Low-Level Mercury

Controlling Contamination: Focus on Sampling Procedures

Although laboratories are concerned with controlling sources of mercury contamination, experience has taught us that perhaps a bigger problem in obtaining reliable low-level mercury data is controlling contamination during sampling. The efforts necessary to control contamination increase significantly as detection limits and sample concentrations decrease.

Mercury tends to "stick" to surfaces so pumps and tubing used for composite sampling can be reservoirs of contamination. Equipment exhaust and dust can also be contributors. Even the sampling crew themselves can be a source of mercury contamination. In addition to worrying about contamination on hands and clothing, for very low level mercury sampling, your breath can contribute measurable amounts of mercury, particularly if you have amalgam dental fillings.

It might seem like collecting a reliable sample is an impossible dream, but it is possible to obtain a reliable sample for low level mercury by paying attention to hygiene. EPA method 1669: Sampling Ambient Water for Trace Metals at EPA Water Quality Criteria Levels (EPA 821-R-95-034) describes a "clean hands-dirty hands" procedure that has been shown to be effective. How rigorously you need to follow this procedure depends on the type of sample being collected, the sensitivity or detection limits desired, and the environment in which the sample is being collected.

The wastewater permits program is developing guidance for collecting samples for compliance. When this guidance is completed, it will be posted on the program's website.

For questions related to permit compliance, contact Tom Mugan (608.266.7420).