I agree with you that these particles should be studied for their potential health and environmental impact, but combustion has been around much longer than humanity. I think that not all these particles are made equal and that being said I don't think that the nanotubes found in this study are much like what we are trying to create for technological purposes. They are probably very short/small and the article mentioned "[these] nanotubes are unlikely to have the cancer-causing potential of asbestos fibres, which are much larger and can get trapped in the lining of the lung." I believe their impact should be studied but there are also many other combustion products that probably have a larger negative impact.