Source-Specific Probabilistic Risk Assessment of Microplastics in Soils applying Quality Criteria and Data Alignment Methods

Summary

The risk characterization of microplastics (MP) in soil is challenging due to the non-alignment of existing exposure and effect data. Therefore, we applied data alignment methods to assess the risks of MP in soils subject to different sources of MP pollution. Our findings reveal variations in MP characteristics among sources, emphasizing the need for source-specific alignments. To assess the reliability of the data, we applied Quality Assurance/Quality Control (QA/QC) screening tools. Risk assessment was carried out probabilistically, considering uncertainties in data alignments and effect thresholds. The Hazardous Concentrations for 5% (HC5) of the species were significantly higher compared to earlier studies and ranged between 4.0×107 and 2.3×108 particles (1-5000 µm)/kg of dry soil for different MP sources and ecologically relevant metrics. The highest risk was calculated for soils with MP entering via diffuse and unspecified local sources, i.e., “background pollution”. However, the source with the highest proportion of high-risk values was sewage, followed by background pollution and mulching. Notably, locations exceeding the risk threshold obtained low scores in the QA/QC assessment. No risks were observed for soils with compost. To improve future risk assessments, we advise to primarily test environmentally relevant MP mixtures and adhere to strict quality criteria.

Environmental significance
With the detection of high microplastic concentrations in soils globally, there is a growing concern about their potential threat to soil biota. However, no risk assessments have been conducted yet for microplastics in soils accounting for the non-alignment and the quality of the data. We characterize the probabilistic risks of microplastics using plastic source-specific data alignment methods and applying strict quality screening tools. We show that risks from microplastics cannot be excluded in soils with mulching or sewage, nor in soils with microplastics entering via diffuse and local sources. Our risk analysis provides important information for environmental management and policy.

Graphical abstract