Other studies have suggested an association between FA exposure and development of lymphohematopietic malignancies (IARC 2006
). A proportional mortality study in embalmers in California that comprised 1,007 white males who had died, thus showed a mortality significantly elevated for total cancer (PMR: 121) and for leukemia (PMR: 175) (Walrath and Fraumeni 1984
). In a retrospective cohort of 2,317 anatomists in the US, the standardized mortality ration (SMR (95% CI)) was marginally and non-significantly elevated (1.2 (0.7–2.0), which was mainly due to a non-significant increase in leukemia (1.5 (0.7–2.7)) (Stroup et al. 1986
). The causes of mortality among 4,046 male US embalmers and funeral directors, who had died, were investigated in a proportional mortality study. Lymphohematopoietic malignancies (PMR: 139), myeloid leukemia (PMR: 157) and other unspecified leukemia (PMR: 228) were significantly increased (Hayes et al. 1990
). On the contrary, in a population-based case–control study in Iowa and Minnesota that included 513 leukemia cases and 1,087 controls, no association was found between leukemia and FA exposure. Thus, in the low exposed FA group, comprising 61 cases, the OR (95% CI) was 1.0 (0.7–1.4) and 0.7 (0.2–2.6) in the high FA group, comprising three cases (Blair et al. 2000
). The lack of exact exposure concentrations is a general limitation of these studies. In contrast, exposure levels were addressed in the two recent studies (Zhang et al. 2010
; Hauptmann et al. 2009
Hematopoietic tissue damage was studied in 43 FA exposed workers, which were compared with 51 controls. The 8-h time-weighted average was 1.57 and 0.032 mg m−3
, respectively, and the 90 percentile 3.09 and 0.032 mg m−3
, respectively. Peak exposure concentrations were not reported. FA exposures were associated with reduced blood lymphocyte, granulocyte, platelet, red blood cell and total white blood cell counts. For example, the total white blood cell count was reduced by 13.5% in the FA-exposed workers. Urinary benzene concentrations were low in both groups, excluding benzene exposure as a confounder. The findings were considered consistent with a bone marrow toxic effect due to FA (it is noted that it is not possible to evaluate whether the hematologic parameters were outside the normal ranges as they were not provided). Peripheral blood cells from FA exposed and controls were cultivated to derive blood myeloid progenitor cells. The colony formation was decreased non-significantly by 20% in the FA exposed workers that was considered a toxic effect on the myeloid progenitor cells. Blood mononuclear cells from volunteers were cultivated in vitro to derive different lines of progenitor cells. Different FA concentrations were added to the cultures, showing that FA decreased the number of generated colonies from all progenitor cell lines. This demonstrated that FA can inhibit the proliferation of all progenitor cells if the endogenous FA level is increased due to FA exposures. Blood progenitor cells of the myeloid line were derived from ten high exposed workers (8-h time-weighted FA concentration at 2.63 mg m−3
and 90 percentile at 5.09 mg m−3
) and 12 controls (8-h time-weighted FA concentration at 0.032 mg m−3
and 90 percentile at 0.032 mg m−3
). FA-exposed workers showed increased monosomy (loss) of chromosome 7 and increase in trisomy of chromosome 8; these chromosome changes are observed in myeloid leukemia and myelodysplastic syndromes (Zhang et al. 2010
). It is noted that the study has limitations in relation to risk characterization of FA exposures at indoor air relevant levels. First, the exposures are extremely high and the unreported peak exposure concentrations may have been at extremes. Second, no exposure response relationship was established. Third, the very high exposure concentrations may be expected to cause mucosal damage that may influence both the nasal metabolism and the absorption into the blood compartment; no information is available on the mucosal tissue. Fourth, the in vitro cell culture study is relevant for mechanistic considerations. However, taking into account that no increase in FA has been observed in the blood compartment of humans due to FA exposures that is supported by model calculations at about 2 ppm (similar results were reached if using extrapolations up to 10 ppm, but such an extrapolation may not be valid due to the toxic effects on the mucosal membrane at 2 ppm and above), the interpretation in relation to risk characterization is unclear. Fifth, the lowest in vitro tested concentration (100 μmol FA l−1
) decreased colony formation in human blood progenitor cells. However, a five times lower concentration (20 μmol FA l−1
) decreased colony formation in the lung epithelial A549 cell line (Speit et al. 2008
), suggesting that the observed effects in progenitor cells reflect cytotoxicity under in vitro cell culture conditions in general. Finally, for transparency it would have been desirable that all measured chemical exposures in addition to FA had been reported.
In a US case–control study (Hauptmann et al. 2009
), 168 professionals employed in the funeral industry who died from lymphohematopoietic malignancies were compared with 265 deceased matched controls from the same industry. The 8-h time-weighted average FA intensity was about 0.1–0.2 ppm, the average FA intensity while embalming was about 1.5–1.8 ppm and peak exposures about 8.1–10.5 ppm. Four cases died from nasopharyngeal cancer, but only two had embalmed, OR (95% CI): 0.1 (0.01–1.2). No increase was observed in lymphoid malignancies (ICD 8 200–204), including Hodgkin lymphoma (0.5 (0.1–2.6)), which was consistently increased in the previous industrial cohort studies (Hauptmann et al. 2003
; Freeman et al. 2009
). The study observed a specific association with embalming and myeloid leukemia ((ICD 8 205). Thus, using a reference group of never exposed individuals containing one myeloid leukemia subject, the odds ratio (OR (95% CI)) of myeloid leukemia was 11.2 (1.3–95.6) in the FA-exposed individuals.
