Effect of environmentally relevant concentrations of potentially toxic microplastic on coastal copepods

Tire wear particles (TWP) are both abundant and potentially toxic types of microplastic (MP) in the coastal ocean. We tested the effects of TWP type (new tires, old tires, rubber granules from artificial turfs) and concentration (10-10,000 TWP L^-1) on feeding, reproduction and fecal pellet production of two common coastal copepods at high (400 μg C L^-1) and low (40 μg C L^-1) food concentration consisting of a cryptophyte Rhodomonas sp. We did not observe any effect of TWP on copepods at environmentally relevant concentrations of <10 TWP L^-1. At TWP concentrations that were >100 times higher than the MP concentrations measured in coastal waters, food concentration, copepod feeding mode, TWP concentration and TWP type interacted to influence copepod feeding and pellet production, while reproduction was unaffected. Our results suggest that TWP at the current measured concentrations in the ocean environment is not likely to be a threat to the common coastal copepods.