Soil enzyme activities and bacterial communities respond to co-exposure of butyl benzyl phthalate and TiO2 nanomaterials: Earthworm-mediated effects

Abstract

Phthalic acid esters (PAEs) are widely used due to their advantageous properties, which enhance the durability, flexibility, and transparency of plastic products. Nanomaterials are also commonly used in plastic additives and agricultural fertilizers. However, both are easy to fall off, diffuse, and release into the environment during production, use, and disposal. The adsorption and transportation of PAEs by nanomaterials may jointly affect soil health. However, less attention is paid to the soil microorganisms caused by co-exposure between PAEs and nanomaterials, especially mediated by earthworms. The present study investigated the effects of BBP (1 mg kg⁻¹) and nTiO₂ (1 mg kg⁻¹), alone and in combination, on soil enzyme activities, microbial composition, and bacterial community diversity, with and without mediation by the earthworm Metaphire guillelmi. Results showed that co-exposure to BBP and nTiO₂ activated enzyme activities in earthworm-mediated soil. Both contaminants, individually and combined, altered the composition, distribution, diversity, and complexity of the soil bacterial community mediated by earthworms. Bacteroidetes, Proteobacteria, and Actinobacteria were the dominant phyla. However, the complexity of soil bacterial community networks decreased. The findings highlight the importance of considering co-exposure and soil fauna mediation when evaluating the ecological impacts of emerging contaminants and fill the lack of ecotoxicity data on the co-exposure of PAEs and nanomaterials, thus promoting the design and synthesis of safer and more efficient nanomaterials.