Slicking the light fantastic

Using sunlight to remove oil from polluted beaches.

Following the disastrous spill from the oil tanker Prestige in November 2002, scientists in Barcelona, Spain, have developed a system for removing oil from rocks and sand that is much faster than conventional methods. Current Fenton-type systems use high concentrations of hydrogen peroxide and require between one and three hours to be fully effective. The system described by Jos? Bourdelande and colleagues from the Universitat Aut?noma de Barcelona, uses low hydrogen peroxide concentrations (10 per cent) with iron salts and the process is complete in only eight minutes in natural light or 15 minutes in the dark.

The Prestige disaster was particularly poignant for Bourdelande as one of the beaches affected, Vidiago’s beach, was near the village of Llanes where he was born and he had spent much time playing there as a child. Reflecting on the event and how it inspired him as he watched it unfold on television he said that ’at that moment, I asked myself what part of the scientific knowledge acquired over 25 years could be devoted to accelerating degradation of the oil’. The answer to this question was to use an iron salt [Fe(NH₄)(SO₄)₂], hydrogen peroxide and sunlight (or a lamp). Bubbles of oxygen literally blast the oil off contaminated rocks dipped into this solution, quickly leaving a completely clean surface and an oily foam which floats to the top and can be sucked off. Rocks too large to treat in this way have to be sprayed with a more concentrated solution and then scratched clean. Other salts were tested, including sodium salts, obviously in abundant supply on beaches, but they cleaned the contaminated rocks much more slowly; the analogous sodium salt system took a relatively lengthy 27 minutes.

Commenting on the work, Silvia Braslavsky from the Max-Planck-Institut f?r Bioanorganic Chemie in M?lheim, Germany, said: ’the method proposed here is very simple, fast, cheap, and environmentally friendly. It is very satisfying seeing the application of photochemical knowledge to solve some very obnoxious environmental questions’. Looking towards further applications of their technique Bourdelande pointed out that ’at present, only fuel from the oil tanker Prestige has been tested. Other fuels with different compositions have to be tested and the scale increased’. It will be interesting to see how this work progresses.

Steven Evans