Plastic soup is prepared on land!

Rigid Plastics

While writing this blog I am watching the Giro d’Italia. While everything goes forward, every couple of seconds things go sideways: bidons. Below you see a picture of Tom Boonen getting rid of his drinking bottle (ok, not in the Giro….)

It makes sense that these guys do this with their bottles while racing, but recreational bikers do the same. What happens with these bottles? Here you see one that I found while letting my dog out.

crushed bidon

crushed bidon

A couple of cars must have been driving over it. Where is the cap? Ah, there is one in Meers,

bottle cap

bottle cap

Where is the rest of this bottle? My guess is that it is crushed in tiny fragments and washed away with the rain.

Here we may find a fragment of it…

Cleanup Meuse near Borgharen
Cleanup Meuse near Borgharen

But I think it is more realistic to look for its fragments right here!

micrplastics on river bank Borgharen
microplastics on river bank Borgharen

You can picture the way these pieces have travelled:

Thrown away on a curbside or road, get crushed by cars, separating bottle from cap. Fragmented to a size that makes it easy for transportation by rain. Transported further by sewer systems, passing through purification plants, get transported by smaller creeks towards the Meuse. Get deposited for a while on the bank, but transported further after a high water period until flowing into the sea. Adding some more grammes to the plastic soup.

Flexibles

I follow a plastic bag already for a couple of months. This is how he looked while I first met him on January 1st 2012, being entangled in barbed wire.

plastic bag 1 jan 2012

plastic bag 1 jan 2012

A couple of months later this is how he looked:

plastic bag 12 may 2012

plastic bag 12 may 2012

Slowly disintegrating and showing the characteristic wrinkling of a weathered plastic film:

plastic bag wrinkled

plastic bag wrinkled

And where are the blown off pieces? Maybe here…

plastic nest

plastic nest

There is a general idea that plastics in the oceans get ever smaller through the impact of UV-light and wave-action. But I think the fragmentation is already far on it’s way when litter is still in a river.

So whenever we want to stop plastics flowing into the seas, we better be aware that we have to stop these little particles being transported. But that we can solve on land and we do not have to fish them out of the sea!

Maybe that is some good news

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Wind pushes plastics deeper into oceans.

The effect of the surface to volume ratio demonstrated in the oceans. Same phenomenon as we have found in the river.

Wind pushes plastics deeper into oceans, driving trash estimates up with video — University of Washington – washington.edu.

How does a river transport litter?

First findings

Based on observations and our first test runs, we can get some clues on how a river transports litter. Three basic elements must be considered:

  1. The river
  2. The weather
  3. The litter

1 The river

The Meuse is a river that is completely determined by meteorological events in its catchment area. It starts in the north-east of France, flows through Belgium and the Netherlands.

meuse-catchment

meuse-catchment

It’s throughput is quite fluctuating through the seasons as the graph below shows:

debiet Eijsden 1990-2000 (m3/s)

debiet Eijsden 1990-2000 (m3/s)

This difference in throughputs implies that there is an intensive interaction with the river banks. Every peak leaves a mark on the bank, washed away whenever a higher peak follows. These lines on the picture below have been deposited during the peaks in the winter periods of the last couple of years.

high water lines on river bank

high water lines on river bank

At high throughputs the river is very turbulent. This turbulence pulls a lot of debris under the surface, only a small part of the debris stays afloat. Trees and bushes on the banks catch these suspended litter fragments, resulting in highly decorated trees after a period of high waters.

tree after high water

tree after high water

2 The weather

Rain and wind contribute to the transport of litter by a river. When it’s raining streets are washed clean, litter is transported through sewer systems and smaller rivers to the Meuse. Small litter passes through purification plants, where only big parts are collected.

Some installations catch the “first flush”, but most of the “clean” rainwater from the streets is directly discharged into a stream.

litter pushed by wind to shore

litter pushed by wind to shore

Wind creates small waves, picking up litter deposited on the banks, mixes it in the top water layer of the river, or pushes very buoyant parts onto another part of the riverbank. This intermittent way of transportation is very typical for the way a river transports litter.

3 The litter

With our first catches and a lot of searching along the riverbanks, we get a first glimpse of the kind of litter transported by the river. There are numerous divisions you can make, but one is most certainly related to the “surface to volume”-ratio. The larger this ratio, the more suspended a piece of litter will be, depending on the turbulence of the river.

A simple demonstration with plastic films with different thickness demonstrates shows clearly the impact of this “specific surface” aspect. The thinner the product is, the longer the product stays in suspension.

When the river is calm, like in summer with no wind, almost all floating (specific mass < 1) products will slowly drift to the surface. As soon as the wind starts to blow or the speeds and turbulence of the water increases, ever more litter will go in suspension at ever greater depths.

Litter with a high specific surface like leaves, packaging films, thin walled plastic products will disappear from the surface. It can be entangled in the flooded parts of the trees or just flow downstream towards the sea.

Litter with a low specific surface, like twigs, treestumps, PET and glass bottles, EPS foam and metal cans stay on the surface, even at the highest throughput rates. They get deposited on downwind banks or get concentrated in calm spots next to the current. Together with the films caught in the trees, they create the very visible litter fraction people get annoyed about in early spring.

big and visible litter with small surface to volume ratio blown ashore

big and visible litter with small surface to volume ratio blown ashore

Another characterisation is between big, small and very small. The next picture shows the results of a mechanical clean-up of the river bank. You can clearly see both the small and the big pieces, all very buoyant and therefore present on the river bank.

a pile of mecanically collected litter, big floating parts very visible

a pile of mechanically collected litter, big floating parts are very visible

small rigid plastic litter pieces between organic material

small rigid plastic litter pieces between organic material

In this pile hardly any flexible plastics are found. The larger film pieces (like bags) hang in trees or might have entered the North Sea, together with all the other small pieces of flexible film products.

These are some of the first qualitative observations we have made. Now our job is to get a more quantitative and statistically valid approach towards all these phenomena we are discovering.

Interesting stuff for students!