What heavy metals? Leaded fuels aren't used for decades. Diesel exhaust doesn't really leave anything worth caring about on the crops, "natural" pollution from

What heavy metals? Leaded fuels aren't used for decades. Diesel exhaust doesn't really leave anything worth caring about on the crops, "natural" pollution from rain, soil, bugs and birdshit is an order of magnitude more relevant than exhaust, and the things intentionally sprayed on fields - fertilizer, herbicides, pesticides - is much worse than those, even for organic farms manure and their range of approved pesticides are applied in huge quantities and will mean polluted crops that (obviously) need to be washed and will have all kinds of harmful residue anyway. If the device was solar instead of diesel, that wouldn't move the needle on the dirtiness of the crops. Even the pollution from wear&tear on tires and brakes is more relevant than fuel - we worry about fossil fuels due to the global effect of greenhouse gas emissions, we also care about people breathing in small particles from diesel exhaust, but it doesn't really harm food in farms.