Practically all of it. I grew up in a nice semi-rural area with minimal industry, and the environment is *still* cleaner than it was when I was a kid -- they shut down the local lead bullet factory when I was two years old (it has been a Superfund site since then), and of course they got rid of the leaded gasoline in cars. (Horrifically, private planes are still allowed to use leaded gasoline, which is an atrocity and a crime against humanity.)
Leaded gasoline burning is, historically, the major source of enviromental lead which poisons children. It's much larger than the lead paint or lead pipe sources. Trump was exposed to large amounts of all three; New York City had particularly high exposure due to high numbers of cars and trucks, ancient buildings, *and* gasoline refineries and chemical factories spewing lead in the air right across the river in New Jersey.
My SO's father started out as a mechanic. He was a forensic air crash investigator in the USAAF in WW II (the engine guy on the team) and was offered a job at Boeing after the war, but her mother hated Seattle so he didn't take it. Instead he became a car mechanic and ended up owning some car dealerships in Portland. His family had zero history of Parkinsons, but he developed it. His doctor thought it was probably from various chemicals he was exposed to working on cars.
I don't know how much of Trump's problems are from lead exposure. One of his sisters is a retired appellate court judge (Donald wanted to put his sister up for the first SCOTUS opening, but she is very pro-choice and is 81). The other sister worked in banking and is also retired. His youngest brother has worked for Donald and is rabidly pro-Trump. His oldest sister is best known other than Donald and by all accounts is quite sharp.
Donald almost certainly has a Narcissistic Personality Disorder that has turned into Malignant Narcissism (the worst form). Nobody knows what causes personality disorders. It runs in some families, but in other cases it just crops up with no family history. From what I've read of Fred Trump Sr, he may have been a sociopath/psychopath and Donald has some of those same traits. It's possible Donald picked up some of those traits from his father (genetically or learned or a bit of both) and the other kids took more after their mother.
It can be tough to figure out where traits come from. Some are certainly genetic, others happen from conditions in the womb, and yet more happen due to childhood experiences and exposure to various things growing up. It's all a mix of nurture and nature and we still haven't figured out what causes what in most situations.
Some studies have shown that Borderline Personality Disorders are both a mix of nature and nurture. In a study done on BPDs, they did brain scans of Borderlines and they had a control group. They found that Borderlines had a misfiring in the emotion centers of the brain, but they found the same patterns in some non-Borderlines. When they interviewed the controls with the same condition, they found these people could be emotionally labile, but didn't have the break with reality characteristic of BPD.
For most people there is a cause and effect connection with their emotion centers, but some people have emotion centers that cook off emotions spontaneously. It's beginning to be thought of as a form of epilepsy. For people who had a good upbringing, they just feel things from time to time and might be considered "touchy" by those around them, but they can be talked down. For people with this condition who suffered some kind of childhood abuse, when they feel emotions come up from nowhere, they invent causes and spin stories to back-fill for the emotion they're feeling.
I've never seen any similar research on NPD, but there may be some combination of childhood stuff combined with some miswiring of the brain.
And there's basically no emissions regulations on light planes, either, meaning that horrific amounts of unburned hydrocarbons during climb, and NOx during cruise are spewed. (This happens at high altitudes, which... is a double-edged sword, some pollutants AFAIK are worse at high altitudes, some are better at high altitudes.)
A lot of the aviation engines still being produced today are fundamentally 1930s technology: here's a huge displacement aircooled pushrod flat 4 with a carb or two on top, with manual mixture control during climb, and magneto ignition with fixed timing.
Granted, fuel injection is more common, but even then mixture control is often manual. On a few of the newer engine designs, watercooling is a thing. And, some engines are designed to run on "mogas" (unleaded, lower octane gasoline meant for cars), but often it needs to be ethanol-free for various reasons, so availability isn't great.
Europe is ahead on some of these regulations, and for a while, diesel was being pushed as the general aviation engine solution, but AFAIK the diesel stuff turned out to be too expensive and far too heavy (or rather, light diesels were tried, but they were too unreliable), so now it's basically "IDK, mogas and maybe fuel injection on a gasoline engine I guess?" for general aviation there (with some work being done on hybridization and electrics, but airplanes are far more weight sensitive than cars, and regen doesn't really help much because most flight is steady-state)...
It's going to be a long time before we see practical electric planes. Batteries don't get lighter as they discharge, liquid fuel tanks do and the energy density of the best batteries is about 1/30 that of liquid fuel.
The Germans had some diesel powered aircraft in WW II, but they were mostly lower powered transport aircraft. Diesel engines need to compress the fuel more than a gasoline engine and have to be able to handle the higher internal pressures. We do have more sophisticated materials now, but that meant a heavier engine block then, which is not a good thing for an aircraft.
The problem with using unleaded gas in any engine without a catalytic converter is the exhaust is spewing carcinogens. Even cars with catalytic converters spew the carcinogens until the engine warms up. If I smell that raw exhaust smell coming out of a cold ICE, I hold my breath.