Benzoylthiourea based polymers as new binding agents for diffusive gradients in thin films technique in labile mercury determination in freshwaters

In this study, the diffusive gradient in thin film (DGT) has been developed using three new materials derived from benzoylthiourea (PBTU, BTP1 and BTP2) for the determination of bioavailable mercury (Hg). The efficiency of these DGT devices was compared with the well-established 3-mercaptopropyl functionalized silica gel (3MFS) in laboratory and field conditions. It was found that PBTU lacked of consistency for handling and assembling in the DGT device, whereas the other two polymers provided mechanically stable binding gels and extracted satisfactorily Hg. However, BTP2 showed no correlation between Hg uptake and Hg present in the aqueous solution, and therefore, BTP1 gels was chosen as the binding layer used for DGT technique. The calculated diffusion coefficient of DGT-BTP1 was 4.0 10−6 cm 2 s−1 at 25 °C in 0.8 mm thick diffusion layer and 2.3% w/v of material in gel, whereas for DGT-3MFS, the D value was 9.1 × 10−6 cm 2 s−1. Moreover, it was found that neither the pH (range 4.5 – 9.5) nor the ionic strength (range 0.005–0.1 mol L−1) significantly affected the binding behavior of Hg (p > 0.05). Finally, the DGT-BTP1 devices were successfully used for in-situ measurements of Hg in Quito River (Colombia), impacted by artisanal gold mining, and were compared with DGT-3MFS. Results showed a good performance with values of the labile Hg concentration between 5 to 8% of the total Hg in water. This study demonstrates that benzoylthiourea based DGT is a useful tool for in situ monitoring of Hg in freshwaters.

This work has been supported by the Ministry of Science, Technology and Innovation (MINCIENCIAS) in Colombia through project: Evaluation of the degree of contamination by mercury and other toxic substances and its impact on human health in the populations of the Atrato River basin, as a consequence of mining: financing contract RC No. 849-2018, MINCIENCIAS Code: 1112-894-66291. This work was also funded by the Ministerio de Ciencia, Innovación y Universidades (MCIU) through project PID2019-107033GB-C22/AEI/10.13039/501100011033, and the Spanish National Research Council (CSIC)[http://dx.doi.org/10.13039/501100003339] through project iCOOP 2018-COOPA20490. The authors would also like to acknowledge the CYTED (Programa Iberoamericano de Ciencia y Tecnología para el Desarrollo) , for financing the MercuRed Network (420RT0007). The authors thank the members of the Toxicology and Environmental Management Laboratory of the University of Córdoba, and the members of the Technological University of Chocó ‘DLC’ (Colombia).

Peer reviewed