The first analysis of myeloid leukemia used a reference group of subjects that had not performed embalming. In this reference group, one subject had myeloid leukemia. The duration (years (y)) of working in jobs with embalming showed a significant trend (p
= 0.02). In the categories >0–20, >20–34 and >34 years, the odds ratio was 5.0 (0.5–51.6), 12.9 (1.4–117.1) and 13.6 (1.6–119.7), respectively. No significant trend was observed with the number of embalmings. However, several significant ORs were observed. Thus, the number of performed embalmings were divided into >0–1422, >1422–3068 and >3068 where the OR was 7.6 (0.8–73.5), 12.7 (1.4–116.7) and 12.7 (1.4–112.8), respectively. Exposure–response relationships for the different FA metrics were established. The peak exposure metric was the only FA metric that showed a significant trend (p
= 0.036). Peak FA exposures were divided into >0–7.0, >7.0–9.3 and >9.3 ppm where the OR was 15.2 (1.6–141.6), 8.0 (0.9–74.0), 13.0 (1.4–116.9), respectively. The cumulative FA exposure (ppm-h), average FA intensity (ppm) while embalming, and the 8-h time-weighted average intensity (ppm) showed no FA exposure dependent trend. The cumulative FA exposures (ppm-h) were divided into >0–4058, >4058–9253, and >9253 where the OR was 10.2 (1.1–95.6), 9.4 (1.0–85.7) and 13.2 (1.5–115.4), respectively. The average FA intensity (ppm) while embalming was >0–1.4, >1.4–1.9 and >1.9 and the OR was 11.1 (1.2–106.3), 14.8 (1.6–136.9) and 9.5 (1.1–86.0), respectively. The 8-h time-weighted FA intensity (ppm) was divided into >0–0.10, >0.1–0.18 and >0.18 where the OR was 8.4 (0.8–79.3), 13.6 (1.5–125.8) and 12.0 (1.3–107.4), respectively. It is noted that within each of the FA exposure metrics, the ORs showed little difference and had highly overlapping confidence intervals. This suggests that the statistical significances are driven mainly by exposure versus non-exposure and less by differences in FA exposure levels. Also in each of the FA metrics, none of the trend tests within the FA groups themselves was statistically significant. Additionally, a few cases in a reference group have previously been shown to cause unstable risk estimates (Marsh et al. 2007b
The second analysis of myeloid leukemia used a reference group in which the subjects performed fewer than 500 lifetime embalmings. It comprised five cases with myeloid leukemia. The duration of working in jobs with embalming showed a significant trend (p = 0.02). In the categories <20, >20–34 and >34 years, the odds ratios were 0.5 (0.1–2.9), 3.2 (1.0–10.1) and 3.9 (1.2–12.5), respectively. No significant trend was observed with the number of embalmings, but significant ORs were observed at the highest exposure level. Thus, the number of performed embalmings were divided into ≥500–1422, >1422–3068 and >3068 where the ORs were 1.2 (0.3–5.5), 2.9 (0.9–9.1) and 3.0 (1.0–9.2), respectively. The peak exposure metric was the only FA metric that showed a significant trend (p = 0.036) in the FA metrics. Peak FA exposures were divided into ≤7.0, >7.0–9.3 and >9.3 ppm where the ORs were 2.9 (0.9–9.8), 2.0 (0.6–6.6), 2.9 (0.9–9.5), respectively. The trend was not statistically significant in the cumulative FA exposure, the average FA intensity while embalming or the 8-h time-weighted intensity group. Only the highest cumulative FA exposure group (>9,253 ppm-h) had a statistically elevated OR (3.0 (1.0–9.2)). Except for this, the other ORs were elevated (2.0–2.9) and very similar within each of the metrics, but none was significantly increased. Also in each of the FA metrics, none of the trend tests within the FA groups themselves was statistically significant. It is noted that the overall picture was similar to that in the first analysis except for the fact that the ORs decreased by 1/3 in this analysis, where a larger number of case subjects were available in the control group. Only one significant OR appeared in the FA exposure metrics, which was in strong contrast to the ten significantly elevated ORs in the first analysis.
It is noted that there is a lack of exposure-dependent differences in OR within the different FA exposure levels in the different metrics. A lack of exposure-dependent effect could be due either to an inappropriate exposure assessment or to the lack of causality between FA exposure and myeloid leukemia. The method of FA exposure has limitations as the estimates were predicted by means of interviews and mathematical models and were not based on measured exposures. It is mentioned by the authors that the peak model was not validated. On the whole, this study cannot be used for risk assessment as it does not provide a convincing exposure–response relationship.
The comparison of the Zhang et al. (2010
) and the Hauptmann et al. (2009
) studies shows some differences. The Zhang-study suggests an effect on all progenitor cells resulting in a decrease in the production of lymphocytes, granulocytes, platelets and red blood cells. Similar results were obtained from the in vitro cell cultures with different progenitor cell lines. In the Hauptmann-study, the effect was selective at the myeloid progenitor line. Overall, these studies have very high exposure intensities and thus do not contradict the conclusion that lymphohematopoietic malignancies are not observed at lower levels as derived from the Hauptmann et al. (2003
) study and its re-analysis by (Marsh and Youk (2004