M A Smith




Tentative Trigger Concentrations









The earliest version of the ICRCL guidelines (e.g. ICRCL 1979) covered only a selected range of elements including lead, cadmium, and arsenic (see Table 1). Numbers were provided for "acceptable" concentrations of contamination, i.e. they were derived on the basis that a soil could be contaminated but not necessarily pose any significant additional risk to users of a site - the soil was clean enough for the intended land use. However, by 1982 the term "trigger value" was being employed to describe a concentration above which thought should be given as to whether there were any additional risks and whether any remedial measures should be carried out (Smith 1982). Values were originally provided for four different land uses (later reduced to two) - see Table 1. The differentiation was made on the basis of presumed different exposures by site users, particularly children, and the different routes of exposure presented by the different land uses, particularly the likelihood of consumption of vegetables grown on the site.

The orignal numbers were assembled by the then Secretary of the ICRCL (M A Smith) from a number of sources including:

  • site-specific risk assessments made for cadmium in the UK,

  • work by the Greater London Council's Scientific Branch to develop trigger concentrations,

  • established guidelines for the disposal of sewage sludge to agricultural land,

  • statutory limits on lead and certain other elements in toys and graphic materials,

  • various literature sources including accounts of site-specific assessments and judgements that had been made,

  • established guidance on the assessment of the phytotoxicity of zinc, copper and nickel.

In the early versions of the guidelines the thinking that had gone into them was explained and the value for a number of elements discussed in detail. 

The early versions were circulated widely for comment. In practice, although there was substantial discussion of principles, the numbers themselves were never seriously challenged. Such changes as were made in the values, were made in the light of additional information as it became available. Although the values for cadmium and lead were subjected to detailed review (Simms & Beckett 1987), this did not result in any changes.


Extension to Embrace Coal Carbonisation Sites

In 1979 a contract was placed with AEA Harwell Laboratory to make a detailed audit of the coal carbonisation industry - to identify the nature of contamination that could arise and the hazards it could pose. The report, later revised (DOE 1987), included proposals for two trigger values for a range of contaminants typical of coal carbonisation sites, including  polycyclic aromatic hydrocarbons (PAHs) and phenols, and recognised two principal land use categories (see Table 1). The lower, or "trigger threshold value," corresponding to those existing for lead etc, indicated a need to consider action. The higher "action trigger value" was set at a concentration at which there was a presumption that some form of action would be required. The suggested values were incorporated into the formal DOE/ICRCL guidelines.

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1987 VERSION (current to 2002)

Land Use Catergories

Small gardens

Large gardens and allotments

Amenity grass

Public open space

Domestic gardens and allotments

Parks, playing fields, open space


Domestic gardens and allotments, play areas

Landscaped areas, buildings, hard cover*









Chromium (VI)







ref. phytotoxicity:











Chromium (VI)







ref. phytotoxicity:






Polycyclic aromatic hydrocarbons (PAHs)



Free cyanide

Complex cyanides







* General groupings of categories: some variation with contaminant

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Version Current in 2002

The DOE/ICRCL guidelines in use in 2002 when they were replaced by the existing Soil Guideline Values, were contained in a document issued in 1987 (ICRCL 1987). This contained general advice on how contaminated sites should be approached (e.g. the principles of site investigation) and the way in which the guidelines should be applied. As can be seen in Table 1, the number of potential inorganic contaminants for which there were values was reduced in later versions of the guidance.

The values in use immediately before their formal withdrawal by the Department for Environment, Food and Rural Affairs (DEFRA) in 2002 can be found elsewhere on the web.

There is also a separate ICRCL document (ICRCL 1990) dealing with old metalliferous mining sites but this is not entirely consistent with the main guidance document (see below).

The guidelines suffered from a number of deficiencies, including:

  • the limited range of contaminants covered (see Table 1),

  • the lack of "action" values for lead, cadmium etc.,

  • the failure to take certain risks to human health into account when setting the values,

  • the absence of a source document to which people can refer to find out the basis of the values for lead etc.,

  • environmental hazards are generally not taken into account,

  • potential to affect ground or surface waters is not covered,

  • here are no guidelines for groundwater, and

  • the analytical methods to be employed are not specified.

Risks to human health not taken into account (by the author when producing the first versions of the guidelines) were contact hazards for nickel and the human toxicity of copper. These elements are only covered in respect of phytotoxicity (toxicity to plants). These limitations were pointed out in early versions but are not explicitly stated in the 1987 version.

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Guidance on Old Metalliferous Mining Sites

In 1990 the ICRCL issued separate guidance (ICRCL 1990) on old metalliferous mining sites to be used for agriculture or similar uses. The document, originally produced by the Agricultural Development and Advisory Service (ADAS) with input from MAFF, was endorsed by the ICRCL, without apparently considering whether it was consistent with the existing guidance. It has resulted in certain anomalies particularly for example in respect of guidelines for lead and cadmium (e.g. the trigger value for lead for pasture is less than that for domestic gardens) . The approach to derivation of the values was not particularly conservative and the action values have been set at a level at which there may be overt damage to the health of livestock. The approach appears to be basically to allow the farmer to produce rather than to ensure protection of human health or the environment in the longer term.

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DOE (1987) (Department of the Environment), "Problems arising from the redevelopment of gas works and similar sites (second edition), HMSO, London.

ICRCL (1979) (Interdepartmental Committee on the Redevelopment of Contaminated Land), Acceptable levels of toxic elements in soils, ICRCL 16/78, Department of the Environment, London.

ICRCL 1987 (Interdepartmental Committee on the Redevelopment of Contaminated Land), Guidance on the assessment and redevelopment of contaminated land, Guidance Note ICRCL 59/83 (2nd edition), Department of the Environment, London UK.

ICRCL (1990) (Interdepartmental Committee on the Redevelopment of Contaminated Land), Notes on the restoration and aftercare of metalliferous mining sites for pasture and grazing, Guidance Note 70/90, Department of the Environment, London UK.

Simms D L and Beckett M J (1987), Contaminated land: setting trigger concentrations, Sci Total Environ 65, 121-134.

Smith M A (1982), Acceptable concentrations of contaminants in soils, Proc. Conf. Redevelopment of Contaminated Land, Woolwich 1981, London Borough of Greenwich, London.


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The Numerical Values & Documentation

The numerical values contained in ICRCL 59/83 (2nd Edition) can be found at www.zeroenvironment.co.uk/icrcl.htm

The document itself can be found at: www.eugris.info/envdocs/ICRCL59_83.pdf