by Neeko Felten, Steven Broker, and Adam Kay. This post is the results from a project conducted by Neeko and Steven as part of the Environmental Science Capstone course at the University of St. Thomas. Neeko and Steven designed and carried out the research. Neeko and Adam (faculty collaborator) wrote the post.
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An Iranian water bottle enjoying the view
Americans buy more than a ½ BILLION bottles of water every week! Why? Bottled water is as much as 2000 times more expensive than tap water. It also leads to mountains of plastic bottle waste of which a small fraction (8-14%) is recycled (American Plastics Council, 2005). It may even be less healthy than tap water. Some studies suggest that bottled water could be dangerous to human health because it contains harmful endocrine disrupting compounds that have leached into the water from the plastic.
Endocrine disruptors are compounds that have similar structures to our hormones. Endocrine disruptors can bind to our receptors, causing processes like gene expression to be turned on or off, sometimes with negative consequences.
Phthalates are classified by the EPA as endocrine disruptors and have also been linked to causing abnormalities such as reproductive problems and increased risks of cancer (EPA, 2012). These phthalate compounds are common in the plastic types PET and PETE, which are often used to make clear plastic bottles for water, soda, sports drinks, and condiments.
Leaching of chemicals from plastic will happen naturally over time, but the concentration of leachates in the water can be increased by factors such as duration of storage time (Casajuana and Lacorte, 2003), exposure to ultraviolet radiation (Schmid et al., 2008), the acidity of the beverage (Bosnir et al., 2007) and exposure to increased temperatures (Farhoodi et al. 2008).
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Figure 1. Water bottles after being incubated at 70C for 1 day (left) or 40C for 3 days (right)
Here, we report on a study in which we tested whether increased temperature affects water quality in plastic bottles. The study was conducted in spring 2013 as part of the Environmental Science Capstone course at the University of St. Thomas (UST). First, we showed that heating bottles increased the rate at which they lose mass (Table 1). Specifically, we heated Celtic Spring-brand and Fiji-brand bottles in an incubator for either 1 or 3 days and at either 40°C or 70°C. We chose these temperatures and time periods to mimic situations that water bottles might be exposed to: 40°C would be the temperature in a car on a warm day; 70°C was used as a proof of concept. Bottles were sealed and contained their original contents. After incubation at 70°C, the water bottles lost 2-4x as much mass as bottles kept at room temperature, and were literally warped as they lost their structural integrity (Figure 1). However, even room temperature conditions saw a loss in plastic mass over only three days! These results suggest a significant amount of leaching from plastics occurs, and it increases significantly at higher temperatures. Note however that these results are based on only 1 bottle per condition and we did not measure chemical concentrations in the water after exposure. Further study on this issue is needed.Image may be NSFW.
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Our main project involved using a biological assay to test whether heating affects the quality of water in plastic bottles. Specifically, we measured population growth rates for Daphnia magna, small aquatic organisms called water fleas, after incubating water at different temperatures and for different lengths of time. We’re ultimately interested in how heating can affect water quality for humans. However, there are some minor Image may be NSFW.
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ethical issues associated with giving potentially contaminated water to humans and measuring impacts on population growth. It’s also important to note that a treatment that affects a small aquatic organism like a water flea may not have any impact on humans. Our story should be viewed only as a cautionary tale.
We conducted two experiments. In the first (“Original water”) experiment, we tested D. magna population growth in bottles that contained their original contents. Initially, we heated (as above) Celtic Spring-brand and Fiji-brand bottles in an incubator for either 1 day or 3 days and at room temperature (25°C), 40°C, or 70°C. In the second (“Combo water”) experiment, we tested D. magna population growth in plastic bottles that contained a standardized water referred to as “Combo” (hyperpurified water with added salts and minerals to mimic the osmolarity in lake water). For this study, we incubated Combo water in Celtic Spring bottles, Fiji bottles, or sterilized glassware for 1 day or 3 days and at either room temperature (25°C), 40°C, or 70°C. In both studies, after incubation, we created replicates by putting 100 mL of treated water into a sterilized glass mason jar; we then added five D. magna per jar. We had six replicates per treatment for a total of 150 mason jars and ~700 D. magna. We provided the D. magna with algae (their natural food source) during the study. We reared them for 18-21 days and counted final population size under a microscope. We tested for effects of incubation temperature, incubation time, and water bottle brand using a statistical technique called analysis of variance (ANOVA). For complete methods, see here.
We found that heating water in plastic had a substantial negative impact on D. magna populations. Figure 2 (left) shows that D. magna populations grew much slower in bottled water that had been incubated at high temperatures. D. magna populations did particularly poorly when water was incubated for 3 days at 70°C. The brand of water bottle had no overall effect on D. magna populations. In the “Combo water” study in which we incubated standardized water in glass or plastic water bottles, we found that incubation temperature, incubation period, and container type all affected Daphnia success. Most notably, D. magna did much better in water warmed in glass than in water warmed in plastic (for complete statistical analysis, see here). The differences among treatments are striking: for example, D. magna populations in water incubated at 70°C in the original water study were only about a third as large as populations in room temperature water.Image may be NSFW.
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The findings of these studies suggest that exposing plastic water bottles to high temperatures for short time periods (up to 3 days) can reduce water quality enough to impact the survival and reproduction of aquatic animals.
These tests were done on Daphnia, so they have nothing to do with humans, right?
It’s true that our experiments were done on small aquatic animals over a short time period and under limited conditions. The results should be interpreted with caution as we didn’t test anything specifically related to human health. However, people regularly let their bottled water sit in their car on a hot summer day or even reuse bottles for days if not weeks. Emergency bottled water supplies are stored for months on end. The findings of these studies saw bottle mass loss after only 3 days and at room temperature. What happens when water bottles are stored in periodically warm conditions (e.g., during transport) over the course of weeks? At a minimum, results from this study will hopefully motivate folks to learn about the risks associated with water from plastic bottles. Along with the financial and ecological costs of this product, the potential water quality effects suggested by our study and others like it make tap water seem like a much better option.
References
American Plastics Council (2005). National post-consumer plastics recycling report.
Bošnir J, Puntarić D, Galić A, Škes I, Dijanić T, Klarić M, et al. (2007) Migration of phthalates from plastic containers into soft drinks and mineral water. Food Technol Biotechnol. 45: 91–95.
Casajuana N, Lacorte S. (2003) Presence and release of phthalic esters and other endocrine disrupting compounds in drinking water. Chromatographia 57: 649–655.
Farhoodi M, Emam-Djomeh Z, Ehsani MR, Oromiehie A. (2008) Effect of environmental conditions on the migration of di-(2-ethylhexyl) phthalate from PET bottles into yogurt drinks: influence of time, temperature, and food simulant. Arabian J Sci Eng. 33: 279–287.
Schmid P, Kohler M, Meierhofer R, Luzi S, Wegelin M. (2008) Does the reuse of PET bottles during solar water disinfection pose a health risk due to the migration of plasticisers and other chemicals into the water? Water Res. 42: 5054–5060.
Much thanks to Kyle Zimmer for help with experimental design and logistics!
About the authors: Neeko Felten and Steven Broker are 2013 UST graduates who majored in Environmental Science (Biology concentration) and Geology. Adam Kay is the Director of the Environmental Science Program at UST.
Image may be NSFW.
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