Prafulla Kumar Sahoo

A review of the arsenic concentration in paddy rice from the perspective of geoscience

Along with contaminated drinking water, arsenic (As) contamination in rice has become a global concern as a potential dietary risk to human health. Arsenic naturally occurs in paddy soil and can be increased by irrigating with As-rich groundwater, which may have subsequent impact on rice grains. There have been many studies on As concentration in rice. Some studies have revealed that As concentration in rice depends on the As content in irrigated groundwater and soil, whereas others have shown that various other factors control As solubility, bioavailability and uptake in the soil-rhizosphere-plant system. This review discusses the major factors controlling As behavior in the soil-rhizosphere-plant system and the current status of As contamination in paddy rice from different parts of the world. Understanding this aspect is crucial for minimizing As toxicity in rice plants.

Current Approaches for Mitigating Acid Mine Drainage

AMD is one of the critical environmental problems that causes acidification and metal contamination of surface and ground water bodies when mine materials and/or over burden-containing metal sulfides are exposed to oxidizing conditions. The best option to limit AMD is early avoidance of sulfide oxidation. Several techniques are available to achieve this. In this paper, we review all of the major methods now used to limit sulfide oxidation. These fall into five categories: (1) physical barriers,(2) bacterial inhibition, (3) chemical passivation, ( 4) electrochemical, and (5) desulfurization.We describe the processes underlying each method by category and then address aspects relating to effectiveness, cost, and environmental impact. This paper may help researchers and environmental engineers to select suitable methods for addressing site-specific AMD problems.Irrespective of the mechanism by which each method works, all share one common feature, i.e., they delay or prevent oxidation. In addition, all have limitations.Physical barriers such as wet or dry cover have retarded sulfide oxidation in several studies; however, both wet and dry barriers exhibit only short-term effectiveness.Wet cover is suitable at specific sites where complete inundation is established, but this approach requires high maintenance costs. When employing dry cover, plastic liners are expensive and rarely used for large volumes of waste. Bactericides can suppress oxidation, but are only effective on fresh tailings and short-lived, and do not serve as a permanent solution to AMD. In addition, application of bactericides may be toxic to aquatic organisms.Encapsulation or passivation of sulfide surfaces (applying organic and/or inorganic coatings) is simple and effective in preventing AMD. Among inorganic coatings,silica is the most promising, stable, acid-resistant and long lasting, as compared to phosphate and other inorganic coatings. Permanganate passivation is also promising because it creates an inert coating on the sulfide surface, but the mechanism by which this method works is still unclear, especially the role of pH. Coatings of Fe-oxyhydroxide, which can be obtained from locally available fly ash are receiving attention because of its low cost, self-healing character, and high cementation capacity. Among organic coatings, lipids and natural compounds such as humic acid appear to be encouraging because they are effective, and have a low environmental impact and cost. Common advantages of organic vs. inorganic coatings are that they work best at low pH and can prevent both chemical and biological oxidation.However, organic coatings are more expensive than inorganic coatings. Furthermore,while organic coatings are effective under laboratory conditions, they often fail under field conditions or require large amounts of reagents to insure effectiveness.Electrochemical cover technology may become a suitable technique to prevent AMD, but the mechanism by which this technique operates is still under investigation.Limitations of this method include the initial capital cost and ongoing costs of anodes and cathodes.Desulfurization is an alternative process for managing large-scale sulfide wastes/tailings. This process can separate sulfide minerals into a low-volume stream, leaving mainly waste with low sulfur content that will be non-acid-generating. The attractiveness of desulfurization is that it is simple and economic.Our review has clearly disclosed that more information is needed for most of the AMD-mitigation techniques available. Silica passivation has shown promise, butmore extensive field-testing is needed to reduce it to commercial viability. Silica is the dominant element in fly ash, and therefore, its use as a low-cost, easily accessible coating should be evaluated. Permanganate passivation also requires further study to understand the role of pH. The secondary formation of Fe-oxyhydroxide minerals from Fe-oxyhydroxides, from the standpoint of their phase transformation,stability and effectiveness, should be assessed over longer experimental periods. All inorganic coatings are designed to inhibit abiotic oxidation of pyrite; however, their effect on biotic pyrite oxidation is not well known and should be further studied.Currently, there is no information available on longer-term field application of organic reagents. Such information is needed to evaluate their lifetime environmental and performance effects. Future studies require spectroscopic analyses of all coating types to achieve a better understanding of their surface chemistry. In addition,a thorough mineralogical and geochemical characterization of waste materialsis essential to understand the acid generating potential, which can indeed help to select better prevention measures.From having performed this review, we have concluded that no single method is technologically mature, although the majority of methods employed are promising for some applications, or at specific sites. Combining techniques can help ac~Ie:eAMD containment in some cases. For example, applying dry cover (e.g., sml) mcombination with liming material or a bactericide, or applying inorganic coatings(e.g., silica) along with organic reagents (e.g., lipids or humic acid) may be moreeffective than utilizing any single technique alone.

