In total, emissions of four body bags were tested. Short term testing was sufficient in order to reveal information about the emission potential and released main compounds of the body bags, as illustrated in Fig. 1. Even though the bags differed in material and colour, the spectrum of released substances was nearly the same with just differing concentrations. A variety of iso-alkanes and cyclo-alkanes was emitted as main substance group with levels ranging between approximately 3 mg m−3 and 4.5 mg m−3 after 24 h testing time. In addition, 2-ethyl-1-hexanol and phenol were released in high concentrations. Also, 1,4-dioxane was identified in concentrations of up to 133 µg m−3 and might be used as solvent during the production of tissue cleaners, colorants and degreasing agents.

T(V)VOC-values (total (very) volatile organic compounds) obtained by sampling body bag air and room air. Bag Bx: Body bag of body number x

Figure 2 provides an overview of the obtained sum concentrations of VVOCs and VOCs (T(V)VOC, total (very) volatile organic compounds). Detected concentration levels were highest in decomposition stage 3, but varied from body to body in all stages with no clear dependence on the decomposition stage. Concentrations of both VVOCs and VOCs were much lower in room air than in body bag air. Table 3 lists all identified substances emitted from deceased persons in different decomposition stages.

Most abundant substances and substance groups released by body bags. Bx: Body number x, Room: Autopsy room

Most abundant substances identified in the environmental room air were alcohols (ethanol, 2-propanol) and glycol ethers (2-phenoxy ethanol, butyl glycol, butyldiglycol) which can be traced back to cleaning agents and disinfectants. In body bag air, around 350 individual organic substances were detected in total. Table 3 lists all substances which have been identified during this study by giving CAS-no, substance names, categorization as VVOC or VOC and the detected concentration range (arithmetic mean values ± standard deviation) within each decomposition stage as concentration in the body bags. If a clear identification was not possible, these compounds were summarized as a sum parameter of unidentified substances in the specific chemical group. Figure 3 illustrates the identified substance groups in each decomposition stage.

Most abundant substances and substance groups released by human bodies in dependence of the decomposition stage. Bx: Body number x

Three bodies with no visible signs of decomposition were selected for stage 1 (fresh bodies). In comparison, body no. 1 showed the lowest emission potential, which can be explained by the fact that the person was only recently passed away (1 d). TVVOC and TVOC-values were much higher regarding body no. 2 and no. 3 with 4 and 5 days since death. Both a broader range of identified substances and higher concentrations might be therefore be attributed to a longer PMI. Most abundant substance groups were alcohols (ethanol, 1-propanol, 2-propanol, 1,2-propanediol, 2-ethyl-1-hexanol) and n-alkanes. Some of these are attributed to the breakdown of sugars during early decomposition [1, 27]. However, pyruvic acid, which is described as an important intermediate product in the breakdown of carbohydrates and precursor substance for several alcohols, such as e.g. ethanol, butanol and 1,3-propanediol [1], was not found. Just 1,2-propanediol was emitted by bodies no. 2 and 3 (161 ± 39 µg m−3 and 13 ± 2 µg m−3) [1, 28]. Also, a variety of iso-/cyclic alkanes was measured, but could not be further identified. Very similar emission patterns and concentrations were detected for bodies no. 2 and 3 regarding the aldehydes n-pentanal, n-hexanal, 2-ethylhexanal and n-heptanal with concentrations between 6 µg m−3 and 48 µg m−3. Acetaldehyde was just detected for body no. 2 with the highest concentration within the group of aldehydes (62 ± 26 µg m−3). Already after a PMI of just 1 d (body no. 1), the alcohols ethanol and 2-propanol (254 ± 47 µg m−3 and 190 ± 1 µg m−3) and the ketone acetone (209 ± 4 µg m−3) were already detected as most abundant substances. Acetone is formed by microbial activity from carbohydrates under anaerobic conditions and is most frequently detected in exhaled air [29,30,31]. Similar acetone concentrations were determined for bodies no. 2 and 3. 3-Hydroxy-2-butanone (acetoin) was just identified as emission from body no. 1 (27 ± 1 µg m−3). It is released during the anaerobic glucose metabolism and as metabolic product of e.g. enterobacteria or lactic acid bacteria [32].

