Concentrations of plastic debris in surface waters of the Mediterranean Sea at basin scale, and compared to the plastic concentrations reported for the global ocean.
From
Haaretz by Ruth Schuster
It's hard to know how much plastic is reaching the seas, let alone what's happening to it.
New study estimates Med load alone is one item per four square meters of water.
The Mediterranean Sea is just as badly afflicted by plastic dumping
as the rest of the world's oceans, despite being relatively isolated,
scientists say.
The team, from the universities of Cadiz and
Barcelona in Spain and the King Abdullah University of Science and
Technology in Saudi Arabia, found that an average plastic density of one
item per four square meters of water in the Mediterranean Sea.
Some 250 billion plastic particles weighing a total of 500 tonnes litter the Mediterranean, threatening sea life which can suffocate when eating them
Just as
horrifyingly, they found plastic debris in every single one of the sites
they sampled, the team
reported in PLOS ONE this week.
That's about the same as the accumulation level found in the five subtropical ocean gyres – circulating ocean currents.
Bathymetry of the Mediterranean Sea (IBCM)
How much plastic is actually there in the Mediterranean Sea?
The team's best estimate is 1,000 to 3,000 tons and counting.
One would think it possible to reach a narrower
range of estimates, but one would be wrong. Nobody knows how much
plastic is entering the ocean from waste generated on land or by ships.
A
study published in February 2015 (the first of its kind for 40 years)
tried to put together worldwide data, adjusting for population density
and economic status: it estimated that in 2010, the 192 coastal nations
of the world produced 275 million metric tons of plastic waste.
Of that,
anywhere from 5 million tons to 13 million tons wound up in the water.
To put that into proportion, in 2012 scientists
estimated that all humanity together weighed 316 million tons.
In other
words, according to that estimate, humans are putting around 2% of their
total weight worth of plastic into the sea each year.
Moreover, the same 2012 study, which was done by a
team of American scientists and published in Science, forecasts that by
the year 2025,
people will have dumped 155 million tons of plastic into the oceans – half of mankind's total weight.
Size distribution and aspect of the floating plastic debris collected in the Mediterranean Sea.
And it will stay there
Plastic famously fails to biodegrade.
Nobody
actually wants to eat it, though plenty of sea animals do so by mistake,
often fatally: it cannot be digested and even if it doesn't choke them,
their digestive systems get impacted.
But over time, plastic does break
down into tiny pieces, eventually down to the level called
"micro-plastics" which can be accidentally – fatally - eaten by the
microscopic animals on which the entire global food chain depends.
Anyway, what plastic does not do is vanish.
The
team estimates that the total amount discarded and floating in the
Mediterranean Sea is between 1,000 and 3,000 tons.
Surface samples found that the dominant plastic debris in the Mediterranean Sea was millimeter-sized fragments.
If the Mediterranean Sea was distinguished from the
great oceanic gyres – the circulating currents - in one way, it was a
higher prevalence of large plastic objects.
That, postulate the
scientists, is because by the time the plastic detritus reaches the
"plastic islands" – such as the famous "Great Pacific Garbage Patch" -
in the oceans, it has traveled a long way and disintegrated into tiny
pieces.
In the small Mediterranean Sea, the distance from the sources of
the pollution to the detritus is small.
Ranges of surface plastic concentrations measured in the Mediterranean Sea,
and reported for the open ocean.
Whodunit? And where is it?
Perhaps the most worrying thing of all, for the
oceans and the Mediterranean Sea too, is that the great garbage islands
turn out to be a drop in the sea, so to speak.
Total global plastic production is at least 300
million tons a year.
If in 1975, a National Academy of Sciences study
estimated that about 0.1% of global plastic went out to sea each year –
now the thinking is that
the real proportion is 15% to 40%.
Scientists have long demonstrated the existence of
five so-called "plastic islands" in the oceans, which accumulate plastic
that arrives on the ocean currents.
Each contains millions of pieces of
plastic per square kilometer.
Though make no mistake, the plastic is
everywhere in the water.
Scientists had assumed that most of the plastic
tossed into the sea wound up in these mounting piles on the water
surface, created by powerful oceanic currents.
But if that were the
case, the garbage patches should be much, much bigger than they are.
Ergo, most of the plastic is not ending up in the great plastic islands.
Photograph of typical textile fiber (red) and fishing thread (blue)
So where is it?
Scientists now admit they have no
idea where 99% of ocean plastic ends up, though clearly some
micro-plastic is ending up on the sea floor.
Sadly for them, marine animals are eating at least
some of the missing plastic, mistaking the small bits for food.
It isn't
though.
It isn't nutritious for just about anybody – with one possible
exception.
If there's hope, it's that some of the missing
plastic is actually being eaten by microbes.
If there's one thing that
characterizes life on this planet in general , it's adaptability.
Otherwise there would be no life.
Maybe there's some germ down there in
the depths, or on the surface, that's evolved a taste for plastic. We
just haven't found it yet.
