Ten people have been arrested as part of an investigation into the dumping of hazardous waste including heavy metals and asbestos by an Avonmouth company.
Sixty Environment Agency investigators along with Avon and Somerset Police carried out dawn raids on several sites.
The Environment Agency said it was the UK's biggest ever hazardous waste raid and they are looking into whether there is any risk to public health.
The ten have been released on bail until January. The investigation is expected to take several months to complete.