Sources of copper (Cu) from Navy activities, such as antifouling agents on ship bottoms and dredging operations, require active monitoring and sensing of Cu(I) and Cu(II) individually to ensure environmental compliance and protection. Because of the toxicity of copper, especially in estuary environments, all sources of copper must be monitored to account for the relative impacts of the various sources. The objective of this SERDP Exploratory Development (SEED) project was to develop a miniaturized sensor system based on ion-selective electrodes and other electrochemical measurements that individually detect Cu(I), Cu(II), pH, temperature, conductivity, chloride (or sodium), and turbidity. Because the measurements are determined in seconds, this sensor package would be suitable for rapid surveying of the marine environment.
A number of sensor systems were developed and packaged together. Copper(I), Cu(II), chloride, and pH were detected by modification of membrane ion-selective electrodes. Conductivity, oxidation/reduction potential, temperature, and turbidity were detected through miniaturization of existing technology. Of the desired sensor systems, only Cu(I) required extensive experimentation. To demonstrate that Cu(I) ion-selective electrodes are feasible, a hydrophobic (a requirement for membrane electrodes) carrier molecule for Cu(I) was synthesized and incorporated into a liquid-filled electrode. The sensor arrays developed were then evaluated in both laboratory and marine environments to determine stability, specificity, and sensitivity.
The mechanism for the detection of copper by ion selective electrodes in seawater was examined. Contrary to common perception, the direct detection of copper with ion selective electrodes is unlikely to be possible due to the low levels of uncomplexed copper present. Instead, it is proposed that the ion selective electrodes are measuring the activity of naturally occurring binding ligands for copper and thereby an indirect measurement of uncomplexed copper, which is the species most likely to be toxic to organisms. A potentially automated system was developed to measure the complexing ability of the seawater system for copper and other metals. This system can allow the determination of excess binding capability for the water system and thereby predict if a water body is likely toxic to an organism.
This platform sensor system enables a number of important parameters describing marine ecosystem health to be rapidly mapped. Such a system would be invaluable for monitoring metal toxicity in estuary environments and could provide a demonstration platform for the development of other miniaturized sensor systems. (SEED Project Completed - 2003)