The data do not indicate that there is a loss of rainfall. Actually, hail suppression and rainmaking are two different technologies, or rather, two different paths of the same technology. You can have an effort to suppress hail or an effort to make rain, or you can combine them. The procedures are similar but different enough that it takes close management. Silver Iodide is a salt.
Silver is a heavy metal, but the amounts being distributed are very small.
That is very low. The amount is low. That is water that the U.S. Environmental Protection Agency says you can drink every day. Your bladder might pop from drinking that much water, but you would not die from silver poisoning. There are no data available to support or contradict that concept.