## 4 Findings and Discussion
### Type and Composition  
Nonpharmaceutical interventions to physically cut off COVID-19 contagion by wearing PPE include the use of face masks, gloves, wet wipes, face shields, safety glasses, shoes, \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**A** & **B** & **C** & **D** & **E** & **F** & **G** \\ \hline \multicolumn{6}{c}{2020} \\ \hline Human & 66 & 21 & 30.56 & 2017 & 1301.08 & 313.97 \\ Procedures & 31 & 12 & 20.35 & 631 & 555.38 & 80.22 \\ Viral disease & 20 & 14 & 56.9 & 1138 & 244.77 & 79.46 \\ Hand washing & 22 & 11 & 29.27 & 644 & 276 & 29.3 \\ Disease transmission & 18 & 9 & 55.39 & 997 & 299.33 & 25.52 \\ SARS-CoV-2 & 22 & 12 & 37.91 & 834 & 275.34 & 30.72 \\ Infection prevention & 15 & 8 & 25.47 & 382 & 195.32 & 19.38 \\ Health personnel & 6 & 4 & 8.33 & 50 & 88.41 & 39.74 \\ Plastic & 4 & 4 & 209.75 & 839 & 25.57 & 23.81 \\ Decontamination & 4 & 3 & 25.5 & 102 & 45 & 12.19 \\ \hline \multicolumn{6}{c}{2021} \\ \hline Human & 140 & 28 & 17.9 & 2506 & 735.48 & 154.01 \\ Marine pollution & 27 & 18 & 37.3 & 1007 & 175.66 & 51.75 \\ Health care personnel & 28 & 8 & 13.82 & 387 & 139.3 & 27.38 \\ Virus transmission & 45 & 15 & 14.64 & 659 & 212.48 & 44.65 \\ Coronavirus & 69 & 25 & 24.42 & 1685 & 242.28 & 27.01 \\ Hospital waste & 20 & 12 & 24.4 & 488 & 125.99 & 9.7 \\ Face masks & 37 & 19 & 22.41 & 829 & 117.54 & 11.32 \\ Personal protective equipment (PPE) & 7 & 5 & 67.57 & 473 & 27.82 & 13.11 \\ Public health & 5 & 4 & 21.6 & 108 & 35.71 & 8.62 \\ \hline \multicolumn{6}{c}{Until 15 June 2022} \\ \hline Human & 72 & 7 & 2.28 & 164 & 722.83 & 176.15 \\ Nonhuman & 32 & 6 & 3.25 & 104 & 317.76 & 36.15 \\ Waste disposal & 32 & 6 & 2.81 & 90 & 243.23 & 26.04 \\ Environmental impact & 16 & 4 & 3.19 & 51 & 145.79 & 32.63 \\ Polypropylenes & 18 & 4 & 2.67 & 48 & 120.63 & 13.35 \\ Plastic waste & 11 & 4 & 4.36 & 48 & 78.07 & 23.5 \\ Recycling & 7 & 1 & 1.14 & 8 & 54.37 & 12.69 \\ Epidemic & 6 & 2 & 3 & 18 & 64.61 & 14.62 \\ Coronavirus & 4 & 2 & 3.25 & 13 & 17.96 & 12.5 \\ \hline \hline \end{tabular} (A) The name name; (B) number of documents including the theme; (C) theme h-index; (D) theme average citations; (E) theme number of citations; (F) theme centrality: considered as theme’s importance in overall development of the scientific field analyzed; (G) theme density: considered as theme’s degree of internal cohesion.  
\end{table} 
Table 6: Performance measures for themes for subperiods of the time horizon. gowns, and aprons, all of them containing a substantial proportion of plastic [2]. For example, in the case of face masks, different polymers and materials, including polypropylene, polyacrylamide, and/or polyurethane, are used, with latex, synthetic polymers, vinyl, and/or nitrile being used in the case of disposable gloves. An interest in the contribution of PPE to plastic production was revealed in our science mapping analysis that identified plastic as the term with the highest average citation value, followed by polypropylene and plastic waste (Figures 13b and 14). The use of medical gloves, surgical face masks, face shields, safety glasses, shoes, gowns, and aprons has been recommended for healthcare service staff [42; 43]. However, face masks, gloves, and wet wipes have also been recommended for wide use in the general population. Specifically, wearing face masks has been considered as the most-effective method to interrupt disease transmission for the general population [15]. Additionally, in many cases, their use has been mandated [42; 43]: in 2020, in over 50 countries, the use of face masks by the population was mandatory in public places [5]. Different types of face masks have been used, including disposable medical or single-use face masks and N95 masks, as well as cotton gowns and sponges, which are reusable after washing [16].Single-use face masks are produced from polymers and polymer fibers, such as polyethylene, polypropylene, polyvinyl chloride, polyurethane, polyacrylamide (PAN), polystyrene, and polycarbonate, among others [3; 14; 44].