Metal concentrations in transitional and coastal waters measured by passive (Diffusive Gradients in Thin-films) and spot sampling: MONITOOL Project Dataset

The MONITOOL project (2017–2023) was carried out to describe the relationships between total dissolved and labile metal concentrations measured in spot water samples and in concurrently deployed Diffusive Gradients in Thin-films (DGTs) passive samplers, respectively. The ultimate aim was to adapt existing marine metal Environmental Quality Standards (EQS marine water) for DGTs, enabling their use in the context of the European Directives (the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD)). Time-integrated metal concentrations provided by DGTs, representing several days, are an advantage compared to conventional spot sampling, especially in highly dynamic systems, such as transitional waters. Hence, the MONITOOL project aimed to provide a robust database of dissolved and labile metal concentrations in transitional and coastal waters, based upon co-deployments of DGTs and collection of spot water samples at several sampling sites (England, France, Ireland, Italy, Northern Ireland, Portugal, Scotland and Spain), followed subsequently by DGT and water metal analysis. Samplings were carried out in 2018 and 2022, following agreed protocols developed in the framework of the project. The MONITOOL dataset includes metal concentrations from DGTs, measured with Inductively Coupled Plasma Mass Spectrometry (ICP-MS: Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) and in concurrently collected spot water samples by ICP-MS (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and Anodic/Cathodic Stripping Voltammetry (ASV/CSV: Cd, Pb, Ni). Moreover, data on seawater physical-chemical parameters (salinity, temperature, dissolved oxygen, pH, turbidity, total suspended solids, dissolved organic carbon, and total organic carbon) is provided. This database presents the results obtained using, concurrently, different forms of sampling and analytical techniques, enabling the comparison of the results obtained by these strategies and allowing the adaptation of EQS in marine water (EQS marine water) to DGTs (EQS DGT), in the context of the WFD. Moreover, due to the large number of sampling sites, it could also be used for other types of research, such as those dealing with metal speciation or the determination of baseline levels.

The MONITOOL project (2017-2023) was carried out to describe the relationships between total dissolved and labile metal concentrations measured in spot water samples and in concurrently deployed Diffusive Gradients in Thin-films (DGTs) passive samplers, respectively.The ultimate aim was to adapt existing marine metal Environmental Quality Standards (EQS marine water ) for DGTs, enabling their use in the context of the European Directives (the Water Framework Directive (WFD) and the Marine Strategy Framework Directive (MSFD)).Time-integrated metal concentrations provided by DGTs, representing several days, are an advantage compared to conventional spot sampling, especially in highly dynamic systems, such as transitional waters.Hence, the MONI-TOOL project aimed to provide a robust database of dissolved and labile metal concentrations in transitional and coastal waters, based upon co-deployments of DGTs and collection of spot water samples at several sampling sites (England, France, Ireland, Italy, Northern Ireland, Portugal, Scotland and Spain), followed subsequently by DGT and water metal analysis.Samplings were carried out in 2018 and 2022, following agreed protocols developed in the framework of the project.The MONITOOL dataset includes metal concentrations from DGTs, measured with Inductively Coupled Plasma Mass Spectrometry (ICP-MS: Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) and in concurrently collected spot water samples by ICP-MS (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) and Anodic/Cathodic Stripping Voltammetry (ASV/CSV: Cd, Pb, Ni).Moreover, data on seawater physical-chemical parameters (salinity, temperature, dissolved oxygen, pH, turbidity, total suspended solids, dissolved organic carbon, and total organic carbon) is provided.This database presents the results obtained using, concurrently, different forms of sampling and analytical techniques, enabling the comparison of the results obtained by these strategies and allowing the adaptation of EQS in marine water (EQS marine water) to DGTs (EQS DGT ), in the context of the WFD.Moreover, due to the large number of sampling sites, it could also be used for other types of research, such as those dealing with metal speciation or the determination of baseline levels.
© • This data can be used for baseline studies on the levels of dissolved metals in seawater.

