United Nations health experts say they fear the toxic waste dumped in Ivory Coast's main city Abidjan may seep into the local food chain.
The experts expressed their concern Tuesday as Ivorian, French, and U.N. officials tried to locate all the sites where the waste was dumped.
U.N. officials say probable dumping sites include the sea, a lagoon, and an area near a market gardening zone.
Six people have died after exposure to the waste. Ivory Coast's health ministry says nearly 16,000 others have sought medical treatment.
The waste is a combination of oil residue and a caustic soda used to clean the residue from cargo tanks. Experts say the waste contains a toxic and foul-smelling chemical, hydrogen sulphide.
An Ivorian company named Tommy is blamed for dumping the waste around Abidjan on the night of August 19.
The company was paid to dispose of the waste by a Dutch company, Trafigura, which insists it believed Tommy would do the job properly.
Ivorian authorities have arrested seven people in connection with the scandal, which led to the mass resignation of the cabinet of Prime Minsiter Charles Konan Banny.
Some information for this report was provided by AP and Reuters.