If ultraviolet light decontamination is not supported for class II biosafety cabinets in BSL-2 labs, and UV bulbs consume so much energy, why are most new BSC cabinets still ordered with UV lamps? Spoiler alert: some burgeoning bioscience applications require it, and fortunately, there are some options to improve its sustainability.
The downsides of Ultraviolet lamps
Class II biological safety cabinets (BSCs) are necessary to protect biological samples, scientists, and the environment. High-efficiency particulate air (HEPA) filters are an intrinsic feature. However, ultraviolet (UV) light decontamination at 254 nm wavelength in BSCs has been considered superfluous at best and harmful at worst.
The drawbacks of UV in practice run the gamut from questionable efficacy to environmental, health, and safety risks. First of all, lab users overestimate its decontamination capabilities, which leads to less thorough surface wipe-downs inside BSC cabinets. Another tricky thing about mercury-based UV bulbs is that they can lose effectiveness without any perceivable change to their appearance when lit. Maintenance tends to be lax even though performance isn’t assured if the bulbs aren’t cleaned weekly and validated with a UV meter - according to the CDC’s 6th edition of Biosafety in Microbiological and Biomedical Laboratories. Another practical drawback is that UV has extremely limited penetration. Light has to hit surfaces at just the right distance and dosage to work. It’s not top of mind that any surface micro-shadows or items left inside the hood with surface sides that aren’t hit by the light are not sterilized. Mercury UV bulbs are also environmentally hazardous waste. They must be disposed of in hazardous waste collections or recycled. UV 254 nm light use also poses potential eye cornea burns and skin cancer hazards for scientists working in the labs. This Position Paper on the Use of Ultraviolet Lights in Biological Safety Cabinets is a detailed overview of how the risks outweigh the benefits. Biosafety certification providers and research organizations do not promote UV in BSCs. The National Sanitation Foundation (NSF) does not recommend UV light use in BSCs. The National Institute of Health (NIH) does not permit the installation of UV lamps in Class II Biological Safety Cabinets.
Despite all this, more than 80% of biological safety cabinets manufactured in the United States today have UV-C lighting installed. Let’s take a look at what underlies this demand.
Biologists hold contamination prevention sacrosanct
Contamination is a constant concern that carries different meanings in life science lab work. Good sterile technique is a must, as is the understanding that bacteria, spores, toxins, fungi, viruses, and nucleic acids, by their natures, have different resistances to different inactivation treatments. Each step of a biological workflow is built upon the success of priors. When I developed monoclonal antibodies with cultured hybridomas, the loss of clones to mycoplasma or yeast was unthinkable. When I was chasing a virulence gene from a strain of pathogenic E. coli using shotgun cloning, contamination between samples would have been unconscionable. My point is that with any experiment, the goal is to control what you are working with to keep results meaningful.
Scientists order UV lamps in new biosafety cabinets because ultraviolet irradiation is a low-cost way to inactivate bacteria, viruses, and contaminant nucleic acids. Improper UV light application is almost paradoxical to its capabilities. Germicidal UV 254nm lamps can rapidly decontaminate Bacillus anthracis spores in BSCs. These are extremely tough spores that can live for decades in soils. Their superior stress resistance makes them a standard for heat sterilization. The UV 254nm emission band of mercury gas is the approximate wavelength of UV absorption by DNA. Surface rate constants for microbes and viruses are used to predict effective UV dosage for equipment sterilization. It’s never intended as complete surface decontamination of BSC hoods on its own. Rather, labs rely on multi-layered and overlapping approaches, including chemical and physical methods. Decontamination must be validated in individual conditions with each target.
Stipulations for UV in Biosafety cabinets
Green lab teams looking for good opportunities to remove UV lamps from BSCs should keep in mind that some scientific requirements preclude this initiative. Certain molecular and cellular techniques require UV decontamination of biosafety cabinets. It’s a precaution taken when culturing human cell lines with the potential to carry bloodborne pathogens. Clinical labs also use UV to decontaminate BSCs when handling infectious materials. Then there are the burgeoning biomedical applications, sequencing-based diagnostics, and the research, development, and scale-out of cell therapies for patients.
