Passage III

Antimony trioxide (Sb₂O₃) is a chemical compound that is used as a flame retardant in manufacturing plastic bottles made of polyethylene terephthalate (PET). PET bottles can retain some Sb₂O₃ after manufacturing, and small amounts of the antimony ion (Sb³⁺) can be absorbed out of the plastic by water stored in those bottles. Two experiments were performed to study the absorption of Sb³⁺ by water stored in clear plastic bottles made of PET.

Experiment 1

The following steps were performed:

1. An unused PET bottle was filled with 2.0 L of pure water and sealed.

2. The bottle was placed into a box that was maintained at 10°C. An ultraviolet (UV) lightbulb was mounted inside the box (see diagram); only UV light was shone upon the bottle for 16 hr.

3. The bottle was then removed from the box, opened, and a 2.0 mL sample of water was removed. The concentration of Sb³⁺ in the sample of water, in nanograms per liter (ng/L; 1 ng = 10⁻⁹ g), was determined.

4. The bottle was emptied, cleaned, and air-dried.

5. The same bottle was then refilled with 2.0 L of pure water and sealed.

6. Steps 2−5 were repeated until the bottle had been reused 28 times at the temperature of 10°C.

Steps 1−6 were repeated 2 more times, except that the box was maintained at temperatures of 30°C and 50°C, respectively. The results for each of the 3 temperatures are shown in Figure 1.

Experiment 2

The procedure in Experiment 1 was repeated, except that in Step 2, the lightbulb inside the box was one that emitted only visible light. The results for each of the 3 temperatures are shown in Figure 2.

Figures adapted from S. S. Andra, K. C. Makris, and J. P. Shine, “Frequency of Use Controls Chemical Leaching from Drinking-water Containers Subject to Disinfection.” ©2011 by Elsevier, B. V.