Martin Weber, Holger Schulz
Central Institute of the Bundeswehr Medical Service, Munich, Toxin Chemistry/Warfare Agent Analysis Laboratory Unit, Humboldtstr. 1, D-29633 Munster
Many toxic chemicals and chemical warfare agents can penetrate the skin or can produce toxic effects in the skin. Obviously, these substances must be rapidly removed after contact, which is why the decision on a suitable skin decontaminant for CBRN Special Forces is of outstanding importance both for the performance and health of the soldier.
Skin detoxification can be achieved by different solutions and approaches, but our in vitro testing showed that not all of them react the same way and dissolve all chemical and biological agents within the same amount of time. Before getting straight to the results, I will start with a short overview of dermal toxicity of chemical warfare agents and respective requirements for skin decontaminants before evaluating advantages and disadvantages of solutions that are available on the market.
2. DERMAL TOXICITY OF CHEMICAL WARFARE AGENTS AND REQUIREMENTS FOR SKIN DECONTAMINANTS
Table 1 shows NATO-defined skin damage thresholds at which the listed agents cause adverse effects on the skin or through the skin. The thresholds for sulfur mustard and lewisite, which are vesicant chemical agents, are based on the quantity of the agent per surface area. By contrast, the thresholds for VX, sarin and cyclosarin, which are systemically acting nerve agents, depend on the total quantity of the absorbed chemical agent. Whereas VX readily passes through the skin, sarin and cyclosarin are poorly absorbed through the skin.
The functional requirements for skin decontaminants defined by the Bundeswehr are as follows: “Decontaminants are part of CBRN individual decontamination kits and remove, absorb, detoxify or disinfect biological and chemical agents that persist on affected areas of the non-injured or injured body surface and on parts of the personal equipment as well as minor items of equipment. Decontaminants that are part of CBRN decontamination kits are applied during self and buddy aid.”
However, there are a few further requirements for a skin decontaminant:
- Removes or detoxifies a chemical or biological agent within one minute
- Universally effective, also against biological agents
- Easy to use, also at low temperatures
- Certified as a medical device and/or authorisation as a biocidal product
- Storable and transportable at high temperatures
- Environmentally compatible, safe handling for the user
In addition, one must consider a list of legal requirements. As skin decontaminants are used in cases of exposed skin, damaged or incomplete protective clothing, removal of PPE after contamination (from casualties) possibly including the exposure of wounds, they also must be certified as a medical device for this purpose and classified as a biocidal product type 1: “Human hygiene biocidal products”. For personal protective equipment about 100 ml are necessary for hospitals, decontamination points of CBRN defense units, casualty decontamination and CBRN defense teams of fire departments and other emergency services stations several litres are required. Also, for certification as a medical device in the EU, a number of further requirements must be met.[i]
3. METHODS OF DECONTAMINATION: ADVANTAGES AND DISADVANTAGES
Chemical decontamination can be accomplished by different methods. Advantages and disadvantages are shortly listed below:
- Dissolution of thickened agents
- Dissolution of mixtures of agents, e.g. mixtures of sulfur mustard and arsine or sulfur mustard and lewisite
- Removal of agents from tiny creases in the skin
- Removal of agents from the cornea / defatting of the skin
- Almost universal applicability
- May accelerate passage through the skin
- PH value should not be in the alkaline range
- No degradation of toxicants
- Easy to remove
- Easy to handle
- Almost universally applicable
- Desorption is possible.
- Dust that contains the toxicant builds up in the air.
- Almost universally applicable
- May cause irritation of the skin
- Cannot be stored for a long period of time
- Strong oxidants can cause exothermic reactions
- May contribute to the formation of environmentally hazardous substances.
- Can be stored for long periods of time
- May cause irritation of the skin
- Can detoxify only hydrolysable substances
- Can accelerate passage through the skin in the case of alkaloids/amines
- Requires only modest material resources
- Does not irritate the skin
- Enzymes act only in a substance-specific manner.
- They require an optimum pH level and a temperature of approximately 30 degrees Celsius.
- They require an aqueous medium. The dissolution of highly lipophilic compounds or thickened agents is difficult.
Combination of methods
A combination of decontamination methods offer the advantage that the dissolution of toxicants improves the desired reaction. However, a combination can adversely affect storability.
4. DESCRIPTION AND EVALUATION OF AVAILABLE DECONTAMINANTS
Let me now describe and evaluate available skin decontaminants on the basis of the criteria composition, mechanism of action against chemical and biological agents, legal status, stability, environmental compatibility and costs.
For a long time, the German Bundeswehr used a mixture of calcium hypochlorite and talc as decontamination powder. The active principle was oxidation and adsorption. The powder was highly irritating to the skin.
It has currently no certification as a medical device and a limited stability and is therefore no longer used.
The civilian sector usually recommends the use of polyethylene glycol 400 for the management of skin contamination. Polyethylene glycol 400 dissolves lipophilic and hydrophilic chemicals, is environmentally compatible and inexpensive but there is no chemical degradation.
Worldwide, there are several working groups that are currently concerned with developing suitable enzyme preparations. The aim is to develop a mixture of enzymes with different modes of action, but until now there is no suitable product commercially available.
Probably only lyophilized powders are stable. The preparation of a solution prior to application is necessary.
Disadvantage of enzymes is their high selectivity against individual agents and their activity only in aqueous systems.
RSDL is a product that was originally developed in Canada and is a solution of butanedione monoxime and potassium salt in a solvent similar to polyethylene glycol. Principal is the dissolution and alkaline hydrolysis of agents. It is certified as a medical device and currently available only as a sponge impregnated with the lotion. RSDL has a shelf life of 4 years. As our in vitro testing results will show, all agents are readily soluble in RSDL, but only the Sarin Group is broken down sufficiently quickly. Sulfur mustard and lewisite are not degraded; VX has a half-life of 5 minutes. Likewise RSDL does not act as a disinfectant.
