Announcements Bisphenol-A Question #1 • Final exam structure details • How long does it take to breakdown? – In river water it takes about 5 days – In the body it reacts with a sugar and is ultimately removed within 3 days Bisphenol-A Question #2 Bisphenol-A Question #3 • How much are we exposed to? • Does exposure change based on – CDC study says average concentration is lifestyle issues (drinking soda, etc.)? under 50 ng / (kg day) – From CDC study – Because it is rapidly metabolized, this • Mexican Americans have lower levels that means low-level exposure is likely others continuous • Women have higher levels than men • Lower income people have higher levels • Children have higher levels than adolescents who have higher levels than adults Bisphenol-A Question #4 Bisphenol-A Question #5 • Does anything increase risk? • What is meant by “being exposed”? – To release bisphenol-A from polycarbonate – The most likely method of exposure is requires a reaction called hydrolysis through swallowing it after it has leached (essentially adds back the water from into food or liquids. polymerization and breaks up the bond.) – Touching polycarbonate materials is NOT a route for exposure. – Heating and exposure to basic solutions – It’s probable that the primary source of increases hydrolysis bisphenol-A is the resins that coat food containers. Bisphenol-A Question #6 Bisphenol-A Question #7 • How does it work as an estrogen mimic? • How do we know about human effects? – Basic mechanism is that it binds with receptors – In addition to whole animal studies on rats, that influence calcium ion movement into or out of studies can be done on cell lines - cells. including human cells. – Looking at data from previous study, points to a challenge, effects don’t always increase with greater amounts. – Suggests low dose exposure may be more worrisome (but proves nothing.) Bisphenol-A Question #8 Risk - benefit analysis • Are there alternatives? • Should we regulate polymers that – Polycarbonate has many favorable properties contain bisphenol A to remove them including… • High strength from consumer products? • Scratch resistant • • Lightweight – It’s possible to make other polymers with similar properties (likely more expensive). • – Coatings on cans need to be able to withstand sterilization procedures - so alternatives are harder to find, perhaps. The fate of disposed plastics What factors matter most? • Plastics comprise about 11% of the • Think of advantages of each - paper or garbage - by volume - in the US. plastic • Paper vs. plastic. • Think of disadvantages of each • What is the best way to bring home • your groceries? • Note figure 9.12 (weight and volume of 100 bags: 17 lbs & 1219 in3 vs. 122 lbs and 8085 in3) Recycling plastic Collection • The process for recycling plastics • About 7500 cities have curbside requires several steps. collection • Collection • About 12,000 additional cities have • Sorting collection centers. • Processing • Most of the collection co-mingles the • Creation and sale of new products plastics with other recyclable materials which requires additional handling Processing Closing the triangle • Separation is often based on density • One of the most important steps in any • In Milwaukee they use a machine that recycling is the product that results. jostles the co-mingled materials and the • If nobody purchases a product made from plastics end up on the top for the most recycled materials, the materials won’t be part. recycled any longer. • Can also use floating techniques. • A key challenge for plastic because it tends to degrade through the processing in must undergo.
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