[katieHaylor (OP)]

Bobby asks:

Can plastic in our oceans break down into particles small enough to be within the water vapour being evaporated, then end up in our rain water?

What do you think?

[alancalverd]

Not by the normal textbook process of molecular evaporation, but strong wind or surf could carry microparticles to cloud height - it happens to fish, and even boats, in a waterspout!

[evan_au]

It can happen if gases are released in the manufacture or decomposition of plastics.

A Swiss greenhouse gas monitoring station high up in the Alps can detect when a particular factory in Italy is producing a batch of teflon.
Listen here: http://www.bbc.co.uk/programmes/w3csvpfz

[chris]

Water evaporates from the sea surface when energy from the Sun, arriving at the rate of about 1 kW/m², excites water molecules sufficiently to break the bonds that hold liquid water together. This allows water molecules to turn into water vapour, which is carried aloft. Eventually it cools and coalesces with other water molecules to form clouds, which ultimately drop the water over land as rain.

Most plastic particles in the ocean are orders of magnitude larger than the water molecules, so they find it much harder to break free from the surface and rise into the air like would-be rain. Instead the microplastics are becoming incorporated into marine sediments in a detectable layer that will mark out mankind's presence on Earth for alien visitors in future who arrive after we've wiped ourselves out and want to find out how we messed up our planet.

I interviewed Professor Martin Rees about his suggestion that we are into a new epoch - "The Anthropocene" in this item last year.

[RD]

... microplastics are becoming incorporated into marine sediments in a detectable layer that will mark out mankind's presence on Earth ... "The Anthropocene"

Surely it should be "The Plasticine™" 

[syhprum]

I think the plastics in the ocean problem will solve its self with the evolution of plastic eating organisms, bacteria live in abandoned nuclear power stations cooling ponds chomping up Plutonium so plastic bags should be no big problem