A warning sign at Llwyneinion Acid Tar Lagoon in Wrexham - a new BBC documentary with actor Michael Sheen has investigated claims Monsanto dumped tonnes of toxic PCB chemicals there over decades. “The site was investigated with assistance from Wrexham Council as a potential special site, given the nature of the acid tar waste present. Llwyneinion Acid Tar Lagoon in Wrexham - residents and campaigners believe toxic chemicals dumped here over decades has caused a spike in rare cancers in the area. In a statement Wrexham Council said: “Wrexham County Borough Council takes its responsibilities for protecting public health and the environment extremely seriously. “We have undertaken extensive investigations over many years into both the Llwyneinion Acid Tar Lagoon and the adjacent Monsanto Chemical Waste Tip.