It can take up to 1,300 years for LEGO bricks to break down in the ocean, according to new research published in the journal Environmental Pollution. The pieces of the iconic children’s toy, which is made from a strong plastic material called acrylonitrile butadiene styrene (ABS), are commonly found in ocean trash hotspots and wash up on shores across the globe by the thousands. Scientists say the findings are another reminder for people to be careful of how they dispose of everyday household items.

“LEGO is one of the most popular children’s toys in history and part of its appeal has always been its durability,” Andrew Turner, an environmental scientist at the University of Plymouth in the United Kingdom and lead author of the new study, said in a statement. “However, the full extent of its durability was even a surprise to us.”

For the study, Turner and his colleagues analyzed 50 pieces of weathered LEGOs collected from beaches, confirming their age, and compared them to unweathered LEGO sets from the 1970s and 1980s. They were able to determine how much the weathered LEGOs had been worn down by ocean waves, sand, and salt over time. They then projected it takes between 100 and 1,300 years for the bricks to completely disintegrate.

“The pieces we tested had smoothed and discolored, with some of the structures having fractured and fragmented, suggesting that as well as pieces remaining intact they might also break down into microplastics,” Turner said.

LEGO has acknowledged the environmental impact of its products, and has launched a goal to make its bricks from more sustainable sources by 2030. ABS, which the bricks are currently made out of, is a petroleum-based plastic. LEGO said it will start developing bricks using sugarcane-based polyethylene, aiming for the same rigidness and play durability as the original bricks, as well as improving recycling and reusing of old LEGO plastic.