While photos of littered beaches and floating garbage patches are unsettling, perhaps the most problematic plastic is barely visible to the naked eye. Called microplastics — chunks less than 5 millimeters across — these bits have been detected everywhere from Arctic sea ice to national parks. These pervasive particles are harder to clean up than larger plastics, allowing them to accumulate in the environment and inside living creatures. As their quantities rise, UC Davis researchers are racing to understand the risks they pose to ecosystems, animals and humans.  “If these things are getting into our drinking water sources, we should really care,” said Katie Senft, a staff research associate at UC Davis’ Tahoe Environmental Research Center, “especially if they’re not going anywhere and we don’t know the long-term implications.”