Friday, June 19, 2009

More Answers to Student Questions

"Here in Maine we have problems with chemicals in the ocean such as mercury, PCB, and Dioxon. It is such a big problem that we can't eat the fish. Do you have the same chemical problems in the pacific and does the plastic leech some of their chimcals into the water? thanks ." -Sal and Cleo, Homeschool, Maine, USA-

Sal and Cleo,
I am back with an answer to your excellent question regarding chemicals in our ocean. I consulted with Dr. Lorena Rios (picture above) from the University of the Pacific in Stockton on this one. She was on the 2007 voyage from Long Beach to Hawaii, and spent time collecting samples to analyze for chemical contaminants. Here is what she had to say:

" Definitely, we have a huge contamination problems in the San Francisco Bay and along to the California Bay (La Cuenca de las Californias). In the Pacific Gyre we found PCBs on plastic debris though I did not analyze mercury and dioxins. We did not analyze fish and plastic at the same time. However, I think the PCBs on plastic can affect fish when they eat the plastics. These contaminated plastics are a source of persistent organic pollutants for fish."

Lorena also shared some of her preliminary results with us, showing that plastic debris found in the gyre contains 100,000 to 1,000,000 times more contaminants than the ambient sea water.

"I am having a hard time visualizing what 334,271 pieces of plastic/km2 and roughly 5,114 g/km2 of plastic would look like when you bring it up after trawling? Would this fill a 500 ml bottle for instance? Is it all small stuff? Why are your measurements in area (km2) and not volume? Is that because you trawl on the surface because most of the plastic is lightweight and floating?" East Hills 4-H San Leandro, CA, USA"

Dear East Hills 4-H,

ScubaDrew and Capt. Moore both came up with some great examples of how to visualize the density and count of plastic pollution per area. Capt. Moore likened 334, 271 pieces/km2 to a quarter on your bed and ScubaDrew likened the plastic per volume to a cheerio in a bathtub.

Regarding the kim2 vs. km3 question: The reason we measured using km2 was to compare our results with the data presented by Dr. Day in his 1989 paper on plastic pollution in the Pacific. Because we expressed our data in such a way we found that Dr. Day’s highest found concentration of plastic was 300,000 pieces/km2 while the worst we sampled was 900,000 pieces/km2. Our results were published in Marine Pollution Bulletin 42:12. We have data by the cubic meter as well. If you would like to see some of that data let us know!

You are right. Much of the plastic is positively buoyant, which means it floats on the surface. however we know there are certain kinds of plastics which do not float, called negatively buoyant plastics (such PVC, polycarbonate, PET and PETE, and nylon). These plastics have been found in the sediments in river beds for instance. By sampling at the surface we are only gaining a notion of the density of positively buoyant particles, which there is a lot of plastic out there that we have not been able to account for.

Thanks for all the great questions! Keep’em coming!
From the Pacific,

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