Chemical BURN is given as follows ==> Nitromethane (CH3-NO2) & Alcohol (CH3OH-methanol) & Castor/Synthetic Lube Oil (polymer) & Air (diatomic N2 & diatomic O2 & others)
Plants & animals (biology) do not respond well to carbon/hydrogen/nitrogen/oxygen fuels. Hydrogen & Oxygen are especially reactive, especially in the presence of heat (like even sunshine - also, see Space Shuttle main fuel tank (H2) & oxidizer (O2) tanks) ,,, however slowly they may react. Nitrogen Oxides compounds (like R-NO2 - see nitromethane) are reactive as well - again, especially in the presence of heat. Further, when a biological system has Nitromethane/Alcohol/Lube Oil wetted onto the surface/skin, some fluid will soak-in or be absorbed ... then these biological systems will process these fluids ... which chemically are like a "poison" to their respective cellular processes .... OOOUUUCCCHH! There is no good news here.
As for exhaust gases/fluids - primarily composed of CO2 (carbon dioxide-greenhouse gas) & H2O (dihydrogen oxide-water) & N2 (diatomic nitrogen) & un-burned lube oil plus some other small amounts ... these are returned to the atmosphere. These gases mostly cool and condense into vapor in the air ... which under a body force like gravity ... slowly settle out. Simply put - 2-cycle model engines are not much for generating acid rain or smog or large amounts of greenhouse gases ... at least not until these sport engines become much more popular than they enjoy today!