Levels of ethanol and 2-propanol were in a similar range than acetone concentrations, whereas body no. 2 emitted ethanol in elevated concentrations of 2228 ± 967 µg m−3. Also, 2-ethyl-1-hexanol was released in high concentrations by bodies no. 2 and 3 (1596 ± 95 µg m−3 and 1484 ± 62 µg m−3). Moreover, both bodies emitted a broad range of aromatic hydrocarbons, namely benzene, toluene, ethylbenzene, xylene isomers, styrene, isopropylbenzene as well as methylstyrene derivatives and naphthalene derivatives, which could not be further identified. Highest levels were measured for phenol with 727 ± 141 µg m−3 (body no. 2) and 766 ± 20 µg m−3 (body no. 3). However, this can mainly be traced back to emissions of the body bags themselves. This also applied for 1,4-dioxane, which was just detected as emissions from body bags no. 2 and 3 (133 ± 11 µg m−3 and 96 ± 3 µg m−3). The occurrence of aromatic hydrocarbons is due to the breakdown of aromatic amino acids [15, 28]. Elevated concentrations of butylcyclohexane were analysed for bodies no. 2 and 3. In comparison, body no. 1 released a broad range of terpenes as listed in Table 3. Sabinene, myrcene, (alpha-) terpinolene, beta-pinene, eucalyptol, camphene and limonene were detected in just minor concentration (2 ± 1 µg m−3 to 11 ± 1 µg m−3). In contrast, alpha-pinene and 3-carene were identified in elevated concentrations (38 ± 1 µg m−3 and 60 ± 1 µg m−3, respectively). It is interesting to note that these terpene levels were detected for body no. 1, even though this person passed away just one day before the measurements. Alpha-pinene and limonene were also released in higher concentrations from body no. 2 (60 ± 1 µg m−3 and 70 ± 3 µg m−3, respectively). In addition, also acetic acid was released in significant concentrations (170 ± 23 µg m−3) from body no. 1, whereas the detected amounts were much lower in body bags of bodies no. 2 and 3 (32 ± 4 µg m−3 and 30 ± 11 µg m−3). Sulfurous and nitrogenous compounds are mainly associated with putrefaction [14]. Measured data are illustrated in Fig. 4. Even though the selected bodies showed a PMI of 1–5 d, dimethyl disulfide (DMDS) was detected in significant concentrations in all investigated body bags (289 ± 6 µg m−3 to 378 ± 14 µg m−3). DMDS is caused by oxidative reactions of methanethiol and hydrogen sulfide [1]. While methanethiol will not be trapped by Tenax® TA due to its low boiling point (5.9 °C), it can be sampled by Carbograph™ 5TD. Dimethyl trisulfide (DMTS) and dimethyl sulfide (DMS) as further oxidation products were just identified in levels in the range of the LOQ. No nitrogenous substances were analysed one day after death (body no. 1). Few days later, the odourous compound trimethylamine (TMA) was already detected in significant concentrations (bodies no. 2 and 3: 44 ± 1 µg m−3 and 71 ± 3 µg m−3, respectively). TMA is formed by dicarboxylic oxidation of proteins and can occur paired with dimethylamine (DMA) which was not determined [33]. As conspicuous finding, bodies no. 1 and 2 released sevoflurane, a narcotic agent. This was surprising since person no. 1 died a natural death. The person was neither reanimated nor intubated and was not under the influence of medication. Whereas detected concentrations were very low (7 ± 1 µg m−3), concentrations released by body no. 2 were significantly higher (247 ± 33 µg m−3). This person was both reanimated and intubated and died due to suicide (mixed intoxication). However, the use of sevoflurane for intubation is quite uncommon. Instead, lidocaine, an amino amide, is used.

