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CBRNe: Immediate decontamination. Update on RSDL (Reactive Skin Decontamination Lotion)

In this paper, we summarize the scientific studies showing the action of RSDL in the field of the chemical agents decontamination. Studies have been conducted in animals (physiological and toxicological studies) or in situ (by measuring the remaining contamination) or by nuclear magnetic resonance spectrometry that analyses the chemical degradation process of molecules.

Skin decontamination must prevent a chemical contaminant to enter the dermis, whatsoever a chemical warfare agent or other toxic industrial chemicals . The product has to be transferred from the skin and, if possible, inactivated in order not to create a secondary contamination or cross contamination. RSDL (Reactive Skin Decontamination Lotion) meets these requirements.

Skin
In case of contamination of an unprotected skin by a toxic, the stratum corneum mainly composed of dead cells represents the first line of defense.
Containing water, this layer retains the hydrophilic chemicals. To reach the blood capillaries the contaminant must cross this protective layer, the dermal cells and the connective tissue. This natural barrier helps to delay products such as nerve agents before they invade bloodstream. On the other hand, blister products (mustard gas, lewisite) or strong acids and bases, directly destroy cell layers, exposing underlying tissues on which they exert their toxic effects with side effects such as the swelling of the skin with large volumes of liquids. In addition, the products that are soluble in lipids pass easily through the skin barrier thanks to the lipoid stratum corneum.
It is therefore essential to act as quickly as possible to avoid systemic toxic effects (neurotoxic) or local.

Immediate decontamination
Different decontamination systems called "immediate" can be used. Water or better, soapy water, available and not expensive, achieves a transfer of the product from the skin to the outside and also acts by dilution. Nevertheless the harmful effluents have to be treated in a second time. Hydrolysis of chemicals is possible in an alkaline medium. The hydroxyl ion produces a nucleophile attack on the phosphorus atom leading to the hydrolysis of organophosphorus (OP) and VX. Sodium hydroxide solutions at pH 11 are effective, but they should not be applied at concentrations greater than 0.5% on the skin. Nucleophile detoxification of HD is also possible but it is very slow because of the low solubility of the toxic in water. The oxidation with chlorinated products such as hypochlorite is still possible by generating very nucleophile positive charges. This agent will be preferred since it also acts on the OP. The US military use 0,5 % calcium or sodium hypochlorite for the decontamination of the skin and at 5% for the equipment.
Dry decontamination uses solid adsorbent binding the toxic liquid to form a residue then removed from the skin. Some products fall into this category: sand, talc, Fuller earth (clay) or diatoms for example. These powders must be collected carefully because the fine dust or particles could be inhaled or redeposited on the skin during the disrobing: it is called re-aerosolization. Product M291 Skin Decontamination Kit (SDK M291) is a combination of an activated carbon adsorbent and two neutralizing ion exchange resins. The latter activity is slow and, in practice, the product acts only as an adsorbent material.

Decontamination with aqueous products
The effectiveness of a liquid decontaminant is defined as the time required to remove the entire product from skin. The efficiency of a water shower against an aqueous product such as HD is about 90 seconds.
We must therefore develop products that increase the "wash-in" effect i.e. which don’t just remove the product, but also adsorb it, in order the contact time between the product and the skin be as short as possible.
An excellent review concerning the principles of skin decontamination has been recently published (1). Another one is an update of all the treatments being developed against organophosphate poisoning (2).

RSDL
This product destroys VX, G agents, HD and Lewisite. The nerve agent that inhibits the cholinesterase is released from the enzymatic site while a glycol carrier dissolves oily agents such as HD and retains it in the sponge away from the skin.
RSDL is a mixture of potassium 2,3-butanedione mono-oximate (KBDO 1.25 M) having the enzymatic action and 2,3-butanedione mono-oxime (5% DAM) in a polyethylene glycol carrier monomethyl ether (SMEs) in water.
Freezing occurs between 0 and 5 ° C and it is inactivated at 200 ° C. Its pH is alkaline, between 10.35 and 10.85. The solution is included in a sponge that is specific and permits a good contact between toxic products and enzyme.

