Use of plastic shopping bags in China has dropped 50 percent since the government required stores to charge customers for the bags, according to a new study. Researchers at the University of Gothenburg in Sweden conducted surveys that found that consumers in Beijing and Guiyang used an average of 21 new plastic bags weekly before the bag-fee ordinance was passed in June, 2008, and rarely used the same bag twice. But after the law was imposed, consumption dropped 49 percent and nearly half of the bags were re-used. While that represents a significant reduction, researchers say there is much room for improvement, especially when it comes to enforcement. Months after the law was enacted, the researchers say, nearly 60 percent of all plastic bags were still given away free. “What’s most important is to make sure that the ordinance is complied with,” said Haoran He, the lead researcher. Similar ordinances have achieved major success elsewhere, including Ireland, where the average consumer now uses only 20 plastic bags a year compared to 330 annually when the bags were free.