Birling Gap beach was evacuated on Sunday [August 27] after people reported breathing difficulties, stinging eyes and vomiting when a "mist" appeared.
Sussex Police said on Monday morning the gas cloud appeared to have cleared.
Agencies are investigating the cause and have not ruled out either on-shore or off-shore locations.
In the past, chemicals have drifted across from European industrial units, but Sussex Police said: "Weather models suggest that an onshore source in northern France is very unlikely."
The Coastguard said it was working with its French counterparts and looking into vessels that were in the area at the time.
East Sussex Fire and Rescue Service said it was "extremely unlikely" the substance involved was chlorine.
First it was a sonic attack on US diplomats in Cuba, now potentially a chemical attack on British beach goers. What gives?
(Score: 3, Interesting) by bob_super on Thursday August 31 2017, @06:13PM
I'm betting on one of the many many chem carriers going through the Channel deciding to do some discreet cleanup at night, and the byproducts (either as-is, or after sun or sea exposure) drifting towards the land.
There were a few high-profile cases of ships caught in French or UK territorial waters with mile-long oil slicks trailing them, but go prove I just cleaned my chemical powder tanks...