Growth Inhibition of marine microalgae by water-soluble extracts from automobile tires and identifying key chemical contributors to toxicity.

Automobile tires are a major source of pollution, releasing complex mixtures of chemicals into aquatic environments. Although the toxicity of tire leachate has been frequently documented, the specific chemical drivers affecting marine microalgae remain largely unidentified. This study investigated the effects of water-soluble leachates from two passenger car tires (Tire A and Tire B) on four marine phytoplankton species: the diatoms Skeletonema costatum and Chaetoceros lorenzianus, and the flagellates Chattonella antiqua and Karenia mikimotoi. Leachates from both tires inhibited growth and photosynthesis in all species, with flagellates showing greater sensitivity than diatoms. Tire B leachate exhibited significantly higher toxicity. Chemical analysis using liquid chromatography-mass spectrometry (LC-MS/MS) identified the vulcanization accelerator 1,3-diphenylguanidine (DPG) at 11.37 mg L− 1 in the more toxic Tire B leachate, which was not detected in the Tire A leachate. Subsequent exposure experiments with pure DPG confirmed its high toxicity, with 96-hour EC50 values for growth inhibition ranging from 0.93 to 2.59 mg L− 1. The flagellate Chat. antiqua was the most sensitive species. DPG was estimated to contribute 49.4–78.5% of the overall toxicity of Tire B leachate, confirming it as a primary toxicant for the tested species. A potential toxic mechanism is proposed in which the cationic form of DPG electrostatically interacts with negatively charged microalgae cell surfaces, disrupting membrane integrity. These findings identify DPG as a key toxicant from tire wear particles for foundational marine producers, warranting further investigation into its ecological risk.