Pentaerythritol tetranitrate (PETN), produced for use as an explosive and a vasodilator, is not known to occur naturally, so the production and use of this kind of compound can lead to contamination of the environment. PETN is subject to biodegradation in untreated or unpreserved urine and feces. There also have been some reports of its degradation by bacteria, whose PETN reductase sequentially denitrates PETN into tri- and dinitrates ([http://www.ncbi.nlm.nih.gov/pubmed/8932320|French et al., 1996]). The last compound shown in the pathway, pentaerythritol dinitrate, is degraded further to unknown products.