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New method to eliminate ibuprofen from polluted waters using ultrasound
12 February 2009
An international team of scientists, in which researchers from the University of Barcelona (UB) have participated, has applied ultrasound treatment that enables ibuprofen to be eliminated from waters polluted with this drug. This method could be used in water purification plants, which would avoid the emission of pharmaceutical pollutants into rivers, lakes, seas and other surface waters.
The team of scientists at the laboratories of the Federal Polytechnic School in Lausanne, Switzerland has developed a novel method for eliminating pharmaceutical products from water. The substance chosen for the study was ibuprofen, as it is one of the drugs that appears with the most frequency in the analyses of waste waters due to its high consumption as an anti-inflammatory and analgesic.
"Pharmaceutical compounds are pollutant substances from the moment in which they maintain their pharmacological activity outside the environment for which they were designed", Fabiola Méndez-Arriaga explains to SINC. She is the co-author of the study and a researcher at the Department of Chemical Engineering in the University of Barcelona (UB).
The new technique consists of subjecting water polluted with ibuprofen to ultrasonic waves that are generated by a piezoelectric generator, which converts electrical energy into mechanical energy and is located at the bottom of the reaction tank. In this way the drug is totally eliminated.
During the application of ultrasonic waves to the polluted liquid a physical and chemical reaction is generated known as "sonolysis", in which water (H2O) is disassociated in highly oxidant radicals such as hydroxyl (-OH). This radical facilitates the oxidation and breaking down of ibuprofen into other low-molecular mass compounds.
How is this drug eliminated?
In this process, during which carbon dioxide (CO2) is produced, "cavitation bubbles" are generated. These bubbles look similar to those generated in boiling water, but they are microscopic in size, and a large quantity of energy accumulates inside the bubbles (up to a pressure of 200 bar and 2,000 oC in temperature).
"Ultrasonic waves are applied for half an hour and this enables up to 98% of ibuprofen to be broken down and after two hours of irradiation the drug is eliminated completely and transformed into biodegradable substances which can be removed or eliminated in a conventional purification plant", states Méndez-Arriaga.
"Although this is not the case with ibuprofen", remarks the researcher, "sometimes during the breaking down process of the pharmaceutical compounds, substances more toxic than the original compound itself are produced. For this reason the evolution of this toxicity has been studied using other advanced oxidation techniques and their hybrid combinations".
One of these techniques is heterogeneous photocatalysis (a reaction in which a semiconductor such as titanium dioxide absorbs UV light to break down the organic pollutants into CO2, water and mineral acids, which are harmless to the environment). Another technique is the photo-Fenton reaction in which iron salts, oxygenated water and light are used to break down the compounds).
Méndez-Arriaga points out that the final objective of these techniques is to eliminate pharmaceutical compounds from the environment, where they end up after consumption, thanks precisely to the chemical properties they were created with, namely their biological resistance and high solubility.
Pharmaceutical products or their metabolised forms are released into the environment through excretion (domestic, veterinary or hospital), disposal of unused surplus or expired products and also with the waste from drug manufacturing plants.
Consequences for the fauna
In nature it is the fauna which is mainly affected by these compounds. Scientists from North American universities have shown, for example, that exposure to anti-depressants delays the development of the legs in tadpoles and that pharmaceutical products and toiletries, such as perfumes, cause toxic effects in the swordfish and other marine species.
Méndez-Arriaga''s study highlights that it is very difficult to know the quantity of pharmaceutical pollutants found in water; however it can be asserted that it is a world-wide health problem, for which there is still no defined legal framework.