Alldecont consists of the two separate solutions of sodium hypochlorite and a glycol derivative in which a fatty acid is dissolved. It is an oxidant spray, which can be activated by mixing the two components upon actuation of the spray head. The activated solution dissolves and decontaminates all chemical and biological agents within a maximum of one minute (half-life) and is particularly active against anthrax spores. It can be obtained from the German company OWR.
It is certified as a medical device, available as an item of personal equipment or in large quantities for decontamination stations. The only disadvantage is the limited shelf life of one of the two components. The less durable component can be exchanged without problems because the manufacturing is inexpensive. Nevertheless alldecont should be stored in the refrigerator.
Previn, which is also known under the name of Diphotérine, is manufactured in France.
It is a sterile, buffered, hypertonic, aqueous solution of cyclodextrines and is certified as a medical device, applicable to damaged skin.
Against chemical and biological agents it is not more effective than water. Advantage is the possible use in open wounds. But for this any other sterile infusion solution will work as well.
Soft soap is the simplest means of decontamination and has been used for a long time.
It is classified as a cosmetic product, stable, environmentally compatible and inexpensive.
Soft soap removes all hydrophilic and lipophilic preparations and there is a limited hydrolytical degradation.
5. IN VITRO TESTING OF AVAILABLE DECONTAMINANTS
Results of our in vitro testing of available decontaminants showed a very clear result: in contrast to the commercially successful RSDL™, only the alldecont solution dissolves and decontaminates all chemical and biological agents within a maximum of one minute (half-life). The in vitro testing carried out in our laboratory was designed to investigate the kinetics of degradation of chemical agents and the decontamination of pig skin.
Table 2 provides an overview of the in-vitro half-lives of chemical agents in minutes when 2 mg of an agent are mixed with 600 mg of a decontaminant. If a chemical agent does not dissolve in a decontamination product, a half-life cannot be determined.
In RSDL only cyclosarin is degraded in an acceptable period of time. By contrast, alldecont is sufficiently effective against all chemical agents listed in this table. PEG 400 is a pure solvent and does not chemically degrade chemical agents.
On the basis of STANAG 4650 and other sources, post-decontamination target concentrations were determined for the four chemical agents that are addressed in our tests.
The acceptable residual concentrations on the skin after decontamination for sulfur mustard and lewisite are 9 and 5µg/cm². To account for the total intake of nerve agents a total contaminated surface area of 25 cm² was assumed, resulting in the target concentration for VX of 0,58 mg/25 cm² and for cyclosarin of 5 mg/25 cm². Figures 2-5 show the results of in-vitro studies on pig skin. Approximately 5 cm² of pig skin were exposed to approximately 1.5 mg/cm² of a chemical agent and decontaminated in accordance with the applicable instructions for use. After two minutes, decontamination was discontinued and the pig skin was extracted with dimethyl sulfoxide. The bar chart shows the residual agent concentrations in the skin after decontamination.
Sulfur Mustard: When the skin was exposed to sulfur mustard and thickened sulfur mustard, alldecont was the most effective decontaminant. Solvents also reduced the amount of the agent considerably. By contrast, aqueous systems were poorly effective. Especially when alldecont was used, the residual agent concentration was considerably below the target concentration of 9 µg/cm².
VX: When pig skin was exposed to VX and thickened VX, alldecont again proved to be the most effective decontaminant. All other products did not have sufficient effects. Only with alldecont the target concentration of 0,58 mg/25 cm² was nearly reached.
Lewisite: Alldecont was the most effective decontaminant also against lewisite and thickened lewisite. The effects of all other products were insufficient. Only with alldecont a residual concentration of non-thickened lewisite below the target concentration of 5 µg/cm² was achieved.
Cyclosarin: Since cyclosarin is poorly absorbed through the skin, all products – even water – easily reduced the concentration of the agent to a level below the target concentration of 5 mg/25 cm². RSDL™ and alldecont were the most effective decontaminants.
Biological agents: The most important militarily significant toxin is ricin. Ricin in alldecont causes immediate denaturation and detoxification. Therefore a half-life cannot be specified.
In experiments with anthrax spores, it was shown that alldecont reduces the number of spores by a factor of 100,000 within one minute. Thus, the requirements of the European standard EN 131 704 were exceeded. Alldecont is the only sporicidal product which is suitable for application to the skin.
Armed Forces and civilian emergency management services need a rapid-acting skin decontaminant that is universally applicable. It must be provided to soldiers and first responders as part of their personal equipment and must be available in large quantities at decontamination stations and treatment facilities. The decontaminant must be certified as a medical device for this purpose and classified as a biocidal product type 1: “Human hygiene biocidal products”. It should be stable, inexpensive and environmentally compatible.
However, it is surprising that only one tested product completely fulfills the mission to dissolve and decontaminate all chemical and biological agents within a maximum of one minute. Alldecont meets all demands with the exception of stability which must be taken into consideration in logistics planning.
Literature can be requested from the author.
[i] Requirements are that the solution determines the classification of the product, provides evidence for the claimed efficacy of the product, provides easy-to-follow instructions for use, describes manufacturing and testing procedures in detail, describes and minimizes possible undesired effects, takes appropriate risk management measures, provides information on stability and appoints a safety representative. The Biocidal Products Directive 98/8/EC, the classification of biocides, is broken down into 22 product types, with several comprising multiple subgroups. A disinfectant of the skin is to be classified in the MAIN GROUP 1: “Disinfectants and general biocidal products” and the Product-type 1: “Human hygiene biocidal products”. The type of authorization as a biocidal product depends on whether a new or an already known active substance is used.