16. Cleaning and decontamination

Introduction

Appropriate chemical disinfectants must be used for cleaning equipment, materials and work surfaces. All laboratory wastes must be assigned to a category and placed in clearly labeled bins from where the waste will be disposed of appropriately. This is an important area of laboratory management and is covered only in a superficial manner in this manual. Further reading is recommended.

Alcohol

A 70 percent volume/volume solution of alcohol diluted with water is useful for wiping down benches and disinfecting the outside of eggs before inoculation and harvesting of allantoic fluid. The addition of 2 percent iodine will increase the effectiveness of this solution.

Note that 70 percent solution of alcohol is flammable!

Chlorine

There are several chlorine compounds that are used as disinfectants. Sodium hypochlorite (NaOCl) or household bleach is readily available and cheap. Soaking overnight in a 2 percent solution of chlorine is useful for disinfecting plastic materials for example V-bottom microwell plates.

Note that commercial bleach contains 12 to 14 percent hypochlorite when manufactured but this concentration deteriorates with time. Powdered chlorine-based disinfectants are available.

Follow the manufacturer's instructions for the recommended weight of powder to dissolve in a volume of water.

Note that chlorine damages fabric and corrodes many metals!

Wide spectrum hospital grade disinfectants

There is a range of products in this category. Check availability and price. Pearson Medol is a product that is widely used at the University of Queensland. The active ingredient is 4-chloro-3, 5-xylenol.

A 2 percent solution is used for wiping down benches, cleaning incubators and disinfecting contaminated objects such as plastic egg racks and discarded tips.

Formaldehyde

Formaldehyde is available as a 37 to 40 percent aqueous solution known as formalin. Paraformaldehyde is a solid polymerized form of formaldehyde. Formaldehyde is a potential carcinogen, causes burns and the vapour irritates the eyes and respiratory tract. It must be handled with caution and only used as a disinfectant when there are no suitable alternatives.

Formaldehyde vapour is useful for fumigating egg incubators and animal houses. Eggs suspected of being contaminated with bacteria can be fumigated prior to incubation. There are two methods for generating the vapour.

1. Heating 91 percent paraformaldehyde at the rate of 5 grams per cubic metre of space in an electric evaporator. An electric frying pan on a low temperature setting is suitable.

2. Adding 35 mL of formalin (40 percent formaldehyde) to 10 g potassium permanganate per cubic metre of space.

Note:

Prior to fumigation, seal all openings and wet the surfaces.

Wear protective clothing, gloves, mask and safety glasses.

Beware of splashing as the reagents react. The reaction generates heat.

Avoid inhalation of the fumes.

Do not carry out this procedure alone.

Allow 24 hours for the vapour to penetrate all the surfaces.