Decontamination of Bacillus Spores with Formaldehyde Vapor under Varied Environmental Conditions

Abstract

Introduction: This study investigated formaldehyde decontamination efficacy against dried Bacillus spores on porous and non-porous test surfaces, under various environmental conditions. This knowledge will help responders determine effective formaldehyde exposure parameters to decontaminate affected spaces following a biological agent release.

Methods: Prescribed masses of paraformaldehyde or formalin were sublimated or evaporated, respectively, to generate formaldehyde vapor within a bench-scale test chamber. Adsorbent cartridges were used to measure formaldehyde vapor concentrations in the chamber at pre-determined times. A validated method was used to extract the cartridges and analyze for formaldehyde via liquid chromatography. Spores of Bacillus globigii, Bacillus thuringiensis, and Bacillus anthracis were inoculated and dried onto porous bare pine wood and non-porous painted concrete material coupons. A series of tests was conducted where temperature, relative humidity, and formaldehyde concentration were varied, to determine treatment efficacy outside of conditions where this decontaminant is well-characterized (laboratory temperature and humidity and 12 mg/L theoretical formaldehyde vapor concentration) to predict decontamination efficacy in applications that may arise following a biological incident.

Results: Low temperature trials (approximately 10°C) resulted in decreased formaldehyde air concentrations throughout the 48-hour time-course when compared with formaldehyde concentrations collected in the ambient temperature trials (approximately 22°C). Generally, decontamination efficacy on wood was lower for all three spore types compared with painted concrete. Also, higher recoveries resulted from painted concrete compared to wood, consistent with historical data on these materials. The highest decontamination efficacies were observed on the spores subjected to the longest exposures (48 hours) on both materials, with efficacies that gradually decreased with shorter exposures. Adsorption or absorption of the formaldehyde vapor may have been a factor, especially during the low temperature trials, resulting in less available formaldehyde in the air when measured.

Conclusion: Environmental conditions affect formaldehyde concentrations in the air and thereby affect decontamination efficacy. Efficacy is also impacted by the material with which the contaminants are in contact.

Keywords: Bacillus spores; Paraformaldehyde; air sampling; environmental; formaldehyde; formalin.

Figure 1.

Test chamber configuration. (1) HEPA filters for rapid evacuation of H₂CO, (2) heat exchanger-fan unit to circulate air and control test chamber temperature, (3) circulating water-bath to cool test chamber temperature, and (4) HOBO data-logger.

Figure 2.

Test 1: efficacy determinations for vaporization of 1 g PF, room temperature, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Test conducted at room temperature (▲) with initial 70%–75% RH ( × ) environmental conditions. B globigii and B thuringiensis were concurrently tested but represented on separate graphs for clarity.

Figure 3.

Test 2: efficacy determinations for vaporization of 5.2 g PF, approximately 10°C, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Low temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration. B globigii and B thuringiensis were concurrently tested but represented on separate graphs for clarity.

Figure 4.

Test 3: efficacy determinations for vaporization of 1 g PF, room temperature, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Room temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration.

Figure 5.

Test 4: efficacy determinations for vaporization of 5.2 g PF, approximately 10°C, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Low temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration.

Figure 6.

Test 5: efficacy determinations for vaporization of 1 g PF-equivalent mass of formalin, room temperature, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (D) Room temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration. B globigii, B thuringiensis, and B anthracis were concurrently tested but represented on separate graphs for clarity.

Figure 7.

Test 6: efficacy determinations for vaporization of 5.2 g PF-equivalent mass of formalin, approximately 10°C, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (D) Low temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration. B globigii, B thuringiensis, and B anthracis were concurrently tested but represented on separate graphs for clarity.

Figure 8.

Test 7: decontamination efficacy of 1 g PF, approximately 10°C, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (D) Low temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration. B globigii, B thuringiensis, and B anthracis were concurrently tested but represented on separate graphs for clarity.

Figure 9.

Test 8: decontamination efficacy of 1 g PF-equivalent mass of formalin, approximately 10°C, initial 70%–75% RH, 48-hour exposure duration. (A) Decontamination efficacies determined at 5 time-points for B globigii on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (B) Decontamination efficacies determined at 5 time-points for B thuringiensis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (C) Decontamination efficacies determined at 5 time-points for B anthracis on wood (•) and painted concrete (□), and concentration × time (ppm-hours) of H₂CO vapor calculated at each time-point (---). (D) Low temperature (▲) with starting 70%–75% RH ( × ) environmental conditions over a 48-hour exposure duration. B globigii, B thuringiensis, and B anthracis were concurrently tested but represented on separate graphs for clarity.

Figure 10.

Regression analysis of exposure duration and decontamination efficacy for 3 spore types inoculated on wood from 5 separate tests that used PF to generate H₂CO vapor. (A) B globigii on wood, (B) B thuringiensis on wood, (C) B anthracis on wood.

Figure 11.

Regression analysis of exposure duration and decontamination efficacy for 3 spore types inoculated on wood from 3 separate tests that used formalin to generate H₂CO vapor. (A) B globigii on wood, (B) B thuringiensis on wood, (C) B anthracis on wood.