Distribution of Al, Fe, Si, and DOC between size fractions mobilised from topsoil horizons with progressing degree of podzolisation.

Aluminium, Fe, Si, and dissolved organic C (DOC) accumulate in the subsoil of Podzols after mobilisation in the topsoil. We conducted laboratory experiments with topsoil horizons with progressing degree of podzolisation by irrigation with artificial rainwater at varying intensity and permanence. We monitored the concentrations and distribution of mobilised Al, Fe, Si, and DOC between size fractions (< 1000 Dalton, 1 kDa- < 0.45 µm, and > 0.45 µm). Total eluate concentrations were increased at the onset of the experiments and after the first irrigation interruption, indicating non-equilibrium release. There was no statistical effect of the degree of podzolisation on element concentrations. Release of Al, Fe, and DOC was mostly dominant in the fraction 1 kDa- < 0.45 µm, indicating metals complexed by larger organic molecules and colloids. Silicon released was dominantly monomeric silicic acid < 1 kDa. Particularly with the least podzolised soils, Al and Si concentrations < 1 kDa might have been controlled by short-range ordered aluminosilicates, while their transport in colloidal form was unlikely. Our study pointed to both quantitative and qualitative seasonality of element release during podzolisation, to decoupling of Al and Si release regarding size, and to different minerals that control element release as a function of the degree of podzolisation.

Mobilisation of Al, Fe, and DOM from topsoil during simulated early Podzol development and subsequent DOM adsorption on model minerals.

Podzols are characterised by mobilisation of metals, particularly Al and Fe, and dissolved organic matter (DOM) in topsoil horizons, and by immobilisation in subsoil horizons. We mimicked element mobilisation during early podzolisation by irrigating the AE horizon of a Dystric Arenosol with acetic acid at different flow velocities and applying flow interruptions to study rate-limited release in experiments with soil cylinders. We used eluates in batch experiments with goethite and Al-saturated montmorillonite to investigate DOM reactivity towards minerals. Both the flow velocity and flow interruptions affected element release, pointing to chemical non-equilibrium of release and to particles, containing Fe and OM mobilised at larger flow velocity, characteristic of heavy rain or snowmelt. Based on chemical extractions, the source of mobilised Al and Fe, the vast majority of which was complexed by DOM, was no oxide phase, but rather organic. Rate limitation also affected the composition of DOM released. Carboxyl and phenolic species were the most important species adsorbed by both minerals. However, DOM composition affected the extent of DOM adsorption on goethite more distinctly than that on montmorillonite. Our findings evidence that the intensity of soil percolation affects quantitative and qualitative element release during early podzolisation and adsorptive DOM retention in subsoil horizons.

Suspect Screening and Regulatory Databases: A Powerful Combination To Identify Emerging Micropollutants.

This study demonstrates that regulatory databases combined with the latest advances in high resolution mass spectrometry (HRMS) can be efficiently used to prioritize and identify new, potentially hazardous pollutants being discharged into the aquatic environment. Of the approximately 23000 chemicals registered in the database of the National Swedish Product Register, 160 potential organic micropollutants were prioritized through quantitative knowledge of market availability, quantity used, extent of use on the market, and predicted compartment-specific environmental exposure during usage. Advanced liquid chromatography (LC)-HRMS-based suspect screening strategies were used to search for the selected compounds in 24 h composite samples collected from the effluent of three major wastewater treatment plants (WWTPs) in Sweden. In total, 36 tentative identifications were successfully achieved, mostly for substances not previously considered by environmental scientists. Of these substances, 23 were further confirmed with reference standards, showing the efficiency of combining a systematic prioritization strategy based on a regulatory database and a suspect-screening approach. These findings show that close collaboration between scientists and regulatory authorities is a promising way forward for enhancing identification rates of emerging pollutants and expanding knowledge on the occurrence of potentially hazardous substances in the environment.