Geochemical fractions and indicators of sedimentation conditions in the Barents sea

Research results of geochemical fractions and distribution pattern of the major and trace elements in the sediment cores of the Barents Sea are presented. In the sediment core AMK- 5193, located in the central part of the sea, Al, Cr and Ni were detected predominantly in the lithogenic form (75−97% of the total content) throughout the core. A large or a noticeable portion (from 65% to 30% from total contents) of Pb, Cd, Cu, Ni, Co, Mn, and As was found to be accumulated due to hydrogenous processes, such as adsorption on amorphous Fe-Mn oxyhydroxides and clay particles. In the uppermost oxidized layer (0−6 cm) of St. AMK-5193, where the most intensive exchange processes between the solid and liquid phases of bottom sediments happen, a significant increase in the proportion of geochemically mobile fraction of most metals was found. In this part of the core, the maximum content of Fe and Mn in the form of authigenic oxy-hydroxides which serve an effective sorbent of most trace elements, including heavy metals, was recorded. At st. 5194, the downcore rythmic covariation of the Si/Al, Ti/Al and Fe/Al ratios reflecting contribution of terrigenous matrix, as well as Al/Ca ratio (indicator of physical and chemical weathering) was revealed. Moreover, the Al/Ca ratio exhibited an asynchronous change with the Si/Al and Fe/Al ratios. Also, the downcore variation in the Ti/Al ratio was opposite to that of Mn/Fe (an indicator of geochemically mobile fraction). Variation of the Ti/Zr ratio, reflecting the range of aerosol transport of clastic material, is weakly expressed in the AMK-5194 core, which supports the proximity of the terrigenous source.

Toxic Elements in Soil and Rice in Ecuador

The concentration of trace toxic metals (Cr, Zn, As, Pb, Cd, Cu, and Ni) in soil and rice plants, including the stems, leaves, and grain, from the main rice-producing provinces in Ecuador, was determined. Additionally, the soils were analyzed to determine their properties, composition, total content, bioavailable fraction, and geochemical fractions of toxic elements. Approximately 30% of soil samples in the case of Cr and Cu and 10% of samples in the case of Ni exceeded the legal thresholds for Ecuador. Moreover, for Cr and Cu, approximately 4% and 13% of samples, respectively, exceeded the threshold value of 100 mg kg−1 proposed for these two elements in several international regulations. Concentrations of As, Pb, and Cd in the soils were below the threshold values established both by Ecuadorian laws and by other countries. The concentrations of metals in rice plants did not correlate linearly with the total metal concentrations in the soil, nor with their bioavailability. However, the bioconcentration factors for As, Cd, Cu, Ni, and Zn could be predicted from bioavailability by a power law with exponents ranging from −0.724 to −1.625, which is typical of accumulator plants, where trace metal homeostasis plays an important role.

Geochemical Fractions of Heavy Metals in Bottom Sediments of the Pobeda Hydrothermal Cluster in the Mid-Atlantic Ridge (17°07′–17°08′ N)

