Good point. Legos are made of acrylonitrile butadiene styrene, a type of plastic. Unfortunately, this type of plastic does not do well with salt water. It can deform and possibly just destroy these Lego bricks. Including the fact that these Legos have been in the water for 25 years, they have probably softened to the point that stepping on one would immediately break it. Most fish have also eaten this, probably mistaking it for small life forms, lowering the chances of stepping on one, or even finding it.
The sad thing about this is that Ukraine is looking for allies, to help keep their country alive. The only problem is that Russia has WoMD, and most countries are too afraid to go against Russia; nuclear weapons can now violently decorate more than just a city. Without allies, Ukraine will fall into the hand of Russia. Let God have mercy on Ukraine.
I hate to break it to you, but this technology only works for metallic substances (Specifically strong aluminum or steel) and not anything else, due to the fact that it changes the chemical makeup of the car. If it were possible to chemically change the color or fabric on command, your shoes may be changing in the near future. Until then, we must come up with a new technology for chemical changing.