Jeff Wagg notes:
Paper or Plastic? How do you answer? If you give what you think is the 'correct' answer, you say ‘paper' or you've brought your own bags. Let's examine that choice.
The paper bags used in the grocery stores begin in the forest, with the clear-cutting of forests. Even though trees are a renewable source, there is more to producing new paper than planting new trees. The paper industry is one of the dirtiest industries we have. The chemicals used in the paper pulp process include sulfur, bleaches, and acids. The process uses huge quantities of water, which must be treated and cleaned, a process which also uses chemicals. According to a representative of the Texas Commission on Environmental Quality, paper manufacturing also receives a larger number of complaints than refineries on ‘nuisance odors ‘ which is a term meaning that the facilities emit very strong, disagreeable odors, as unpleasant to live near as a feedlot. Processing facilities must control odors to the same extent that they must control pollutant emissions.
Paper has a limited ability to be recycled. On each trip through recycling, paper must be chopped and shredded, which shortens the fiber length. Eventually, the fibers become too small to use and must be land filled, as do the manufacturing byproducts.
What about plastic? Grocery stores bags are made of polyethylene, which begins as the ethane component of natural gas. The only emissions from polyethylene manufacture are from natural-gas fired heaters, which supply heat or steam for the process. Natural gas is the cleanest burning fuel, and natural gas wells are clean and low-profile - a valve sticking up out of the ground as opposed to the ‘pumping units' associated with oil wells. The conversion of ethane into polyethylene is close to 99% efficient. Additionally, polyethylene can be recycled almost infinitely. Even though the molecular weight of the polymer chains will change with recycling, it's still the same plastic and can be reused. It is also inert- in some locations, polyethylene has been chopped into sand-sized bits and incorporated into heavy clay soils, to lighten them as you would do with sand.
Transportation adds more cost to the paper product than to plastic. Paper is heavier, so trucking costs are higher, as is the amount of pollution from the gasoline needed to transport the denser product.
The option with the least environmental impact is to carry reusable shopping bags, which are made of polypropylene, or carry personal bags. However, if you are faced with a choice between paper or plastic, plastic is the environmentally responsible decision.