# Microplastic Pollution on the Beaches of the Black Sea in Romania and Bulgaria
## 4 Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Abbrev.** & **Specific Toxicity [51]** & **Recyclability** & \multicolumn{2}{c}{**Degradation Pathways**} & \multicolumn{2}{c}{**Degradation Products**} \\ \cline{3-6} PET & \begin{tabular}{c} Dysfunction of the \\ endocrine system \\ \end{tabular} & \begin{tabular}{c} Mechanical recycling \\ to obtain clean raw \\ materials, solvolysis \\ of plastic waste to \\ \end{tabular} & \begin{tabular}{c} Hydraulic degradation, \\ dilation/cleavage, \\ UV degradation, \\ thermal oxidation, \\ photo-oxidation, \\ pyrolysis, \\ hydrogenolysis [50] \\ \end{tabular} & \begin{tabular}{c} Microfluid degradation, \\ chemical degradation, \\ physical degradation, \\ thermal oxidation, \\ hydrolysis in [52; 48; 53] \\ \end{tabular} & \begin{tabular}{c} Microfluids, \\ nanoparticles, \\ two-molecular, \\ weight \\ compounds, \\ dissolved \\ degradation at high \\ temperature [48; 52] \\ \end{tabular} & \
\begin{tabular}{c} Microplastics, \\ nanoparticles, \\ NO-molecular, \\ weight \\ compounds, \\ dissolved \\ organic carbon [48; 52] \\ \end{tabular} &
\begin{tabular}{c} Organic acids, \\ CO\({}_{2}\) methane, \\ microplastics, \\ organic carbon, \\ mineralized \\ carbon [48; 52] \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Ecological and environmental impacts of synthetic polymers on beaches, shallow coastal waters, and sand. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Abbrev.** & **Synthetic Polymers** & **Chemical Formula** & **Chemical Structures** & **Source/Origin [47]** \\ \hline PS & Polystyrene & (C\({}_{8}\)H\({}_{8}\))\({}_{n}\) & \begin{tabular}{c} Anthropogenic activity, urban \\ sewage, plastic industries, domestic \\ sources, agriculture. \\ \end{tabular} \\ PVC & \
\begin{tabular}{c} Polyvinyl \\ chloride \\ \end{tabular} & (C\({}_{2}\)H\({}_{3}\)Cl)\({}_{n}\) &
\begin{tabular}{c} Building industry, urban sewage, \\ food packaging. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 1: _Cont._(PCL) and polyvinyl chloride (PVC), reaching up to 469.73 \(\upmu\)m per year, highlighting the variability in plastic breakdown processes under different environmental conditions. The synthetic polymers were analyzed to determine their structural characteristics using computational chemistry. Molecular structure modeling was performed in a vacuum using semi-empirical methods (AM1, RHF). The structures were optimized using the Polak-Ribiere algorithm, achieving an RMS maximum energy gradient of 0.01 kcal/A-mol. The system's energy and other molecular properties were calculated using the Schrodinger equation. Table 3 presents data on the calculated properties of the synthetic polymer structures. The structural characteristics of polymers significantly influence their biodegradability, toxicity, and recyclability. Microplastics are a challenge for protecting the environment due to their resistance to biodegradation, their complex toxicity, and difficulties in recycling them [56; 57]. The biodegradability of polymers is influenced by the presence of functional groups such as esters or amides, the degree of crystallinity of the material, and the structure of the polymer chains, with simpler and more hydrophilic chains being more easily degraded by microorganisms [52]. In the case of microplastics, the biodegradability is lower due to the chemical composition of resistant polymers and the limited presence of microorganisms in environments such as water or sand [58]. Microplastics are toxic not only due to the chemicals they release but also because of the pollutants they absorb, having a negative impact on the organisms that ingest them and on the food chain [59]. The recyclability is determined by the nature of the polymer, with thermoplastics being easier to process and reuse, while thermosetting polymers or complex blends have reduced recycling efficiency and require the use of more advanced technologies.