Security
The product is not intended to be used in eyes, mucous membranes, wounds or damaged skin. However, the DAM enters the skin and acts on the toxic before it reaches the vascular system. It has been shown that it is neither teratogenic, nor genotoxic. Injected intravenously, it gives serious toxic effects, so it is not recommended to use the product in excessive quantities or for the decontamination of the entire body. Skin irritation was sometimes observed after application so, when it is possible, we should rinse the treated area with water.
Effectiveness
All studies were conducted in animals with the nerve agents (G and Vx) and blistering (HD). In vivo, the pigs, guinea pigs or rabbits have been widely used. The efficiency can be expressed by means of morbidity (cholinergic poisoning syndrome, skin changes (HD), mortality (LD50, TL50), biochemical measurements of toxicity (% inhibition of cholinesterase (ChE)) and the protection ratio (PR).
Table 1 from the publication of Schwartz et al. shows that in all cases, RSDL is significantly more effective in immediate decontamination (2 minutes), than comparable products as M291, bleach, soap and water and fuller’s earth.

Table 1 from reference 3
FE: Fuller’s Earth
RSDL is also the most active product when the decontamination is delayed (after 30 minutes).

In this review, the product has not been tested against Industrial toxics but the structural similarities between the OP and pesticides suggest that RSDL can be effective on these products.

Effectiveness of RSDL against other toxic products
Using the nuclear magnetic resonance spectroscopy, the authors of the paper in press (4) tested RSDL against 13 pesticides and 9 nerve agents. This analytical method allows to follow the chemical degradation products and gives kinetics measurements. The results have shown that all the G agents have been degraded with a half-life of less than 30 seconds leading to a total breakdown in less than 3 minutes. In contrast, the half-life of agents V degradation was measurable and slightly longer (maximum 440 seconds for the VE). Amongst the 13 pesticides tested, 9 have been degraded very quickly (half-life less than 30s) and only 4 had upper half-lives (maximum 549 sec for Ethotrophos). This technique also shown that the degradation reactions were not all similar: the degradation pathways depended on the structure of the molecule to be destroyed.
It has also been shown (5) that RSDL was active against the following products: parathion, paraoxon, methyl-parathion, malathion, malaoxon, chlorpyrifos
However, there is no data regarding products such as petroleum hydrocarbons, agrochemicals products and those of industry. A recent publication (6) gives some results for O-cresol and acrylonitrile but only the in situ decontamination on textile or steel plates were measured.

Conclusion
RSDL was developed as an alternative to adsorbents used for decontamination of chemical warfare products. Its superiority against blistering (HD) and neurotoxic organophosphates (G, Vx Series) is undeniable. This product can be used in conflict situations by the military but also in civil scenarios to decontaminate chemicals threats by first aid, civil security ... Effective against pesticides, it can be used in industrial or agricultural environments.
Approved by the FDA, it is in line with European requirements (CE marking).

References

1- Skin decontamination : principles and perspectives. HP Chan, H Zhai, X Hui, HI Maibach. Toxicology and industrial Health, 2013, 29, 955-968.
http://tih.sagepub.com/content/29/10/955.full.pdf+html
2- Developments in alternative treatments for organophosphate poisoning. R Ier, B Iken, A Leon. Toxicol. Lett (2015), http://dx.doi.org/10.1016/j.toxlet.2015.01.007.
3- Reactive Skin Decontamination Lotion (RSDL) for decontamination of chemical warfare agent (CWA) dermal exposure. MD Schwartz, CG Hurst, MA Kirk, SJD Reedy, EH. Braue Jr. Current pharmaceutical Biotechnology, 2012, 13, 1971-1979.
http://www.ingentaconnect.com/content/ben/cpb/2012/00000013/00000010/art00015
4- Detoxification of organophosphorus pesticides and nerve agents through RSDL : efficacy evaluation by 31P NPR spectroscopy. PW Elsinghorst, F. Worek, M. Koller. Toxicol. Lett.(2015),http://dx.doi.org/10.1016/j.toxlet.2014.12.004
5- http://www.rsdl.com/skin-decontamination/rsdl/
6- Ensuring of individual decontamination of hazardous chemicals in the fire rescue service of the Czech republic. Part 2 : comparison of decontamination effectiveness of selected means and procedures. T Cpoun, J Krykorkova. The science for population protection 2/ 2014
http://www.population-protection.eu/prilohy/casopis/eng/20/92.pdf

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21-24
Nov. 2017
Paris-Nord Villepinte
France

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