Do microplastics mediate the effects of chemicals on aquatic organisms?

Microplastics are ubiquitous in both marine and freshwater ecosystems, where they can act as a physical contaminant, as well as interact with chemicals present in the environment. It has been suggested that chemical contaminants can sorb to microplastics, such that microplastics act as a vector for chemicals into aquatic biota and enhance their negative effects. It has been repeatedly suggested that the main factors underpinning the binding of chemicals to microplastics are hydrophobic partitioning and the size of microplastic particles. Therefore, we used the hydrophobicity of chemicals, as log Kow, as well as the size of microplastic particles to conduct a quantitative analysis of published results to evaluate the influence of microplastics on chemical toxicity. We collated data from 39 laboratory studies that assessed the effects of microplastics, chemicals and their combination on several ecotoxicological responses of freshwater and marine organisms. Each chemical was assigned the relevant octanol / water partition coefficient (log KOW) as a measure of its hydrophobicity, and the mean size of microplastics particles used in each study was recorded. We found no effect of log KOW or the size of microplastic particles on the interaction between microplastics and chemicals with regards to any of the relevant ecotoxicological responses (behaviour, growth, survival and cellular) considered in this study. These findings are significant in showing that the effect of microplastics on the toxicity of chemicals is more complex than just considering hydrophobicity of chemicals and size of microplastics. We call for more mechanistic experiments to motivate a robust risk assessment and mitigation of microplastic toxicity in the environment.

Climate change impacts on contaminant loads delivered with sediment yields from different land use types in a Carpathian basin.

Soil runoff and sediment transport are considered as an important vector for particle-bound contaminant transfer from source to receiving waters. Under changing climate conditions and rapid basin development, identification of sediment origins is critical for planning further action to reduce erosion effects, and further pollution to surface waters. The goal of this study was to distinguish sediment sources in a Carpathian basin (Wolnica River, southern Poland) and to perform source-oriented contaminant load estimations. Sediment yields (SYLD) and land use specific sediment yields (LUSY) were modeled with the use of the Macromodel DNS/SWAT (Discharge-Nutrients-Sea/Soil and Water Assessment Tool). Sorting of sediment sources was performed by the fingerprinting method using variability of the geochemical composition of soils (Pb, Zn, Cd, Cu, Mn, Ni, Fe, Hg, total N and P, Σ16 PAHs, and 137Cs) of four land use (LU) types: arable lands (A), grasslands (G), residential areas (R), and forests (F). Statistical analysis revealed six metals (Pb, Zn, Cd, Cu, Ni, and Hg) as fingerprint properties providing the best source discrimination in this basin. The contribution of particular land use origin assessed with the use of the mixing model varied in the range of 20-30%. Finally, estimation of land use specific contaminant loads in suspended sediments was performed as a result of a modeling and sediment fingerprinting combination. The final estimates revealed yearly LUSY values varying between 716 t/y for A, 12 t/y for F, and metal loads from 31 kg/y for Zn to values below 100 g/y for Cd and Hg. Long-term predictions (2046-2055) of the metal loads revealed an increase by 75% under the combined RCP 8.5 climate change and land use scenarios. These findings are of great value for land management in the Carpathian basins, especially with regards to the predicted increase of forest cover which significantly alters contaminant signals conveyed through the system.