There is no evidence that cloud seeding operations have had adverse environmental impacts over the first phase of the trial (SPERP 1), based on Snowy Hydro’s environmental monitoring results. There is no evidence that the chemicals used as the seeding agent and tracer (silver iodide and indium trioxide) have accumulated in sampled soils, sediments, water or moss in the areas being tested. There is also no evidence of impacts on snow habitats, or of difference in the concentrations of ammonia and nitrogen oxides in seeded and unseeded snow. The monitoring results have detected no adverse impacts on rainfall in downwind areas during the first phase of the trial.”

from site.
I just dont know how they can say this after not a very long time to actually see if there are long lasting effects.