TIANJIN - Investigators looking into Wednesday's explosion in Tianjin believe sodium cyanide may have been stored at the site.

At a press conference Saturday morning, Gao Huaiyou, vice head of the Tianjin bureau of work safety, said that chemicals stored in the warehouse possibly include sodium cyanide, but further confirmation is needed. The containers were not open, and some were not even registered.

Some local media reported earlier that Rui Hai International Logistics, owner of the warehouse, had as much as 700 tonnes of sodium cyanide, but Gao said it was not yet verified.

Measures have been taken to prevent secondary disasters, such as inviting sodium cyanide producers to help at the site, using hydrogen peroxide to reduce the amount of sodium cyanide, sending a taskforce to locate and measure the contaminated area and prevent its spread in sewage.

Some other dangerous chemicals likely to be stored include potassium nitrate and ammonium nitrate.

At 17 monitoring sites, no cyanide was detected as of the early morning of Saturday, although at one site the density of xylene exceeded normal standard, said Bao Jingling, chief engineer of the municipal bureau of environmental protection.

Air quality at the sites was between good and slightly polluted, he said.

In waste water, density of cyanide have dropped from 10.9 times of normal standard on Thursday to 2.1 times, while that of ammonia nitrogen was lowered from 5.1 times of normal standard to 1.9 times.

The State Oceanic Administration (SOA), meanwhile, said no traces of cyanide or volatile phenol have been detected in waters off the Tianjin port.

Test results on samples taken on Friday did not show any anomaly in major measurement of seawater composition when compared with historical records, the SOA said in a statement.

In waste water, density of cyanide have dropped from 10.9 times of normal standard on Thursday to 2.1 times, while that of ammonia nitrogen was lowered from 5.1 times of normal standard to 1.9 times.