Can terrestrial isopods (Isopoda: Oniscidea) make use of biodegradable plastics?

摘要

Biodegradable plastics more and more replace conventional plastics, because they are considered environmentally friendly. Soil macro-invertebrates have been demonstrated to consume some of these biodegradable plastics, but studies usually do not go beyond notice of consumption and possible shortterm ecotoxicological effects on organisms. This study uses the terrestrial isopod Porcellio scaber as a soil detritivore model and three biodegradable plastics (starch-, cellulose- and poly(3-hydroxybutyrate) (PHB)-based films) to evaluate both the contribution of isopods to the disintegration of biodegradable plastics and the effects of plastic-feeding on isopod ecology. Consumption rate of starch-based plastic was similar to that of leaf litter (mainly beech) and on average higher than those of the other two plastic types. Digestibility, however, was highest for cellulose-based plastic. HPLC results show that isopods break down starch-based plastic into maltose and glucose, and cellulose-based plastic into cellobiose. No glucose was present in feces of isopods having fed cellulose-based plastic, either for inability of breaking down cellobiose into glucose, or due to a rapid uptake of the glucose by isopods. Growth rates were negative, but not significantly different from zero, for all food sources; cellulose-based plastic caused the highest biomass loss to isopods. Toughness of starch-based plastic diminished over time when litter and/or isopods were present. Cellulose-based plastic increased in toughness over the disintegration experiment, possibly affecting its consumption by isopods. Overall, isopods increased the disintegration rates of starch- and cellulose-based plastics, but no PHB film was consumed, and its disintegration rate was low. We conclude that starch-based plastic is comparable to a natural low-quality food source (e.g., beech litter), and isopods would probably consume starch- and cellulose-based plastics in the field