China’s customs authority has already seized 110,000 tonnes (122,356.5 tons) of smuggled solid waste this year and smashed 25 smuggling rings, state media said on Tuesday, as the country works to enforce a ban on overseas trash imposed last year.

China told the World Trade Organization (WTO) in 2017 that it would stop accepting imports on 24 types of foreign waste, including paper and textiles, by the end of the year, and that it would eventually ban shipments of all waste products readily available from domestic sources.

The crackdown on trash imports, which stood at as much as 47 million tonnes in 2015, is part of China’s “war on pollution” and designed to help the country upgrade its economy and move up the global supply chain. Enforcing the ban is one of the government’s priorities this year.

But it remains a lucrative business. The U.S. Institute of Scrap Recycling Industries said at the time of the ban that U.S. exports of scrap to China were worth $5.6 billion in 2016.

Citing figures from the General Administration of Customs, the People’s Daily said this year’s intercepted shipments included 64,700 tonnes of waste slag from mines. It said 52 people had been arrested by April 2 this year.

China arrested 259 people for smuggling foreign waste last year, with some criminal gangs accused of taking containers of electronic waste from Hong Kong to North Korea and then smuggling them across the border into China in order to circumvent restrictions.

The newly formed Ecology and Environment Ministry said at its inaugural meeting last week that it would step up the fight against foreign waste, describing it as “a symbolic measure for the creation of an ecological civilization in China”.

Last month, the United States asked China not to implement the ban, saying it could disrupt global scrap material supplies.

In a strongly-worded response, state newspaper China Daily accused the United States of hypocrisy, saying developed nations ought to have a “guilty conscience” for being “unwilling to pay the costs of processing their hazardous waste themselves”.