How often have you heard proponents of plastic carry out bag bans say that Californian’s use 20 billion plastic carry out bags per year or 531 bags per capita.  Have you ever  asked yourself the following questions:

• Where did this number comes from?
• How is this number is calculated?
• Is the number is reasonable?
• Is there a more reasonable number?

Quick Sanity Check

First, let’s do a quick sanity check.  At  531 plastic carryout bags per capita, a family of four would use 4 x 531 or 2,124 bags per year or about 41 plastic carry out bags per week.   This number is simply too large.  A more appropriate number might be in the range of 15 to 20 bags per week.  Especially, if the family does most of their shopping at the big box stores, like Costco and Sam’s Club.  So, the 20 billion number does NOT pass the quick sanity check.

Where Does the Number Come From?

Many people will be surprised to learn that the 20 billion plastic carry out bag number comes straight from the landfill.  Yes, you read that right, straight from the landfill.  The California Integrated Waste Management Board (CIWMB), a now defunct agency, published a report titled “California 2008 Statewide Waste Characterization Study” wherein they identified the composition of material dumped in California’s landfills by different material classes.  The material class we are interested in is called “Plastic Grocery and Other Merchandise Bags.” The weight of material in each class was determined by sampling and extrapolating the results to the weight of all material dumped in the landfill during the reporting period. 

How The Quantity Of Plastic Carry Out Bags Are Calculated?

For California, the estimated weight of “Plastic Grocery and Other Merchandise Bags” in landfills is 123,405 tons.  The weight per HDPE bag is 5.5 grams or 0.01213 lbs.  Dividing the total weight in the landfill by the weight per HDPE bag yields 20,347,073,372 plastic carryout bags.  Dividing the quantity of plastic carryout bags by California’s 2012 population of 38,041,430 yields 535 bags per capita.

For the United States, the estimated weight in landfills is 770,000 tons and yields 126,958,000,000 plastic carryout bags when divided by the weight of an HDPE bag.  Dividing the quantity of plastic carryout bags by the U.S. population of 313,914,040 yields 404 bags per capita.

Are The Quantities Calculated From Estimated Landfill Weights Accurate?

The “Plastic Grocery and Other Merchandise Bags” material class is defined in the Waste Characterization Study as follows:

Plastic Grocery and Other Merchandise Bags means plastic shopping bags used to contain merchandise to transport from the place of purchase, given out by the store with the purchase. This type includes dry cleaning bags intended for one-time use. Does not include produce bags.

In other words, the estimated weight of 123,405 tons for the “plastic grocery and other merchandise bags” material class is corrupted by the inclusion of the weight of dry cleaning bags!  

Since the proportion of dry cleaning bags cannot be determined, there is no way to adjust the estimated weight to remove the effect of the dry cleaning bags.  Since dry cleaning bags are not regulated in the proposed ordinance or alternatives, and since dry cleaning bags weigh more than HDPE plastic carry out bags, the result of any calculation will result in an inflated number of plastic carry out bags.

In addition, the “plastic grocery and other merchandise bags” material class contains not only grocery store bags but also other plastic merchandise bags from other retailers.  These bags are made not only from different plastic resins but also different sizes and have different weights.  For example, Target’s LDPE bag weighs 9.3 grams and HDPE bags from a variety of grocery stores and retailers can weigh between 4.0 and 6.5 grams each.  The average weight of an HDPE bag is 5.5 grams.  The average weight of plastic carry out bags in the landfill is unknown.  Therefore calculating the quantity of bags from landfill weights using the average weight of an HDPE bag will provide inflated and  incorrect quantities.  

The population of California is 38,041,430 and the population of the USA is 313,914,040.  California reportedly uses 20,347,073,372 and the US reportedly uses 126,958,000,000.  From this data we see that California has 12% of the nation’s population and yet uses 16% of the nation’s plastic carry out bags.  Again this is an indication that this methodology does not provide a reasonable quantity. 

How To Determine A Reasonable Number Of Plastic Carryout Bags

In 2006, the California legislature passed AB 2449.  AB 2449 among other things, required grocery and retail stores subject to AB 2449, to report the total weight of plastic carry out bags purchased and the total weight of plastic carry out bags that were recycled on annual basis.  CalRecycle then compiled the data submitted and published it.   

For 2008, the weight of bags purchased was 54,000 tons.  Dividing this number by the weight of an HDPE bag of 0.01213 lbs. yields 8,903,544,930 plastic carryout bags.  Dividing the quantity of plastic carryout bags by California’s population of 38,041,430 yields 234 bags per capita.

It should be noted that the 2008 data should be used to determine bag quantities because in 2007 the County of San Francisco adopted a ban on plastic carryout bags.  Hence this is the best data available to calculate the total number of plastic carryout bags used by Californian’s including the bags per capita.

If we use the 8.9 billion bag figure with 234 bags per capita, a family of four would use 936 bags per year or 18 bags per week.  This number is more reasonable and corresponds more closely with reality.

Even if the number was bumped up to 10 billion plastic carry out bags per year, in order to ensure that all bags were accounted for by retailers not subject to AB 2449, the per capita quantity would compute to 263 bags.  For a family of four this would mean 1052 bags per year or 20 bags per week.  This number is more reasonable than the 20 billion bags estimated from landfill quantities.

Summary

Using the number of 20 billion plastic carry out bags used by Californians is unreasonable.  As stated, the origin of the number as calculated from the estimated weight of plastic bags in the landfill and is fraught with error of one type or another.  Only the weight of plastic carry out bags purchased by California grocery and retail stores reported under AB 2449 provides a reasonable ball park estimate for the total number of plastic carry out bags purchased and distributed by retailers targeted by proposed ordinances  in California.