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1.0 Introduction

1.1 This Guidance was issued to advise members of the University on appropriate procedures for disposal of substances into the drainage system.

1.2 It is the responsibility of Heads of Department to ensure that either this Guidance, or local procedures incorporating this Guidance, are adopted by their departments. They should ensure that anyone likely to be in a position to discharge materials to drains is familiar with this Guidance or local procedures. The task of ensuring this is done (but not the responsibility) may be devolved to laboratory managers and supervisors.

1.3 It is the responsibility of anyone discharging waste materials to drains to satisfy him/herself that such a discharge is permitted. In most instances consulting the relevant section of this Guidance or local procedures will allow this judgement to be made.

2.0 Trade effluent consents

2.1 University scientific and technical sites are deemed to be trade premises under the terms of the Water Industry Act 1991. As a consequence, the discharges of wastewater from the principal scientific and technical sites are covered by trade effluent consents, which place strict limits on the nature and composition of effluent that can be discharged into the sewer system. These restrictions are intended to protect the integrity of the sewage treatment process and the quality of the effluent discharged into the River Cam.

2.2 The discharges are designated as 'special category effluents' due to the potential presence of prescribed substances (e.g. mercury). The consents are monitored and enforced jointly by the Environment Agency and Anglian Water. Any exceedance of consent conditions is a criminal offence, which could lead to enforcement action by the Regulatory Authorities, leading to fines of up to £20,000 for each offence under the provisions of the Water Industry Act.

2.3 Sites covered by a trade effluent consent (as at July 2021) are:

•    Anne McLaren Building
•    Biochemistry (Sanger Building)
•    Biotechnology (Gleesson Building)
•    Chemical Engineering and Biotechnology
•    Chemistry Laboratory
•    Cancer Research UK (Li Ka Shing Centre)
•    Department for Applied Maths & Theoretical Physics
•    Downing Site
•    Engineering
•    Gurdon Institute
•    Jeffrey Cheah Biomedical Centre
•    New Museums Site
•    Pharmacology
•    Pathology
•    Physics
•    University Farm 307 Huntingdon Road
•    Vet School
•    West Cambridge Data Centre

2.4 The trade effluent consents cover only the 'foul sewage' discharges from sites, including drainage from laboratories, workshops, toilets, washrooms and kitchens. External drainage are intended only for the discharge of uncontaminated rainwater from roofs, pavements and roadways. On no account should these gullies or drains be used for the disposal of any other substance or contaminated wastewater. Any pollution of controlled waters is a criminal offence under the terms of the Water Resources Act, 1991, which could lead to prosecution by the Environment Agency.

3.0 Chemical substances

3.1 The foul sewer should not be viewed as a disposal route for waste chemicals; in line with the University's 'Zero Hazardous Chemicals to Drains Policy' wherever possible, waste chemicals should be collected in suitable containers for disposal by way of the Hazardous (Chemical) Waste Disposal Service administered by the Health and Safety Office.

3.2 You should check your own building or site's Trade Effluent consent (available on request from your departmental Safety Officer or from the Sustainability Team) for details of what chemicals are explicitly NOT suitable for disposal to foul sewer, however as general guidance the following are typically included on each Trade Effluent Consent:

•    Petroleum spirit and other volatile or flammable organic solvents.
•    Calcium carbide.
•    Cyanide salts.
•    Waste liable to form viscous or solid coatings or deposits on or in any part of the sewerage system through which the trade effluent is to pass.
•    Substances of a nature likely to give rise to fumes or odours injurious to persons working in the sewers through which the trade effluent is to pass.
•    Halogenated hydrocarbons.
•    Halogen substituted phenolic compounds.
•    Thiourea and its derivatives.
•    Ethidium Bromide.

Substances listed in Schedule 1 of the Trade Effluent (Prescribed Processes and Substances) Regulations 1989 Prescribed Substances - Schedule 1, are also banned, i.e.

