Are there potential adverse health consequences of the thousands of tons of microplastics falling from the sky, and are there sinister origins in this coming about?

Both of these things are true. It is not healthy to ingest microparticles of any foreign material. This will cause an ongoing inflammatory response that can have adverse consequences with chronic exposure and buildup. The body will not be able to clear these things very effectively except as they can be expelled through the normal ciliary clearance process. When deep in the lungs, they can become a chronic irritant. This is a consequence of your technology creating a cheap substitute for products that are cheap to make and likely to not last long or may be designed to be expendable, and then the disposal not being done properly, so that the degradation will contaminate the environment and then the waste products becoming airborne and breathed in. What is needed here is greater enlightenment about this cycle of events, so it can be monitored and adjusted to do what has true value while also minimizing the risks of creating materials that damage the environment and human lifespan.