, 2013). Within the present context, the AEGL program provides the most suitable and most extensive information and AEGLs are the most used worldwide. The second tier (i.e. AEGL-2) can

be regarded as the most important from a health risk point of view and can be considered as the most appropriate external guidance value to serve as basis for a biological guidance value. At present, no methodology to derive these values is available. A concept for the derivation of Biomonitoring Equivalents (BE) to interpret biomonitoring information has been proposed (Hays et al., 2008 and Hays and Aylward, 2009). This concept describes how information Thiazovivin price on kinetics can be used to estimate the concentration GSK2118436 of a chemical (or its metabolite) in a biological medium that is equivalent with an existing external guidance value. Although this concept is developed for chronic exposures, it may be worthwhile to verify its

applicability to AEGLs which are derived for single exposures. However, it should then be realised that significant differences exist in the derivation and applicability of guidance values for chronic exposure and AERVs, and these should be taken into account. For some chemicals, AEGL values have been derived by physiologically based pharmacokinetic (PBPK) models (Bruckner et al., 2004, Boyes et al., 2005 and Bos et al., 2006). These models can directly be used to derive BEs for these chemicals. It has been recommended to derive specific guidance values for professional first responders, in addition to AERVs (Bos et al., 2013). In the UK, Public Health England (then the Health Protection Agency)

set up a working group to review the Phospholipase D1 most common substances identified in public health chemical incidents and to determine whether human biomonitoring could be useful in such instances (HPA, 2011). Some of the most frequently identified substances (ammonia, chlorine, inorganic acids) were unsuitable for biomonitoring assessments whereas others (carbon monoxide, organophosphorous pesticides) could have biomonitoring results directly interpreted against early health effect guidelines. A further set of around 17 chemicals (of the top 30 reported agents) were suitable for human biomonitoring. The group produced protocols for each suitable chemical and collated the available interpretation (usually background reference ranges and occupational guidance values). Recognising the difficulties of arranging appropriate sample collection within a reasonable timeframe of an incident, sampling kits were prepared and made available in Accident and Emergency departments. Maintaining the currency of such kits and knowledge of their existence and use for infrequent occurrences, such as chemical incidents, is an on-going challenge. Biological monitoring is a useful aid to the assessment of systemic exposure following chemical incidents.