Concentrations of sulfurous and nitrogenous compounds released by deceased bodies. Bx: Body number x

Even though the time since dead was similar to those corpses selected for stage 1, greenish discolouration in the lumbar region was already visible. As can be seen in Fig. 3, the most abundant substance groups were very similar to those identified for stage 1, namely n-alkanes, iso-/cyclo-alkanes, aromatic hydrocarbons, ketones, aldehydes and sulfurous substances. Thus, there are no clear differences between the emission characteristics of the corpses investigated in stages 1 and 2. In contrast to body no. 5, body no. 4 emitted carboxylic acids in moderate concentrations of 108 ± 27 µg m−3. Terpenes were released to a greater extent. Again, alpha-pinene and 3-carene were identified as most abundant substances, which is identical to the findings obtained for stage 1. It is interesting that a range of different naphthalene derivatives was released in elevated concentrations from body no. 5 (22-171 µg m−3) as a similar emission pattern was detected for bodies no. 2 and 3 (stage 1), but with lower concentration levels. However, those substances could not be identified to be released from body no. 4 even though it showed the same signs of decomposition than body no. 5. Among aromatic hydrocarbons, phenol was released as most abundant substance, but in significantly lower concentrations (157 ± 24 µg m−3 and 152 ± 62 µg m−3, respectively) than detected for the fresh bodies (stage 1). The same applied for 2-ethyl-1-hexanol, whose concentrations were lower by a factor of 2 regarding body no. 5, but could just be identified in trace concentrations in body bag air of body no. 4 (11 ± 1 µg m−3). Concentrations of ethanol were in the same range as those released by fresh bodies (stage 1). Regarding body no. 4, again acetoin was detected in low concentrations (31 ± 4 µg m−3).

However, due to initial signs of decomposition, one could have assumed that sulfurous and nitrogenous compounds will be emitted by the corpses in higher concentrations than by those with no visible decay (stage 1). However, this was just confirmed for body no. 4, which released dimethyl disulfide (DMDS) as main substance in high concentrations (1280 ± 155 µg m−3). Levels measured for body no. 5 were several factors lower with 447 ± 23 µg m−3. Dimethyl sulfide (DMS) and dimethyl trisulfide (DMTS) were identified as further sulfurous substances. Comparable to the findings obtained in stage 1, nitrogenous compounds were not released in significant concentrations. Again, trimethylamine (TMA) was identified but just in moderate concentrations (body no. 4: 42 ± 8 µg m−3 and body no. 5: 75 ± 6 µg m−3). Pyridine which is described in the literature to be one of the key substances to be emitted during the decomposition of humans and pigs [13, 16, 34] was detected in trace concentrations for body no. 4 (3 µg m−3), but could not be identified as emission from body no. 5.

A total of four persons with significant signs of advanced decay was emission tested. Body no. 7 was a very strong emission source. Aldehydes were identified as most abundant substance group in the body bag air due to glyoxal which was released in highly increased concentrations (20,222 ± 2141 µg m−3). Glyoxal is the smallest dialdehyde and can be used as a bio-marker to detect the development or progression of degenerative diseases, such as e.g. Alzheimer’s disease, chronic kidney disease and diabetes [35]. The occurrence in such high levels like those for body no. 7 cannot easily be explained. It can be assumed to be a degradation product of hydrocarbons or a combustion product of biomass. It also might be released by textiles where it is used to tear the strength of fibrous materials due to its ability to react with hydroxy and amino groups of proteins and cellulose [36]. Glyoxal was not detected in the other body bags of stage 3. Even though acetone was already identified as main substance in stages 1 and 2, it was released in concentrations by a factor of 10 higher from the advanced decomposed bodies no. 7 and 9 (3098 ± 10 µg m−3 and 1903 ± 557 µg m−3). The same applied for phenol (body no. 7: 906 ± 176 µg m−3) which, however, might be evaluated as background value due to body bag emissions. A unique finding for body no. 7 is the detection of the fatty acids oleic acid, stearic acid, and palmitic acid, the latter determined in highest concentrations. The combination of these three compounds is commonly released during the splitting of fats [27] and might be addressed to specific ambient conditions like high temperatures during death. In addition, several alcohols and aldehydes are associated with the breakdown of lipids through oxidative reactions [33]. In addition, just body no. 7 released urea in low concentrations (14 ± 6 µg m−3). It can occur as a metabolic product or as a component of barbiturates (sleeping pills, narcotic agents). Moreover, the substance methyl thiocyanate was emitted by body no. 7 (139 ± 69 µg m−3). It is difficult to trace this substance back to a specific source. As it is used as insecticide agent and fumigant, it can be assumed to be part of the impregnation of the tent (see Table 1).

