This work aims to contribute to the

This work aims to contribute to the knowledge of the impacts of olive oil waste discharge to freshwater and oligotrophic marine environments, since the ecological impact of olive oil wastes in riverine and coastal marine ecosystems, which are the final repositories of the pollutants, is a great environmental problem on a global scale, mostly concerning all the Mediterranean countries with olive oil production.

Messinia, in southwestern Greece, is one of the greatest olive oil production areas in Europe. During the last decade around 1.4 × 106 tons of olive oil mill wastewater has been disposed in the rivers of Messinia and finally entered the marine ecosystem of Messiniakos gulf. The pollution from olive oil mill wastewater in the main rivers of Messinia and the oligotrophic coastal zone of Messiniakos gulf and its effects on marine organisms were evaluated, before, during and after the olive oil production period. Elevated amounts of phenols (36.2–178 mg L− 1) and high concentrations of ammonium (7.29–18.9 mmol L− 1) and inorganic phosphorus (0.5–7.48 mmol L− 1) were measured in small streams where the liquid disposals from several olive oil industries were gathered before their discharge in the major rivers of Messinia. The large number of olive oil units has downgraded the riverine and marine ecosystems during the productive period and a period more than five months is needed for the recovery of the ecosystem. Statistical analysis showed that the enrichment of freshwater and the coastal zone of Messiniakos gulf in ammonia, nitrite, phenols, total organic carbon, copper, manganese and nickel was directly correlated with the wastes from olive oil. Toxicity tests using 24 h LC50 Palaemonidae shrimp confirm that olive mill wastewater possesses very high toxicity in the aquatic environment.