Types of Analysis to Detect Polychlorinated Biphenyls (PCB's)

Ask the Expert Question:

What types of analysis can be used to detect Polychlorinated Biphenyls (PCB’s)?

Experts Response:
PCB’s are normally reported on the basis of Aroclors, but can also be reported as congeners or homolog totals. The following will provide information on each.

Aroclors- Usually, seven to nine commercial mixes are evaluated and reported as total concentration for each Aroclor. This is always done by EPA Method 8082. There are some subtle differences among laboratories, but generally, the detection limit is determined by a statistical MDL, based on the analysis of seven low-spiked blanks. The RL must generally be above the MDL (usually by a minimum factor of 3), and must be supported by a valid calibration point. It is not uncommon for typical MDL’s to run from 0.1 to 0.5 ug/L, with RL’s running about 1 ug/L. This is the least expensive option for testing PCB’s.

Individual Congeners- Usually 12 to 64 individual compounds can be reported by method 8082 or the NOAA Status and Trends method.  As above for aroclors, detection limits are generally determined by a statistical MDL.  The RL must generally be above the MDL and must be supported by a valid calibration point. It is not uncommon for typical MDL’s to run from 0.3 to 0.8 ng/L, with RL’s running about 1 ng/L. This is the least expensive option for testing PCB’s congeners, although the price is considerably higher than PCB aroclors (above).

All 209 congeners, or any subset of them are also analyzed and reported by EPA Method 1668A or 1668B. The detection limit used here is a sample-specific signal-to-noise measurement performed for each analyte on the actual sample. Average detection limits run around 0.005 ng/L. Typical RLs run from 0.02 to 0.2 ng/L. This method is the most comprehensive and provides the lowest detection limits.  As a result, it is also the most expensive option for PCB analysis.

Homolog totals- These can be reported by a modification of EPA Method 8270. A homolog total is a result for all the congeners at a given level of chlorination. Typical detection limits from 0.0025 to 0.02 ug/L for individual homolog totals. The RL for the total of all homologs is 1 ug/L. This is the medium cost option compared with the other two methods.

If lower RL’s are needed, TestAmerica has a variety of options that can be explored such as higher sample volumes, clean hands/dirty hands techniques, etc.  These usually involve some modification to your sampling plan. 

Questions related to Mercury

Ask the Expert Question: 

What species of mercury is most commonly found in fish tissues?  Is it typically considered solid or is it dissolved mercury that they take in through their use of the water?

Expert Response: 

Methyl mercury is the most common mercury species that bioaccumulates in the food chain, but there have also been reports of other organo mercury species found in aquatic tissues. Although methyl mercury does have some water solubility, most of the methyl mercury accumulated in fish is from the food consumed by the fish rather than being absorbed directly from the water. So the mercury is ingested either as food or on solid particles consumed along with the food source.

Ask the Expert Question:

What is the solubility and volatility of methyl mercury?

Expert Response:

Physical properties for methyl mercury are available at this link:   http://www.scorecard.org/chemical-profiles/html/mercury.html.  The boiling point is about 357°C. Methyl mercury is considered insoluble in water. Measured concentrations in water are in the parts per trillion range or lower.

Ask the Expert Question:
What forms of mercury would you expect to see in an industrial scrap yard?

Expert Response: 

An industrial scrap yard could have a variety mercury species. Elemental mercury was commonly used in switches and other electrical equipment for many years. It was also common in thermometers and gas pressure measurement devices. Mercury was used in paint in various organic and inorganic forms. Mercury has also been a minor component in some metal alloys. Mercury was common in some batteries, lighting equipment and as an industrial catalyst. Thus, the specific mercury species would be highly dependent on the type of scrap brought in and how well segregated the scrap streams were.

 

Ask the Expert Question:

How well can the lab define the type of mercury that we are dealing with in the <100 ng/l range?

Expert Response: 

TestAmerica can measure total mercury down to 0.5 ng/L and methyl mercury down to 0.05 ng/L.  We do not currently have the capability to measure other mercury species.