JINAN - Over 40 tonnes of undeclared waste plastics have been returned overseas and a total of 200 tonnes of hazardous zinc tailings innocuously disposed, according to Qingdao customs in east China's Shandong Province on Sunday.

In accordance with orders by the country's General Administration of Customs, Qingdao launched "Operation Green Fence" in February and has since stepped up management of imported solid waste and crackdown on illegally imported garbage.

Customs officials said demurrage of solid waste not only squeezes operations space and slows turnaround times in the port, but also leads to secondary pollution and contaminates the environment.

As of mid-December, Qingdao customs had busted 101 cases of smuggling solid waste and captured 37 suspects. Over 10,000 tonnes of waste paper, plastics and tailings have been returned or disposed.

Official data on China's imports of solid waste show sustained growth in the past decade, with imports reaching 40 billion US dollars in 2012.

Chinese law on the control of solid waste bans imports that cannot be used as raw materials or recycled through harmless means. High profits, however, have fueled smuggling, which is often carried out by conspiring with overseas organizations.