[eurodomenii]

Living nearby river, downstream 10 km from the original industrial source of pollution, toxic VOCs(volatile organic compounds) are still harmful, or at such distance they would be already completely evaporated?
I apologize if my question is inappropriate for this forum.

[P]

It would depend upon the VOC (some are harmless, some not), how environmentally damaging it was, how soluble/miscible with water, what concentration was it originally and what is the ppm now 10 miles downstream etc..

So I would say it would depend upon what specific VOC you were concerned about - they are all different. 

[eurodomenii]

Thanks for the reply!

https://pubs.usgs.gov/circ/1995/circ1133/organic.html matches your statement that there are different degrees of volatility.
Volatile organic compounds (VOC) appear to be short lived in the Mississippi River, as would seem to be self-evident from the fact that the compounds are called "volatile." However, considerable effort was spent in testing the waters of the Mississippi River for their presence because (1) there are degrees of volatility and (2) some of the compounds are highly toxic.

On the other hand,  the greatest frequency of detections and highest concentrations occurred during the fall and winter. During the winter (data not shown in the graphs) concentrations increase significantly in the reaches of the river that become ice covered.

I think of a worst case scenario: Let's say the river is polluted in a cold day. The VOCs travel downstream without evaporation. If after several days is getting hotter, the evaporation occurs downstream

[P]

Again - it depends on the compound  -  some are harmless. Any river pollutant evaporating away from the river will be of such low content as not to be an issue for humans....   but for the fish it could be a different matter  -  again - it depends on the chemical, some are harmless, some are deadly to aquatic life. Either way they shouldn't really be dumped into the river - I am sure there are regs against that sort of thing in most countries.

You said in your OP that they were 'toxic' VOCs? Can you expand further? What toxic VOCs are being dumped in the river? Not all VOCs are toxic - most probably aren't otherwise they would be too dangerous to use (manufacturers would be poisoned when using them). Some alcohols aren't harmful at low levels but are considered VOCs because they are volatile. A VOC (Volatile Organic Component) is pretty much defined by it's boiling point not by how harmful it is.

Hope that helps.