Introduction

Decontamination is a crucial step in the care to victims exposed to CBRN agents [1]. To be beneficial to victims, it must be performed as quickly as possible following exposure, and as thoroughly as possible on the body surface which not only includes skin but also wounds, hair, eyes, and other mucous membranes.

Decontamination is defined by NATO as the process of making any person, object, or area safe by absorbing, destroying, neutralizing, making harmless, or removing chemical or biological agents, or by removing radioactive material clinging to or around it [2]. Human decontamination has two main objectives [3]: firstly, to improve the prognosis, functional and vital, of contaminated victims, and secondly, to reduce the transfer of contamination from the body surface to media, including noncontaminated skin, with which it interacts.

From a practical point of view, decontamination is usually performed in two consecutive steps: the first one, “emergency decontamination” (ED) consists in partial disrobing and use of emergency decontamination kit on the unprotected body surfaces, and the second one, “thorough decontamination ” (TD) consists in total disrobing followed with showering.

Emergency decontamination kits include absorbents, for example, handkerchief, paper, towel, clean fabric, and adsorbent powders such as Fuller’s earth, talcum, flour, clean sand, and cat litter [3]. Adsorbent powders are poured on the contaminated area, then either left until a shower can be performed or, after a short contact time, removed with a towel or more effectively with water.

For instance, Fuller’s earth has a relatively high affinity for lipophilic chemicals and has been shown to be highly effective as a skin decontaminant against SM and VX [4, 5]. However, if the decontamination is delayed after exposure, it is slightly less effective than the RSDL® kit, which consists of a polylethylene glycol (PEG) and oximate-based lotion, applied with a sponge [4, 6, 7].

Showering can be performed with different systems, for example, fixed shower, mobile decontamination unit, ladder pipes from the Fire Services, and by implementing different protocols varying according to the duration, water temperature, additive to water, water flow rate, and pressure [8].

When choosing a decontamination kit, one has to consider not only effectiveness but also skin, wound and eye biocompatibility, ease and restrictions of use, cost, stability and storage conditions, and elimination after usage.

Evaluation of human skin decontamination effectiveness against CBRN agents is limited by at least two factors: firstly, for obvious ethical reasons, highly toxic or infectious CBRN agents cannot be used on human volunteers, and secondly, their disposal is restricted to a few laboratories, usually from the Army.

To cope with this issue, laboratories refer to human skin models and, if they cannot dispose of CBRN agents, they use simulants, that is, agents with physicochemical properties very close to that of the real agents and, usually, much less toxic or pathogenic [9].

Human skin models currently consist of in vitro human or animal skin, or in vivo pig or rodent skin [10].

Without standardized tests available at the international level, evaluation of skin decontamination effectiveness relies on highly variable models and procedures [11–16]. Tests heterogeneity is mainly related to agents (liquid or vapor, amount, diluted or not in a solvent), skin models (in vitro or in vivo; animal species: human, pig, rat, guinea pig, etc.; anatomic site: ear, flank, back, abdomen, etc.), skin preparation (e.g., hair cut or not, in vitro full-thickness skin or split-thickness skin), environmental conditions (temperature, relative humidity, and air flow rate), exposure duration before decontamination (1 min, 5 min, 15 min, 30 min, etc.), and decontaminant operating procedures.

In such heterogeneous conditions, results are not comparable from one test laboratory to another. Furthermore, it is quite complex for the users to evaluate the efficacy claims and determine whether the products correspond to their operational needs, particularly since the results have to be extrapolated to human beings who would be exposed to real agents in the same test conditions.

In this context, a French working group comprising scientists from tests and research laboratories, end users and industrials, supported by the national standardization institute (AFNOR), has recently validated a French standard test method (FSTM) (NF X 52-122) to evaluate the effectiveness of skin decontaminants against CBRN agents [17]. The main objectives of this STM are to provide relevant information to the customers and to facilitate comparison between tests through the evaluation of normalized parameters.

The main elements of this STM are addressed in this chapter.

Effectiveness of a Skin Decontamination Kit or System: What Does It Mean?

In this STM, decontamination effectiveness is defined as the ability to remove CBRN agents from the skin surface or neutralize them on the skin surface, without enhancing deleterious effects of CBRN agents already absorbed in the skin before the use of decontaminant. The skin surface is the interface between the first layer of cells from the stratum corneum and the environment. It includes the hair and skin appendages such as the hair follicles and sweat glands.

Emergency Versus Thorough Decontamination

ED aims at improving the vital and functional prognosis of contaminated victims and at reducing the irreversible cellular lesions due to CBRN agents. The main goal of ED is therefore to reduce the exposure duration to CBRN agents and skin absorption of these agents.

The main objective of TD is to limit the transfer of contamination from the skin to other surfaces.

