Mercury / Low Level Mercury

Mercury testing in water and in soil is becoming more common due to contamination in the environment. The presence of mercury in our waterways is a real threat to maintaining a clean environment. As NPDES permits are renewed, States are placing progressively lower permit limits on mercury in water. In response, low level mercury testing is replacing traditional high level mercury analysis. EPA method 1631 or EPA 245.7 allow for detection of low level mercury in water and in soil.

Teklab is a NELAP accredited environmental testing laboratory that performs low level mercury (Hg) testing in wastewater effluent, groundwater or special waste samples. Due to its increased sensitivity, low level mercury testing is rapidly replacing traditional Hg methods. This newer technology meets the new MCLs for the Clean Water Act.

Our low 0.5 part per trillion (ppt) reporting limit satisfies the requirements for EPA method 1631. We routinely perform specialty analysis like low level mercury testing by EPA Method 1631 or EPA 245.7 for other environmental testing labs. Our metals testing lab performs these methods using a state of the art Leeman Labs HYDRA AF Gold mercury analyzer.

Whether you are testing for high or low levels of mercury in your water or soil samples we recommend that you contact a NELAP accredited environmental testing laboratory for all your regulated environmental lab needs. In fact, we recommend that you select a NELAP accredited lab for all of your environmental testing needs.



This procedure is applicable to low level mercury testing in filtered and unfiltered water samples. It is done by oxidation, purge and trap, de-sorption, and cold vapor atomic fluorescence spectrometry (CVAFS). The reporting limits for this method is 0.5ppt for mercury and is determined on aqueous/water samples, ranging from 0.5-100ng/L. The low level mercury MDL has been determined to be 0.2ppt. Reference for this procedure is EPA 1631E.

Sample Collection, Preservation & Storage

Collection Bottle Preparation: Typically a case (24jars) of 250mL jars is received, marked open, recorded and numbered. Jars are leached with a 1:1 HCL solution for a minimum of one hour. Jars are then rinsed with de-ionized water and tightly capped. One jar out of 24 is filled with mercury free reagent water and bromine chloride, and treated like samples in order to verify clean lots of sample/ field blank jars.

When a bottle order is received from a client these jars are leached, rinsed and 1.25mL of bromine chloride added. Jars are labeled for low level mercury testing and given to login for proper packaging in plastic bags, etc. for shipping or pick up.

When jars go out without bromine chloride, samples must be preserved within 48 hours of collection with BrCl onsite at Teklab. Per every 100mL of sample, 0.5mL of BrCl should be added. After preservation samples have 90 days to be analyzed.

Approved collection procedure for EPA 1631E is EPA 1669.

When samples are received from clients, there must be a yellow color present from the bromine chloride. Samples may be tested with starch iodide indicating paper and care must be taken to avoid mercury contamination. If indicating paper is not a dark purple color or sample is not yellow, more bromine chloride (1.25mL) must be added plus an additional 12 hours waiting time until color remains.  A clean hands/dirty hands sampling approach is one of the best methods for reducing the possibility of mercury contamination while collecting the water samples.


A minimum of 250mL of sample is needed. Add to a 250mL sample; 1.25mL of pre-tested BrCl, and let sit for at least 12 hours. This step oxidizes the Hg to Hg(II). The samples are placed in a 50ºC oven for 6 hours. If yellow color disappears then more BrCl must be added to sample and one of the blanks, then placed in 50ºC oven until yellow persists. Add 0.5mL NH2OH•HCL to clear up yellow BrCl, swirl, wait 5 minutes. Run curve and samples.