We record the pollution released into the environment by industrial sites under the EC Integrated Pollution Prevention and Control Directive (IPPC). Operators must measure or make an estimate of the amount of emissions of each controlled substance every year. They must also specify "notifiable" releases in a year. These are where there has been an emergency, mis-management, accident or plant failure which has caused pollutants to be released. 

Where the emissions exceed a set threshold for a substance, the operator must report this. If the emission falls below the threshold level this is indicated by “< (less than) threshold value”. From this data we have created an inventory of 170 chemical substances and 65 radioactive substances released into air, water and sewers by sites in England and Wales. You can see this data if you look at the data search pages.