treatment can't build her out the micro particles. that's set to change like switzerland many european countries want to do more to protect the aquatic environment by introducing a fourth purification step that removes micro particles by either chemical or mechanical means. to calculate how effective this fourth stage might be researchers are studying fish and algae. they've seen positive effects in laboratory tests especially in the development of fish embryos . experiments with tiny freshwater crustaceans shows similar results and vertebrates like that. are vulnerable to micro contamination to find out how the tiny creatures react the scientists put them in a testing apparatus with their favorite food for three weeks in different types of water. similar tests near sewage treatment plants have shown that crustaceans and