As was discussed in the previous article, the plastics we use typically come in one of six forms: (1) polyethylene terephthalate (PET), (2) high-density polyethylene (HDPE), (3) polyvinyl chloride (PVC), (4) low-density polyethylene (LDPE), (5) polypropylene (PP), and (6) general purpose polystyrene (PS); all others grouped into a miscellaneous category (7). As can be seen in the figure below (measurements taken in 2015), a large majority of the plastics produced globally in terms of weight fall within one of these six categories with PP and LDPE being the most common types. According to the EPA report Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figure for 2012, plastics were near the top in terms of weight produced and near the bottom in terms of weight recovered during the year 2012.
Taken from https://commons.wikimedia.org/wiki/File:Primary_plastic_production_by_polymer_type,_OWID.svg
The first step in the life cycle of a single-use plastic product is the collection and processing of plastic resin from derivatives of refined natural gas and petroleum. Acquisition of these derivatives first involves the extraction and refining of both types of fossil fuels. These derivatives then need to be transported to plastics manufacturers who convert them into plastic resin. The resin is finally converted into the forms that we are more familiar with through processes referred to as extrusion blow molding (e.g. PET in water and soda bottles) and injection molding (e.g. HDPE crates). Therefore, greenhouse gas emissions associated with the manufacture of plastic products includes emissions from the following three sources: (1) extraction and refining of petroleum and natural gas, (2) transportation of derivatives from petroleum and natural gas to plastic manufacturers, and (3) conversion of resulting plastic resin into usable plastic products.
The second step of a plastic product's life cycle, which is referred to as "retail transportation", involves the transportation of the manufactured plastic product from the manufacturer to the retailer or directly to the consumer; this can be by truck, rail, water, or other forms of transportation. The emissions from this step depend on the form of transportation and the average distance over which the product is transported. After reaching the retailer or consumer, the next step involves the actual use of the plastic product by the consumer, the emissions from which are difficult to estimate.
The final step in the life cycle is disposal by the consumer. Disposal can come in the form of recycling (limited primarily to HDPE and PET plastic types), landfilling, or combustion. Due to the fact that plastic is made from fossil fuels, combustion results in these fossil fuels being released into the environment and thus represents an anthropogenic source of carbon emissions. Different types of plastic have different carbon contents; most types have a carbon content of 86% or greater, whereas PVC has the lowest carbon content at 38% followed by PET at 63%. Emissions from transporting the plastic products to a combustion or waste-to-energy facility also needs to be included. With regard to waste-to-energy facilities, the energy created by burning the plastic products will reduce the amount of direct burning of fossil fuels that is needed; this "emissions savings" must also be taken into account.
Dumping plastics in a landfill has a negative impact on the environment due to the fact that plastics will never break down completely and will therefore remain in the environment. The one advantage, if it can be labeled as such, is that landfilling creates almost zero carbon emissions. Due to the fact that the carbon stored in plastics is not biodegradable, little if any of this carbon will be released to the environment. The only emissions that result from landfilling, therefore, are due to transport of the material to the landfill and moving waste within the landfill.
Given all of the information provided above, the table below gives concrete numbers in terms of the pounds of carbon equivalents produced per pound of each type of plastic consumed; I will not go into detail in terms of what carbon equivalents means at this point except that it takes into account other greenhouse gases in addition to carbon dioxide. Use this table when attempting to estimate your own carbon footprint due to your consumption of single-use plastics. Given the numbers below, you may think that recycling is just adding more emissions, but it should be remembered that when a bottle made from recycled material is purchased, any emissions shown in the "Manufacturing" column do not apply to that bottle. Also, as mentioned above, even though emissions from landfilling are minimal, landfilling represents a major contribution towards the overall problem of plastic pollution.
Type | Manufacturing | Recycling | Combustion | Landfill |
PET (1) | 2.44 | 1.04 | 1.37 | 0.04 |
HDPE (2) | 1.62 | 0.55 | 1.40 | 0.04 |
PVC (3) | 2.16 | - | 0.74 | 0.04 |
LDPE (4) | 1.98 | - | 1.40 | 0.04 |
PP (5) | 1.71 | - | 1.81 | 0.04 |
PS (6) | 2.76 | - | 1.40 | 0.04 |
Table: Carbon emissions caused by manufacturing and disposal of each type of plastic (pounds CO2e per pound of plastic).
Action
Focus on avoiding one form of plastic (e.g. water bottles, soda bottles, plastic utensils, plastic milk jugs, etc.) over the next one month.
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