A temporal record of microplastic pollution in Mediterranean seagrass soils.

Carmen Leiva-Dueñas,Maria Granberg,Candela Marco-Méndez,Nerea Piñeiro-Juncal,Martin Gullström,Mats Björk,Martin Dahl,Kerstin Magnusson,Sanne Bergman,Miguel Ángel Mateo,Elena Diaz-Almela

doi:10.1016/j.envpol.2021.116451

Abstract

Plastic pollution is emerging as a potential threat to the marine environment. In the current study, we selected seagrass meadows, known to efficiently trap organic and inorganic particles, to investigate the concentrations and dynamics of microplastics in their soil. We assessed microplastic contamination and accumulation in 210Pb dated soil cores collected in Posidonia oceanica meadows at three locations along the Spanish Mediterranean coast, with two sites located in the Almería region (Agua Amarga and Roquetas) and one at Cabrera Island (Santa Maria). Almería is known for its intense agricultural industry with 30000ha of plastic-covered greenhouses, while the Cabrera Island is situated far from urban areas. Microplastics were extracted using enzymatic digestion and density separation. The particles were characterized by visual identification and with Fourier-transformed infrared (FTIR) spectroscopy, and related to soil age-depth chronologies. Our findings showed that the microplastic contamination and accumulation was negligible until the mid-1970s, after which plastic particles increased dramatically, with the highest concentrations of microplastic particles (MPP) found in the recent (since 2012) surface soil of Agua Amarga (3819 MPP kg-1), followed by the top-most layers of the soil of the meadows in Roquetas (2173kg-1) and Santa Maria (68-362kg-1). The highest accumulation rate was seen in the Roquetas site (8832 MPP m-2 yr-1). The increase in microplastics in the seagrass soil was associated to land-use change following the intensification of the agricultural industry in the area, with a clear relationship between the development of the greenhouse industry in Almería and the concentration of microplastics in the historical soil record. This study shows a direct linkage between intense anthropogenic activity, an extensive use of plastics and high plastic contamination in coastal marine ecosystems such as seagrass meadows. We highlight the need of proper waste management to protect the coastal environment from continuous pollution.

Highlights

Global plastic consumption is increasing (Neufeld et al, 2016; Wang et al, 2016) and have become a major source of pollution in the world’s oceans (Browne et al, 2011; Lebreton et al, 2012)
The soil characteristics differed among the three sites, with higher mud and total organic carbon (TOC) contents at RO.S and AG.S when compared to SM (Table 2)
DBD and organic matter (OM) values were similar in all cores except for SM25, which showed higher DBD and lower OM compared to the other sites (Table 2)

Summary

Introduction

Global plastic consumption is increasing (Neufeld et al, 2016; Wang et al, 2016) and have become a major source of pollution in the world’s oceans (Browne et al, 2011; Lebreton et al, 2012). Plastics can be found in all marine habitats (Barnes et al, 2009; Thompson et al, 2004) and the concentrations are likely to increase in the coming decades (Everaert et al, 2018). The size of plastic particles in the environment is decreasing globally (Barnes et al, 2009), causing an increase in microplastic particles (< 5 mm) that could cause significant harm to the marine ecosystems.

Methods

Results

Discussion

Conclusion