrochemical raw materials. Oil Gas Bus. 2020, 4, 57–73. [CrossRef] 41. Interstate Standard 8728-88. Plasticizers. Specifications; IPK Publishing House of Standards: Moscow, Russia, 2003; p. 11. 42. Gray, T.J.B.; Gangolli, S.D. Aspects of the testicular toxicity of phthalateesters. Environ. Health Perspect. 1986, 65, 229–235. 43. Richburg, J.H.; Boekelheide, K. Mono-(2-ethylhexyl) phthalate rapidly alters both sertoli cell vimentin filaments and germ cell apoptosis in young rat testes. Toxicol. Appl. Pharm. 1996, 137, 42–50. [CrossRef][PubMed] 44. Lovekamp-Swan, T.; Davis, B.J. Mechanisms of phthalate ester toxicity in the female reproductive system. Environ. Health Perspect. 2003, 111, 139–145. [CrossRef] 45. Swan, S.H.; Main, K.M.; Liu, F.; Stewart, S.L.; Kruse, R.L.; Calafat, A.M.; Mao, C.S.; Redmon, J.B.; Ternand, C.L.; Sullivan, S.; et al. Decrease in anogenital distance among male infants with prenatal phthalate exposure. Environ. Health Perspect. 2005, 113, 1056–1061. [CrossRef] 46. Pant, N.; Shukla, M.; Patel, D.K.; Shukla, Y.; Mathur, N.; Gupta, Y.K.; Saxena, D.K. Correlation of phthalate exposures with semen quality. Toxicol. Appl. Pharmacol. 2008, 231, 112–116. [CrossRef] 47. Fan, J.; Traore, K.; Li, W.; Amri, H.; Huang, H.; Wu, C.; Chen, H.; Zirkin, B.; Papadopoulos, V. Molecular mechanisms mediating the effect of mono-(2-ethylhexyl) phthalate on hormone-stimulated steroidogenesis in MA-10 mouse tumor leydig cells. Endocrinology 2010, 151, 3348–3362. [CrossRef][PubMed] 48. Mayachkina, N.V.; Chugunova, M.V. Features of soil biotesting for the purpose of their ecotoxicological assessment. Bull. Lobachevsky Univ. Nizhny Novgorod 2009, 1, 84–93. 49. Bubnov, A.G.; Buymova, S.A.; Gushchin, A.A.; Izvekova, T.V. Biotest Analysis-an Integral Method for Assessing the Quality of Environmental Objects; ISCTU: Ivanovo, Russia, 2007. Molecules 2021, 26, 4833 15 of 15

50. Melekhova, O.P.; Egorova, E.I.; Evseeva, T.I. Biological Control of the Environment. Bioindication and Biotesting; Moscow Academy: Moscow, Russia, 2007. 51. Interstate Standard 18329-2014. Liquid Resins and Plasticizers. Methods for Determination of Density; FSA STANDARTINFORM: Мoscow, Russia, 2015; p. 8. 52. Interstate Standard 12038-84. Agricultural Seeds. Methods for Determination of Germination; IPK Publishing House of Standards: Мoscow, Russia, 2004; p. 24. 53. Volkova, I.I. Ecological Soil Science; YarSU: Yaroslavl, Russia, 2013. 54. Bagdasaryan, A.S. The effectiveness of the use of test systems in assessing the toxicity of natural environments. Ecol. Ind. Russ. 2007, 1, 44–48. 55. Kabirov, R.R.; Sagitova, A.R.; Suhanova, N.V. Development and use of a multi-component test system for assessing the toxicity of the soil roof of an urban area. Ecology 1997, 6, 408–411.