MERCK Sharp & Dohme (Ireland) has invested over £30 million since the mideighties in the continuous upgrading of its environmental systems, the company said yesterday. The plant at Clonmel, Co Tipperary, has been 21 years in operation this month. The general manager, Mr Declan Buckley, said the company is very proud of the contribution it has made to the local and national economy. The company employs 350.