Microplastics occurrence and frequency in soils under different land uses on a regional scale

Fabio Corradini,Francisco Casado,Vanessa Leiva,Esperanza Huerta-Lwanga,Violette Geissen

doi:10.1016/j.scitotenv.2020.141917

Abstract

The growing evidence of microplastic pollution in terrestrial ecosystems reveals adverse effects of microplastics on soil biota and plant growth. However, since large scale assessments are lacking, it is possible that the laboratory based experiments conducted have assumed unrealistic microplastic concentrations in soils. In this paper we present regional scale data on the presence of microplastics in soils under different land uses in the central valley of Chile, which is characterized by urbanization, agricultural, and mining operations. We identified microplastics in soils under four different land use systems having different management intensities (crop lands, pastures, rangelands, and natural grasslands), and all somewhat prone to accumulate microplastics from different sources. We analyzed 240 soil samples from Chile's central valley, trying to identify the most probable sources of the microplastics. Our hypothesis was that microplastics were ubiquitous in the environment and that their concentration peaks follow the intensity of fertilizer use (phosphorus), soil heavy metals concentrations derived from nearby mining operations (Zn and Cu), and distance to roads and urban areas. We did find evidence of microplastic pollution in crop lands and pastures (306 ± 360 and 184 ± 266 particles kg−1, respectively), but we did not observe pollution of rangelands and natural grasslands. Distance to mining operations, roads, or urban areas did not increase the microplastic particles count. Our observations contradict the common belief that microplastics are ubiquitous in the environment and relate the pollution problem more to agricultural activities. However, our data do not provide sufficient evidence to identify the pollution source. This is the first study that reports on microplastic occurrence in soils at a broad geographical scale. For greater insight on this topic more studies that contribute monitoring data about microplastics in soils are urgently needed.

Highlights

In recent years the scientific community has recognized plastic pollution as a major environmental threat (Isobe et al, 2019)
Microplastic pollution was less frequent in natural grasslands (20%) and rangelands dominated by shrubs (3%) (Table 2)
Samples from crop lands and pastures had, respectively, a 38% and 23% higher chance of presenting microplastic pollution than samples from rangelands dominated by shrubs and natural grasslands

Summary

Introduction

In recent years the scientific community has recognized plastic pollution as a major environmental threat (Isobe et al, 2019) Their concerns eventually reached society (Henderson and Green, 2020) and, as a consequence, policy-makers began drafting the first regulations to mitigate the problem at its source (e.g. EU Directive 2019/904). Soil scientists are still working to better understand the problem and its ramifications, primarily focusing on determining the magnitude of the problem (i.e. frequency of occurrence and potential effects). In their work, they stress the need for more field data on the occurrence of microplastics

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Discussion

Conclusion