In this study, to better understand the influence of hydrothermal processes on ore metal accumulation in bottom sediments, we examined distribution of Fe, Mn, Cu, Zn, As, and Pb in core of metalliferous sediments from the Pobeda hydrothermal cluster, and in core of non-mineralized (background) carbonate sediments (located 69 km northwards). Mechanisms of Fe, Mn, Cu, and Zn accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including a conditional mobile (F-1, exchangeable complex; F-2, authigenic Fe-Mn oxyhydroxides and associated metals; F-3, metals bound to organic matter/sulfides), and residual (F-4), fixed in crystalline lattices ones. The element contents were determined by the XRF and AAS methods, total carbon (TC) and total organic carbon (TOC) were determined using a Shimadzu TOC-L-CPN. Mineral composition and maps of element distribution in sediment components were obtained using the XRD and SEM-micro-X-ray spectrometry methods, respectively. In metalliferous sediments, according to our data, the major Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis, cfb). In the metalliferous core, average contents (cfb), of Fe and Mn were 32.1% and 0.29%, whereas those of Cu, Zn, Pb, and As, were 0.74%, 0.27%, 0.03%, and 0.02%, respectively. Metalliferous sediments are enriched in Fe, Cu, Zn, Pb, and As, relatively to background ones. The exception was Mn, for which no increased accumulation in metalliferous core was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes mineral debris. Among geochemically mobile fractions, to 80% Fe of the (F-1 + F-2 + F-3) sum was determined in the form of F-2, authigenic oxyhydroxides. The same fraction was a predominant host for Mn in both metalliferous and background sediments (to 85%). With these Fe and Mn fractions, a major portion of Cu, Zn, and Pb was associated, while a less their amount was found in sulfide/organic fraction. In the metalliferous sediment core, maximal concentrations of metals and their geochemically mobile fractions were recorded in the deeper core sediment layers, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that ore metals are mostly accumulated in sediment cores in their contact zone with the underlying serpentinized peridotites.

Invasive Weed Asystasia gangetica as a Potential Biomonitor and a Phytoremediator of Potentially Toxic Metals: A Case Study in Peninsular Malaysia

The invasive weed Asystasia gangetica was investigated for its potential as a biomonitor and as a phytoremediator of potentially toxic metals (PTMs) (Cd, Cu, Ni, Pb, and Zn) in Peninsular Malaysia owing to its ecological resistance towards unfavourable environments. The biomonitoring potential of PTMs was determined based on the correlation analysis of the metals in the different parts of the plant (leaves, stems, and roots) and its habitat topsoils. In the roots, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 2.18, 9.22 to 139, 0.63 to 5.47, 2.43 to 10.5, and 50.7 to 300, respectively. In the leaves, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.16, 7.94 to 20.2, 0.03 to 6.13, 2.10 to 21.8, and 18.8 to 160, respectively. In the stems, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.25, 5.57 to 11.8, 0.23 to 3.69, 0.01 to 7.79, and 26.4 to 246, respectively. On the other hand, the phytoremediation potential of the five metals was estimated based on the bioconcentration factor (BCF) and the translocation factor (TF) values. Correlation analysis revealed that the roots and stems could be used as biomonitors of Cu, the stems as biomonitors of Ni, the roots and leaves as biomonitors of Pb, and all three parts of the plant as biomonitors of Zn. According to the BCF values, in the topsoil, the “easily, freely, leachable, or exchangeable” geochemical fractions of the five metals could be more easily transferred to the roots, leaves, and stems when compared with total concentrations. Based on the TF values of Cd, Ni, and Pb, the metal transfer to the stems (or leaves) from the roots was efficient (>1.0) at most sampling sites. The results of BCF and TF showed that A. gangetica was a good phytoextractor for Cd and Ni, and a good phytostabilizer for Cu, Pb, and Zn. Therefore, A. gangetica is a good candidate as a biomonitor and a phytoremediator of Ni, Pb, and Zn for sustainable contaminant remediation subject to suitable field management strategies.

Geochemical Fractions of Heavy Metals in Bottom Sediments of the Pobeda Hydrothermal Field, Mid-Atlantic Ridge (17°07′–17°08′ N)

