An Automated, Atomic Fluorescence-Based, Field Deployable Groundwater Mercury Monitoring System

Mercury is a hazardous pollutant that threatens human and ecosystem health, and exists in many contaminated subsurface environments. Monitoring mercury contamination in groundwater is challenging due to the considerable effort and expense involved in collecting samples, maintaining sample integrity during transport and storage, and subsequent laboratory analysis. These constraints often make high frequency sampling unfeasible and limit opportunities for long-term monitoring. Yet mercury export from contaminated subsurface systems and input to surface waters is often episodic, with the majority of the load coming during storm events. At present, it is virtually impossible to characterize the mercury dynamics of such systems. In order to decrease the effort and expense associated with field sampling and subsequent laboratory analysis for mercury determination, we propose an automated, field-deployable mercury monitoring system for groundwater and surface water. This system will run unattended, and will be capable of storing data or transmitting it to a remote location. In order to have sufficient sensitivity to measure mercury concentrations in uncontaminated waters, as well as the dynamic range required to measure contaminated sites, the system will incorporate an atomic fluorescence detector. To avoid the use of reagents, the system will be based on thermal decomposition of the sample and catalytic oxidation of combustion products. The proposed system will use a sample injection loop system to introduce a sample into a combustion chamber. The sample will be evaporated and later combusted in the chamber, before being swept downstream, through a catalytic oxidation chamber, under purified air flow, to a gold amalgamation trap. The sample will be thermally desorbed from the gold amalgamation trap under ultra-pure argon flow, and will be quantified by a highly sensitive atomic fluorescence detector. The proposed system will be useful to the managers of sites contaminated with mercury in the subsurface and surface water, including the U.S. Department of Energy, because it will reduce the cost of monitoring and increase the amount of data available. It will be useful to researchers involved in long-term monitoring projects, studying remote sites, or interested in increasing the efficiency of field sampling campaigns. It will also be useful to the operators of large environmental monitoring networks, such as the Mercury Deposition Network or the U.S. Geological Survey stream gauge network, because it will allow for data collection at greater frequency than is currently available.