The findings confirmed that DMDS and DMTS are released in high concentrations at advanced decomposition, whereas DMDS levels were significantly higher by a factor of 2 to 4 than those of DMTS. However, the assumption that levels of sulfurous compounds will be higher at that stage due to advanced decomposition is not entirely valid since also in early stages of decay sulfurous substances were be detected in high concentration ranges, such as e.g. for body no. 4 (stage 2). In comparison to stages 1 and 2, nitrogenous substances were emitted by all bodies of stage 3 in significant levels (560 ± 107 µg m−3 to 1975 ± 57 µg m−3). This substance group can be traced back to the deamination of proteins [1, 27]. Trimethylamine and (dimethylamino)acetonitrile occurred as main abundant substances. Pyridine was detected in the air of five body bags (stages 1-3) and mostly in low or trace concentrations (1–22 µg m−3). It was just determined in higher levels in body bag air of body no. 4 (143 ± 2 µg m−3). Similar to the other stages, the same range of terpenes was identified with highest levels detected in body bag air of body no. 8 with alpha-pinene (1365 ± 45 µg m−3) and 3-carene (913 ± 57 µg m−3) as most abundant substances. Several short-branched alcohols are fermentation products of the amino acids valine, leucine and isoleucine and are formed via the Ehrlich pathway, such as 1-propanol, isobutanol, 2-methyl-1-butanol and 3-methyl-1-butanol [28, 33]. None of the bodies emitted all these compounds in parallel, but just few of them. Whereas low concentrations were measured in body bags of stages 1 and 2, higher levels were released at advanced decay with isobutanol and 3-methyl-1-butanol determined as main substances.

With the exception of body no. 7, aromatic hydrocarbons were released in much lower concentrations so the levels decreased from stage 1 to stage 3. Thus, it can be assumed that decomposition of aromatic amino acids starts right after dead and decreases with advanced decay. The process seems nearly to be finished at advanced decay. Indole was just released by bodies no. 6, 7 and 9 in low concentrations. It is known to be formed by the breakdown of phenylalanine, tryptophan and tyrosine. The same applies for skatole, which was not detected during the experiments [33].

The air in seven body bags was additionally sampled for GC-O analysis (see Table 1). Three samples belonged to decomposition stage 3 (advanced decomposition), two to stage 2 (initial decomposition) and another two to stage 1 (fresh bodies). Figure 5 visualizes the cumulative intensity of odour active substance groups identified by GC-O. As shown, the sulfurous compounds contributed most to the odour perception of the investigated air samples. A slight increase in intensity was observed from decomposition stage 1 to stage 3. The sulfurous substances dimethyl sulfide (DMS), dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS), which are well-known for their unpleasant sulfurous, cabbage-like odour, were identified in all samples and evaluated as significantly too strong (intensity stage 3 to 4), see Fig. 5. As an exception, for body no. 2 (stage 1) DMS was just detected in minor concentrations (20 ± 7 µg m−3) by sampling VVOCs on Carbograph™ 5TD. It was neither identified by GC-MS according to ISO 16000-6 [22] nor by GC-O after sampling on Tenax® TA. However, the fact that several sulfurous compounds were identified by GC-O for stage 1 bodies shows that even those substances, which were not identified as most abundant compounds, were clearly perceptible due to their very low odour threshold. In addition, carbon disulfide was detected in stage 2 (body no. 4) and stage 3 (bodies no. 7, 8 and 9) samples, whose odour patterns were described as rotten, cheesy and fishy. Moreover, another sulfurous substance was identified in all air samples at a retention time of ~ 20 min (RI ~ 1245). Based on the mass spectrum and the odour description, it can be assumed to be dimethyl tetrasulfide. However, a clear identification was not possible because no liquid analytical standard was available. The same applied for a sulfurous substance which was detected at a retention time of ~ 7 min (RI ~ 815) in air samples of bodies no. 8 and 9 (stage 3) which could be perhaps addressed to methyl ethyl disulfide. Body no. 7 (stage 3) also released methyl isocyanate, which was just detected by GC-O and which has a strong and unpleasant odour described as sharp and radish-like. 3-(Methylthio)propione as further strong smelly substance with a fatty, cheesy, bready and vegetable odour type was identified by GC-O as emissions from bodies no. 4 (stage 2) and no. 3 (stage 1).

