In today´s society, it becomes more and more important to reuse, recycle and return as much as possible of what we use, in order to reduce the use of the earth´s resources. Sludge is a waste product that is formed when we purify waste water and can be used as construction soil, as final cover of landfills or as fertilizer by spreading it on fields. Then it becomes a cycle of nutrients, just as you want it. Sewage sludge contains nutritional substances that you want to bring to agriculture but also it contains environmental and health-disrupting substances that exist in the society including heavy metals, pharmaceutical residues, pesticides and persistent organic substances. In addition, little is known about the cocktail effect. We received sludge from two sewage treatment plants and performed ecotoxicity tests which are a method that shows the total toxicity of a test. We saw the acute and chronic response of the organism Hetrocypris incongruens Ostracoda. The results showed a clear increase in the chronic response with more sludge added to the test.