Submitted to: Environmental and Experimental Botany
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/12/2003
Publication Date: 1/14/2004
Citation: Krizek, D.T., Mirecki, R.M. 2004. Evidence for phytotoxic effects of cellulose acetate in UV exclusion studies. Environmental and Experimental Botany. 51(1):33-43. Interpretive Summary: Since the early 1970's there has been growing concern about the possible adverse effects of stratospheric ozone reduction and the accompanying increase in ultraviolet-B (UV-B) radiation. The plastic film cellulose diacetate (CA) has been widely used in UV-B enhancement and UV-B exclusion studies under field and controlled-environment conditions to remove wavelengths below 290 nm. However, in the course of conducting UV exclusion studies outdoors in window boxes covered with CA or in Plexiglas chambers lined with CA, curvature of the cotyledons and yellowing along the margins of the first true leaves were observed in `Ashley' cucumber, a cultivar found previously to be resistant to elevated UV-B. At the same time, seedlings grown under polyester film to exclude UV-B and those grown without any covering were free of visible injury. These findings suggested that the CA filter itself may be causing damage. To test this idea, an UV exclusion study was conducted in which CA and/or Teflon (T), both UV-B and UV-A transmitting films, were used to cover window boxes in the following four combinations, one layer on top of the other: CA/CA, CA/T, T/CA, and T/T. The objective was to compare growth and injury responses of cucumber plants grown in window boxes under the four combinations of CA and T filters with those grown in unfiltered window boxes in open air. When CA was used as the bottom filter (CA/CA and T/CA), the plants were stunted and showed visible injury. When T was used as the bottom filter (CA/T and T/T), or the plants were grown in open air without any covering, they plants produced vigorous growth and were free of injury. These findings suggest that damage is caused by the CA itself rather than by solar UV-B radiation, possibly as a result of inadvertent release of a substance known to be used in the manufacture of CA or some breakdown product. This is the first report of CA toxicity in UV studies and should be of interest to researchers and policy makers involved in assessing the effects of global change, manufacturers in the plastics industry, and agencies concerned with examining the biological effects of plasticizers and other volatile organic compounds.
Technical Abstract: Cellulose diacetate (CA) has been widely used in UV-B enhancement and UV-B exclusion studies. In recent UV exclusion studies conducted at Beltsville, MD under field conditions, cucumber plants were found to develop marginal chlorosis under CA filters. To test the hypothesis that CA was responsible for the phytotoxic effects observed, an experiment was conducted in which CA and/or Teflon (T), both UV-B and UV-A transmitting films, were used to cover `Ashley' cucumber plants grown from seed under ambient solar UV radiation in window boxes under the following four combinations (top layer/bottom layer): CA/CA; CA/T; T/CA; and T/T. When CA was used as the bottom filter (CA/CA and T/CA), the plants were stunted and showed marginal chlorosis and epinasty of the cotyledons and first true leaf. However, when T was used as the bottom filter (CA/T and T/T), or the plants were grown in open air without any covering under ambient solar radiation, the plants produced vigorous growth and were free of injury. These findings suggest that toxicity is caused by the CA itself rather than by solar UV radiation, possibly as a result of outgassing of a phthalate known to be used as a plasticizer in the manufacturer of CA or some breakdown product. This is the first report of CA phytotoxicity in UV studies.