Moritz Bigalke

Copper Isotope Fractionation during Complexation with Insolubilized Humic Acid

The bioavailability, mobility, and toxicity of Cu depend on Cu speciation in solution. In natural systems like soils, sediments, lakes, and river waters, organo-Cu complexes are the dominating species. Organo-complexation of Cu may cause a fractionation of stable Cu isotopes. The knowledge of Cu isotope fractionation during sorption on humic acid may help to better understand Cu isotope fractionation in natural environments and thus facilitate the use of Cu stable isotope ratios (delta(65)Cu) as tracer of the fate of Cu in the environment. We therefore studied Cu isotope fractionation during complexation with insolubilized humic acid (IHA) as a surrogate of humic acid in soil organic matter with the help of sorption experiments at pH 2-7. We used NICA-Donnan chemical speciation modeling to describe Cu binding on IHA and to estimate the influence of Cu binding to different functional groups on Cu isotope fractionation. The observed overall Cu isotope fractionation at equilibrium between the solution and IHA was Delta(65)Cu(IHA-solution) = 0.26 +/- 0.11 per thousand (2SD). Modeled fractionations of Cu isotopes for low- (LAS) and high-affinity sites (HAS) were identical with Delta(65)Cu(LAS/HAS-solution) = 0.27. pH did not influence Cu isotope fractionation in the investigated pH range.

Polycyclic aromatic compounds (PAHs and oxygenated PAHs) and trace metals in fish species from Ghana (West Africa): Bioaccumulation and health risk assessment

We report the concentrations of 28 PAHs, 15 oxygenated PAHs (OPAHs) and 11 trace metals/metalloids (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, and Zn) in muscle and gut+gill tissues of demersal fishes (Drapane africana, Cynoglossus senegalensis and Pomadasys peroteti) from three locations along the coast of the Gulf of Guinea (Ghana). The concentrations of ∑28PAHs in muscle tissues averaged 192ngg(-1) dw (range: 71-481ngg(-1) dw) and were not statistically different between locations. The concentrations of ∑28 PAHs were higher in guts+gills than in muscles. The PAH composition pattern was dominated by low molecular weight compounds (naphthalene, alkyl-naphthalenes and phenanthrene). All fish tissues had benzo[a]pyrene concentrations lower than the EU limit for food safety. Excess cancer risk from consumption of some fish was higher than the guideline value of 1×10(-6). The concentrations of ∑15 OPAHs in fish muscles averaged 422ngg(-1) dw (range: 28-1715ngg(-1)dw). The ∑15 OPAHs/∑16 US-EPA PAHs concentration ratio was >1 in 68% of the fish muscles and 100% of guts+gills. The log-transformed concentrations of PAHs and OPAHs in muscles, guts+gills were significantly (p<0.05) correlated with their octanol-water partitioning coefficients, strongly suggesting that equilibrium partitioning from water/sediment into fish tissue was the main mechanism of bioaccumulation. The trace metal concentrations in the fish tissues were in the medium range when compared to fish from other parts of the world. The concentrations of some trace metals (Cd, Cu, Fe, Mn, Zn) were higher in guts+gills than in muscle tissues. The target hazard quotients for metals were<1 and did not indicate a danger to the local population. We conclude that the health risk arising from the consumption of the studied fish (due to their PAHs and trace metals content) is minimal.

Cadmium Isotope Fractionation in Soil–Wheat Systems

Analyses of stable metal isotope ratios constitute a novel tool in order to improve our understanding of biogeochemical processes in soil-plant systems. In this study, we used such measurements to assess Cd uptake and transport in wheat grown on three agricultural soils under controlled conditions. Isotope ratios of Cd were determined in the bulk C and A horizons, in the Ca(NO3)2-extractable Cd soil pool, and in roots, straw, and grains. The Ca(NO3)2-extractable Cd was isotopically heavier than the Cd in the bulk A horizon (Δ(114/110)Cdextract-Ahorizon = 0.16 to 0.45‰). The wheat plants were slightly enriched in light isotopes relative to the Ca(NO3)2-extractable Cd or showed no significant difference (Δ(114/110)Cdwheat-extract = -0.21 to 0.03‰). Among the plant parts, Cd isotopes were markedly fractionated: straw was isotopically heavier than roots (Δ(114/110)Cdstraw-root = 0.21 to 0.41‰), and grains were heavier than straw (Δ(114/110)Cdgrain-straw = 0.10 to 0.51‰). We suggest that the enrichment of heavy isotopes in the wheat grains was caused by mechanisms avoiding the accumulation of Cd in grains, such as the chelation of light Cd isotopes by thiol-containing peptides in roots and straw. These results demonstrate that Cd isotopes are significantly and systematically fractionated in soil-wheat systems, and the fractionation patterns provide information on the biogeochemical processes in these systems.