•    Mercury and its compounds
•    Dichlorvos
•    Cadmium and its compounds
•    1,2-Dichloroethane
•    Gamma-hexachlorocyclohexane
•    Trichlorobenzene
•    DDT
•    Atrazine
•    Pentachlorophenol
•    Simazine
•    Hexachlorobenzene
•    Tributyltin compounds
•    Hexachlorobutadiene
•    Triphenyltin compounds
•    Aldrin
•    Trifluralin
•    Dieldrin
•    Fenithrothion
•    Endrin
•    Azinphos-methyl
•    Carbon Tetrachloride
•    Malathion
•    Polychlorinated Biphenyls
•    Endosulfan

3.3 The Environment Agency are particularly concerned about the discharge of mercury and mercuric compounds from University sites and have included a specific discharge limit of 1 µg/l (1 ppb) for mercury on the trade effluent consents. All procedures using mercury should be notified to the Departmental Safety Officer who will liaise with the Chemical Safety Advisor over correct procedures for the collection and disposal of contaminated waste from the process.

3.4 There are many substances in regular use which contain significant amounts of mercury, that are not readily identifiable from the common or trivial names, e.g. Nesslar's Reagent, Zenker's Solution and Thimerosal. A comprehensive list of some of the more commonly encountered substances is shown in Annex 1. For advice concerning the use and disposal of any of these substances (or other materials that you may suspect contain mercury) please contact the Health and Safety Office.

3.5 Mercury has been widely used throughout the University for many years. Investigations have found that there is widespread contamination of internal and eternal drainage systems due to the presence of metallic mercury from thermometers and manometers that has gained entry to the sewage system and collected in sink traps and joints in pipework, leading to elevated concentrations of mercury in the wastewater discharges. Extensive drain cleaning operations have been carried out by EM to safely remove this contamination to comply with Environment Agency discharge conditions. However, it is important to ensure that any spillage of mercury into the drainage system is immediately notified to the Departmental Safety Officer who will arrange for the cleaning of the drainage system to remove any trapped mercury.

3.6 Wherever possible, departments are encouraged to withdraw the use of mercury thermometers and manometers. Any equipment containing mercury should be used within a containment system (e.g. wide-brimmed tray) to prevent the escape of mercury in the event of spillage or leakage. A typical mercury thermometer contains enough mercury to exceed consent conditions every day for several months.

3.7 All other substances in the Prescribed Substances List are prohibited for discharge, and must not be present in concentrations greater than 'Background Concentration', which is considered to be the concentration contained in the water supplied to the site.

3.8 In addition to the above conditions, certain sites have restrictions on the concentration of heavy metals, e.g. Cadmium, Chromium, Copper, Lead, Mercury, Nickel, Silver, Zinc. Please check the consent for your site to establish the existence of any additional consents pertaining to individual sites: contact the Environment and Energy Section with questions. There are also a series of hazardous substances which may not be discharged to drain.

3.9 For details on which substances can be disposed to foul sewer, for instance by diluting with copious amounts of water, check the Safety Office Disposal of Chemical Waste guidance.

3.10 Environmental Hazards / Risk Phrases of any substance poured down the drain MUST be checked prior to disposal. As a non-exclusive guide, substances with the following risk phrases are NOT suitable for discharge to drain and must be disposed of by way of the Hazardous (Chemical) Waste Disposal Service:
•    N Dangerous for the environment. Chemicals that may present an immediate or delayed danger to one or more components of the environment. Characterised by the 'dead tree and fish' symbol
•    R50 Very toxic to aquatic organisms
•    R51 Toxic to aquatic organisms
•    R52 Harmful to aquatic organisms
•    R53 May cause long term adverse effects in the aquatic environment.

4.0 Radioactive material

4.1 Environmental Permits are issued to certain University sites by the Environment Agency. Under the conditions of these permits, water miscible radioactive liquids and dispersible solids and gels may be disposed of to foul sewer via a designated sink. Such sinks are identified as suitable for the disposal of radioactive waste. Departmental Radiation Protection Supervisors (RPSs) must be consulted if there is any doubt as to whether disposal via a particular sink is permitted.

