Jos Vaessen (Ph.D. Maastricht University) is adviser on evaluation methods at the Independent Evaluation Group, World Bank Group. Since 1998 he has been involved in evaluation research activities, first as an academic and consultant to bilateral and multilateral development organizations and from 2011 to 2015 as an evaluation manager at UNESCO. Jos firmly believes in a strong link between research and practice. His ongoing involvement in some evaluation-related research and teaching activities as honorary lecturer at Maastricht University contributes to the necessary cross-fertilization between these two domains. Jos has been author of several internationally peer-reviewed publications, including three books. He regularly serves on reference groups of evaluations for different institutions and is a member of the Board of the European Evaluation Society.
When the LOQs are high relative to the decision criteria for congeners, therefore adding significantly to the estimated toxic equivalents, use of the upper-bound LOQ can result in artificially high toxic equivalents. This should be considered in defining background contamination, monitoring tolerances or estimating intake. In methods with insufficient sensitivity, the difference between lower-bound and upper-bound concentrations may be 10–100 or, in extreme cases, even higher. For example, if the sensitivity of a method is inappropriate for monitoring a tolerance, use of the concept of upper-bound LOD leads to estimates of toxic equivalents that are ‘false-positive’ results. This is a clear indication that a more sensitive method is needed. In particular, use of low-resolution MS in analysing food or samples of low weight or quantity (for a quick, easy analysis) can result in relatively high values for dioxin content as the upper-bound LOD. This bias cannot be seen in reported toxic equivalents, unless results for individual congeners are available. Thus, in defining background contamination or evaluating exposure, published data must be reviewed critically to eliminate relatively high values that are the result simply of inadequate LODs.
Although these methods are promising, dietary intake of PCDDs, PCDFs and coplanar PCBs is usually estimated from data on food consumption and concentrations measured in foods and food groups. The latter method is also recommended by WHO (2000), and was used in the assessment described below. National monitoring programmes and surveys and food consumption surveys provide data on concentrations and food consumption, which were used here (section 6.2.3). Intake was also evaluated on the basis of the GEMS/Food regional diets (section 6.2.4).
For setting and monitoring tolerances on the basis of toxic equivalents, the closeness of the LOQ to the appropriate tolerance must be evaluated as part of a decision to accept or reject a food. High LODs relative to the tolerance should lead to rejection of an analytical result for a sample on the basis of poor quality assurance, and consequently poor reliability of the estimate of toxic equivalents. Therefore, some governments may choose to apply upper-bound estimates of toxic equivalents, with a preference for the upper-bound LOQ rather than the upper-bound LOD, as a screening method in order to remove questionable foods from the marketplace. In the absence of these steps, there is a risk that foods in which a maximum level of a toxicant is exceeded will reach consumers. It is the responsibility of laboratories to achieve the required sensitivity in order to avoid unnecessary rejection of analytical results or of foods.