Supriyo Kumar Das

Assessment of trace metal toxicity in soils of Raniganj Coalfield, India

Soil, rock and water samples were collected from India’s oldest coalfield Raniganj to investigate trace metal contamination from mining activity. Our data reveal that trace metal concentration in soil samples lies above the average world soil composition; especially, Cr, Cu, Ni and Zn concentrations exceed the maximum allowable concentration proposed by the European Commission for agricultural soils. In particular, Cr, Cu and Ni exceed the ecotoxicological limit, and Ni exceeds the typical value for cultivated soils. Mineral dissolution from overburden material and high adsorption capacity of laterite soil are responsible for the elevated concentrations. This is evident from enrichment factor (Ef), geoaccumulation index (Igeo) and metal pollution index values. Sediment quality guideline index indicates toxicity to local biota although enrichment index suggests no threat from consuming crops cultivated in the contaminated soil.

Phosphorus dynamics in shallow eutrophic lakes: an example from Zeekoevlei, South Africa

Zeekoevlei is the largest freshwater lake in South Africa and has been suffering from hyper-eutrophic conditions since last few decades. We have used total P (TP), dissolved phosphate (PO43−), organic P (OP), calcium (Ca) and iron (Fe) bound P fractions to investigate the relevant physical, chemical and biological processes responsible for sedimentation and retention of P and to study phosphorus (P) dynamics in this shallow lake. In addition, redox proxies (V/Cr and Th/U ratios) are used to study the prevailing redox conditions in sediments. Adsorption by CaCO3 and planktonic assimilation of P are found to control P sedimentation in Zeekoevlei. Low concentration of the labile OP fraction in surface sediments restricts the release of P by bacterial remineralisation. Low molar Ca/P and Fe/P ratios indicate low P retention capacity of sediments, and P is most likely released by desorption from wind-induced resuspended sediments and mixing of pore water with the overlying water column.

Cryogenian evolution of stigmasteroid biosynthesis

Biosynthesis of C29 sterols, enhancing eukaryotic temperature resistance, evolved during the global Neoproterozoic glaciations. Sedimentary hydrocarbon remnants of eukaryotic C26–C30 sterols can be used to reconstruct early algal evolution. Enhanced C29 sterol abundances provide algal cell membranes a density advantage in large temperature fluctuations. Here, we combined a literature review with new analyses to generate a comprehensive inventory of unambiguously syngenetic steranes in Neoproterozoic rocks. Our results show that the capacity for C29 24-ethyl-sterol biosynthesis emerged in the Cryogenian, that is, between 720 and 635 million years ago during the Neoproterozoic Snowball Earth glaciations, which were an evolutionary stimulant, not a bottleneck. This biochemical innovation heralded the rise of green algae to global dominance of marine ecosystems and highlights the environmental drivers for the evolution of sterol biosynthesis. The Cryogenian emergence of C29 sterol biosynthesis places a benchmark for verifying older sterane signatures and sets a new framework for our understanding of early algal evolution.

Synthesis and characterisation of cerium(IV)-incorporated hydrous iron(III) oxide as an adsorbent for fluoride removal from water

Surface-altered hydrous iron(III) oxide incorporating cerium(IV) (CIHFO) was prepared and characterised via modern analytical tools for applications in fluoride removal from groundwater. The material with a Fe : Ce ratio of 1.0 : 0.5 (mol : mol) calcined at 473 K shows 24.8 ± 0.5 mg F− g−1 adsorption capacity at pH 5.0–7.0 from a solution with a concentration of 15.0 mg L−1; the material was established to be microcrystalline (∼5 nm) with a 140.711 m2 g−1 surface area, irregular surface morphology and porous structure. The time-dependent fluoride adsorption capacities of CIHFO at 293, 303 and 313 K are well described by the pseudo-first order, pseudo-second order and Weber–Morris kinetic models, respectively. The adsorption reaction occurs via a film/boundary layer diffusion process. The very low Arrhenius activation energy (Ea = 0.026 kJ mol−1) indicates the high feasibility of fluoride adsorption over CIHFO. The equilibrium data fit better with the Freundlich and Redlich–Peterson (g < 1.0) isotherms than with the Langmuir isotherm, which suggests multilayer adsorption. The values of the Freundlich parameters, n = 3.10, 4.47 and 7.57 and KF = 8.58, 10.88 and 11.25 at 293, 303 and 313 K, respectively, indicate high affinity for fluoride. Thermodynamic analysis of the reaction equilibrium shows that the reaction is highly exothermic (ΔH0 = −25.924 and −36.279 kJ mol−1 for Ci = 25.0 and 35.0 mg L−1), whereas the negative ΔG0 values indicate the spontaneous nature of the reaction. The fluoride adsorption over CIHFO occurs via ion-exchange that progresses to chemisorption. The presence of sulphate shows an adverse influence on fluoride adsorption by CIHFO, and the fluoride level of 2.4 g per L groundwater (9.05 mg F L−1) can be reduced below the permissible value.