Microplastics - tiny plastic particles less than 5mm long - were first identified in the ocean but are now known to be ubiquitous throughout the environment, within soil, air food and water. Recently, microplastics have been detected in human blood, placenta, and other tissues (liver, lung, colon) raising concerns about potential adverse health effects. This lecture reviews the science on microplastics and whether we should be concerned about them, compared with other known environmental hazards