The construction sector generates a larger amount of waste each year. That is why new laws and rules, which regulate the management of such waste, are appearing continuously, in order to end the problem that these wastes cause by throwing into the environment, without any control or regulation. One of the main objectives of this project was to study both Finnish and Spanish legislation as well as the regulations, methods and treatments necessary for the use of these wastes as new by-products or raw materials. To determine if a particular type of waste is suitable for reuse, three samples of bottom ash provided by the company Lahti Energy, were treated by a leaching behaviour test. This test makes it possible to obtain some liquid samples from the previous solids. Then these liquid samples have been analysed through an ecotoxicological pilot test with Artemia Salina and in addition, a photometer was also used to determine the concentrations of chromium and copper present in the samples. The results of the tests indicate that although the three samples have some type of harmful substance for the environment, only sample number 2 exceeds the limits established by the Government decree (591/2006) of Finland and therefore cannot be reused. Also, it has been verified that the ecotoxicological test with Artemia Salina is a good option to determine the toxicity of the samples to be analysed.