It's not known at this time what they were exposed to but I suspect some type of interaction between chemicals.  
http://www.kswo.com/story/36690653/2-texas-lawn-care-workers-die-following-chemical-exposure
	
		
			
		
		
	
			
			http://www.kswo.com/story/36690653/2-texas-lawn-care-workers-die-following-chemical-exposure
 
				