Cumulative intensity of odour active substances identified by GC-O after active sampling of body bag air. Bx: Body number x

Apart from the sulfurous substances, nitrogenous compounds were also identified. However, the nitrogenous substance trimethylamine was almost exclusively identified in decomposition stage 3. The exception was sample no. 5 (stage 2), where this strongly fishy smelly compound could also be detected. The sample air of body no. 9 (stage 3) contained, in addition to trimethylamine, the odour active compounds isobutylamine, (dimethylamino)acetonitrile, 2,5-dimethylpyrazine, 2-acetyl-1-pyrroline (only detectable via GC-O) as well as the substance pyrazine. All substances reveal an unpleasant odour quality and are perceived by the human nose as fishy, cheesy (trimethylamine, isobutylamine, (dimethylamino)acetonitrile) or toasty as well as roasted (2,5-dimethylpyrazine, 2-actyl-1-pyrroline, pyrazine). Also, the aromatic hydrocarbon phenol, which was identified in all stages of decomposition, was detected by GC-O due to its unpleasant, rubber- and plastic-like odour (intensity stage 3). An intensive unpleasant odour can be also caused by (un-)saturated aldehydes due to their low odour thresholds. The human nose has a higher detection sensitivity for these substances than the routine GC-MS method. Thus, several (un-)saturated aldehydes were just detected by GC-O and could only be partially identified by GC-MS, such as ethyl acrolein, trans-2-hexenal, octanal and nonanal. The substance groups of (un-)saturated aldehydes were associated with an unpleasant, strong, fatty and cheesy odour.

Ketones were also detected in trace concentrations by the human nose and caused a noteworthy contribution to the odour perception of bodies no. 7, 8 (stage 3) and body no. 4 (stage 2) with an intensity of about 2 to 3. However, ketones played a rather minor role in the odour perception of bodies no. 9 (stage 3) and no. 5 (stage 2). In nearly all air samples, 2-butanone was detected which is described as ethereal, fruity and camphor-like smelly substance. An exception was the air sample of body no. 5 (stage 2), in which 2-butanone could not be identified by GC-O. Moreover, in several samples further ketones were determined and confirmed via GC-MS, such as 2-pentanone, acetophenone, 3-methyl-2-butanone (MIPK) and 3-hydroxy-2-butanone. Substances with low odour thresholds are also the carboxylic acids butanoic acid and valeric acid. It is important to highlight that very polar carboxylic acids are relatively difficult to identify on a non-polar GC-MS column. Moreover, several intensive smelling alcohols have been detected, such as e.g. isobutanol, 1-butanol, 3-methyl-3-buten-1-ol. As shown in Fig. 5, this substance group has a minor odour impact of the seven examined body samples. Furthermore, a large number of unknown compounds was detected by GC-O and might be contributors for the overall odour of the samples. However, since these compounds were not detected by GC-MS analysis and because there was no indication from the internal odour database (retention index, odour type description), these compounds could not be identified further.