Ecological risk assessment of PBAT/PLA mulch-derived microplastics on vegetable growth using a species sensitivity distribution approach

Biodegradable mulch films (BDMs) are considered a promising alternative to conventional polyethylene films, yet their ecological impacts remain poorly characterized. This study evaluated the ecotoxic effects of two biodegradable microplastics (Bio-MPs), namely WBio-MPs and BBio-MPs, derived from white and black poly(butylene adipate-co-terephthalate)/polylactic acid (PBAT/PLA) mulch films, on the growth of eight vegetable species commonly cultivated in Southwest China. The plant height, chlorophyll content, shoot biomass and root biomass were employed as testing endpoints. Dose-response relationships of all endpoints under Bio-MPs exposure were well fitted by a three-parameter logistic model, with shoot biomass exhibiting the lowest 50 % inhibitory effective concentration (EC₅₀). Species sensitivity distribution (SSD) curves based on the shoot biomass EC₅₀ values indicated that green pepper, tomato, spinach and radish were sensitive to both Bio-MPs. The hazardous concentration for 5 % species (HC₅) was 2.60 g·kg⁻¹ for WBio-MPs and 4.81 g·kg⁻¹ for BBio-MPs, which substantially exceeded the dose of BDMs with a thickness of 0.02 mm applied continuously for ten years. Considering the biodegradability of BDMs and local mulching frequency, the average steady-state risk quotient (RQ_ss) values ranged from 0.031 to 0.077 for WBio-MPs and from 0.051 to 0.128 for BBio-MPs, suggesting a low to moderate potential ecological risk to vegetable growth. This is the first study to quantify toxicity thresholds of Bio-MPs on vegetable growth and to assess their ecological risks using SSD and risk quotient methods. It provides empirical evidence and technical support for the risk assessment and management of BDMs in agriculture.