Relations of arsenic concentrations among groundwater, soil and paddy from an alluvial plain of Korea

Serious groundwater arsenic (As) contaminations are frequently associated with alluvial plains, and which are mostly used for rice cultivation in Asian countries. Because rice cultivation requires large quantities of irrigation, the long-term use of Ascontaminated groundwater for irrigation may cause As contamination in the soil with a consequent impact on rice grains. In this study, we investigated As concentrations in groundwater, soil and rice and the soil properties from an alluvial plain of the Mankyeong River, Korea, to understand their relations from the viewpoint of As contamination in rice. Arsenic in the rice varied from 0.03 mg/kg to 0.22 mg/kg, with a mean of 0.13 mg/kg, which is much lower than the World Health Organization’s maximum permissible limit of As in rice (1.0 mg/kg). Some groundwater samples showed As concentrations much higher than the drinking water standard (10 ug/L). Despite the rice As is independent of groundwater As it showed a good relation with soil As and Fe-oxide fractions. Because As is mainly occurred in Fe-oxide fractions and the soil is mostly silty, it is speculated that under flooding conditions arsenic can easily mobilize to the soil solution and potentially be available for plants. However, this availability can be controlled by As uptake mechanisms and/or incomplete reduction of Fe-oxides. It is observed that rice As is significantly correlated with soil exchangeable-PO4 (r = −0.41, p < 0.05), indicating that PO4 competition in the soil-rhizosphere may be one of the factors controlling rice As.

Modern pollen rain as a background for palaeoenvironmental studies in the Serra dos Carajás, southeastern Amazonia

Several alternative interpretations of the pollen records of lake sediments in the Amazonia may arise due to a lack of understanding of the modern environments, mainly related to pollen–vegetation relationship. Therefore, in this work, we studied the modern pollen rain in sediments of the Amendoim Lake, plateaus of the Serra Sul dos Carajás, southeastern Amazonia. This study indicates the predominance of pollen grains from forest formation (ombrophilous forests and capão florestal) over montane savanna in the lake sediments, despite the fact that montane savanna occupies ~90% of the drainage basin. Additionally, these sediments reflect stronger signal of pollen from ombrophilous forests that occur in the slopes of the plateau. Important components of montane savanna such as Vellozia and Cereus were not observed in the modern pollen rain, which may be related to their shorter flowering periods restricted to the beginning of wetter conditions. The absence of Sacoglottis, Trichilia, Clusia, Emmotum, Guapira and Simarouba in the pollen rain is likely associated with different pollination strategy. The occurrence of windblown pollen of Alchornea, Pseudolmedia, Ilex and Cecropia, which are found from low to highlands of the Carajás region, reinforces a regional vegetation signal in sediments. Several plants from the studied site have been improperly described, according to taxonomy and ecology. For example, the current occurrence of Ilex and Styrax in the study site clearly suggests that they cannot be used as indicators of colder palaeoclimate conditions, as previously described. In addition, Poaceae can be found in drier to wetter substrate conditions, and abundance of their pollen grains in lakes can significantly vary according to relief morphology and cannot indicate palaeovegetation openness. Therefore, this work is a good background for further palaeobotany studies for this region.

