I found more information about this, and since there hasn't been a single answer so far I'm going to self-answer my question based on what I found.
- There is a EU-sponsored research project called MERMAIDS that investigates this problem and links to various related and interesting news articles.
- The Plastic Soup Foundation is cooperating with the MERMAIDS project and clothing manufacturer G-STAR to address the problem. G-Star and the Plastic Soup Foundation are calling upon other manufacturers to sign their Ocean Clean Wash Charter which also contains some interesting information about the research that was done so far.
- The researcher Mark Brown mentioned in the question, has initiated a project called Benign by Design with the goal to "propel the textile industry toward cost effective fabrics that emit fewer and less toxic fibers"
There are several aspects that make this a rather worrying problem:
First of all recent research found that clothing gives off much more particles in a washing machine than previously thought. The 2011 paper written by Mark Browne mentioned over 1900 fibers per garment, but new research has found that a single polyester fleece sweeter gives off almost 1.000.000 fibers per wash. Especially polyester, acrylic and nylon are mentioned as bad materials.
Second, we know from past research that plastic particles in (sea)water absorb other toxins present in the water. We also know microplastics are eaten by marine animals, thus introducing toxic pollutants into the food chain.
Additionally waste water treatment plants lets microfibers through, so it could very well be that microfibers are also present in our drinking water. However I haven't been able to find any confirmation of this. It seems there hasn't been any research on microfibers in drinking water yet!?
As far as I've read there still is no direct evidence linking microfibers found in oceans to clothing but, as was also mentioned in the question, we do know that microfibers are released during washing and that microfibers make up 85% of all man-made materials found in various ocean water samples. Also the types and amount of fibers found on shores matches those used in the clothing industry. Based on these facts this article says that this could very well make microfibres from clothes the biggest source of plastic pollution in the ocean.
Although research is still in progress, the MERMAIDS website mentions several solutions to at least reduce the problem:
Furthermore the Ocean Clean Wash Charter mentions a few potential future solutions:
- Develop washing machine filters that catch the microfibers
- Develop synthetic fabrics or that don't give off microfibers
- Develop impregnation that prevents the release of microfibers.
Of course you could also try to avoid buying polyester, acrylic and nylon clothing until a good permanent solution has been found and implemented.