Field Test of the IMEEDS Radionuclide Sampling System
This report describes the function and performance of a seawater sampling system. The purpose of the sampling system is to process water and isolate, or concentrate man-made
radionuclides present in the marine environment. Many of these isotopes are present in natural waters at extremely low levels, if at all. Also, biogeochemical processes in the environment sequester elements so that any given analyte may be in a compound, molecular, or ionic state, and associated with solid, colloidal and dissolved phases. The distribution of radioisotopes in natural waters is controlled by chemical speciation, pH, temperature, redox conditions, complex formation, adsorption and desorption, salinity, conductivity, and hydrolytic colloid formation (Harvey et al., 1990; von Gunten and Benes,
1995). Therefore, the goal of this work is to develop a sampler that is capable of isolating
suites of radionuclides as they are found in the environment.
The design of this sampling system is simple and requires minimal technical interface. Radionuclides in suspended material (e.g., plankton, particles) are isolated using physical filtration methods, while those in the dissolved phase are sequestered with chemical sorption material. These chemical methods isolate dissolved radionuclides on sorbent beds
without recourse to pretreatment or extraction using chemical reagents or solvents. Field testing the sampler function was conducted on a small research vessel in local coastal waters along large salinity (O-30%0) and suspended material (I-200mg/L) gradients. This is necessary, because extreme salinity and turbidity variation can degrade the efficiency and have deleterious effects on chemical and physical isolation methods. These tests determined isolation efficiency of the sampler in fresh high turbidity (river), brackish moderately turbid (estuary), and saline low turbidity (coastal) waters.
Results were validated using trace element and isotopic analytic analysis of processed samples returned to the lab. With several exceptions man-made radionuclides are absent in most domestic coastal waters. This is due to the absence of source input (power plant, enrichment, medical, etc.), or the passing of sufficient time for high specific activity isotopes from atmospheric testing three decades ago to decay to levels below measurement capabilities. Therefor, the performance of the system was evaluated using measurement of fallout radiocesium (137Cs), which is present at very low levels in California coastal waters, and stable natural isotopes in lieu of man-made radioactive isotopes (e.g., a0,52j2,53*54Cr for 5’Cr).