Testing for the presence of the chemicals is only the first step. Let the test evidence,  amount present, local , distance from test site to possible soureces, local records etc. Lead to an undeniable RIGHT source for this contamination.
Source guessing on a public stage is counterproductive unless your a pitchfork and torch salesperson. 
"It is the province of knowledge to speak and it is the privilege of wisdom to listen"........ on the bottom of an upper bunk.  DaNang Republic of South Vietnam