Four people were arrested on Friday for selling tainted masks after a customs check on Hong Kong shops and stalls offering essential protection gear during the Covid-19 pandemic.The four brands, which authorities said people should stop using, contained a bacterial count that exceeded the maximum allowed. They posed a risk to the public, especially the elderly and children, as well as people with a weak immune system. The brands were ONEMED, Atos, Q-FREZZ and AD PRO.They were sold at four shops…