Presence of humic acid in the environment holds promise as a potential mitigating factor for the joint toxicity of polystyrene nanoplastics and herbicide atrazine to Chlorella vulgaris: 96-H acute toxicity

Abstract

Increasing amounts of amino-functionalized polystyrene nanoplastics (PS-NH₂) are entering aquatic ecosystems, raising concerns. Hence, this study investigated 96-h acute toxicity of PS-NH₂ and its combination with the pesticide atrazine (ATZ) in the absence/presence of humic acid (HA) on the microalgae Chlorella vulgaris (C. vulgaris). Results showed that both PS-NH₂ and PS-NH₂+ATZ reduced algal growth, photosynthetic pigments, protein content, and antioxidant capacity, while increasing enzymatic activities. Gene expression related to oxidative stress was altered in C. vulgaris exposed to these treatments. Morphological and intracellular changes were also observed. The combined toxicity of PS-NH₂+ATZ demonstrated a synergistic effect, but the addition of environmentally relevant concentration of HA significantly alleviated its toxicity to C. vulgaris, indicating an antagonistic effect due to the emergence of an eco-corona, and entrapment and sedimentation of PS-NH₂+ATZ particles by HA. This study firstly highlights the role of HA in mitigating the toxicity of PS-NH₂ when combined with other harmful compounds, enhancing our understanding of HA's presence in the environment.

Keywords: Antioxidant capacity; Eco-corona; Gene expression; Photosynthetic pigments; Protein content.