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Inside the Trash Pollution Component

Plastics are featured this month because they form the bulk of marine trash, one of the four components of the Clean Waters goal. Marine plastics have received a great deal of publicity as the public has learned about the swirling concentration of plastic in gyres like connection with the ‘Great Pacific Garbage Patch.’ In addition, the March 2011 tsunami in Fukushima, Japan has sent an estimated 5 million tons of detritus sailing across the Pacific Ocean.

The most common plastics found at the beach are cigarette butts, plastic water bottle caps, plastic bags and styrofoam pieces.

The Clean Waters goal evaluates four major components of pollution. They are:

•       Pathogens (disease-causing bacteria, parasites and viruses from sewage outflow)

•       Chemicals (harmful organic and inorganic substances of many kinds)

•       Excessive Nitrogen and Phosphorus that cause overgrowth of algae and dead zones

•       Trash (debris on the beach or at sea, most of which is now plastic)

Figure 1.  From the Clean Waters Goal Page of the Ocean Health Index

Because global data do not yet exist for oil spills, toxic algal blooms, dead zones, turbidity (sediment input), radioactivity or floating trash we could not include them, but hope to do so in the future when/if those data are developed.

For aesthetic and health reasons, people value marine waters that are free of pollution and debris, so each component has a reference value of zero, that is, clean water is defined as zero pollution. 

Direct measurements of pollution do not exist in all countries, so we approximated its intensity using related global data.      

•       We estimated pathogen pollution by evaluating the number of people living within 50 km of the coast multiplied by the percentage without  access to adequate sanitary facilities.

•       We estimated nutrient pollution using data on the amount of fertilizer used by each country and modeling its flow into the ocean

•       We estimated chemical pollution using data on the amount of pesticides used by each country and modeling their flow into the ocean

•       We estimated trash input by the tons of litter per km of beach collected during beach cleanups organized by the Ocean Conservancy’s Trash Free Seas Alliance in 96 countries and locations. (See what they found here.)   

When pollution is present for a component, its status score is (1– pollution intensity of that component, expressed as a decimal fraction). If water is clean, the intensity for each component is zero, and each component status is (1– 0) = 1.  Status values for the four components are combined as a geometric mean to produce the clean waters goal score using the formula in Figure 2:

Figure 2.

We use a geometric mean because it penalizes poor scores more heavily than does a simple arithmetic mean (average). For example, if a, u and l all equal 0.5 and d = 0.25, the geometric goal score would be 42; the arithmetic score would be 44.

The world scored “78” in the Clean Water goal. This indicates that the ocean may have lower levels of pollutants than anticipated, but is still not on a sustainable path. The likely future state is assessed as “+0,” indicating that the score is unlikely to change in the next five years.

You can see which countries scored highest or lowest for clean waters here. There you can use the up and down arrow indicators at the top of each column to sort Ranks and Scores (top down or bottom up) and Countries (alphabetically).  

In the end, much of the waste we produce finds its way to the ocean, so cleaning its waters will require changes---some little, some big--- in everything we do personally, commercially or in other ways. But achieving clean waters will bring huge benefits to ocean life, human health and coastal economies, so this goal deserves all of our efforts.