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Uric acid from bird dropping

Effects on copper and bronze - 2009

University of Bologna Team Leader: Morselli Luciano - Professor - Dep. of Industrial Chemistry and Materials.

University of Bologna Research Group: Morselli Luciano - Professor - Dep. of Industrial Chemistry and Materials; Bernardi Elena - Research Fellow - Dep. of Industrial Chemistry and Materials.

Partner/Collaborations: P. Brimblecombe, D.J. Bowden - School of Environmental Sciences, University of East Anglia, Norwich (UK)

Context and objectives

Bird droppings are often considered as an agent of decay for outdoor materials and public money are spent annually cleaning up bird excrements.

The aesthetic and, sometime, functional damage (i.e. blockage of roof gutters) on monuments and buildings is evident, but the extent of the chemical damage is not so clear: so far, there are mixed opinions about the importance of bird droppings in damaging cultural heritage and relatively little research has been done on this topic.

The aim of this research has been to investigate the potential for bird droppings to chemically affect copper and copper alloys, which make such an important contribution to architectural elements of buildings and outdoor sculpture.

Methodologies and equipment

Laboratory investigation of the short-term effects of pure uric acid and real bird droppings on copper have been carried out ageing copper samples in a humidity cabinet. Analysis of real bird dropping stains from outdoor copper and bronze statues have also been performed. Colour change, erosion and secondary compound formation have been evaluated.

Results

Uric acid contained in bird droppings could cause appreciable damage to copper used in buildings and monuments, considering that uric acid chemically affects copper and bronzes by modifying the metal appearance and forming urates.

Uric acid corrosiveness increases when the acid remains wet, but its biodegradation under humid conditions seems to suggest a temporary corrosive action.

The role of water in enhancing corrosion by bird droppings appears of particular significance in management, suggesting that cleaning might be particularly appropriate if conditions are likely to remain wet.

For further details

  • E. Bernardi, D. J. Bowden, P. Brimblecombe, H. Kenneally, L. Morselli, The effect of uric acid on outdoor copper and bronze, Sci Tot Environ, 407(7) (2009) 2383-2389.