4.2 Where relevant, and in consultation with the Radiation Protection Officer (the University’s Radioactive Waste Adviser under the Environmental Permitting Regulations), departments are issued with sub-permits which allow a monthly quota for radioactive substances that may be discharged to foul sewer. Each user of radioactive substances is required to register and undergo training, and users must follow the written arrangements for the disposal of radioactive waste. The sub-permit limits must not be exceeded.

Note: The University Policy document is the ‘Management of Work with Ionising Radiations’ and more detailed guidance is also available on the Safety Office website. Contact the Radiation Protection Officer at the Safety Office regarding radiation matters. 


Substance (Details)

•    Acetic acid (Mercury is an impurity in commercial grades)
•    Alum Hematoxylin (Solution A)
•    Bakers dimercurial
•    Bleach (Mercury is an impurity in commercial grades)
•    Bouins Fixative
•    B5 Fixative (Mercuric chloride)
•    Channing's Solution
•    CarnoyLeburn Fixative
•    Carbol-Fuchin Stain (Mercuric chloride)
•    Carbol Gentian Violet Stain (Mercuric chloride)
•    Cajol's
•    Channing Solution (Potassium tetra-iodomercurate)
•    Chloromerodin (Chloro mercuric-2-methoxy propyl urea)
•    CMMPU (Chloro mercuric-2-methoxy propyl urea)
•    CNP (Chloro mercuric nitrophenol)
•    DMA (Di mercuric acetate)
•    DMMA (Hg2(CO2)2 (oxalate/malonate))
•    DMHg (Dimethyl mercury)
•    Elcide (Thimerosal)
•    EMCl (Ethyl mercuric chloride)
•    EMP (Ethyl mercuric phosphate)
•    EMTS (Ethyl mercuric thiosalicylate)
•    Formalin (Mercury contaminant)
•    FTA Buffer
•    Gomori's Stain (Mercuric chloride)
•    Gram Iodine Satin (Mercuric chloride)
•    Helly Fixative (Mercuric chloride)
•    HgdUTP (Mercuric deoxyuridine triphosphate)
•    Hydrochloric acid (Mercury is an impurity in commercial grades)
•    Immu-sal
•    Mercurochrome
•    Mercuric chloride
•    Mercuric iodide
•    Mercuric nitrate
•    Mercuric oxide
•    Mercury sulphate
•    Mercurial Diuretic (mercupurin)
•    Meralyl
•    Merthiolate (Thimerosal)
•    Merzonin (Thimerosal)
•    Millon's Reagent (Mercuric nitrate)
•    MMBr (Methyl mercuric bromate)
•    MMOH (Methyl mercuric hydroxide)
•    Mucolexx (Thimerosal)
•    Nesslar's Reagent (Potassium tetra-iodomercurate)
•    Ohlamacher Fixative (Mercuric chloride)
•    PCMB (p-chloromercuric benzoate)
•    PCMBS (p-chloromercurci benzene sulphonate)
•    PCMPS (p-chloromercuric phenyl sulphonate)
•    PHMB (p-hydroxy mercuri benzoate)
•    PHMPS (p-hydroxy mercuri phenyl sulphonate)
•    PMA (Phenyl mercuric acetate)
•    PMC (Phenyl mercuric chloride)
•    PMG (Phenyl mercuric glyoxal)
•    PMTI (Potassium mercuric tetra iodide)
•    SET (Sodium ethyl mercuric salicylate)
•    Shardin Fixative
•    Shaudrins Fixative (Mercuric chloride)
•    Sodium Hydroxide (Mercury is an impurity in commercial grades)
•    Sodium Hypochlorite (Mercury is an impurity in commercial grades)
•    Stabilur Tablets (Mercuric oxide)
•    Sulphuric Acid (Mercury is an impurity in commercial grades)
•    Susa Fixative (Mercuric chloride)
•    TAMM (Tetrakis (acetoxy mercury) methane)
•    Takata's Reagent
•    Thimerosal (Mercury carboxy phenyl thioethyl sodium salt)
•    Zenker's Solution (Mercuric chloride)