Traces of cotton from Xinjiang were found in nearly a fifth of samples from American and global retailers, highlighting the challenges of complying with a US law aimed at blocking imports that could be linked to forced labour in China.

Traces of banned Chinese cotton were found in 19 percent of a sample of merchandise selling at US and global retailers in the past year, a study showed, highlighting the challenges of complying with the US law aimed at blocking imports of cotton linked to forced labour in China.

In the study released on Tuesday, researchers from natural resource analytics, isotope testing firm Stratum Reservoir and DNA lab Applied DNA Sciences analysed garment samples, cotton swabs and shoes from big box retailers and e-commerce platforms. The firms declined to name the retailers whose merchandise they tested.

The scientists used isotopic testing, which can link cotton to specific geographic areas by analysing the concentration of stable elements like carbon and hydrogen present in both the crop and the environment in which it has been grown, experts say. They tested the merchandise for traces of cotton from Xinjiang, the far western region of China.