Reusable bags can become breeding ground for bacteria, yeast and mold

study conducted by three independent testing laboratories has concluded that reusable shopping bags can pose a significant health risk by acting as a breeding ground for bacteria, mold and yeast. The study was commissioned last fall by a consumer coalition to gain a better understanding of how people use reusable packaging and to address any concerns for public health and safety. It builds on consumers’ growing interest in using reusable containers for food packaging (e.g. bringing containers from home into the store).

Mold growing in petri dishes.
The plastics industry strongly supports reduction and reuse and recognizes the use of reusables as a good environmental practice. But, it does not want to see these initiatives inadvertently compromise public health and safety. The industry believes that results attained in the study warrant the need for further independent research and investigation.

Pilot to determine merit in further testing

The study began with pilot test done in November 2008 on two plastic reusable containers and one 12 month-old reusable shopping bag. Results showed considerable bacteria build up on both the reusable bag and on one of the two reusable containers. Mold and yeast were also present, and there was a significant level of coliform. In fact, the bag test results showed an elevated bacterial count of 1,800 colony-forming units (CFU) – more than three times the level of 500 CFU considered safe per millilitre of drinking water. The coliform (faecal bacteria) count of 10 exceeded the recommended drinking water level of 0. The mold count of 290 was higher than the normal mold count of 150 or fewer per cubic metre of room air in the Canadian fall and winter months.

The results of the first pilot study determined that further testing on a larger sample of reusable packaging was merited. This second phase took place in March and April of 2009 and involved 25 reusable bags and four control bags (three popular reusables and one single-use bag). All of the “used” reusable bags used for the study were attained from ordinary shoppers as they left grocery stores.

Second phase

The larger study found that 64 per cent of the “used” reusable shopping bags (16 of the 25 bags) showed the presence of some level of bacterial contamination. Close to 30 per cent of the bags had elevated bacterial counts higher than the 500 CFU/mL standard for drinking water. Additionally, yeast was found in five of the bags and mold was found in six. An unacceptable total coliform count was found in three of the bags: total coliform counts were 300, 100 and 10. The bags had been in use for one, two and three years. On the other hand, both the single-use shopping bag and the first-use reusable bag (the control bags) showed no evidence of bacteria, mold, yeast or total coliforms.

A second look

The results from the larger sample of reusable shopping bags clearly show that the bags have the potential to become a public health hazard. These study results indicate that the use of reusable bags warrants further consideration. At the very least, what needs to be developed are appropriate protocols on the use, care and storage of these bags.