Thursday, September 8, 2016

Coral Killing Sunscreens

More than a year ago, a study involving marine scientists from Virginia, Florida, Israel, the US National Aquarium and the US National Oceanic and Atmospheric Administration, identified a common chemical component of sunscreens capable of damaging coral reefs.
This chemical is commonly known as oxybenzone and its structure is shown below:
This molecule has the systematic IUPAC name of (2-hydroxy-4-methoxyphenyl)(phenyl)methanone
Notice how every carbon atom (except that of the terminal methyl group, the carbon atom of the methoxy group) is involved in a double bond?
This kind of arrangement leads to some interesting properties. One of these properties is that molecules like this one are good at absorbing UV light. So, oxybenzone is added to products such as plastics, sunscreens, hairsprays, nail varnish and cosmetics like lipstick and mascara, as a UV filter.
Sunscreen lotion can contain between 1 and 10% oxybenzone.
Unfortunately, oxybenzone enters the water when people wearing sunscreens or other cosmetics decide to go for a swim. Researchers estimate that between 6,000 and 14,000 tonnes of sunscreen lotion are emitted into the waters of coral reefs each year.
The same property that makes it ideal as a sunscreen makes it a catastrophe for our coral reefs! Blocking UV light to baby corals causes growth deformities, and worse, the coral becomes encased in its own skeleton and dies.
In 2016, a study of Hawaii's sea waters found the oxybenzone concentration ranged from 0.8 to 19.2 µg/L. A previous study found that oxybenzone concentrations as low as 0.062 µg/L could harm the coral.
Hawaii's government asked swimmers, surfers and divers to avoid using sunscreens that contain oxybenzone as a measure towards protecting their reef.

Hawaii targets sunscreens with oxybenzone 

Suggested Study Questions:
  1. Draw a molecule of oxybenzone, and, locate and name each functional group
  2. Give the molecular formula for oxybenzone.
  3. Calculate the molar mass of oxybenzone.
  4. Draw the 2-dimensional structural formula for oxybenzone.
  5. Oxybenzone readily dissolves in ethanol. Explain how oxybenzone can dissolve in ethanol.
  6. Oxybenzone does not dissolve in water. Explain why oxybenzone dissolves in ethanol but not in water.
  7. Given the data in the article, calculate the mass of oxybenzone that could be emitted into coral reef waters each year.
  8. Convert the following concentrations of oxybenzone to concentrations in parts per million
    • 0.062 µg/L
    • 0.8 µg/L
    • 19.2 µg/L
  9. Convert the following concentrations of oxybenzone to concentrations in moles per litre (molarity)
    • 0.062 µg/L
    • 0.8 µg/L
    • 19.2 µg/L
  10. Assume a 375 g tube of sunscreen lotion contains 10% by mass oxybenzone. Use the data in the article to calculate an "average" number of tubes of sunscreen that washed into the ocean each year. Justify your answer.

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