This meta-analysis concluded that PM2.5 exposure was associated with increased risks of ASD in children, particularly with exposure windows during the third trimester and early childhood period. The effects of PM2.5 exposure per 10 μg m−3 increment revealed an exposure-responsive manner. Our findings suggested that PM2.5 exposure could possibly affect vulnerable populations at a low PM2.5 background level. [UNQUOTE]
I can certainly envisage how genetic disposition might have panned out in my own case. (It's perhaps worth noting that a environmental geneticist was involved in the above study.)
Since self-identification about 6 years back, I have often reminded myself that decades ago I lived on a hill above a large long-established paper mill, in a fairly constricted valley. The boilers were then coal-fired (changed to oil while I was there), but paper mills have long been known to be quite heavily polluting (with other chemicals) of the air, soil and water. The main chimney stack was originally down in the valley, but was moved decades before I lived there because it was too low for the valley sides. So the main stack was actually on the same hill as my home. There was also the water pollution from aniline dyes. In those days, waste-water was just discharged into a fairly small river, just a bit downstream of the water intake. That river exited into the sea just a few hundred yards further down, so that the local sea water was often colored by the dyes in quite a strong way. Us kids used to spend hours playing and swimming on that beach. A few years after that they were forced to build a wastewater treatment plant (that also served the town), but the outfall was not into the river, but through a tunnel through another hill to a quieter beach, with a very long outfall pipe running away to below the low-water mark. There was even quite a lot of pollution from artic trucks moving uphill to leave the mill. And also a lot of coal-fired trains. We even lived near a coal-fired town gas plant. Again, I doubt the chimney stack was really high enough for the local terrain.
So I have often wondered if there might be a local 'hotspot'. That town had its fair share of childhood health & education problems; despite the fact that most people would consider it a rural area.
It would be rather difficult to prove anything after all these years; particularly as the mill closed down just a few years ago. It was said to be still profitable, but its then current owners were known to have realised that eventually they might run into massive environmental remediation costs.
I was actually born at home. My parents had lived there for several years before hand. It does seem as if I had some problems at birth, and at three I had an unidentified metabolic disorder that was almost fatal. So there you perhaps have the exposure at third trimester and early childhood. I also lived in an even more polluted location in my teens; one in which there was a great deal of childhood illness.
I can't see myself ever being able to amass enough hard evidence to back up my suspicions; and arguably I have better things to do in my retirement. But I strongly believe that we will eventually find further links to air, soil and water pollution. I have received a diagnosis, but I'm sure many of you here will know only too well the diagnosticians are still decades away from being able to accurately pin-point causes. And which of the said comorbidities are most significant anyway , I wonder.
If you are in an area known for pollution problems, I can only guess that it might be worth contacting nearby universities that have say medical & pharmaceutical faculties; the nearest equivalent organisations to the ones involved in this research. I'm an expat, and so don't have too many UK leads now.
I still live in an area of the World with large amounts of particulate pollution. (But sure, I know that has nothing to do with a neuro-developmental concerns for young people. I'm just noting that there has been very little global remediation, so far.)