Efficient agent degradation within skin is important for decontamination of percutaneously exposed VX

Abstract

Aim of the study: Following percutaneous exposure to the nerve agent VX, the remaining intact agent within the skin after decontamination is of great concern. Consequently, this leads to prolonged agent release to the blood circulation resulting in sustained intoxication, which may complicate the medical management. The decontamination procedure used should therefore possess the ability for agent removal both on and within the skin. The efficacy of three decontamination procedures was evaluated by measuring VX and the primary degradation product ethyl methyl phosphonic acid (EMPA) penetrated through human skin and the amount remaining within the skin. Materials and methods: Decontamination was initiated 5 min post-exposure to VX on human dermatomed skin. Experiments were conducted using an in vitro skin penetration model and the amount remaining within the skin was determined by combining the tape-stripping technique and acetylcholinesterase activity measurements. Results: In control experiments without decontamination, higher amounts of VX were recovered in the deeper layers of skin compared to EMPA, which was primarily located in the stratum corneum. Both Reactive Skin Decontamination Lotion (RSDL) and the RSDL training kit (TRSDL) significantly reduced the amount of VX within the skin and decreased the penetration through the skin. However, the degradation ability of RSDL was demonstrated to be beneficial by the reduction of intact agents remaining in the skin compared to TRSDL without agent degradation capability. Soapy water decontamination caused a "wash-in" effect of VX with decreased agent amounts within stratum corneum but increased the amount VX penetrated through the skin. Conclusion: Efficient skin decontamination of VX requires skin decontaminants reaching deeper layers of the skin, and that both absorption and degradation properties are important. In addition, the "washin" effect by using soapy water may enhance VX release to the blood circulation.

The wash-in effect and its significance for mass casualty decontamination

“…While most studies occurred at room temperature (approximately 25°C), Thors et al ( 2021a ) also conducted soapy water decontamination at −5°C and −15°C. While the cumulative penetration of VX significantly increased (66.5 ± 5.5 μg/cm 2 compared to no-decontamination control of 24.6 ± 6.6 μg/cm 2 ) following wet decontamination at room temperature as previously identified (Thors et al 2021b , 2020 ), there was no significant alteration at either −5°C (36.0 ± 3.7 μg/cm 2 compared to 28.9 ± 8.9 μg/cm 2 ) or −15°C (35.8 ± 9.4 μg/cm 2 ompared to 34.4 ± 5.3 μg/cm 2 ). Skin penetration of VX was significantly reduced at lower temperatures when compared to room temperature, although this is based upon cumulative dose over 5 hr, and presence of any temporal phenomenon is not mentioned within the study.…”

“…Skin penetration of VX was significantly reduced at lower temperatures when compared to room temperature, although this is based upon cumulative dose over 5 hr, and presence of any temporal phenomenon is not mentioned within the study. Thors et al ( 2020 ); (2021b) ) suggested that the lack of wash-in effect at lower temperatures may be due to freezing of water on the surface of the skin (despite the skin being held at 32°C) and that cold soapy water reaching into the skin may have delayed further VX penetration within the skin. While this is an important consideration for incidents that occur at sub-zero temperatures, the design of decontamination interventions at low ambient temperatures requires redesign to prevent hypothermia.…”

“…Both Misik et al ( 2012 ) and Thors et al ( 2020 ) also partly attributed instances of the wash-in effect for paraoxon and VX, respectively, to surfactants. Thors et al ( 2021b ) identified a significant increase in in vitro penetration rate of neat VX (1 µl) through human skin (50 min post-exposure onwards) when decontaminating with soapy-water (initiated 5 min post exposure) and compared to a no decontamination control. There was also a significantly larger cumulative penetration between soapy-water wash (0.87 ± 0.18 µg/cm 2 ) and the control condition (0.26 ± 0.07 µg/cm 2 ) (both n = 4), despite there being a significant decrease in the amount of VX identified in the SC following soapy-water intervention compared to controls.…”

“…There was also a significantly larger cumulative penetration between soapy-water wash (0.87 ± 0.18 µg/cm 2 ) and the control condition (0.26 ± 0.07 µg/cm 2 ) (both n = 4), despite there being a significant decrease in the amount of VX identified in the SC following soapy-water intervention compared to controls. Thors et al ( 2021b ) postulated that the wash-in effect was primarily due to the soapy-water wash releasing the dermal depot of VX, and removal from the application site prevented reservoir replenishment. Importantly, evidence indicated that this increase in cumulative VX penetration is sufficient to enhance the probability of the onset of cholinergic symptoms, resulting in a shorter timeframe for initiation of medical treatment following exposure.…”

Do cold weather temperatures affect the efficacy of skin decontamination?

“…The cause for lowered VX skin penetration following soapy water decontamination in cold air temperature could in future studies should be evaluated by using skin stripping methodology or similar techniques to determine the agent amounts in different skin layers (Thors et al, 2021). Although the low air temperature beneficially influenced the efficacy of soapy water decontamination, cold water on skin is also a potential cause for environmental injuries such as hypothermia (Cheshire, 2016).…”