Not just UGL's but protein and creatine have all been found to have a higher than usual level of HM. Are they bad - for sure. No one, in my 38 years of lifting experience, has been able to say they have 100% 'suffered' due to them.
That doesn't mean a lab or a company should be lazy ass mo-fos with regards to product purity. If they are lazy on the metals they may well cut corners in other areas of product purity.
Google 'protein spiking' for where corners have been cut.