An average time for a plastic bottle to biodegrade fully is approximately 450-1000 years. However, there are many different kinds of plastic in the world, most commonly the hard and reusable ones, which take a longer time, and the soft and non-reusable ones, which take a shorter time. Time also varies with the size of the bottle. The obvious disadvantage is the length of time it takes plastic to break down as well as the harmful chemicals that will be released. You may find that in garbages 90% or more will be of plastics only. so its main disadvantage is its non bio degradable nature.. nd by some means if tried to burn it then it will create much envi pollution!! Advantages The durability, strength, low cost, water and chemicals resistance, welding properties, lesser energy and heavy chemicals requirements in manufacture, fewer atmosphere emissions and light weight are advantages of plastic bags. Many studies comparing plastic versus paper for shopping bags show that plastic bags have less net environmental effect than paper bags, requiring less energy to produce, transport and recycle; however these studies also note that recycling rates for plastic are significantly lower than for paper. 2] Plastic bags can be incinerated in appropriate facilities for waste-to-energy. Plastic bags are stable and benign in sanitary landfills.  Plastic carrier bags can be reused as trash bags or bin bags. Plastic bags are complimentary in many locations but are charged or “taxed” in others. Disadvantages The following disadvantages have also been identified: Plastic bags are made of petrochemicals, a nonrenewable resource. Plastic bags are flimsy and often do not stand up as well as paper or cloth.
When disposed of improperly, they are unsightly and represent a hazard to wildlife. Conventional plastic bags are not readily biodegradable in a sanitary landfill. Plastic bags can cause unsupervised infants to suffocate.  They clog roadside drains, which could cause the flooding of the street at heavy rainfalls. Advantages: It’s useful for carrying things, and can be reusable. Disadvantages: It takes 100 years to biodegrade, and if plastics are thrown and left anywhere it could get to animals and harm them
The disadvantages of using plastic bags is that you cant recycle them and that’s horrible for our planet , like what the world is saying to us, “help make me stay green” —— As a self declared environmentalist, I am at odds with using plastic bags versus using reusable cloth bags (also called reuse bags), because both types of bags have advantages and disadvantages. Here is why. First, plastic bags are cheap, so they can be given away free without thought. Cloth bags are much more individually expensive, and only become cost effective in the very long term assuming they last a long enough time.
Second, plastic bags can be found everywhere. Only large chain stores carry reusable bags and for a cost. So you need to remember to bring enough cloth bags each time you go to the store. Third, I reuse plastic bags at home as trash bags instead of buying trash bags. Why pay for trash bags when plastic bags are free? And trash bags are only used once, unlike plastic bags that can be used at least twice. Also, plastic bags are great for wet and messy waste that you wouldn’t want to dirty a cloth bag with. For example, plastic bags are perfect for dirty diapers or gooey kitchen waste.
Fourth, after I’ve collected a large number of plastic bags, they are easy to recycle. Are reuse cloth bags recyclable? Will they degrade over time buried in a landfill? I don’t know which type of bag is more environmentally friendly. Finally, cloth bags are much sturdier than plastic bags, so you can put more in cloth bags thus carry more per bag and they last a lot longer if you are careful with them. As a result, I find that I use both reuse cloth bags and plastic bags, since I have a reasonable need for both types of bags.