Decontamination is critical to PCR and next-generation sequencing in molecular diagnostics laboratories. Amplicon, carryover, and cross-contamination of nucleic acids are particularly dreaded in clinical PCR. While routine PCR is often conducted at the bench, high throughput molecular diagnostic PCR should be conducted in laminar flow PCR workstations or biosafety cabinets. Built-in UV lights help to eliminate contamination alongside unidirectional workflows, room air pressure, and chemical surface cleaning. The WHO Global Malaria Programme's Dos and Don’ts for molecular testing recommends 30 minutes of irradiation with UV light in biosafety cabinets when using 70% ethanol instead of 10% sodium hypochlorite for PCR decontamination. Molecular diagnostics labs using PCR for next-generation sequencing (NGS) analyses scrutinize decontamination efficacies to degrade nucleic acids in the air and on surfaces. This recent study, Evaluation of the ability of commercial disinfectants to degrade free nucleic acid commonly targeted using molecular diagnostics, demonstrated that only hypochlorite-based commercial surface disinfectants were effective. Another recent study reports that chlorine disinfectant could lead to the failure of library preparation in NGS. To deal with contamination, they forbid hypochlorite use in their lab and included UV light irradiation for one hour after watering can spraying to decontaminate bioaerosols. The consensus is that multiple barriers minimize risk - especially in a clinical lab setting when hundreds or thousands of samples are processed.
Infographic Description: Critical use cases for UV in Biosafety cabinets include PCR for next generation sequencing, pathogens, and cell and gene therapy bioprocessing.
State-of-the-art cell and gene therapies also require strict contamination avoidance. The field of Chimeric Antigen Receptor (CAR) T-cell therapies has produced eight medical treatments so far. Emerging studies tackle diseases such as multiple sclerosis, Parkinson’s, and pediatric leukemia. Potentially, tens of thousands of human cell therapies are on the horizon. Most cell and gene therapy manufacturing processes have been developed in academia with open processing systems that use small-scale tissue culture manufacturing with biosafety cabinets. UV dosing in biosafety cabinets has promising results for minimizing cross-contamination risks in cell processing for that important work. Undoubtedly, UV has a place within complex pharmaceutical quality system designs involved in live human cell sorting and bioprocessing.
These kinds of critical use cases are reflected by an acknowledgment of lab-specific standard operating procedures to turn the UV lights when required in the Center for Disease Control (CDC) training for the safe use of Biological Safety Cabinets.
And perhaps also why manufacturers have improved biosafety cabinet UV lamp features.
Helpful features in newer biosafety cabinets
Biosafety cabinet manufacturers have addressed many problems with UV light use. I admit I routinely left UV lights on overnight using of those older model tissue culture hoods. Old habits die hard! This wasted energy use is now preventable with built-in programmable timers for UV lamps. BSC sashes are interlocked with UV lamp switches to deny any bold reaches into the cabinet to grab forgotten items after the UV is lit. A warning for UV lamp life span prompts bulb replacement.
The pièce de résistance will be replacing mercury-based UV bulbs with LEDs. There was a push in response to the COVID-19 pandemic by electronics and biological researchers to accelerate the uptake of germicidal 254 nm to 285 nm UV-C light-emitting diodes. UV-C-LEDs have comparable inactivation activity and improved energy efficiency versus mercury lamps - but their durability is problematic. UV-C-LEDs currently have a lifetime of a few hundred or thousand hours, whereas ten thousand hours is desirable. The energy savings and the elimination of mercury pollutants are big enough environmental benefits for UV-LEDs to be incorporated into water and air mechanical systems for their germicidal powers. Perhaps biosafety systems aren’t too far behind?
Environmental stewardship can be compatible with bioscience
As molecular and cellular techniques are broadening in scope, scientists ordering hoods with UV lighting may be planning for critical decontamination today or flexibility for future work. UV-C should not be applied universally in BSCs - but it can be useful for inactivating microbes, viruses, and free nucleic acids. Newer BSCs have features to help to prevent excess or hazardous use. All scientists using BSC Class II cabinets should be trained to understand the limitations of UV and how to avoid generating mercury pollution and energy waste. If your lab is not using UV properly in BSCs, consider posting reminder signs or removing UV lamps until needed.
Thank you for being “labconscious”!