BEIJING (AP) â¿¿ Authorities are investigating rice mills in southern China following tests that found almost half of the staple grain in one of the country's largest cities was contaminated with a toxic metal. The mills in Hunan province's Youxian county were ordered to suspend business and recall their products after samples showed excessive levels of cadmium, according to an official notice issued Tuesday by the county government. It said the mills had been operating legally and sourced their rice from local farmers. The announcement followed reports over the weekend that government inspectors discovered that 44.4 percent of rice and rice products tested this year in the southern city of Guangzhou in Guangdong province showed high levels of cadmium. The carcinogenic metal can seriously damage the kidneys and cause other health problems. Hunan is a heavily agricultural province that borders on Guangdong, although it wasn't clear if there was a direct connection between the mills and Guangzhou's tainted rice. While investigations are continuing, cadmium is believed to have entered the rice from soil polluted with heavy metals. Air and soil pollution are chronic problems in China, caused by poor regulation of industrial emissions and heavy dependence on coal to generate electricity. China's food supply also suffers from deliberate faking or adulterating by unscrupulous operators, leading to occasional public panic over products from infant formula to cooking oil and a deep lack of trust in the government's ability to ensure food safety. In one of the worst scandals, at least six babies died and 300,000 became sick in 2008 after being fed milk powder tainted with the industrial chemical melamine, which was illegally added to watered-down dairy products to make their protein content appear normal.