MICROBIOLOGY IN COSMETIC TESTING 193 sulfate type' shampoo. Pseudomonads have attacked the detergent, causing the product to discolor and separate badly. Figure 3 illustrates what can happen to an inadequately preserved hair styling gel. The control sample on the left represents a clear gel. Mold growth in the sample on the right has caused the gel to become turbid. Aspergillus mold was isolated from the turbid sample. To avoid problems of this type, sanitation techniques and preserva- tive methods need to be selected and employed carefully. They need to be monitored continuously to seek improvements in the systems chosen as they are required. SANITATION During production, common sources of microbial contamination in cosmetic products are raw materials, equipment, and air. Since water for batch-making can be the major threat to product sterility, control over the sanitary quality of this water will be empha- sized in this discussion. Under summer temperature storage conditions, demineralized or deionized water can easily support bacterial populations as large as 10 '• bacteria/mi. In a few cases as many as 10 6 baeteria/ml have been observed. To prevent gross pollution of the batch water supply, the propagation of microflora coming from the undeionized water, the deionizer units, and the storage tanks must be controlled. Although radiation treatment of stored deionized water is not widely practiced in the cosmetic industry, it is potentially a valuable means for controlling water quality. This paper will stress the application of radiation to water sanitation and specifically the uses of ultraviolet (UV) radiation. Effective forms of ionizing radiation include ultraviolet light, cathode rays, and gamma rays. The target theory, hypothesizing electron rays hitting a microbial cell cause vital cell atoms to ionize,'" ! has been used to explain the microbiocidal effect of ionizing radiations (2). In this connection, Hollaender (3) has reported that, when germi- cidal effectiveness of ultraviolet is plotted against wavelength, the resulting curve resembled the absorption curve for nucleic acids. Mercury vapor sources of ultraviolet are classified (3) as either high- pressure (400-60,000 mm Hg) or low-pressure (0.004-0.02 mm Hg) lamps. The peak effectiveness of ultraviolet for microbiocidal activity has been shown by Luckiesh (4) to be at a wavelength around 2600 A, falling virtually to zero at 3200 A. Since low pressure mercury vapor

194 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS lamps exhibit a high output of radiation at 2537 A, this type of lamp is very efficient and is most commonly used industrially about 90% of the emittance from these lamps is microbiocidal. Studies conducted by Koller (5) showed that the killing power of UV is virtually unaffected by temperature in the 5-37øC range. While the shape of the ultraviolet effectiveness curve is generally independent of the type of bacteria, the tendency to spore formation does greatly influence the responses in specific cases. Thus the spore-forming B. subtills is about 5-10 times as resistant to UV as E. coli. Molds and yeasts are usually 100-1000 times more resistant than bacteria. For ex- ample, to obtain a 0.0001 survival ratio in water, a UV exposure of 24,000 uw-sec/cm • would be required for bacterial spores and 192,000 uw-sec/cm • for fungi. "Survival ratio" is the fraction of the number initially present which survives UV radiation. Koller (5) also notes that, in order to sterilize water effectively, the water must have a high transmission for UV. In other words, the water must be free from suspended matter which might shield microbes from radiation. The UV lamps may be installed in reflectors mounted over the water surface. The tank should be deep enough to absorb practically all the UV, since radiation absorbed by the walls is wasted. Arrange- ment of the water inlet and outlet should assure thorough mixing. The degree of disinfection, the survival ratio, depends upon the intensity of the source, the transmission depth, and the rate of water flow. An interesting point, also noted by Koller (5), is helpful to the cosmetic chemist: Those bacteria surviving irradiation are more sus- ceptible to subsequent cidal treatment, being more easily killed by mild disinfectants and exhibiting increased sensitivity to heat. It may be useful now to describe a typical water sanitizing system employing ultraviolet radiation. Our plant employs such a process that has been in successful operation for a number of years. The deionized city water is continuously recirculated from two 5000 gallon storage tanks through an 85 gallon stainless steel UV exposure tank at the rate of 180 gallons/min. The water bed in the exposure tank is 25 cm deep, 90 cm wide, and 91 cm long. Baffles are installed in the tank to decrease the velocity of water flow at the bottom of the tank. This increases UV exposure time at the bottom. Mounted about 30 cm above the exposure tanks are seven General Electric (90 cm long) 30-watt UV lamps. These mlaps are spaced 13 cm apart and have specular aluminum reflectors. The lamps are low-pressure mercury lamps having a rated 4000 hour life. Based on six lamps being operative, the calculated UV