TRAFFIC and trade were brought to a standstill after drums thought to contain a hazardous chemical were dumped.
Several large blue drums were found in the Rainbow Industrial Estate off Trout Road, Yiewsley,on Saturday.
Fire services from Hillingdon, Hayes, Heston, Wembley and Northolt were sent to deal with the containers.
Police shut Trout Road, Tavistock Road and High Street while firefighters investigated the suspicious liquid.
Yiewsley post office owner, Mohammed Chaudhri, said: "It affected a whole day of trade. This was all we needed.
"There was nobody coming in, the roads were empty.
"People were ringing up to see if we were open and the traffic was really bad around the area."
Mr Chaudhri believes the problems cost him about 60 per cent of his day's trade.
The alert was raised at about 12.50pm, and by 2pm firefighters had tested the substance and found one of the drums to contain a non-harmful alkaline solution. All roads were re-opened by 3.30pm.