Data Description
The dataset includes the information from field surveys carried out at 37 sampling sites ( Fig. 1 ).Sampling sites correspond to the following ecoregions: Canary Islands, Iberian Coast, Bay of Biscay and English Channel, Celtic Sea, North Sea and Western Mediterranean Sea.
This database can be handled with any standard database manager or spreadsheet software.There are 24 fields (columns) whose information is detailed below.
Label: It provides a unique value that identifies the row (it has no additional meaning).
Station: Sampling station name.A description for most of the sites is available at [2] .Longitude: Longitude of the sampling station, in decimal degrees.Latitude: Latitude of the sampling station, in decimal degrees.Sampling Campaign: There were three sampling campaigns, which were named: '2018 Wet Season', '2018 Dry Season', and '2022 MONITOOL EXT'.It should be noted that not all sampling sites were sampled in the three campaigns.
Sampling Date, Sampling Time and Sampling Time zone: In the case of spot sampling, it refers to the day/time when the data or water sample was collected or recorded.In the case of time-integrated sampling with passive samplers (Diffusive Gradients in Thin Films (DGT)), it refers to the time when the passive sampler was retrieved.
Sampling DGT Deployment time (days): This field only has information linked to passive samplers.This refers to the number of days the passive sampler was deployed in water.The date and time of the start of deployment of the passive sampler is not given but can be calculated indirectly from available information, as indicated in the repository.
Sampling Research centre: This indicates the research institution that carried out the sampling.
Sampling Level depth (m): This indicates the depth of water sampling, in situ measurement or at which the passive sampler was deployed.
Sampling tide (low, high, no tide): In some cases, it is indicated whether the sampling was done relatively close to high tide (HT) or low tide (LT).It should be noted that some sampling sites were sampled twice on each date, while others were sampled only once.
Sampling sample matrix: In all cases it refers to 'Raw water body'.
Result method: It presents 11 values that capture different types of information: i) 'Diffusive Gradients in Thin Films (DGT)': it refers to the metal content determined in passive samplers by inductively coupled plasma mass spectrometry; ii) 'Spot sampling ICP-MS': it refers to the metal content determined in spot samples by inductively coupled plasma mass spectrometry; iii) 'Spot sampling voltammetry': it refers to the metal content determined in spot samples by anodic/cathodic stripping voltammetry; iv) 'Seawater temperature': it refers to the seawater temperature measured in situ ; v) 'Seawater salinity': it refers to the seawater salinity measured in situ ; vi) 'Seawater pH': it refers to the seawater pH measured in situ ; vii) 'Seawater oxygen': it refers to the concentration of dissolved oxygen (measured in situ) , viii) 'Seawater turbidity': it refers to the turbidity value (measured in situ or in the laboratory); ix) 'Seawater dissolved organic carbon': it refers to the dissolved organic carbon in seawater (measured in the laboratory); x) 'Seawater total organic carbon': it refers to the total organic carbon in seawater (measured in the laboratory); and xi) 'Seawater suspended solid': total suspended solids in seawater (measured in the laboratory).
Result Details on the methodology: a brief description is provided of which method or instrument was used to measure the value indicated in that row.
Result Parameter: it indicates for which metal concentration is provided or for which variable the result is given.
Result Unit: it indicates the units in which the result of the row is provided.
Result Laboratory or research centre: it indicates the Institution/laboratory that measured the value in that row.
Result Precision ( < , > , = ): it is complementary to the value in column 'Result Value'.When 'Result Precision' is ' = ', the result corresponds to the value displayed in 'Result value'.When 'Result Precision' is ' < ', the result is less than the value displayed in 'Result value'; in this case, the value corresponds to the quantification limit of the device or method.When 'Result Precision' is ' > ', the result is greater than the value displayed in 'Result value'; in this case, the result is outside the validated range of values of the device or the method.
Result value: it is the measured value and should be combined with 'Result Unit' and 'Result Precision'.
Result Uncertainty: this refers to the measurement uncertainty in the metal content determined in spot samples measured by voltammetry.
Relative combined standard uncertainty (Nordtest approach,%): this refers to the measurement uncertainty in the metal content determined in spot samples measured by ICP-MS.
Result Quality level or remarks: This field is used to note indications that may be relevant for the interpretation of the results displayed in the row.
Result Field Replicate: This field is only used in those rows with metal results obtained by passive samplers (DGT) or measured voltammetry in spot samples.

