Don't eat (early) snow

[snopes]

Comment: My wife has heard that it's not safe to eat snow unless at least
four inches has fallen at a given time. Before that, snow has picked up
enough pollution from the air (viz acid rain) to be unhealthy for
consumption.

I find this somewhat implausible, but have enough arguments with my wife
that I'd rather not debate this with her absent some credible backup.