Breaking ground: The effect of leachates from conventional and biodegradable mulching films on plants

The increasing use of plastics in agriculture, for instance mulching film, contributes to plastic residues in soils. Biodegradable plastics have been considered as an alternative to conventional plastic due to their assumed faster degradation rate. Both plastic types undergo weathering processes and leach breakdown products into the environment. Until now, little is understood about the effects of these leached chemicals on plant health. This study investigated the impact of artificially weathered plastic leachates on four widely cultivated crops: the monocots barley (Hordeum vulgare) and wheat (Triticum aestivum), and the dicots carrot (Daucus carota) and lettuce (Lactuca sativa), by comparing conventional low linear density polyethylene with a biodegradable starch-polybutylene adipate-terephthalate blend. Effects on plant growth were tested on germination and early development (acute) and in a chronic pot-plant setup (only lettuce and barley), using environmentally relevant concentrations. Limited effects were found, with the root length of both monocots and dicots being the most affected in both experiments. Interestingly, an increase in root length was observed in barley for both exposures, while the root system of lettuce increased in the acute experiment. In addition, lettuce seedlings showed a decrease in shoot fresh weight. During chronic exposure the plant defence mechanisms were upregulated in both plants for both plastic types, highlighting that exposure to leachates causes stress to plants. Our work is one of the first to compare directly the effects of leachates from conventional and biodegradable plastics on plants, thereby providing important new data in this rapidly evolving field of research.