Questions: Marine Pollution: Plastics, Oil, and Persistent Toxins
4 questions to test your understanding
Score: 0 / 4
Question 1 Multiple Choice
Why does floating plastic debris collect in the centers of subtropical ocean gyres?
AThe water there is colder, so plastic sinks less
BWind-driven Ekman transport moves surface water toward the gyre centers, gathering floating material there
CShips dump most of their waste in those regions
DStrong upwelling brings plastic up from the seafloor
In each subtropical gyre, the combined effect of winds and Earth's rotation pushes surface water toward the middle. Floating debris is carried along and collects in these convergence zones, such as the North Pacific gyre between Hawaii and California.
Question 2 Short Answer
Mercury concentrations are usually far higher in large predatory fish, such as swordfish, than in the seawater around them. Explain why.
Think about your answer, then reveal below.
Model answer: Methylmercury is taken up by small organisms and is not easily excreted, so it builds up in their bodies (bioaccumulation). Each predator eats many prey, so it receives the mercury stored in all of them, and the concentration increases at each step of the food chain (biomagnification). Long-lived top predators therefore have the highest levels.
This is why health agencies advise limits on eating some large predatory fish. In the 1950s, methylmercury released from a factory into Minamata Bay, Japan, built up in seafood and caused severe poisoning in people who ate it.
Question 3 True / False
Microplastics are commonly defined as plastic pieces smaller than 5 millimeters.
TTrue
FFalse
Answer: True
Microplastics include fragments from larger items broken down by sunlight and waves, fibers from clothing, and small beads made for products. Their small size lets them be eaten by plankton and filter feeders.
Question 4 Multiple Choice
Which effect of an oil spill most directly kills seabirds?
AOil raises the water temperature
BOil coats feathers, destroying their insulation and waterproofing so birds lose body heat and may drown
COil blocks all sunlight from reaching the seafloor
DOil makes seawater less salty
Feathers keep birds warm and buoyant by trapping air. Oil mats them down, and birds also swallow oil while preening. Spills such as the 1989 Exxon Valdez spill in Alaska killed large numbers of seabirds this way.