Plastic is one of the most useful of all of humanity's inventions, serving valuable and convenient functions in anything from medicine to cleaning to food preservation. However, there are significant downsides to the amount of plastic produced, and the disposal of those items. Various plastics can have significant negative effects on the environment if they are not taken care of responsibly.
One of the major reasons plastic can be harmful is, ironically, the same trait that makes it so useful. Most plastics are durable materials which degrade very slowly. While this is ideal for protecting and preserving, it means that plastics which are thrown away can linger in the environment for decades or even centuries. Though some modern plastics are designed to be biodegradable, many of these only break down when exposed to sunlight, so when buried in landfills they will continue to last. Plastic refuse can be dangerous to wildlife, especially if they eat it or become trapped in discarded wrappings or containers.
Another environmental concern that scientists have only recently become aware of is microplastics. These tiny particles of plastic, usually smaller than a millimeter in diameter, can come from either the breakdown of larger plastic items, or are directly manufactured for various purposes. Microplastics persist for long periods of time, especially in marine ecosystems, and once ingested by an animal they can linger in its systems, or be passed up the food chain through predation. Quantities of microplastics have even been found in samples of the fish people commonly eat.The accumulated particles can block the digestive track and also leach chemicals into the animals that can have negative health effects. Some of the synthetic organic chemicals found in microplastics have been linked to liver and kidney damage and cancer, among other ailments.
As plastics are organic, carbon-based polymers, burning plastic releases carbon into the atmosphere, increasing global warming effects. Biodegradable plastics likewise emit methane as they degrade. Uncontrolled incineration of plastics can also produce carcinogens and other toxic fumes. While municipal waste incinerators use high temperatures and special treatments to handle plastics, a better option is to recycle. Melting down discarded plastic items or grinding them up to serve as filler can reduce manufacturing costs and prevents more plastic from entering the environment.
Though plastic is too useful for people to do without, steps should be taking to reduce its negative impact on the biosphere. For advice and recommendations on the safe disposal of your unwanted plastic items, see this link for more information about plastic recycling in Santa Clara.