TXRF values would (I presume) be more reproducible with an omogeneous film

Dear Melissa, TXRF is a very versatile technique and is capable of analyzing wastewater directly, only homogenizing the possible suspended solids in micrometre sizes using ultrasonic techniques, or after acid digestion, usually in nitric / peroxide medium, to eliminate the suspended organic matter. Both analytical approaches are valid for TXRF quantifying the detected elements present by the conventional internal standard addition method. Thus, the first method is faster and avoids acid digestion, but the detection limits are worse. The second is more expensive, dangerous, but allows detection limits to be reached in the order of a few ppb (ng / mL) for the vast majority of metals detected. Good luck.

Yes, it is necessary to digest wastewater sample before analysis of heavy metal

Depends actually

Waste water that are slurry. May have metals locked up