You are in: Home > Health and Environmental Hygiene - What's new > Reference and HBM Values
Last changed: 10/11/2009
The reference value permit to asses the exposure of individuals or population groups compared to the ubiquitous background exposure. Since environmental conditions are changing reference values are checked continuously and updated if new information becomes available.
The reference value for a chemical substance in human biological material (e.g. blood, urine) is derived according to a defined statistical method from a series of measuring results obtained. Samples to be used for this purpose have to be collected employing a defined group of the general population.
For details about the statistical definition and calculation of a reference value from a series of measuring results, see the relevant IUPAC guideline (O.M. Poulsen, E. Holst and J.M. Christensen: A supplement to the approved IFCC Recommendation on the theory of reference values. In: Pure & Appl. Chem. 69, 7 (1997) 1601-1611). In analogy to this guideline, the Human Biomonitoring Commission uses as reference value the 95th percentile of the measured pollutant concentration levels in the relevant matrix of the reference population. To derive it, it is rounded off within the 95 % confidence interval. In addition, when the data base is appropriate and sufficient to do so, the Commission defines reference values for sub-groups subject being subject or not to specific exposures (e.g., non smoking and cadmium in blood). Wherever possible, reference values are defined using data obtained for a suitable reference population, such as the population studied in the German Environmental Surveys (GerES).
The Commission has pointed out explicitly that the reference values are strictly statistically derived values, which per se are of no health relevance.
Human biomonitoring (HBM) values, in contrast, are derived on the basis of toxicological and epidemiological studies. Two levels are defined: HBM-I and HBM-II.
Damage to health |
Recommendation |
|
| Possible |
|
|
| HBM-II | ||
| Cannot be excluded with sufficient certainty |
|
|
| HBM-I | ||
| Not to be expected according to current knowledge |
|
|
The HBM-I-value represents the concentration of a substance in human biological material below which – according to the knowledge and judgement of the Commission and with regard to the substance under consideration – there is no risk for adverse health effects and, consequently, no need for action.
At a concentration level higher than the HBM-I and lower than the HBM-II-value the result should be verified by further measurements. If these measurements confirm the initial result a march for potential sources of exposure should be undertaken. Exposure to such sources should be minimised or eliminated where necessary and achievable with an acceptable level of input. The HBM-I-value should thus be regarded as a verification or control value.
The HBM-II-value represents the concentration of a substance in a human biological material above which – according to the knowledge and judgement of the Commission and with regard to the substance under consideration – there is an increased risk for adverse health effects and, consequently, an acute need for exposure reduction measures and the provision of biomedical care (advice). The HBM-II-value should thus be regarded as an intervention or action level.
Up to now, the Commission has derived human biomonitoring values for Cd, Hg, Tl, PCP in urine or blood as well as for the sum of DEHP metabolites 5oxo- and 5OH-MEHP in urine, resp. The relatively low number of HBM values is attributable to the lack of studies in humans relevant biological effects which precludes the derivation of HBM values on the basis of the defined criteria. So, the Commission has decided to derive HBM I values for substances for which a toxicokinetic extrapolation is possible which provides a concentration of a substance or its metabolites corresponding to tolerable intake doses derived by broadly accepted expert groups or organisations (like the acceptable daily intake (ADI) or the tolerable daily intake (TDI). Being well aware of the uncertainties of such derivation and estimates, the Commission considers this new approach a possibility to derive urgently needed HBM values for substances or their metabolites for which no appropriate studies on health effects of low dose environmental exposure are currently available. It applied for the first time on DEHP metabolites.