Bull. Environ. Contam. Toxicol. (1995) 54:214--221 9 1995 Springer-Vedag New York Inc. i Environmental Contamination ;iand ~rbxicology Consumption and Degradation of 3H-Polyethylene/Starch Disks by Terrestrial Isopods T. A. Anderson, R. Tsao, J. R. Coats Pesticide Toxicology Laboratory, Department of Entomology, Iowa State University, Ames, Iowa 50011-3140, USA Received: 16 January 1994/Accepted: 30 July 1994 The recent development and commercial use of cornstarch and other additives in plastic formulations to promote degradability is potentially a valid approach for reducing the adverse impact of plastics in terrestrial and aquatic ecosystems. However, the rapid development of starch- based polyethylene plastics has exceeded our understanding of the biological properties of these compounds, such as whether these blended substances are actually more readily degraded and/or deteriorated than pure polyethylene (PE). In addition, the lack of standard tests and definitions regarding the fate of plastics in the environment has allowed the use of terms such as degradable by plastic manufacturers, while confusing consumers (Krupp and Jewell, 1992). Wool (1988) has conducted degradation/metabolism tests with a variety of macroinvertebrates, including crickets, snails, slugs, cockroaches, and millipedes. Changes in film appearance, as well as fecal examinations were used to confirm the extent of film degradation. In general, starch/PE films containing less than 10% starch were not consumed. Furthermore, it has been shown that the degradation of starch/PE films by insects can involve three stages: mastication, digestion, and exo-corporeal degradation. The stages include processes (physical, chemical, and microbial) which contribute to the destruction of the film as the film is ingested, digested, and excreted (Sahlin, 1988; Wool et al., 1989; Wool and Goheen, 1990). Recent studies in an aquatic environment indicated the potential importance of midge-fly larva (Dicrotendipes sp.) in biodegradation of plastic films containing starch (40%), PE, and polyethylene-co-acrylic acid (Imam et al., 1992). Previously, we reported on the primary degradation of a variety of PE films containing different percentages of starch (0%-50%) and other additives (pro-oxidant, oxidized polyethylene) using earthworms (Eisenia fetida, Lumbricus terrestris, Aporectodea trapezoides, Aporectodea tuberculata), cockroaches ( Periplaneta americana, Blaberus sp., Blattella Correspondence to: J. R. Coats 214