answer:“First of all, only one hundred percent biodegradable latex balloons are used in mass releases. Research showed that these balloons degrade about as quickly as an oak leaf under similar conditions. But opponents argue that a balloon floating in the ocean would take a lot longer to degrade than it would on land. While it’s hard to know whether balloons that have turned up in the stomachs of dead marine animals caused their death, the presence of a ribbon would be a very useful piece of information. The other argument is that helium balloons are claimed to reach a height of anywhere up to ten kilometres before shattering into tiny little pieces. These pieces, it is said, would be too small to pose a threat to animals. Now the shattering effect sounds reasonable for two reasons. One is that atmospheric pressure is dramatically reduced at high altitudes, so a helium balloon expands as it rises and eventually explodes. If you inflate a balloon beyond its limits at room temperature, it will break into small pieces up to about ten centimetres long. But the elasticity of rubber decreases at very low temperatures so it is possible that helium balloons shatter into much smaller pieces as is often claimed. Unfortunately, no one has followed a balloon up to see what really happens up there as far as I know. And on top of that, you have to keep adding air without tying a knot to over-inflate a balloon down here at sea level. It’s hard to say whether the knot stays intact when a helium balloon explodes way up there.” Source