# Development of a Novel DGT Passive Sampler for Measuring Cs-137 In Situ in Marine Environments

## TL;DR

A new DGT passive sampler using potassium zinc hexacyanoferrate was developed to accurately measure Cs-137 in seawater over long periods.

## Contribution

A novel DGT sampler with a KZFCN binding layer that overcomes ion competition and high pH challenges in seawater.

## Key findings

- The KZFCN-DGT sampler works effectively in a pH range of 2–12 and ionic strength up to 0.75 M.
- The sampler showed good precision (RSD = 13%) and accuracy (relative error = 8.5%) over 4 weeks.
- The Cs+ diffusion coefficient in the gel was consistent with literature values.

## Abstract

Cs-137 is the most
released fission product in the marine environment.
It is important to develop a robust in situ technique for its monitoring.
The existing diffusive gradients in thin films (DGT) passive sampling
techniques for in situ measurement of Cs+ have some limitations
due to the ion competition and high pH of seawater. A new DGT sampler
based on potassium zinc hexacyanoferrate (KZFCN) as a binding layer
has been developed and investigated for the measurement of the time-weighted
average concentration of Cs-137 in seawater. This binding layer proved
a working pH range of 2–12 and an ionic strength of up to 0.75
M. Two types of diffusive gels were tested and agarose gel (AGE) was
chosen for the KZFCN-DGT sampler. The measured Cs+ diffusion
coefficient (1.71 × 10–5 cm2·s–1 at 25 °C) in the diffusive gel from seawater
was within the expected range published in the literature. The measured
concentrations of Cs-137 in seawater obtained by laboratory deployments
of the KZFCN-DGT samplers for up to 4 weeks showed good precision
(RSD = 13%) and accuracy (relative error = 8.5%) values. The performance
test results demonstrated that the KZFCN-DGT sampler is suitable for
long-term monitoring of Cs-137 in seawater due to its high capacity
and resistance to ion competition and high pH.