After a test showed farmer Zhao Heping's toddler grandson had high levels of lead in his blood two years ago, local officials in China's Hunan province offered the child medicine, he says — and milk. In return, Zhao says, officials asked that he hand over his grandson's blood test results.

Zhao was not alone. Eight residents of Dapu, a rural town of about 62,000 dotted with smelters and chemical plants, say families of children diagnosed with lead exposure were offered milk, but only if they surrendered their test results.

The milk, residents recall officials saying, would flush the lead out of the children's bodies.