A senior Chinese oceanic expert has urged strict safety checks of seafood caught in the country's northern Bohai Bay, part of which was polluted by two oil spills last month.

Local governments along the coast of the Bohai Sea should enhance their inspections of non-farmed seafood in the Bohai after the annual fishing ban is lifted, according to Cui Wenlin, director of the environmental monitoring center with the North China Sea Branch of the State Oceanic Administration (SOA).

The seafood from the Bohai being sold in the market is uncontaminated, because fishing is currently prohibited in the Bohai to preserve oceanic resources and no spilled oil has been detected in the coastal fish farms, said Cui. "But after the annual fishing ban is lifted in September, safety checks of seafood should be beefed up."

The environmental monitoring center Cui directs has been monitoring the impacts of the oil spills on the Bohai's water quality, seabed sediments and marine life.

The leaks, which took place respectively in platform-B and platform-C of the Penglai 19-3 oilfield in Bohai Bay, made the water quality in an area of 840 square km fall to the lowest of the SOA's four categories. The spilled oil has also been detected in seabed sediment samples taken near the oil field.

Only some leaked oil was recovered and some had mixed into the water or sunk into the deep sea, Cui said.

"The oil, containing toxic substances and heavy metals, will greatly affect the growth of marine life that live on the seabed, such as clams, scallops and some kinds of crabs," Cui said.

Bohai is a half-closed sea with comparatively low self-clean ability due to limited water exchange with the outside, he added.

The Penglai 19-3 oilfield is being mined by ConocoPhillips China (COPC), a subsidiary company under the U.S. energy giant ConocoPhillips, under a joint development agreement with the China National Offshore Oil Corporation, the country's largest offshore oil producer.

While COPC said last week that the oil spill had been contained and the clean-up was nearly finished, a statement issued by the SOA on Monday said investigators found that "a small amount" of oil was still leaking from platform-C of the oilfield.

So far, no leaked oil has been monitored in the offshore waters, seaside resorts, marine conservation zones and fish farm zones, according to Cui.

"However, the oil spills will have a long-term influence on the ecosystem of the Bohai, as the oil in the sea will affect plankton, filter feeders that eat plankton as well as those living on the seabed," Cui said.

The environmental monitoring center with the North China Sea Branch will start to comprehensively access the damages of the remaining oil on Bohai's oceanic ecosystem, Cui said.

Oil seepage was first reported to the SOA North China Sea Branch by ConocoPhillips on June 4, with another incident reported on June 17. The leaks were respectively brought under control by June 19 and June 21.

The first leak from platform-B occurred at the seabed and resulted from increased pressure when workers injected water and drill cuttings into the earth. The latter incident from platform-C was due to a surge in the well, said the SOA, without giving details.

The SOA said COPC will be fined 200,000 yuan (30,770 U.S. dollars) for the oil spills. However, Wang Bin, a senior official with the SOA oceanic environmental protection bureau, said maritime authorities will also claim environmental compensation from COPC in accordance with relevant laws, and the figure will be "much more than" 200,000 yuan.