[1] FORTH RIVER PURIFICAT BOARD,EDINBURGH EH14 4AP,SCOTLAND
[2] BRITISH GEOL SURVEY,KEYWORTH NG12 5GG,NOTTS,ENGLAND
[3] UNIV NORTHUMBRIA,DEPT CHEM & LIFE SCI,NEWCASTLE TYNE NE1 8ST,ENGLAND
[4] UNIV LONDON IMPERIAL COLL SCI TECHNOL & MED,ROYAL SCH MINES,DEPT GEOL,LONDON SW7 2BP,ENGLAND