Accumulation of cadmium and uranium in arable soils in Switzerland

Mineral phosphorus (P) fertilizers contain contaminants that are potentially hazardous to humans and the environment. Frequent mineral P fertilizer applications can cause heavy metals to accumulate and reach undesirable concentrations in agricultural soils. There is particular concern about Cadmium (Cd) and Uranium (U) accumulation because these metals are toxic and can endanger soil fertility, leach into groundwater, and be taken up by crops. We determined total Cd and U concentrations in more than 400 topsoil and subsoil samples obtained from 216 agricultural sites across Switzerland. We also investigated temporal changes in Cd and U concentrations since 1985 in soil at six selected Swiss national soil monitoring network sites. The mean U concentrations were 16% higher in arable topsoil than in grassland topsoil. The Cd concentrations in arable and grassland soils did not differ, which we attribute to soil management practices and Cd sources other than mineral P fertilizers masking Cd inputs from mineral P fertilizers. The mean Cd and U concentrations were 58% and 9% higher, respectively, in arable topsoil than in arable subsoil, indicating that significant Cd and U inputs to arable soils occurred in the past. Geochemical mass balances confirmed this, indicating an accumulation of 52% for Cd and 6% for U. Only minor temporal changes were found in the Cd concentrations in topsoil from the six soil-monitoring sites, but U concentrations in topsoil from three sites had significantly increased since 1985. Sewage sludge and atmospheric deposition were previously important sources of Cd to agricultural soils, but today mineral P fertilizers are the dominant sources of Cd and U. Future Cd and U inputs to agricultural soils may be reduced by using optimized management practices, establishing U threshold values for mineral P fertilizers and soils, effectively enforcing threshold values, and developing and using clean recycled P fertilizers.

Microplastics in Swiss Floodplain Soils

Microplastics (MPs) are small (<5 mm diameter) but have clear implications for the environment. These artificial particles are found in and pose threats to aquatic systems worldwide. MPs have terrestrial sources, but their concentrations and fates in the terrestrial environment are poorly understood. While global plastic production continues to increase, so do the environmental concentrations and impacts of MPs. In this first study of MPs in floodplain soils, we developed a method for identifying, quantifying, and measuring the sizes of most commonly produced MPs in soil by FT-IR microscopy. For small MP (<1 mm) analysis, MP were separated by density separation and oxidation of organic matter. In this study we analyzed 29 floodplains in Swiss nature reserves associated with catchments covering 53% of Switzerland. We found evidence that 90% of Swiss floodplain soils contain MPs. The highest MP concentrations were associated with the concentration of mesoplastics (5 mm - 2.5 cm diameter), indicating plastic waste as source. Furthermore, MP concentration was correlated with the population of the catchment. The wide distribution of MPs, their presence in remote unsettled high mountain areas, decoupling of MEP and MP compositions, and the dominance of MPs by small (<500 μm diameter) particles, indicate that MPs enter soils via diffuse aeolian transport.

Fate of Cd in Agricultural Soils : A Stable Isotope Approach to Anthropogenic Impact, Soil Formation, and Soil-Plant Cycling

The application of mineral phosphate (P) fertilizers leads to an unintended Cd input into agricultural systems, which might affect soil fertility and quality of crops. The Cd fluxes at three arable sites in Switzerland were determined by a detailed analysis of all inputs (atmospheric deposition, mineral P fertilizers, manure, and weathering) and outputs (seepage water, wheat and barley harvest) during one hydrological year. The most important inputs were mineral P fertilizers (0.49 to 0.57 g Cd ha-1 yr-1) and manure (0.20 to 0.91 g Cd ha-1 yr-1). Mass balances revealed net Cd losses for cultivation of wheat (-0.01 to -0.49 g Cd ha-1 yr-1) but net accumulations for that of barley (+0.18 to +0.71 g Cd ha-1 yr-1). To trace Cd sources and redistribution processes in the soils, we used natural variations in the Cd stable isotope compositions. Cadmium in seepage water (δ114/110Cd = 0.39 to 0.79‰) and plant harvest (0.27 to 0.94‰) was isotopically heavier than in soil (-0.21 to 0.14‰). Consequently, parent material weathering shifted bulk soil isotope compositions to lighter signals following a Rayleigh fractionation process (ε ≈ 0.16). Furthermore, soil-plant cycling extracted isotopically heavy Cd from the subsoil and moved it to the topsoil. These long-term processes and not anthropogenic inputs determined the Cd distribution in our soils.

