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ICES ExpertsAZTI presents MONITOOL results at different scientific events during 2020

The work conducted and the knowledge gained along MONITOOL lifetime have been presented by AZTI at four different scientific events. One of them was attended face-to-face and the other three events took place virtually due to the COVID-19 restrictions.

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Instituto Tecnológico de Canarias (ITC) carried out a wastewater sampling campaign following the MONITOOL standardized methods

Detecting and monitoring the level of contaminants in water bodies is a key element of the Water Framework Directive, WFD (2000/60/EC). The Directive 2013/39/EU of the European Parliament and of the Council of 12 august 2013 includes some heavy metals as priority substances: Cd, Hg, Ni and Pb. Its transposition to Spanish regulation (Real Decreto 817/2015) also includes Cu, Cr VI and Zn as preferential substances.

Discharges from land-based sources (industries, ships and particularly Wastewater Treatment Plant, WWTP) are one of the main input sources of heavy metals impacting the marine environment, consequently, the evaluation of the metals with quality standards in the effluent before they are dumped into to the coastal waters can help us to the implementation of the WFD, which aims for “good status” for all   water bodies in EU.

Spot water sampling of a discharged effluent at a specific point provides a good snapshot of what is happening at that point in time. However, it does not specify whether that snapshot faithfully reflects what is habitually present in that flow. Given these shortcomings, passive sampling techniques constitute a promising tool since they are continuous sampling methods, providing more representative information about the sampled environment. More specifically, to detect metals in water environments, soils and sediments the Diffusive Gradients in Thin Films (DGT, Research Ltd) are widely used.

Even if the use of DGTs can be extremely advantageous to study the metal concentrations in wastewater effluents due to their high variability, there are not so much studies in the literature in which DGTs are directly deployed in the wastewater discharges pipelines/pit, for the evaluation of metals (Gourlay-Francé, 2011; Thomas, 2009). Some of the reviewed studies consisted on taking wastewater samples and then, at the laboratory, the DGTs were deployed in flasks for a certain period of time, under stirring and temperature controlled conditions (Buzier et al., 2006a, 2006b, 2011; Yapici, 2008).

IMG 8977

In this context, in July 2020, the project partner ITC carried out a study with the objective of comparing the metal concentrations obtained with spot and passive sampling in five wastewater coastal discharges in Gran Canaria Island. Thereby, following the MONITOOL standardized methods, six different wastewater effluents were discrete sampled and simultaneously, DGTs were deployed directly in such effluents, these being:

  • The discharge from one of the biggest WWTP in Gran Canaria
  • Two mixed treated discharges (urban and industrial)
  • The treated discharge from an industrial site
  • The cooling water discharge from a thermal power plant
  • The discharge from a marine fish farm

Seven metals were targeted in these effluents:

  • Cd, Ni and Pb: as priority substances
  • Cr, Cu and Zn: as preferential substances
  • Al, Co, Fe, Mn: for their important role in the marine environment

The discrete water samples and the exposed DGTs are currently still under analysis, but we hope we will soon share the results and to be able to evaluate the DGT sampling techniques as a tool in the monitoring of heavy metals in treated wastewater direct discharges.

Bibliography:

  • BUZIER, Rémy, et al. Trace metal speciation and fluxes within a major French wastewater treatment plant: Impact of the successive treatments stages. Chemosphere, 2006, vol. 65, no 11, p. 2419-2426.
  • BUZIER, Rémy; TUSSEAU-VUILLEMIN, Marie-Hélène; MOUCHEL, Jean-Marie. Evaluation of DGT as a metal speciation tool in wastewater. Science of the Total Environment, 2006, vol. 358, no 1-3, p. 277-285.
  • BUZIER, Rémy, et al. Inputs of total and labile trace metals from wastewater treatment plants effluents to the Seine River. Physics and Chemistry of the Earth, Parts A/B/C, 2011, vol. 36, no 12, p. 500-505.
  • GOURLAY-FRANCÉ, Catherine, et al. Labile, dissolved and particulate PAHs and trace metals in wastewater: passive sampling, occurrence, partitioning in treatment plants. Water Science and Technology, 2011, vol. 63, no 7, p. 1327-1333.
  • THOMAS, Philip. Metals pollution tracing in the sewerage network using the diffusive gradients in thin films technique. Water science and Technology, 2009, vol. 60, no 1, p. 65-70.
  • YAPICI, Tahir, et al. Investigation of DGT as a metal speciation technique for municipal wastes and aqueous mine effluents. Analytica chimica acta, 2008, vol. 622, no 1-2, p. 70-76.

DCU Masters student, Martin Nolan, submits his MSc Thesis based on MONITOOL acquired knowledge

Martin Nolan (Dublin City University, DCU) presented in May his MSc Thesis under the Title "Evaluation of Diffusive Gradients in Thin Films for Trace Metal Monitoring of Coastal and Transitional Waterways", supervised by Dr. Blánaid White and Prof. Fiona Regan, based on works carried out during MONITOOL Project.

This work contains chapters rooted in different phases of MONITOOL Project, as monitoring methods, biofouling studies or voltammetry analysis of the samples. Specifically, the following chapters:

- A review of trace metal monitoring methods including biomonitoring and passive sampling methods and a summary of studies performed linking DGT performance to biomonitor organisms (Title: "Monitoring Trace Metals as Contaminants of Emerging Concern: Towards the Use of Passive Sampling Devices").