Managing Groundwater Nitrate Contamination from Livestock Farms: Implication for Nitrate Management Guidelines

Significant nitrate contamination of groundwater has been observed in various parts of the world; intensive livestock farming is one of the major causes. This paper reviews various guidelines/regulations, which have been developed in advanced countries such as USA, Canada, Australia, and Europe to combat this problem by designing effective monitoring and management programs. Monitoring programs deal mainly with selection of sites, number of monitoring wells, specific parameters, and sampling frequency, which are helpful for identifying the source and extend of the contamination. Management programs deal with selection of suitable location, site characterization, proximity of livestock facilities and drinking wells, and proper storage, maintenance of the facilities, and limits of manures application in order to minimize nitrate leaching into groundwater. The main aim of this paper is to help states/countries, which do not have any guideline, and consulting engineers/consultants/owners of livestock operation in the design of effective strategies for point source nitrate management.

Holocene history of a lake filling and vegetation dynamics of the Serra Sul dos Carajás, southeast Amazonia

Down-core changes in sedimentary facies, elemental geochemistry, pollen, spore, δ13C, δ15N and radiocarbon records from a filled lake, named R4, of the Serra Sul dos Carajás were used to study the relationship between the paleomorphological and paleoecological processes and their significance for Holocene paleoclimatology of the southeast Amazonia. The sediment deposition of the R4 lake started around 9500 cal yr BP. Increase of detrital components from 9500 to 7000 cal yr BP suggests high weathering of surrounding catchment rocks and soils, and deposition into the lake basin under mudflows. At that time, montane savanna and forest formation were already established suggesting predominance of wet climate. However, from 7000 to 3000 cal yr BP, a decline of detrital input occurred. Also, forest formation and pteridophytes were declined, while palms and macrophytes were remained relatively stable, indicating that water levels of the lake is likely dropped allowing the development of plants adapted to subaerial condition under drier climate conditions. After 3000 cal yr BP, eutrophication and low accommodation space lead to high lake productivity and the final stage of the lake filling respectively, and forest formation may has acquired its current structure, which suggests return of wetter climate conditions.

Modern pollen rain raises doubts about the intensity and extension of the Last Glacial Cycle in Carajás: A reply to D’Apolito et al.

In this paper, we presented a reply to the comments on modern pollen rain and interpretations about the Last Glacial Maximum (LGM) by D’Apolito et al. Carajás may be considered as a micro-hotspot of plant endemism, mainly related to edaphic conditions and presence of different micro-habitats for canga vegetation into ironstone domains. These plants developed several survival strategies, including morphological and physiological adaptations, which is difficult for comparisons with any other distinct biomes or ecosystems. Furthermore, inaccurate interpretation of pollen taxa and habitat types by the previous palynological studies in Carajás, which are keys points presented in Guimarães et al., were not questioned by D’Apolito et al. Therefore, incomplete pollen database, uncertainties about pollen descriptions and plant–pollen habitat, poor knowledge about pollen production and dispersion in edaphically conditioned areas, as well as missing of multiproxy evidences about geology, geomorphology, faciology, and geochemistry can make LGM interpretations a very challenging task. This can produce more noises than reliable signals of paleoclimate changes.

Morphology and morphometry of upland lakes over lateritic crust, Serra dos Carajás, southeastern Amazon region

High-resolution satellite images, digital elevation models, bathymetric and sedimentological surveys coupled with statistical analysis were used to understand the physical environment and discuss their influence on water quality of the five upland lakes of Serra Sul dos Carajás, southeast Amazonia. The lakes have mid-altitude ranges (elevation), very small (catchment) and shallow to very shallow (central basins). Based on the length, area and volume, Violão and TI (Três Irmãs)-3 lakes may present large vertical movements of the water due to wind action and weakly stratified waters. Trophic conditions based on depth and shore development (Ld) parameters must be used with caution, since Amendoim Lake is relatively deep, but it is oligotrophic to ultra-oligotrophic. Ld values suggest that the lakes are circular to subcircular and are likely formed by solution process, as also suggested by volume development. TI-2 Lake is only presenting convex central basin and has highest dynamic ratio (DR), thus it may have high sedimentation and erosion rates. Based on the relationship between studied parameters, morphometric index and DR likely influence temperature and dissolved oxygen of waters of TI-2 Lake due to its depth profile and wind-induced surface mixing. Nevertheless, water quality parameters are controlled by catchment characteristics of the lakes.