Ash and sulphur are the two main variables that influence coal quality and are therefore very important contractual
parameters in a coal supply agreement. Coal which is low in ash yield and sulphur content is considered as ‘cleaned
coal’. Nonetheless, combustion of coal is also known to release toxic trace elements, which are known or suspected to
be carcinogenic and may also cause respiratory problems, pregnancy complications, premature mortality and possibly
a wide range of health problems. The two traditionally used coal quality parameters have proven to be insufficient for
defining ‘cleaned coal’. This is evidenced by the low ash and low sulphur Balingian coals that is seen as relatively safe
in environmental terms, but still contains high concentrations of potentially hazardous trace elements which may pose
health and environmental threats during coal combustion. Therefore, a comprehensive assessment of coal quality should
also include information on concentration, spatial distribution and modes of occurrence of trace elements, particularly
the 15 potentially hazardous trace elements identified by the United States Clean Air Act Amendments (1990).