This review summarizes the degradation pathways and potential environmental impacts of plastic polymers in the marine environment. Plastics, widely used in daily life, are produced in large quantities and accumulate in the oceans, with over 60% of floating debris being plastic. Plastic polymers are exposed to sunlight, oxidants, and physical stress, leading to degradation over time. Degradation processes and products are important for assessing environmental hazards. While attention has been given to additives and persistent organic pollutants that sorb to plastic surfaces, the chemicals generated by plastic polymer degradation have not been well studied. The review focuses on the six most commonly used plastic types in Europe: polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polyurethane (PU). Degradation of these plastics can occur through abiotic or biotic pathways. Abiotic degradation, initiated by UV radiation and oxygen, leads to chain scission, producing smaller polymer fragments that are more susceptible to biodegradation. When heteroatoms are present in the polymer chain, degradation proceeds through photo-oxidation, hydrolysis, and biodegradation. PE, PP, and PS are susceptible to photo-initiated oxidative degradation, while PVC is particularly sensitive to UV radiation. PET and PU can degrade through hydrolysis, photo-oxidation, and biodegradation. Degradation of plastics can lead to low molecular weight fragments, such as monomers and oligomers, and the formation of new end groups, especially carboxylic acids. The degradation products may include various chemicals, such as alcohols, aldehydes, ketones, and carboxylic acids. Additives and stabilizers in plastics can influence degradation rates, with some additives inhibiting degradation and others promoting it. The environmental impact of plastic degradation is significant, as the degradation products can release pollutants into the marine environment. However, most studies on plastic degradation have been conducted under non-environmentally relevant conditions, and more research is needed to understand the actual degradation processes and products in marine environments. The review highlights the need for further studies to better understand the environmental impact of plastic degradation in the oceans.This review summarizes the degradation pathways and potential environmental impacts of plastic polymers in the marine environment. Plastics, widely used in daily life, are produced in large quantities and accumulate in the oceans, with over 60% of floating debris being plastic. Plastic polymers are exposed to sunlight, oxidants, and physical stress, leading to degradation over time. Degradation processes and products are important for assessing environmental hazards. While attention has been given to additives and persistent organic pollutants that sorb to plastic surfaces, the chemicals generated by plastic polymer degradation have not been well studied. The review focuses on the six most commonly used plastic types in Europe: polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl chloride) (PVC), poly(ethylene terephthalate) (PET), and polyurethane (PU). Degradation of these plastics can occur through abiotic or biotic pathways. Abiotic degradation, initiated by UV radiation and oxygen, leads to chain scission, producing smaller polymer fragments that are more susceptible to biodegradation. When heteroatoms are present in the polymer chain, degradation proceeds through photo-oxidation, hydrolysis, and biodegradation. PE, PP, and PS are susceptible to photo-initiated oxidative degradation, while PVC is particularly sensitive to UV radiation. PET and PU can degrade through hydrolysis, photo-oxidation, and biodegradation. Degradation of plastics can lead to low molecular weight fragments, such as monomers and oligomers, and the formation of new end groups, especially carboxylic acids. The degradation products may include various chemicals, such as alcohols, aldehydes, ketones, and carboxylic acids. Additives and stabilizers in plastics can influence degradation rates, with some additives inhibiting degradation and others promoting it. The environmental impact of plastic degradation is significant, as the degradation products can release pollutants into the marine environment. However, most studies on plastic degradation have been conducted under non-environmentally relevant conditions, and more research is needed to understand the actual degradation processes and products in marine environments. The review highlights the need for further studies to better understand the environmental impact of plastic degradation in the oceans.