If a corporation emits toxic pollution into an intermittent waterway and subsequent rains move that pollution into a river which eventually drains into another state, then interstate commerce is clearly affected, since downstream water quality, health, and economic vitality are clearly impacted in the downstream state. Pretty much every waterway and and river system eventually crosses state lines. Drainage of pollutants from intermittent waterways is not hypothetical but an everyday occurrence all across the US because water soluble pollutants move with rainwater drainage. There are many examples, like the PCBs at Love Canal,etc. The "constitutionality" is just a red herring to rationalize business decisions that care more about private profit than public health.