The Christmas gifts have been delivered, and Secret Santa is done.

Now, the work begins for Optoro, a start-up company that aims to reduce the financial and environmental costs of another great holiday tradition: returns.

Americans returned $260 billion in merchandise last year, up more than 66 percent from five years ago, according to the National Retail Federation. And a quarter of that was during the holiday season.

As e-commerce sales surge and free return shipping becomes the norm, shoppers are set to return even more this year — a cycle that started in earnest on Monday, the first weekday after Christmas.

Little known to shoppers, however, is that a majority of returned items never make it back to retailers’ shelves. Instead, the items wind their way through liquidators, wholesalers and resellers, many of the purchases ending up in landfills. According to some estimates, as much as two million tons of returned items — most of it undamaged merchandise — are thrown away each year, enough to fill over 200,000 garbage trucks.