15131
In a cross - sectional design , 292 schoolchildren living around a shipyard area , known to be contaminated with lead from shipyard industry , were examined to verify the association between lead exposure and periodontal health .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None