Evaluation of Skin Decontamination Effectiveness (DE) Relatively to Nondecontaminated Skin

According to the FSTM, effectiveness of skin decontamination must be evaluated relative to nondecontaminated skin, exposed to CBRN agents in the same conditions as decontaminated skin.

Agents

Decontamination effectiveness must be evaluated against the same CBRN agents as those claimed by the provider. Storage and use of CBRN agents must be in accordance with the regulations. When CBRN agents cannot be used, they will be substituted with simulants. The choice of simulants must be justified and scientifically validated with references.

Skin Models

There are numerous examples in the literature of reliable correlations between in vitro and in vivo skin permeation studies [18–20].

In vitro skin models must be animal or human skin samples, the latter being more relevant. Pig skin can be an alternative to human skin since their structure and permeability is similar [21, 22]. Rat or guinea pig skin, from the abdomen or back, can also be used. Skin samples are placed into diffusion cells which must be used in nonocclusive conditions and as recommended by the OECD guidelines n°428 [23]. For practical reasons, the donor compartment can be shortly removed to better implement the decontamination protocol.

Freshly excised human skin must be used if CBRN agents are significantly metabolized in the skin (i.e., at least 10% of the applied dose is enzymatically degraded). If the skin metabolism of CBRN agents is relatively low, then samples frozen at –20 °C can be used. Skin integrity of each sample must be checked as recommended [23].The skin thickness must be measured and be lower than 1 mm. Skin surface must be at least 0.6 cm².

Use of animal models in vivo must follow the regulations. The best choice is pig but rat or guinea pig can also be used.

Tests can be performed on human volunteers if the regulations are respected and only with nontoxic or nonpathogenic contaminants. The choice of the anatomic site to be contaminated must be in accordance with real exposure scenarios and must consider health risks assessment.

Skin Contamination

The agent purity must be higher than 95% unless it can be justified. The exposed skin area must be totally covered by the contaminant. As a result, the contaminant can be diluted but the vehicle, preferentially volatile, must not modify the skin permeability or the agent physicochemical properties.

The amount of agent loaded on the skin (Q₀) must be as realistic as possible, that is, for chemicals from a few μg to a few mg.cm⁻². For radioactive agents, it could be between 1 and 10,000 Bq.cm⁻². For biological agents, it must be expressed in colony-forming units (cfu).cm⁻² for bacteria or fungi, or in plaque-forming units (pfu).cm⁻² for virus.

Exposure Durations

Exposure durations , that is, time between contamination (T₀) and decontamination (T₁) will be representative of the context of use. When ED kits are evaluated, they must be of 5 and 30 min, whereas for TD systems, they will be of 30 and 60 min.

Operating Instructions

They must scrupulously respect the instructions of use as given by the provider. In particular, they should indicate how the decontaminant is applied on the skin surface, for example, apply the absorbent on the skin without wiping or wipe back-and-force twice, each time with a new absorbent, or rub the skin in a circular motion. The contact duration with the skin surface and the amount of decontaminant applied per area of contaminated skin must be mentioned. Operating instructions can include several successive steps (e.g., washing, rinsing, and drying).

Skin decontamination with a liquid must include a final drying step, which will be performed with an absorbent applied softly on the skin surface, that is, without scrubbing. This drying process can be repeated several times, each time with a new absorbent sample, until the skin surface becomes dry.

Mass Balance

Mass balance must be evaluated since it is an important parameter to validate the operating procedure. The average mass balance must be of 100 ± 10% for nonvolatile and stable agents, that is, that are not degraded on and in the skin, as recommended by the OECD guidelines number 428 [23].

Indicators of Decontamination Effectiveness

It has been clearly established that chemical agents, more particularly the most lipophilic of them, constitute a reservoir in the skin stratum corneum, from which they are more or less rapidly resorbed in blood [24]. Toxic effects can target the skin itself and/or be systemic. Local skin effects are directly related to the amount of agents present on and in the skin. Systemic effects mainly depend on the amount of agents resorbed and on their skin permeation rate. Skin decontamination must not increase the local and systemic deleterious effects of CBRN agents. Amount of agents and their effects must be evaluated according to scientifically validated or referenced analytical methods.

For in vitro skin models, the amount of agents on the skin surface, in the skin and penetrating through the skin, and the rate of skin permeation must be evaluated. For decontaminated (Q) and nondecontaminated (Q_t) skin samples, the following amounts of agent have to be determined:

• 
  

  Q₀ and Q_0t, loaded on the skin

  
  
• 
  

  Q₁, eliminated from the skin surface

  
  
• 
  

  Q₂ and Q_2t, present on the skin surface immediately after decontamination

  
  
• 
  

  Q₃ and Q_3t, present in the skin at the end of the experimentation

  
  
• 
  

  Q₄ and Q_4t, absorbed through the skin (in the receptor fluid) at the end of the experimentation

  
  
• 
  

  Absorbed through the skin every 30 min and for at least 1h 30 min

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