Effects of micro- and nano-plastics on community assemblages and dimethylated sulfur compounds production

Microplastics (MPs) and nanoplastics (NPs) pollution is broadly acknowledged as an urgent global issue threatening marine ecosystems. Most research on their impacts on plankton has been conducted indoors, with few field studies available. To bridge this gap, a microcosm experiment was performed to investigate how three concentrations (0.1, 1, and 10 mg/L) of 50 nm polystyrene (PS) NPs, 5 μm PS MPs, 20 μm polyethyrene (PE) MPs, and 20 μm polyamide 6 (PA 6) MPs affect zooplankton grazing, abundances of picophytoplankton, bacteria, viruses, and the yield of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP). Our results revealed that copepods and rotifers grazing increased DMS production and DMSP lyase activity (DLA). However, medium and high levels of PS, PE, PA 6 MPs and NPs exposure reduced ingestion rates, and concentrations of DMS, dissolved and particulate DMSP (DMSP_d,p) in copepods and rotifers, exhibiting both dose- and size-dependent effects. In the plankton microcosm, high concentrations of 50 nm PS significantly inhibited chlorophyll a concentrations and picophytoplankton abundances. Additionally, high concentrations of PS, PE, and PA 6 MPs/NPs significantly decreased DMS concentrations, DMSP_d concentrations, DLA, and DMSP-consuming bacterial abundances. Conversely, 50 nm and 5 μm PS at low concentration stimulated the growth of methylmercaptopropionate-consuming bacteria, viruses, and bacteria. These results declared the ecotoxicological influences of MPs and NPs on plankton communities and their implications for organic sulfur cycling.