EQUIPMENT AND SUPPLIES--Sterilization of Microbiological Equipment In Reply Refer To: August 30, 1985 WGS-Mail Stop 412 QUALITY OF WATER BRANCH TECHNICAL MEMORANDUM NO. 85.18 Subject: EQUIPMENT AND SUPPLIES--Sterilization of Microbiological Equipment Recent Water-Quality program reviews have indicated a recurring problem in some Districts--the use of non-approved methods for sterilization of bacteriological filter assemblies; specifically, ultraviolet irradiation. The U.S. Geological Survey's approved method is described in section 7.3, page 37 of TWRI, Methods for collection and analysis of Aquatic Biological and Microbiological Samples. It requires autoclaving for 15 minutes at l2l degrees C at 15 psi. Incomplete combustion of methanol, to produce formaldehyde gas, is permitted for field sterilization, although autoclaving in the laboratory is preferred. The justification most often given for using UV irradiation instead of autoclaving is that the Environmental Protection Agency (EPA) lists ultraviolet radiation, among other techniques, as a method of sterilization acceptable to them in Microbiological Methods for Monitoring the Environment; Water and Wastes, 1978. This manual however, is designed for use by trained microbiologists operating in a laboratory setting. And these alternative methods of sterilization are usually used as adjuncts to primary sterilization to maintain sterility in hoods and glove boxes. That UV irradiation does not guarantee sterility is shown in the EPA manual on pages 198 and 199. Quality control of UV Units requires frequent monitoring with a shortwave UV meter and at least quarterly measurement of effectivness on a coliform culture. The manual states, "UV-irradiated plates should show 99% reduction in the count of the control plate. If count reduction is less than 80%, replace lamp." Further, users of UV units should be aware of the safety hazards attendant to their use. The special media we use for culturing fecal coliform and fecal streptococci promote the growth of the microorganisms we are seeking and inhibit or kill all others. This is why we can get away with performing filtrations in the field under grossly unsanitary conditions. This tolerance of the media however, must not be abused. We must assure that our glassware and everything else that we can control, that comes in contact with the sample, is sterile--not almost sterile. If cost of multiple stainless steel filtration units is a problem, Districts can use the polycarbonate plastic units made by Nalgene and other companies. They can be autoclaved and sealed in kraft paper bags, used once at the field site, and returned to the laboratory for autoclaving. They are cheap enough that dozens can be taken on an extended field trip if necessary. The sampling and analytical methods described in our TWRI's are the methods currently approved for use in obtaining data that will be placed in WATSTORE. Our data users, both within and outside the Survey, have a right to expect that the methods we say we use in obtaining data are the methods we actually use. David A. Rickert Acting Chief, Quality of Water Branch Distribution: A, B, FO, PO This memorandum does not supersede any other memorandum