Passive sampling
The passive samplers used were the LSNM-NP Loaded DGT devices for cationic trace metals in waters consisting of a standard DGT plastic holder with a polyethersulphone filter membrane (0.45 μm pore size), 0.8 mm agarose cross-linked polyacrylamide (APA) diffusive gel and Chelex® binding layer (DGT® Research Ltd, Lancaster, UK; reference: LSNM-NP open-pore Loaded DGT device for metals (A) in solution).The exposure time, i.e. , the deployment time of the passive sampler in water, varied from 2 to 15 days.In most cases, DGTs were used in triplicate.Details on DGT handling guidelines, including DGT pre-deployment storage, DGT assembly, DGT deployment/retrieval and transport and DGT dismantling and pre-analysis extractions, are given in [3] .For further guidance and images of the sampling campaigns performed in the framework of the MONITOOL project, it is recommended to read [4] .
Details of the analytical method used for measuring the accumulated metal content (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) in DGTs and for the back-calculation of metal concentrations in seawater are given in [2] .It should be noted that all DGT analyses were performed in the same laboratory (IFREMER, France).

Spot sampling for voltammetry and ICP-MS analyses
Concurrently with the exposure of DGTs, spot water samples were collected at the same depth with Niskin bottles or directly using collection flasks.The frequency of spot sampling varied between sites.The water samples for voltammetric analysis were filtered (DigiFILTER with 0.45 μm pore size Teflon membrane) and acidified on site (or as soon as practicable) and kept refrigerated until analysis.The samples for ICP-MS analysis collected in 2018 were frozen and sent to a single laboratory (CEFAS, UK), where they were filtered (DigiFILTER with 0.45 μm pore size Teflon membrane) and acidified.The samples for ICP-MS analysis collected in 2022 were filtered (DigiFILTER with 0.45 μm pore size Teflon membrane) and acidified on site (or as soon as practicable) and kept refrigerated until analysis.
Detailed information about the determination of conditional labile Pb and Cd concentrations, by ASV, and total dissolved Ni concentration, by CSV after UV irradiation, and the total dissolved concentrations (Al, Cd, Co, Cu, Mn, Ni, Pb, Zn) by an online pre-concentration seaFAST system coupled with an ICP-MS can be found in [2] .It should be noted that all metal analyses in spot water samples were performed in the same laboratories: IST (Portugal) in the case of the voltammetric analysis, and IPMA (Portugal) in the case of ICP-MS.

Spot sampling for other laboratory analyses
In some cases, complementary water samples were taken for the analysis of dissolved organic carbon, turbidity, etc.It should be noted that, unlike the analytical determinations of metals, the same procedure was not always used to determine these complementary variables.A description of the methods is given in the database.

In situ measurement of other variables
After the collection of each water sample, salinity, temperature, oxygen concentration, etc., were measured in situ , usually with multiparameter probes, as described in the database.It should be noted that the probes varied between the laboratories performing the sampling campaigns.

Fig. 1 .
Fig. 1.Location of sampling sites.Sub-regions according to the EU Marine Strategy Framework Directive (MSFD).

l
Marine Institute, Rinville, Oranmore, Galway, Ireland m Ifremer, LITTORAL, Environmental Resources Laboratory (Normandie), Avenue du Général de Gaulle, 14520 Port-en-Bessin, France n ITC, Instituto Tecnológico de Canarias, Playa de Pozo Izquierdo, S/N.CP: 35119, Sta.Lucía, Las Palmas, Spain o DCU Water Institute, Dublin City University, Dublin 9, Ireland p Ifremer, LITTORAL, Environmental Resources Laboratory (Morbihan Pays de Loire), Rue de l'Ile d'Yeu, 44300 Nantes, France q Lancaster Environment Centre, Lancaster University, Lancaster LA14YQ, UK a r t i c l e i n f o This is the largest dataset in Europe providing DGT-labile metal concentrations and dissolved metal concentrations obtained concurrently and covering a large geographical scale.• These data provide information on the seawater metal concentrations measured by different methods (passive sampling and spot sampling) concurrently, allowing intercomparison of the results obtained with the different methodologies in the framework of environmental monitoring studies.• This data could be used for research dealing with European Directives and those promoting the acceptance of new sampling techniques and the development of EQS for passive sampling.• This data can bring additional value to the research on metal speciation in seawater.