2,359 | Small microplastics (SMPs) in the gulf of Cadiz was sampled at 5 m depth by pumping it through the ship's pipe system and filtered through a 45 μm mesh size net. Our study reveals that higher densities have been found (130 mg·m−3) compared to other regions worldwide and these densities decreased from the coastline to the outer stations, showing a general coastal gradient influenced by estuarine outflows. SMPs with a size range between 45 and 193 μm were predominant and most of them composed by polyethylene and polypropylene. The metals associated with the MPs were mainly Na (21.1%), K (11.3%), Fe (8.5%), Ca (2.1%), Cr (1.8%), Zr (13.3%) and Hf (0.7%). The high proportion of Zr compared to Fe, which is different from what can be found in the environment, suggests that this metal is intrinsic to the materials used in catalytic processes during plastic production.

9 pages, 5 figures.-- Under a Creative Commons license | Small microplastics (SMPs) in the gulf of Cadiz was sampled at 5 m depth by pumping it through the ship's pipe system and filtered through a 45 μm mesh size net. Our study reveals that higher densities have been found (130 mg·m−3) compared to other regions worldwide and these densities decreased from the coastline to the outer stations, showing a general coastal gradient influenced by estuarine outflows. SMPs with a size range between 45 and 193 μm were predominant and most of them composed by polyethylene and polypropylene. The metals associated with the MPs were mainly Na (21.1%), K (11.3%), Fe (8.5%), Ca (2.1%), Cr (1.8%), Zr (13.3%) and Hf (0.7%). The high proportion of Zr compared to Fe, which is different from what can be found in the environment, suggests that this metal is intrinsic to the materials used in catalytic processes during plastic production | Financial support to EGO and the instrument was given by CSIC through Intramural Research program 2018 under grant number 201830I081. MS is grateful to the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva (TJFI-2017-32493) contract. DGF was funded by European Union's H2020-MSCA-IF-2018 846843—LitRivus | Peer reviewed

13 pages. -- File includes: Supplementary Text, Supplementary Figures and tables. -- Figure SI1. Illustrations by dbRDA of the relationships between the predictors modelled and the concentration of microplastics from the DistLM analysis of all sampling stations (n = 28) (the best model, see table 1). -- Figure SI2 SEM image (left) and Optic Microscopy image (right) of two stations sampled. -- Figure SI3. FTIR spectra of microplastic collected from the Gulf of Cadiz. FTIR spectra contain a mixture of all these plastics . -- Figure SI4. Rainfall and Dam freshwater discharge in the Guadalquivir estuary: Average monthly rainfall and dam discharges between March and June from 1997 to 2018. -- Figure SI5. The currents at the near‐surface level (cm/s) superimposed with sea surface temperature (SST in the rage 17-20ºC) and chlorophyll concentration (Chl-a, in the range 0-3.2 mg / m3) for 15th June 2019. -- Table SI1. Dataset with station name, concentration of microplastic, temperature (ºC), salinity, chlorophyll a fluorescence (mg m-3), oxygen (mg L-1), longitude and latitude in June 2019 between the days 14 and 19. -- Table SI2. Test statistics for the Distance-based Linear Model (DISTLM) analyses of the marginal and sequential tests based on ‘Step-wise’ procedure and AICc criteria of the microplastics at the 28 sites sampled. -- Table SI3. Information collected about MP surveys in environmental marine environments. | Peer reviewed

Small microplastics (SMPs) in the gulf of Cadiz was sampled at 5 m depth by pumping it through the ship's pipe system and filtered through a 45 μm mesh size net. Our study reveals that higher densities have been found (130 mg·m⁻³) compared to other regions worldwide and these densities decreased from the coastline to the outer stations, showing a general coastal gradient influenced by estuarine outflows. SMPs with a size range between 45 and 193 μm were predominant and most of them composed by polyethylene and polypropylene. The metals associated with the MPs were mainly Na (21.1%), K (11.3%), Fe (8.5%), Ca (2.1%), Cr (1.8%), Zr (13.3%) and Hf (0.7%). The high proportion of Zr compared to Fe, which is different from what can be found in the environment, suggests that this metal is intrinsic to the materials used in catalytic processes during plastic production.

Small microplastics (SMPs) in the gulf of Cadiz was sampled at 5 m depth by pumping it through the ship's pipe system and filtered through a 45 mu m mesh size net. Our study reveals that higher densities have been found (130 mg.m(-3)) compared to other regions worldwide and these densities decreased from the coastline to the outer stations, showing a general coastal gradient influenced by estuarine outflows. SMPs with a size range between 45 and 193 mu m were predominant and most of them composed by polyethylene and polypropylene. The metals associated with the MPs were mainly Na (21.1%), K (11.3%), Fe (8.5%), Ca (2.1%), Cr (1.8%), Zr (13.3%) and Hf (0.7%). The high proportion of Zr compared to Fe, which is different from what can be found in the environment, | Financial support to EGO and the instrument was given by CSIC through Intramural Research program 2018 under grant number 201830I081. MS is grateful to the Spanish Ministry of Science, Innovation and Universities for the Juan de la Cierva (TJFI-2017-32493) contract. DGF was funded by European Union's H2020-MSCA-IF-2018 846843-LitRivus.