Freshwater benthic communities could be at risk in ecosystems with high concentrations of microplastics. This is suggested by a study carried out by the Ecotoxicology group of the IMDEA Water Institute, in collaboration with Wageningen University (The Netherlands). Researchers have evaluated the risks of microplastic contamination in sediments of freshwater ecosystems on a global scale. The study has been published in the Journal of Hazardous Materials.
To characterize the environmental risk of microplastics, an exhaustive literature search was first conducted to collect data on the concentration of microplastics in sediments of rivers and lakes, as well as data from toxicity studies carried out with benthic species (Figure 1).
Figure 1. Summary of the methodology followed for the selection and alignment of the data included in the characterization of the risks of microplastics in freshwater sediments.
Secondly, the different studies were screened based on 10 quality criteria for exposure data, and 20 quality criteria for toxicity data (Figure 1). These criteria include, for example, the use of negative or positive controls when quantifying microplastics in the sediment, or the need to distinguish between the effects caused by the inert material and the possible chemical additives contained in the plastic.
Thirdly, a method was applied to align the concentrations measured in the sediments of environmental ecosystems with those used in the toxicity tests, and thus correct the differences that exist in terms of evaluated size ranges and shapes (Figure 1).
Finally, two species sensitivity distributions were constructed using volume and surface area as ecologically relevant metrics, which are related to the effects caused by the dilution of the food after the ingestion of microplastics, and the translocation of microplastics, respectively. The HC5 –the concentration of microplastics that affects the 5% of benthic species, considered as a threshold from which there could be a severe impact on the ecosystem– was compared with the concentrations of microplastics quantified in global benthic ecosystems (Figure 2). The lower limit of the confidence interval of the HC5 obtained in both distributions was exceeded by 32% and 17% of the locations, respectively (Figure 2). This means that benthic communities could be at risk in a significant number of freshwater ecosystems.
Figure 2. Cumulative frequency distributions of the minimum, mean and maximum microplastic environmental concentrations (MECs) measured (rescaled to 1 – 5000 µm) in global freshwater sediments, along with the HC5 values (vertical solid line) and their 95% confidence intervals (dashed lines) derived from species sensitivity distributions for volume (purple) and area (green). The colors of the MECs indicate the total cumulative score (TAS) obtained in the QA/QC screening: (black: ≥ 16; red: ≤ 5; blue: 11 ≥ 15; yellow: 6 ≤ 10).