5284
Through this assessment , the authors found that a mixture containing the ions Ca ( + ) , Mg ( + ) , HCO 3 ( - ) , and SO 4 ( - ) , as measured by conductivity , is a common cause of extirpation of aquatic macroinvertebrates in Appalachia where surface coal mining is prevalent .
 Ca ( + ), Mg ( + ), HCO 3 ( - ), SO 4 ( - ), coal
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Ca ( + ), Mg ( + ), HCO 3 ( - ), SO 4 ( - ), coal