Final answer:
Synthetic plastics are largely non-biodegradable and persist in the environment due to their stable polymers derived from petrochemicals. Anoxic conditions in landfills slow down their degradation, which, along with partial photodecomposition, poses environmental risks. Recycling is thus promoted to handle the waste and minimize environmental damage.
Step-by-step explanation:
Synthetic plastics such as polyethylene are largely non-biodegradable due to their high molecular mass and the stable nature of the polymers they are composed of. Although the oxidation of plastics to form carbon dioxide and water is theoretically spontaneous, it happens very slowly in practice. Because most common plastics are derived from petrochemicals, they persist in the environment and are therefore considered candidates for recycling to minimize the environmental damage and conserve non-renewable resources.
Anoxic conditions in landfills further slow down the decomposition of plastics, and even when they do partially break down, it can lead to the formation of hazardous leachates that can contaminate water supplies. Moreover, the residues from partially degraded plastics can still be problematic, as they transform into various harmful compounds, such as branched chain and polyaromatic hydrocarbons. In the oceans, plastics typically break down into smaller fragments instead of fully degrading, adding to the environmental concern.