We examined the distribution of Fe, Mn, Cu, Zn, and Pb in one core of metalliferous, and one core of non-mineralized (background) carbonate sediments (located 69 km northwards), from the Pobeda hydrothermal field. Mechanisms of metal accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including mobile (exchangeable complex, authigenic Fe-Mn hydroxides, and sulfides), and lithogenic (fixed in crystalline lattices) forms. Maps of element distribution in sediment components were obtained using a scanning electron microscope equipped with an energy-dispersive spectrometry detector. In metalliferous sediments, according to X-ray diffraction data, the main Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis). The contents of Fe and Mn reached 31.6 and 0.18%, respectively, whereas concentrations of Cu, Zn and Pb were 0.98, 0.36, and 0.059%. The coefficient of metal enrichment relative to background values varied from 16 to 125 times. The exception was Mn, for which no increased accumulation was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes. Among geochemically mobile fractions, 90–97% of total Fe was found in the form of authigenic oxyhydroxides. The same fraction was the predominant host for Mn in both metalliferous and background sediments (55–85%). A total of 40–96 % of Cd, Cu, Zn, and Pb were associated with these Fe and Mn fractions. The sulfide fraction amounted to roughly 10% of each metal. In metalliferous sediment core, the maximum concentrations of metals and their geochemically mobile fractions were recorded in deeper core intercepts, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that metals are mostly accumulated in carbonate sediments in their contact zone with the underlying serpentinized basalts.

Clays, Limestone and Biochar Affect the Bioavailability and Geochemical Fractions of Cadmium and Zinc from Zn-Smelter Polluted Soils

Ca-bentonite (CB) alone and in a mixture with limestone (L), tobacco biochar (TB) and zeolite (Z) on the fixation, geochemical fractions and absorption of Cd and Zn by Chinese cabbage in smelter heavily polluted (S-HP) and smelter low polluted (S-LP) soils were investigated. The results showed that the CB + TB and CB + L + TB treatments significantly immobilized Cd up to 22.0% and 29.7%, respectively, and reduced uptake by Chinese cabbage shoot to 36.0% with CB + Z + L and 61.3% with CB + L in S-HP and S-LP soils compared with the control. The CB + Z + L + TB treatment mobilized Cd up to 4.4% and increased absorption in the shoot by 9.9% in S-HP soil. The greatest immobilization of Zn was 53.2% and 58.2% with the CB + Z + L + TB treatment, which reduced Zn uptake in the plant shoot by 10.0% with CB + L and 58.0% with CB + Z + L + TB in S-HP and S-LP soils. The CB + Z + TB and CB + TB treatments mobilized Zn up to 35.4% and 4.9%, respectively, in both soils. Furthermore, the uptake of Zn in plant shoot was observed by 59.0% and 7.9% with application of CB + Z and CB + TB treatments, respectively, in S-HP and S-LP soils. Overall, our results suggest that Ca-bentonite alone and in mixtures with different amendments can be used to reduce the phyto-extraction of Cd and Zn in Zn-smelter polluted soils.

Clays, Limestone and Biochar Affect the Bioavailability and Geochemical Fractions of Cadmium and Zinc from Zn-Smelter Polluted Soils

Ca-bentonite (CB) alone and in a mixture with limestone (L), tobacco biochar (TB) and zeolite (Z) on the fixation, geochemical fractions and absorption of Cd and Zn by Chinese cabbage in smelter heavily polluted (S-HP) and smelter low polluted (S-LP) soils were investigated. The results showed that the CB+TB and CB+L+TB treatments significantly immobilized Cd up to 22.03% and 29.68%, respectively, and reduced uptake by Chinese cabbage shoot to 35.98% with CB+Z+L and 61.35% with CB+L in S-HP and S-LP soils compared with the control. The CB+ Z+ L+TB treatment mobilized Cd up to 4.45% and increased absorption in the shoot by 9.85% in S-HP soil. The greatest immobilization of Zn was 53.18% and 58.20% with the CB+Z+L+TB treatment, which reduced Zn uptake in the plant shoot by 9.94% with CB + L and 58.04 with CB+Z+L+TB in S-HP and S-LP soils. The CB+Z+TB and CB+TB treatments mobilized Zn up to 35.40% and 4.80%, respectively, in both soils. Furthermore, the uptake of Zn in plant shoot was observed by 58.96% and 7.82% with application of CB+Z and CB+TB treatments, respectively, in S-HP and S-LP soils. Overall, our results suggest that Ca-bentonite alone and in mixtures with different amendments can be used to reduce the phyto-extraction of Cd and Zn in Zn-smelter polluted soils.