The human bitumen study hits the headlines

Abstract

Besides the current cutting-edge topics in toxicology, such as oxidative stress research (Baird and Dinkova-Kostova 2011; Barcelos et al. 2011; Cadenas et al. 2010), metal toxicity (Antonini et al. 2011; Bolt et al. 2011; Sinicropi et al. 2010), nanotoxicology (Weiss and Diabate 2011), in vitro systems (Heise et al. 2012; Knobeloch et al. 2012; Zellmer et al. 2010), and modelling (Mielke et al. 2011; Hoehme et al. 2010), bitumen research has led an essentially wallflower existence. Fortunately, this has dramatically changed since the recent publications from the Human Bitumen Study (Schluter 2011; Raulf-Heimsoth et al. 2011a). Bitumen was already regarded as a suspected carcinogen in the 1980s (Schluter 2011; Greim 2001). However, the discussion surrounding bitumen exposure as a potential health hazard was always controversial. On the one side, a long-term carcinogenicity study with dermal application yielded positive results (Sivak et al. 1997). Conversely, a long-term inhalation study––probably the more relevant route of application––did not lead to increased tumour incidence in rats (Fuhst et al. 2007). Furthermore, a small biomonitoring study did not show increased levels of DNA strand breaks in lymphocytes of bitumen workers (Fuchs et al. 1996). However, some evidence of increased DNA damage was found in roofers who process bitumen at higher temperatures (Fuchs et al. 1996). Therefore, key questions are whether bitumen causes genotoxicity in exposed workers and whether inhalation is toxic to the airways. The recently published Human Bitumen Study is the largest worldwide and best-controlled study in this field, encompassing 500 exposed workers from 80 construction sites. The results, in a nutshell, show that DNA adducts and strand breaks in bitumen workers were within the range found in healthy individuals. On the other hand, bitumen workers showed chronic inflammation in the lower airways. The practical consequences for both industry and occupational medicine include the need to reduce the processing temperature of bitumen as much as possible, as temperature represents the most critical factor influencing bitumen vapour exposure. Finally, follow-up studies are needed to assess the relevance of the identified airway inflammation. In particular, the relevance of subtle changes of inflammatory mediators in the lower airways (e.g. interleukins) is of general importance in chemically induced airway inflammation and currently discussed in regulatory toxicology. To give our readers a rapid overview, we summarised the key findings of the Human Bitumen Study (Table 1).