Human exposure risks for metals in soil near a coal-fired power-generating plant.

Coal-fired thermal power stations (TPSs) may contaminate the surrounding soil and could lead to pollution levels that can affect human health. Soil samples collected from the immediate vicinity of a TPS were analysed for heavy metals. TPS soils were enriched with arsenic (As), strontium (Sr), copper (Cu), mercury (Hg), barium (Ba), vanadium (V), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), and nickel (Ni). Enrichment factor, principal component, and cluster analyses suggest that As, Cd, Co, Cr, and Hg in TPS soils originated from the TPS, whereas Pb and Zn were from vehicular/traffic-related emissions. The human exposure risk assessment based on different exposure pathways showed that the hazard index (HI) was <1.0 for all of the elements. The relative exposure risk was greater for toddlers. Although the overall risk was within the acceptable limit of 1.00, the HIs of Co (0.15) and Cr (0.082) were close to the threshold limits, which over the long-term may pose a health risk.

Evaluation of the co-application of fly ash and sewage sludge on soil biological and biochemical quality.

Disposal of sewage sludge (SS) and fly ash (FA) is a multifaceted problem, which can affect environmental quality. FA has the potential to stabilize SS by reducing metal availability and making the SS suitable for application in the agricultural sector. An experiment was performed to evaluate soil biological quality changes with the combined amendment of SS and FA (fluidized bed combustion ash (FBCA) and lignite fly ash (LFA)). SS was amended with 0, 10, 30, 50 and 100%, (w/w) of FA, and then the FA-SS mixtures were incubated with red soil at 1:1 (v/v). Soil quality parameters such as pH, electrical conductivity, N, soil enzyme activities such as dehydrogenase (DHA), urease (URE), and catalase (CAT), and microbial biomass carbon (MBC) were evaluated at 20, 30, and 60 days of incubation, pH and EC increased with FA-SS dose; however, N decreased. DHA and URE were found to be increased with 10% LFA amendment; thereafter it decreased. However, URE increased up to 30% of FBCA. CAT and MBC increased with both FA amendments, even up to addition of 50% FA. Bioavailable Zn, Cu, and Co contents were decreased by the addition of FA. Principal component analysis showed that pH is the most influential factor. MBC appears to be a sensitive soil indicator for the effects that result from the addition of FA-SS. Phytotoxicity studies with Zea mays showed optimum performance at 30% FA. Addition of 10-30% FBCA or LFA to SS has a positive advantage on soil biological quality.

An appraisal of the potential use of fly ash for reclaiming coal mine spoil.

Growing dependence on coal-fired power plants for electrical generation in many countries presents ongoing environmental challenges. Burning pulverized coal in thermal power plants (TPPs) generates large amounts of fly ash (FA) that must be disposed of or otherwise handled, in an environmentally-sound manner. A possible option for dealing with fly ash is to use it as an amendment for mine spoil or other damaged soil. It has been demonstrated through studies in India and other countries that FA alone or in combination with organic or inorganic materials can be used in a productive manner for reclamation of mine spoil. The characteristics of FA, including silt-sized particles, lighter materials with low bulk density (BD), higher water holding capacity, favorable pH and significant concentrations of many essential plant nutrients, make it a potentially favorable amendment for mine spoil reclamation. Studies have indicated that the application of FA has improved the physical, chemical and biological qualities of soil to which it is applied. The release of trace metals and soluble salts from FA could be a major limitation to its application. This is particularly true of fresh, un-weathered FA or acidic FA, although perhaps not a concern for weathered/pond ash or alkaline FA. Some potential contaminants, especially metals and other salt ions, could be immobilized and rendered biologically inert by the addition of certain inorganic and organic amendments. However, in view of the variability in the characteristics of FAs that are associated with location, feed coal, combustion conditions and other factors, the suitability of a particular FA for a specific soil/mine spoil needs to be critically evaluated before it is applied in order to maximize favorable results and eliminate unexpected consequences. FA generated in India tends to be mostly alkaline, with lower levels of trace elements than are often found in FAs from other countries. The concentrations of potential chemical stressors, predominantly metals, in Indian FAs are often less than established or proposed permissible limits and are thus better suited for soil application. A major logistic limitation to the use of FA could be the cost involved in transport of ash from production to utilization sites.

Environmental impact of coal washery and Damodar River water on the morphometry and biochemical changes of maize (Zea mays L.) and soil health.

Enormous quantity of water is used for coal beneficiation and accordingly huge amount of effluents are being generated. In this study an attempt was made to evaluate the potential of this effluent water for irrigation. Water samples were collected from three different points (a) feeding point, (b) thickening point, and (c) outlet point of coal washery, and from Damodar River for monitoring the water quality. The samples were analyzed for various parameters and compared with prescribed standard, which revealed that the total suspended solids of thickening point and Damodar River were higher. A pot experiment with maize was conducted to study the suitability of this coal washery water for irrigation. Pots were irrigated with water from the three points of washery and Damodar River in two concentrations (100% and 50% dilution with distilled water); pure distilled water was used for control. There was 100% germination in all the treatments. The plant growth, chlorophyll content and soil quality parameters were significantly better in washery and Damodar River water treated pots. The Damodar River water and washery water from feeding and outlet point could be successfully used for irrigation. In general mixing with good quality water has shown better results.

Management of lignite fly ash for improving soil fertility and crop productivity.

Lignite fly ash (LFA), being alkaline and endowed with excellent pozzolanic properties, a silt loam texture, and plant nutrients, has the potential to improve soil quality and productivity. Long-term field trials with groundnut, maize, and sun hemp were carried out to study the effect of LFA on growth and yield. Before crop I was sown, LFA was applied at various doses with and without press mud (an organic waste from the sugar industry, used as an amendment and source of nutrients). LFA with and without press mud was also applied before crops III and V were cultivated. Chemical fertilizer, along with gypsum, humic acid, and biofertilizer, was applied in all treatments, including the control. With one-time and repeat applications of LFA (with and without press mud), yield increased significantly (7.0-89.0%) in relation to the control crop. The press mud enhanced the yield (3.0-15.0%) with different LFA applications. The highest yield LFA dose was 200 t/ha for one-time and repeat applications, the maximum yield being with crop III (combination treatment). One-time and repeat application of LFA (alone and in combination with press mud) improved soil quality and the nutrient content of the produce. The highest dose of LFA (200 t/ha) with and without press mud showed the best residual effects (eco-friendly increases in the yield of succeeding crops). Some increase in trace- and heavy-metal contents and in the level of gamma-emitters in soil and crop produce, but well within permissible limits, was observed. Thus, LFA can be used on a large scale to boost soil fertility and productivity with no adverse effects on the soil or crops, which may solve the problem of bulk disposal of fly ash in an eco-friendly manner.