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  • Statutory information

    The term “special category” applies to trade effluent which contains one or more prescribed substances at a concentration greater than the background level, which results from a prescribed process, or which contains concentrations of asbestos or chloroform greater than the background level.

    Prescribed substances
    Mercury and its compounds
    Cadmium and its compounds  1,2-dichloroethane
    Gamma – Hexachlorocyclohexane  Trichlorobenzene 
    Pentachlorophenol Simazine 
    Hexachlorobenzene  Tributyletin compounds 
    Triphenyltin compounds 
    Aldrin  Trifluralin 
    Dieldrin  Fenitrothion 
    Endrin  Azinphos-methyl 
    Carbon   Tetrachloride Malathion
    Polychlorinated Biphenyls  Endosulphan 
    Prescribed processes 
    Any process for the production of chlorinated organic chemicals
    Any process for the manufacture of paper pulp
    Any process for the manufacture of asbestos cement 
    Any process for the manufacture of asbestos paper or board
    Any industrial process involving the use (in any 12-month period) of more than 100 kilograms of the product which results from the crushing of asbestos ore
    Any process which occasions liquid discharges containing trichloroethylene or perchloroethylene in quantities of 30 kilograms per year or more

    The responsibility for determining whether a substance is above background levels lies with the Environment Agency (EA), acting for the Secretary of State for the Environment 

    Statutory requirement

    Section 120 of the Water Industry Act 1991 states that where a notice to discharge trade effluent is served on the sewerage undertaker by a trader with regard to any Special Category effluent, it shall be the duty of the sewerage undertaker to refer the notice to the EA for determination. Discharge without consent is therefore illegal.


    The Water Industry Act 1991 contains the principal legislation relating to the discharge of trade effluent to the public sewer.

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