SRM Story: SRM 1641f Mercury in Water

Natural erosion and weathering of rocks and soils, as well as inputs from industrial processes, contribute to the mineral content of groundwater, rivers, lakes, and oceans. Some minerals, such as iron, can cause water to appear discolored, leave staining, or even taste metallic. No one wants rust stains in the shower, but generally, high mineral levels in water are not harmful for use around the house or even to consume. Unlike iron, other metals, such as mercury, do pose a threat to human health under certain conditions. In aquatic environments such as those with low pH, low levels of dissolved oxygen, or high levels of organic matter and certain bacteria, mercury can be converted to methylmercury – the toxic form that bioaccumulates in fish and concentrates in the food chain. Consumption of mercury can result in neurological damage, kidney issues, and cardiovascular problems, so mercury levels in water and ocean life are continuously monitored by the US Environmental Protection Agency and the US Food and Drug Administration. NIST supports accuracy of these monitoring efforts by providing numerous SRMs designed for detecting mercury at low levels.

SRM 1641f Mercury in Water is the seventh iteration of this reference material series, available to support accurate determination of trace mercury levels in natural waters, since 1975. Released in March 2025, the mercury mass fraction was determined using highly precise technology, combining measurements by isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS) and direct combustion atomic absorption spectrometry (DC-AAS). The availability of this SRM and its accompanying Certificate of Analysis (COA) is essential to ensure users can appropriately calibrate and validate their testing methods and ensure the accuracy of mercury monitoring efforts.

As the US National Metrology Institute (NMI), NIST provides materials like SRM 1641f to enable users to establish metrological traceability to the International System of Units (SI). The international network of NMIs, including NIST, maintain measurement equivalence through SI traceability that ensures for decades to come, in laboratories around the world, measurement of trace mercury in water will be accurate and comparable. Mercury is a dangerous contaminant in our environment, but with consistent and accurate monitoring, threat to human health can be prevented through warnings and signage… like the Carson River and its reservoirs in northern Nevada. And hopefully, with remediation, someday these contaminated environments can be restored to their previous glory and confirmed through science!