- The biofouling study, examining the extent of fouling at the studied sites, the speciation of the organisms, and some correlation studies with other water parameters, such as temperature and trace metals (Title: "Impact of Biofouling on Passive Sampling Devices and Examination of Fouling Environments of Atlantic and Mediterranean Waterways").

- Voltammetry chapter documenting the use of the ASV and cathodic CSV methods for the analysis of trace Ni, Cd and Pb (Title: "Stripping Voltammetry for Trace Analysis of Priority Metals in Coastal and Transitional Waters").

This is the first MSc Thesis that comes from MONITOOL. Martin Nolan has been involved in the project from its beginning, participating with DCU (project leader institution) in all the steps of the investigation.

Evaluation of the impact of biofouling on deployments of DGT

Deployments of Diffusive Gradients in Thin Film (DGT) devices in environmental waters can be made challenging due to the impact of biofouling. Biofouling is the attachment and growth of undesirable organisms on a surface and can impact the effectiveness of the DGT device. When microbial species such as bacteria and diatoms grow on the surface, they produce a sugar- and protein- rich substance known as extracellular polymeric substances (EPS). EPS spreads across a surface, forming a biofilm and allowing new organisms to attach more easily, including large organisms such as mussels, barnacles, and seaweed. A developed biofilm can affect DGT measurements by blocking the pores of the device, by binding metals, and introducing a new layer on top of the device, changing how metals move through the device.

There are a number of methods to help control the initial buildup of biofouling on a surface. Surfaces that will be exposed to environmental water for a long time, such as the hulls of ships or the casing of sensors, are often painted with biocidal paints, rich in copper or zinc. Alternatively, modified surface coatings can be used to prevent initial settlement or allow for easier removal of developed biofilms. Some sensors use chlorine jets or brushes to clean themselves allowing for longer deployments. However, these methods cannot be easily applied to DGT, as the results would be affected by metallic paints, chemically active surfaces, or changes to the boundary between the water and the device surface. For DGT, controlling the time the devices are deployed is currently the best solution to the biofouling challenge. Under the MONITOOL Project, DGT devices are deployed for 5 days, but evaluation of the impact of biofouling, and the organisms that cause it, is critical. Because MONITOOL covers such a large geographical region, it was expected that the biofouling would vary between hot and cold climates and during different seasons, both in the extent of fouling and the diversity of fouling organisms.

DGT devices were recovered for biofouling analysis from 31 sites during the cooler wet sampling period and the warmer dry sampling period. In addition, during the dry sampling period, Partners deployed panels designed by Dublin City University holding multiple surfaces to test biofouling for extended periods, including two types of membrane filters commonly used on DGT devices. Light microscopy was used to assess the percentage cover of the surfaces by fouling and Scanning Electron Microscopy (SEM) was used to identify the genera of diatoms and the types of other organisms causing fouling.

Many of the devices deployed for 5 days in MONITOOL experienced minimal impact by biofouling, with about half of the deployed devices having less than 1% surface coverage by fouling. This suggests our deployment period is generally suitable for use across various regions. The most heavily fouled device after 5 days was found during the dry season, with approximately 55% surface coverage. A DGT deployed at a nearby site was only about 9% covered, which demonstrates how unpredictable biofouling may be even at closely related sites. However, the longer deployment of the panels led to more than 99% coverage of the surface after 14 days at one site, pictured below.

Biofouling DCU

SEM imaging of the surface of a DGT membrane deployed for 14 days.

Across the 31 studied sites, there were 28 individual genera of diatoms identified on the standard DGT membrane composition (polyethersulphone). Some of these genera appeared at most sites studied, such as "Amphora", "Navicula" and "Cocconeis", which are among the most common marine diatoms. Some regions had diatoms which were unseen in other locations, and sometimes genera such as "Achnanthes" were almost exclusively present, as seen above. Work is continuing on the second surface type, the polycarbonate membranes, deployed alongside the polyethersulphone to better understand the diversity of fouling across the MONITOOL Project regions.

COVID-19 impact on MONITOOL project implementation

As everybody knows, the spread of the infection by the COVID-19 has been severely affected our lives and, in consequence, also to our planned activities on MONITOOL project.

All partner's institutions are closed and staff are working at home, except for very few people who carry out the critical authorized work.

In this sense, it's time to well organize all the pending MONITOOL works.

For example, a last experiment posed by IFREMER in order to determine metals on seawater samples taken from certain MONITOOL sites, in parallel with the DGT exposition and the filtered seawater analysis (ICP-MS and Voltammetry) under "stable" conditions, was planned for April 2020, as complementary field data to give consistency to DGT EQS determination. This task will be carried out now in the second half of 2020.

On the other hand, the MONITOOL Final Conference, which should have been held in Lisbon on May 2020, must be imperatively postponed. The new date is still pending, but it is most likely to take place in September this year. This event will be timed to coincide with the last Partner´s meeting.

Finally, this period of time will be used by partners to continue working on the processing of the data and publishing the main findings of the MONITOOL project in the more suitable science and technology journals. It is intended that, at least, four papers are ready to be published at project completion.

MONITOOL partnership wants to thank Interreg Atlantic Area program for the automatic extension on the project for 6 months due to the current COVID-19 pandemic situation.

Coronavirus