Evidence for phytotoxic effects of cellulose acetate in UV exclusion studies

Abstract

Cellulose diacetate (CA) has been widely used in UV-B enhancement studies and has also been used along with Aclar and Teflon in UV-B exclusion studies. In recent UV exclusion studies conducted at Beltsville, MD under solar UV, 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 in window boxes under the following four combinations (top layer/bottom layer): CA/CA; CA/T; T/CA; and T/T, one layer on top of the other. 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, 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 manufacture of CA or some breakdown product. To avoid possible confounding effects from use of CA and to obtain maximum transmission of UV and visible radiation, we recommend that Teflon or Aclar be used in UV exclusion studies.