What are DNELs?

On 1 June 2007, Regulation (EC) No 1907/2006 () of the European Parliament and of the Council concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals, known in short as the "REACH Regulation", came into force.

The REACH Regulation assigns greater responsibility to industry for the risk assessment of its chemicals. Manufacturers and importers may place their substances on the European market only if they possess sufficient knowledge of the substances' toxicological data. Manufacturers and importers must compile relevant information on the substances' properties and register it in a central database maintained by the European Chemicals Agency (ECHA ()). More detailed information on REACH is available from the ECHA and from bodies such as the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA).

The substance-specific information required by REACH also includes occupational exposure limits in the form of DNELs (derived no-effect levels). Manufacturers or importers of quantities exceeding ten tons per annum must establish DNELs for the substance subject to mandatory registration for tasks involving the substance, and declare them in the chemical safety report and safety data sheet. Although declaration of the DNELs on the ECHA website is not mandatory, they can already been found there in relatively large numbers.

Definition

Annex I 1.0.1 of the REACH Regulation defines the objective of determining the hazardous effects upon human health. Accordingly, besides classification and labelling of a substance, levels of exposure to it are to be derived "above which humans should not be exposed. This level of exposure is known as the Derived No-Effect Level (DNEL)".

Types of DNEL

As a rule, DNELs must be declared by the registrants, i.e. the manufacturers and importers, for the most probable routes of exposure (inhalative, dermal and oral). For substances of very high concern which are subject to authorisation (SVHC; cf. REACH Regulation, Annex XIV ()), ECHA’s Committee for Risk Assessment (RAC ()) has derived a first short series of "Reference DNELs". The documents presenting the reasons are published on ECHA’s internet site.

A value is required for each relevant population (workers, consumers or humans via the environment). This may also apply to certain vulnerable sub-populations (e.g. children and pregnant women) (Annex I 1.4.1 of the REACH Regulation).

Several DNEL types may therefore be established for one and the same substance. The differences in their significance may not be immediately clear to lay persons. The relevant ECHA guidance document recommends the following types of DNEL for workers and for the general population:

• Acute – inhalation, systemic effects
• Acute – inhalation, local effects
• Acute – dermal, local effects
• Long-term – inhalation, systemic effects
• Long-term – inhalation, local effects
• Long-term – dermal, systemic effects
• Long-term – dermal, local effects
• Long-term – oral, systemic effects (not relevant to workers)

"Local effects" means that the effect upon health can be observed directly at the point of contact or the point of ingress (such as irritation on areas of skin upon which spatter of the substance has landed). Conversely, systemic effects occur in more remote organs (such as damage to the liver as a result of inhalation of a substance).

Besides inhalation, skin exposure may also be a significant factor at the workplace. Since only limited experience has been gained to date from which limit values for dermal exposure can be determined, standardised measurement methods and strategies are not available, and recourse can be made only to a limited body of reference values, the GESTIS DNEL List is confined to workplace DNELs for long-term inhalation.

Deriving of DNELs

The procedure for the deriving of DNELs is set out in Chapter R.8 (PDF, 895 KB) of the ECHA guidance document entitled "Guidance on Information Requirements and Chemical Safety Assessment". Similar to the German criteria for the deriving of health-based atmospheric limit values (German Announcement on Hazardous Substances (BekGS) 901 ()), the ECHA guidance document recommends that the most sensitive toxicological effect with an adverse impact on health be taken as the basis. Based upon the data available, a series of extrapolation factors are to be used for conversion, for example from laboratory animal to human being, oral to inhalative substance intake or short-term to long-term exposure.

Existing atmospheric limit values, for example those found in national regulations, may be considered during specification of the DNELs. In accordance with Chapter R.8 of the ECHA guidance document (Annex 13) referred to above however, an existing limit value may be adopted as a DNEL only when evaluation shows the limit value to be supported by current scientific findings.

Whereas national workplace atmospheric limit values are generally established by larger bodies of experts, the responsibility for deriving DNELs in the REACH process lies with the registrants, who either perform this task themselves or employ private third-party institutes for the purpose (with an exception of "Reference DNELs" established by ECHA’s Committee for Risk Assessment). Documents substantiating the derivation process and making it transparent are not generally published. External quality control therefore presents difficulties, and even the ECHA is only able to have spot-check reviews performed.

DNELs for OSH purposes

In Germany, occupational exposure limits (AGW) of the Technical Rules on Hazardous Substances (TRGS) 900 () continue to constitute workplace atmospheric limit values that are binding upon employers. Should no AGW and for example no maximum workplace concentration (MAK value) of the German Research Foundation (DFG) be available, the employer must also consider the DNEL during risk assessment.

DMEL values and carcinogenic substances

For effects upon human health for which a DNEL cannot be determined, Annex I 6.5 of the REACH Regulation makes provision for performance of a "qualitative assessment of the likelihood that effects are avoided when implementing the exposure scenario". The registrants are advised in this context, not by the REACH Regulation itself but by certain supporting guidance documents, to establish DMELs (derived minimal effect levels). These should also be stated in the chemical safety report.

DMELs are established above all for carcinogenic substances for which a toxicological adverse-effect threshold cannot be determined. For certain carcinogens, it is quite acceptable for a health-based DNEL to be stated, provided it is based upon the available data and findings regarding the mechanism of action. The decision whether a DNEL is permissible in a given case necessitates extensive knowledge of toxicology. The GESTIS DNEL Database draws particular attention to this when DNELs are assigned for a substance classified as a Category 1A or 1B carcinogen.

DMEL values are risk-based exposure limits. In contrast to the German risk concept for carcinogenic substances (see TRGS 910 () "Risk-related concept of measures for activities involving carcinogenic hazardous substances ") no reference risks exist at this stage however for the DMEL values which are considered acceptable throughout the EU. The crucial framework is therefore missing; it is left to the manufacturers and distributors themselves to decide what risk of disease they intend to consider acceptable for the exposed individuals and to take as basis for establishment of DMEL values.

In the absence of indication of the cancer risk associated with a given exposure concentration, DMELs do not provide any information which could be used for evaluation of the exposure. Since the corresponding cancer risk is not generally stated for DMEL values in the ECHA registration entries and the procedure for their derivation is not transparent, DMEL values will not be incorporated into the GESTIS DNEL List.