An in vitro crop plant ecotoxicity test for agricultural bioplastic constituents

摘要

Plastic mulches are widely used in agriculture to improve production, mainly in vegetable crops. Their main drawback is the generation of residues that are hard to manage. Therefore the substitution of traditional plastics by renewable and biodegradable polymers is an environmentally friendly improvement. However, compounds released during (bio)degradation of the mulches may remain in the soil. Consequently, standard ecotoxicity tests are required to ensure the biomaterials' ecosafety. Unfortunately, ecotoxicity tests for terrestrial plants, and specifically for the plant species frequently cultivated with mulches, are poorly developed. Furthermore, most of these tests report seedling emergence and early plant growth, but germination and plant growth have different requirements, and plant growth inhibition by compounds not affecting germination has been frequently reported. Other limitations of ecotoxicity tests are related to environmental variability, interactions of soils/substrates with the chemicals, and to the limited monitoring of plant development over time, especially for roots. The aim of this work has been to develop an in vitro controlled system for testing the ecotoxicity of plastic constituents putatively delivered to the soil during mulch biodegradation on crop plants. Germination and growth of lettuce and tomato were monitored over time in response to adipic, succinic and lactic acids, and to 1,4-butanediol, in concentrations 5-500 mg l~(-1). Although germination was not influenced by most treatments, significant effects were manifested later in plant development. The sensitivity of the system was higher than in standard short-term assays. Results in lettuce and tomato were not substantially different, but indicative of the need to test the precise species targeted. Overall, adipic acid inhibited growth, succinic acid had no effect, and butanediol enhanced growth to some extent. Lactic acid requires further investigation. We highlight the convenience of the system for monitoring root development; roots were more sensitive to the chemicals than shoots and leaves. Proline is shown as a potential marker for ecotoxicoxicity. The in vitro system is proposed as a simple and reliable method to test for ecotoxicity in terrestrial plants.