Micro-plastics and the Specac Diamond Compression Cell

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Courtesy of Specac Limited

The Environmental Audit Committee has called for a global ban on microbeads, minuscule plastic balls used by the cosmetic and cleaning industries for their abrasive properties (exfoliating face-wash, shower gel, toothpaste, etc).

Toothpasteonbrush

According to BBC News, a single shower using a micro-bead product can release up to 100,000 micro-beads into the ocean. These can become ingested by fish, worms, birds and other organisms, causing physical/biological harm or even death and disrupting the marine ecosystem.

 

Every year tons of microplastics enter the oceans through a plethora of sources. But a lesser-talked-about area of this topic is the worrying fraction of micro-plastics emitted into the world’s oceans which since become unaccountable. Where are they?

We've read three scientific studies which suggest the following:

  1. Some of these pollutants have sunk to the deep sea.
  2. There are micro-plastics trapped in Arctic sea ice, which are increasingly being released into the world’s oceans as more ice caps melt.
  3. Inland estuaries, such as the Tamar Estuary in Southwest England, contain floating plastic debris in their surface waters.

Microscopic deep sea secrets

These micro-plastics can be either denser than or lighter than seawater. If the plastics are light and buoyant they float when entering the world’s oceans and remain visible. These often accumulate visibly on shorelines or simply at points on the sea surface.

However, even light and positively buoyant plastics can, over time and due to certain variables, become negatively buoyant and sink. Micro-plastic fragments, some at low-densities, have been reported as present in bulk at extreme depths in the sea.

Independent collecting and analysis of sea sediment in the Mediterranean Sea, South West Indian Ocean and North East Atlantic Ocean, has quantified the abundance and extent of micro-plastic fragment contamination.

In a study coined The deep sea is a major sink for micro-plastic debris, researchers collected ten cm diameter cores of seafloor sediment from submarine canyons, seamounts, basins and continental slopes. Coral specimens were also analysed at the seamounts. This was carried out by researchers in association with the University of Barcelona and the Natural History Museum, London.

Using a Bruker IFS66 FTIR spectrometer with a Specac DC2 diamond compression cell (2 mm diameter), the micro-plastic samples were analysed using IR transmission. Micro-plastics were confirmed as abundant in all 12 sediment samples and coral samples. They were fibrous in shape, commonly 2–3 mm in length and mostly red, black, green or blue, except for some which were purple, pink and turquoise.

A non-plastic man-made polymer known as Rayon was found, accounting for 56.9% of fibres. Polyester (53.4%), acrylic (12.4%) and other plastics (34.1%) made up the rest. The quantity of polymers found frighteningly infers that deep sea micro-plastic contaminants are four times more abundant down below than on surface water.

Frozen in hiding, until now

When forming, sea ice “scavenges and concentrates particulates from the water column” – in the words of Rachel W. Obbard et al. They authored study Global warming releases micro-plastic legacy frozen in Arctic Sea ice with the Thayer School of Engineering at Dartmouth College and School of Marine Science and Engineering at University of Plymouth.

When Arctic sea ice melts, the synthetic particulates are released back into the sea. The recent accelerated melting of Artic sea ice is therefore seeing an accelerated re-introduction of man-made

In the study, 1–3.5 m cores of sea ice, taken from various depths of sea ice across the Arctic Ocean, were cut, melted, filtered and then analysed. FTIR analysis was carried out using a Bruker IFS66 spectrometer with an MCT (mercury cadmium telluride) detector operating at 4000–500 cm -1. A Specac DC2 diamond compression cell (2 mm in diameter) was used to allow the transmission of infrared light through the sample.

Submillimetre synthetic pieces were found in each core. Again, non-plastic Rayon was the most abundant synthetic (54%), followed by polyester (21%), nylon (16%), polypropylene (3%) and acrylic, polystyrene and polyethylene (2% of each).

Such a substantial presence of micro-polymers in the Arctic Sea (38 to 234 particles per m3 of ice) is disturbing. The sheer amount found far exceeds that of the Atlantic waters north of Scotland (0.34 particles per m3 of water) or the North Pacific Subtropical Gyre (0.12 particles per m3 of water).

On Britain’s doorstep

The Tamar-Tavy Estuary is a Site of Special Scientific Interest (SSSI) between Cornwall and Devon, UK. It was designated as an SSSI in 1991 for its biodiversity and variation of habitats which support many wader and wildfowl species, along with some valuable marine species.

Researchers at Plymouth University carried out the study On the quantity and composition of floating plastic debris entering and leaving the Tamar Estuary, Southwest England to report on the quantity and composition of floating plastic debris present in the surface waters of this estuary. They also compared the amount, consistency and composition of this debris according to different stages of the lunar cycle.

These synthetic particulates could either be destined to float into European waters from the UK estuary, or have originated in coastal waters and passed into the UK. Samples were collected from surface waters using a manta net, towed against the tidal flow at four knots for 30 minutes. Transferred to glass jars, samples were taken to the laboratory and sieved with various mesh sizes.

Pieces of plastic and suspected-synthetic materials were categorised by size and then 50% of each size group was analysed with FTIR to indicate the proportions of different polymers. A Bruker IFS66 spectrometer was used with a Specac DC2 diamond compression cell.

204 pieces of suspected plastic were found, 84% later confirmed as being plastic. Polymers consisted of polyethylene (40%), polystyrene (25%) and polypropylene (19%). Polyvinyl chloride, polyester and nylon were also present and 82% of this debris was classified as micro-plastic (

Overall the mean concentration of the plastics in the waters was 0.028 m3 and there was a smaller central tendency of size classes during the neap/ebb tide. As many of these plastics were too dense to have originated from the oceans, it has been suggested their origin lies in UK sewage lines which could contain some packaging materials.

You may have noticed that the Specac Diamond Compression Cell was featured in each of the three studies mentioned. With its high-working pressure and with minimal sample preparation needed for sample introduction, this accessory is ideal for the FTIR analysis of micro-synthetic materials.

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