• The volume of microplastics from paint on steel surfaces that enter the ocean every year could be as high as 1.5-2.25 million tonnes, equivalent to 150-225 billion empty plastic bottles;
  • Putting these new figures in context, they account for a meaningful percentage of the 8 million tonnes of plastic that is estimated to end up in the oceans each year;
  • The microplastics come from the impact of corrosion, wear and tear and, most significantly, from the traditional open-blasting methods used to maintain steel surfaces;
  • More research is urgently needed to raise regulatory and policy-makers’ awareness of the problem and to find new treatment methods to solve it.

Until recently, microplastics that enter the ocean from paint have not received a lot of attention. There has been very little focus on the fact that unless paint residuals are collected during surface preparation and the maintenance process, they will largely end up in the ocean as microplastics.

Uncertain emission estimates

The most quoted source of data on how much microplastics from paint enters the ocean each year gives a figure of 60,000 tonnes per annum. While this is still a big figure – the equivalent of six billion empty plastic bottles being dumped in the ocean every year – it falls short of the real size of the problem. This is because:

For these reasons, the real level of paint microplastics entering the environment and ocean each year could be much, much higher than 60,000 tonnes. Other reports also conclude that paint is the second-largest source of microplastics in the ocean.

The pathway by which plastic enters the world's oceans
The pathway by which plastic enters the world's oceans
Image: Our World in Data

Let’s look at it another way and see what happens to all of the paint on steel assets. It is estimated that more than six million tonnes of paint are applied to industrial and marine steel structures every year.

*Coatings World, **assuming 1-1.2 kg per litre of paint and 40-50% plastic content, ***assuming 50-75% of the paint residuals are not collected
*Coatings World, **assuming 1-1.2 kg per litre of paint and 40-50% plastic content, ***assuming 50-75% of the paint residuals are not collected

Therefore, based on the actual level of paint applied to industrial and marine steel assets each year, it is estimated that the real level of paint microplastics emissions to the ocean every year could be as high as 1.5-2.25 million tonnes. This is based on the assumption that 50-75% of the paint residuals are not collected. Given we know that open blasting without collection holds a higher market share of surface maintenance than this, the actual level of emissions is probably at the higher upper end of the range.

Putting these new figures in context, they are a very meaningful percentage of the 8 million tonnes of plastic that enters the oceans each year. In addition, it can also help us better understand where some of the estimated 12-21 million tonnes of microplastics in the Atlantic Ocean, as highlighted in a recent study, have come from.

What are the risks from all of these paint microplastics? Ingested microplastic particles can physically damage organs and leach hazardous chemicals – from the hormone-disrupting bisphenol A (BPA) to pesticides – that can compromise immune function and stymie growth and reproduction. Both microplastics and these chemicals may accumulate further up the food chain, potentially impacting whole ecosystems, including the health of the soils in which we grow our food. Microplastics in the water we drink and the air we breathe can also hit humans directly.

Harmful open sandblasting and water jetting are the predominant methods of surface maintenance. These are used at an industrial scale worldwide with various, but very limited, degrees of waste collection and recycling. There is a certain level of collection inside controlled environments like shipyards. Offshore, however, on oil rigs, ocean wind farms and ships, and in many situations on-shore, such as bridges, there is considerably less waste collection.

Using innovative solutions in surface maintenance, such as circular sandblasting, can reduce the emissions of microplastics to zero. In addition, the zero-emission, circular solution also recycles the blasting material, reducing grit consumption by 80-90%, which generates significant reductions in CO2 emission.

Microplastics in the surface ocean, 1950-2050
Microplastics in the surface ocean, 1950-2050
Image: Our World in Data

The need for regulatory awareness and enforcement

We need greater awareness of this problem on the part of environmental regulators, and a willingness to enforce existing anti-pollution laws. There should be a requirement to collect the used blasting material, with its heavy metals and other toxic components, and most importantly, the rust and paint residuals as they are blasted off the steel assets. Otherwise, they will largely find their way, directly or indirectly, into the ocean.

Even though there is considerable uncertainty regarding the extent of emissions of microplastics from paint into the ocean, one thing is very clear: it is a significant problem that deserves a lot more research and regulatory and policy-maker attention, so action can be taken to solve it as soon as possible.