Photochemistry and Photobiology, zyxwvutsrqpon Val. zyxwvutsrqpon 6 1, zyxwvutsrqpon No. 3, pp. 276-280, 1995 Printed in the United States. All rights reserved 003 1-8655193 $05.00+0.00 zy 0 1995 American Society for Photohiology CHANGES IN TRANSMISSION CHARACTERISTICS OF POLYMETHYLMETHACRYLATE AND CELLULOSE (111) ACETATE DURING EXPOSURE TO ULTRAVIOLET LIGHT STEEF F. STEENEKEN, ANITA G. J. BUMA* and WINFRIED W. C. GIESKES Department of Marine Biology, Biological Centre, P.O. Box 14, 9750 zyxwv AA Haren, The Netherlands zyxw (Received 31 May 1994; accepted 17 October 1994) Abstract-Ultraviolet-transparent polymethylmethacrylate (PMMA) and cellulose (111) acetate (CA) (often used as a cut-off filter in UVB [280-320 nm] biological effect studies) were exposed to a 20 W Philips TL 12 lamp to examine changes in transmission characteristics due to UVB exposure. Trans- mission of UVB and biologically weighted UVB (UVBBE(DNA)) through PMMA were similar, 88.3 and 83.5%, respectively. The absorption characteristics of PMMA did not change with time at any of the UV irradiance levels applied. However, transmission of UVB and UVBBEpNA)through new CA differed considerably: 59% Venus only 1 1 O/o, respectively. Also, spectral absorption characteristics changed with time due to degradation of CA, at a rate that was dependent on the incident UVB irradiance. The decrease in transmission through CA of both UVB and UVBBEpN,) can be described by exponential functions. The CA that was wrapped around the UV lamp showed dramatic changes in UV absorption over the first few hours of use. However, when CA was placed at a longer distance from the light source initial degradation was less. It is concluded that PMMA can be applied in UV effect studies as a reasonable alternative for quartz. The CA should, however, be used with care, because the large transmission decreases that were observed strongly hamper an accurate calculation of (biologically weighted) UVB dose rates. INTRODUCTION Duc to stratospheric ozone layer depletion, an increasing number of research groups have undertaken laboratory and outdoor experiments using artificial UV sources to measure the influence of UVB (280-320 nm)t radiation on cell com- ponents, organisms and ecosystems. These light sources are used in combination with UV-transmitting materials, in- cluding UV-transmitting culture vessels and filters. For most experiments, an accurate UV dosimetry is essential and, therefore, both the lamp output and the transmission char- acteristics of the applied materials should remain constant. Here, several problems may arise. First, initial lamp emission is not always stable, so that new lamps must be “aged” before use.’,’ Second, special filters are used routinely to eliminate the ecologically nonrelevant UVC (200-280 nm) radiation that is present in many UVB lamps. A popular UVC blocker is cellulose (111) acetate (CA). The disadvantage of CA is that its transmission changes with time as a result of UV exposure, resulting in a shift in intensity and in spectral composition.2 This phenomenon might strongly hamper an accurate calculation of biologically ef- fective dose rates (UVBBE). In order to avoid problems as- sociated with transmission changes, CA is often replaced after *To whom correspondence should be addressed. tAbbreviations: CA, cellulose (111) acetate; IL, International Light; PMMA, polymethylmethacrylate; UVA, ultraviolet A (280-400 nm); UVB, ultraviolet B (280-320 nm); UVBBE(DNA,, biologically effective UVB weighted with the DNA action spectrum of Setlow normalized at 300 nm; UVC, ultraviolet C (200-280 nm). 5-12 h of US^,^-^ or the material is “preburned” for 5-10 h before use.“’ Even though CA is commonly used in UV studies and though the time-dependent changes in transmis- sion as a function of UV exposure were expected to be large, these changes have so far not been described accurately. Quartz is often used as the material for manufacturing cell suspension containers for laboratory and outdoor UV effect studies. Because quartz transmits UV completely, it is very suitable for studies in natural sunlight. However, when using artificial UV sources, a combination with a UVC blocking filter is required since quartz also transmits UVC. Quartz is expensive and fragile. Therefore it seemed useful to look for a reliable alternative material for routine or large-scale use in UV effect studies such as polymethylmethacrylate (PMMA), whose transmission appeared reasonably stable over time. The present work was undertaken to analyze time-depen- dent changes in transmission of CA and UV-transparent PMMA exposed to artificial UVB in order to describe changes in UVBBE-DNA) given to biological samples during long-term UVB exposures. MATERIALS AND METHODS Light conditions and measurements. During all experiments, Phil- ips (TL 12/20 W) lamps were used as the artificial UV source. Lamp emission changes rapidly during the first 40 h of use: we recorded a reduction of 15% of the initial intensity. No significant differences were found in total UVB irradiance or spectral composition oflamps that had been burned for 200-400 h (data not shown). Therefore lamps were used for the experimentsonly after 200 h of preburning. Incident UVB radiation was measured routinely with a UV meter (International Light [IL] 1400a: probe SUL 240 #2906; diffuser W #5682; filter UVB-1 zyxw #lOSSS). The emission spectrum of the lamps 216