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Laboratory Orientation and Testing of Body Fluids and Tissues for Forensic Analysts

Decontamination Practices

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Surfaces

Household bleach is 5.25% sodium hypochlorite (52,500ppm), so a 1% bleach solution is 525ppm and sufficient for inactivating most viruses. Per the Centers for Disease Control and Prevention (CDC), chlorine solutions gradually lose strength, so diluted solutions should be replaced daily.01 Some laboratories have changed from the traditional 10% mix in a bottle to a type of container that mixes neat bleach and water at the time it is expressed from the bottle. Biocidal activity is affected by the presence of organic material, which consumes available chlorine. Some laboratories may employ a detergent based germicidal disinfectant, e.g. Coverage Plus®, or a decontaminant such as DNA Away™ per manufacturer's directions. Cleaning with bleach or detergents may be followed by water and/or EtOH to eliminate the possibility of introducing bleach or detergent into the sample or build up. EtOH alone, even 70% as employed in microbiology settings to prevent transfer of pathogens, is not sufficient to rid a surface of exogenous DNA.

Image of UV light decontamination practices
National Institute of Justice (NIJ) (see reuse policy).

Another means of decontaminating hoods, reagents, pipettes, tubes, etc., is exposure to UV light. Most biological safety cabinets are equipped with a UV light source. It is generally accepted that UV exposure at 254nm for a minimum of 5 minutes is sufficient for disinfection to include the deactivation of nucleases and destruction of extraneous DNA on surfaces. Laboratory SOPs often include UV exposure steps as long as 30 minutes before and after use of hoods for PCR work. Wiping with bleach and/or detergents is still warranted as the penetrating power of UV light is minimal.

Reagents, Consumables, and Tools

Applicable consumables and tools such as scissors, microcentrifuge tubes, spin baskets, racks, glassware, containers, and other items may be autoclaved. Many laboratories, as a part of their quality control program, autoclave some reagents prior to use, and may prepare some reagents from autoclaved solutions. It is a good practice to apply autoclave tape to items being sterilized to test the autoclave's efficacy and differentiate between items that have and have not been autoclaved. Laboratories should pay careful attention to the plastics used in the laboratory if they are to be autoclaved, as some can break down, becoming more porous and prone to harboring contaminants. When using tubes or supplies that have been autoclaved in a container, it is good laboratory practice to pour them onto a clean surface rather than reaching into the container to retrieve them.

 

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