Aluminum toxicity to tropical montane forest tree seedlings in southern Ecuador: Response of nutrient status to elevated Al concentrations

AimsWe determined the reasons why in nutrient solution increasing Al concentrations >300 μM inhibited shoot biomass production of Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha (Jacq.) G. Nicholson while 300 μM Al stimulated root biomass production of Tabebuia chrysantha.MethodsNutrient concentrations in plant tissue after a hydroponic growth experiment were determined.ResultsIncreasing Al concentrations significantly decreased Mg concentrations in leaves. Phosphorus concentrations in roots of C. odorata and T. chrysantha were significantly highest in the treatment with 300 μM Al and correlated significantly with root biomass.ConclusionsShoot biomass production was likely inhibited by reduced Mg uptake, impairing photosynthesis. The stimulation of root growth at low Al concentrations can be possibly attributed to improved P uptake.

Aluminum toxicity to tropical montane forest tree seedlings in southern Ecuador

AimsWe determined the reasons why in nutrient solution increasing Al concentrations >300 μM inhibited shoot biomass production of Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha (Jacq.) G. Nicholson while 300 μM Al stimulated root biomass production of Tabebuia chrysantha.MethodsNutrient concentrations in plant tissue after a hydroponic growth experiment were determined.ResultsIncreasing Al concentrations significantly decreased Mg concentrations in leaves. Phosphorus concentrations in roots of C. odorata and T. chrysantha were significantly highest in the treatment with 300 μM Al and correlated significantly with root biomass.ConclusionsShoot biomass production was likely inhibited by reduced Mg uptake, impairing photosynthesis. The stimulation of root growth at low Al concentrations can be possibly attributed to improved P uptake.

Using isotopes to trace freshly applied cadmium through mineral phosphorus fertilization in soil-fertilizer-plant systems

Applications of mineral phosphorus (P) fertilizer can lead to cadmium (Cd) accumulation in soils and can increase Cd concentrations in edible crop parts. To determine the fate of freshly applied Cd, a Cd source tracing experiment was conducted in three soil-fertilizer-wheat systems by using a mineral P fertilizer labeled with the radio isotope 109Cd and by exploiting natural differences in Cd stable isotope compositions (δ114/110Cd). Source tracing with stable isotopes overestimated the proportion of Cd in plants derived from the P fertilizer, because the isotope ratios of the sources were not sufficiently distinct from those of the soils. Despite indistinguishable extractable Cd pools between control and treatments, the addition of P fertilizer resulted in a more negative apparent isotope fractionation between soil and wheat. Overall, the radio isotope approach provided more robust results and revealed that 6.5 to 15% of the Cd in the shoot derived from the fertilizer. From the introduced Cd, a maximum of 2.2% reached the wheat shoots, whilst 97.8% remained in the roots and soils. The low recoveries of the fertilizer derived Cd suggest that continuous P fertilizer application in the past decades can lead to a build-up of a residual Cd pool in soils.

Sources and fate of polycyclic aromatic compounds (PAHs, oxygenated PAHs and azaarenes) in forest soil profiles opposite of an aluminium plant

Little is known about oxygenated polycyclic aromatic hydrocarbons (OPAHs) and azaarenes (AZAs) in forest soils. We sampled all horizons of forest soils from five locations at increasing distances from an Al plant in Slovakia, and determined their polycyclic aromatic compound (PACs) concentrations. The ∑29PAHs concentrations were highest in the Oa and lowest in the Oi horizon, while the ∑14OPAHs and ∑4AZAs concentrations did not show a consistent vertical distribution among the organic horizons. The concentration ratios of PAHs and OPAHs between deeper O horizons and their overlying horizon (enrichment factors) were positively correlated with the octanol-water partition coefficients (KOW) at several locations. This is attributed to the slower degradation of the more hydrophobic PACs during organic matter decomposition. PACs concentrations decreased from the organic layer to the mineral horizons. The concentrations of ∑29PAHs (2400-17,000 ng g-1), ∑14OPAHs (430-2900 ng g-1) and ∑4AZAs (27-280 ng g-1) in the mineral A horizon generally decreased with increasing distance from the Al plant. In the A horizons, the concentrations of ∑29PAHs were correlated with those of ∑14OPAHs (r = 0.95, p = 0.02) and ∑4AZAs (r = 0.93, p = 0.02) suggesting that bioturbation was the main transport process of PACs from the organic layer into the mineral soil. At each location, the concentrations of PACs generally decreased with increasing depth of the mineral soil. Enrichment factors of PAHs in the mineral horizons were not correlated with KOW, pointing at colloid-assisted transport and bioturbation. The enrichment factors of OPAHs (in mineral horizons) at a site were negatively correlated with their KOW values indicating that these compounds were leached in dissolved form. Compared to a study 13 years before, the concentrations of PAHs had decreased in the O horizons but increased in the A and B horizons because of soil-internal redistribution after emissions had been reduced.