Shellfish from water off the country's shores has become more toxic as more pollutants including heavy metals and oil damaged the marine environment, the State Oceanic Administration (SOA) reported on Thursday.

About 147,000 sq km of ocean failed to meet the standard for clear water last year, an area 7.3 percent greater than the previous year's, the SOA's annual report on the oceanic environment showed.

Most shellfish in offshore areas contained excessive harmful chemicals like lead, cadmium and DDT, a common pesticide in China, the report said.

Lead detected in shellfish was 50 percent higher than standard levels, while cadmium and DDT levels were about 40 percent higher, test results showed.

Lead is a poisonous metal that can damage the nervous system and cause blood and brain disorders if it is consumed. The World Health Organization classifies DDT as "moderately hazardous."

The lead in shellfish must be less than 1 mg for every kg for it to be safe, according to national seafood standards. DDT levels must be less than 1 mg for every 1 kg to meet safety standards.

More industrial and domestic garbage is being discharged into the sea and endangering marine species as a result of fast economic growth, experts have said.

About 74 percent of 457 pollutant-discharging outlets released excessive pollutants in 2009, with less than 14 million tons of heavy metals discharged into the oceans, a year-on-year increase of 16 percent, the report said.

Less than 70 grams of garbage was dumped last year for every 100 square meters of coastal beach, SOA statistics showed. These included about 28 grams of plastic waste like bottles and bags.

The report also said 68 cases of algae blooms, also called red tides, occurred on the country's coasts in 2009. The outbreaks affected 14,100 sq km, about 3.4 times more than the algae blooms that hit in the 1990s.

Harmful algae blooms can have large and varied impacts on marine ecosystems, including massive kills and damage to organisms.

Most marine life near Shenzhen, an economic hub in Guangdong province, was toxic, the Shenzhen Commercial Daily reported in January.

Many consumers have avoided shellfish following the latest findings.

Chen Chen, a 27-year-old editor at the Foreign Language Teaching and Research Press, said she has avoided eating shellfish after hearing of the pollution.

Still, a number of experts said the SOA figures can be "misleading" and "irresponsible."

Zhai Yuxiu, director of the National Center for Quality Supervision and Testing of Aquatic Products in Qingdao, Shandong province, told China Daily the situation is much better than what the latest report implies.

"The frightening figures in the report about heavy metal contamination in shellfish is a little misleading," Zhai said.

"Pollutants in the shellfish include the dirt inside the shells that forms a major part of the animal's weight. It is not part of the flesh of the shellfish that is eaten."