An estimated 3 percent of plastic bags used to carry home groceries and other items end up in creeks, rivers, lakes, and oceans where ducks, turtles, and other wildlife choke on the plastic debris that they mistake for food. sociologists call this situation

These would be the externality costs of using the plastic bags. While they have the benefit of allowing us, as consumers of groceries, to be able to take the items home easier, they also have the unintended (external) costs of causing damage to wildlife who do not benefit from the use of the bags in any appreciable way.