Kamla Kulshreshtha

Chromium accumulation and toxicity in aquatic vascular plants

Chromium poisoning among leather tanners has long been known. The workers have been found to suffer from ulcers, allergic dermatitis, lung cancer, and liver necrosis due to prolonged contact with chromium salts. One of the highly catastrophic incidences of lung cancer as a result of inhaling dust containing Cr (VI) was reported in 1960 from the Kiryama factory of the Nippon-Denko concern on the island of Hokkaido, Japan.Pollution of water resources, both surface and underground, by indiscriminate discharge of spent wastes of chromium-based industries has become a serious global concern, for it has created an acute scarcity of safe drinking water in many countries. In August 1975 it was observed that underground drinking water in Tokyo near the chromium (VI))-containing spoil heaps contained more than 2000 times the permissible limit of chromium. In Ludhiana and Chennai, India, chromium levels in underground water have been recorded at more than 12 mg/L and 550–1500 ppm/L, respectively.Chromium is widely distributed in nature, occupying 21st position in the index of most commonly occurring elements in the earth’s crust. Chromium occurs in nature in the form of a compound (chromium + oxygen + iron) known as “chromite.” The geographical distribution of chromite mines is uneven. Over 95% of economically viable chromite ores are situated in the southern part of Africa. Its annual global production is ca. 9 million tons, mainly mined in the former Soviet Union, Albania, and Africa. In India, over 90% of chromite deposits are located in Sukinda Valley of Orissa.Chromium occurs in several oxidation states, ranging from Cr2+ to Cr6+, with trivalent and hexavalent states being the most stable and common in the terrestrial environment. Chromium (III) is used for leather tanning because it forms stable complexes with amino groups in organic material. In the presence of excessive oxygen, chromium (III) oxidizes into Cr (VI), which is highly toxic and more soluble in water than are other forms. Chromium (VI) can easily cross the cell membrane, whereas the phosphate-sulphate carrier also transports the chromite anions. On the other hand, Cr (III) does not utilize any specific membrane carrier and hence enters into the cell through simple diffusion. The diffusion is possible only after the formation of appropriate lipophilic ligands.Use of chromium as industrial material was discovered only 100 years ago. It was used for the first time in the production of corrosion-resistant steel (stainless steel) and coatings. Subsequently, chromium was widely deployed in various industries; namely, electroplating, dyes and pigments, textiles, photography, and wood processing. The tanning industry is one of the major users of chromium (III) salts. During leather processing the conversion of putrefactive proteinaceous matter, skin, into non-putricible is carried out by the treatment of chromium sulphate solution. According to an estimate, ca. 32 tons of chromium sulphate salts are used annually in Indian tanneries. As a result of unplanned disposal of spent tannery wastes, ca. 2000–3200 tons of chromium as element escapes into the environment. This has raised severe ecological concern and reduced the forest cover considerably.Aquatic vascular plants play an important role in the uptake, storage, and recycling of metals. The uptake of metals depends on the chemical form present in the system and on the life form of the macrophytes (floating, free floating, well rooted, or rootless). The free-floating species (Eichhornia, Lemna, Pistia) absorb elements through the roots/leaves, whereas the rootless speciesCeratophyllum demersum absorbs mainly through the finally divided leaves.Submerged species showed higher chromium accumulation than do floating and emergent ones. The order is:Elodea canadensis > Lagarosiphon major > Potamogeton crispes > Trapa natans > Phragmitis communis. Roots of water hyacinth (Eichhornia crassipes) showed an accumulation of 18.92 μmol (g dry tissue wt-1) Cr. AlthoughCeratophyllum demersum andHydrodictyon reticulatum showed lower levels of chromium accumulation, their bioconcentration factor values were very high.Floating-species duckweeds (Lemna, Spirodela) are potential accumulators of heavy metals. They have bioconcentrated Fe and Cu, as high as 78 times their concentration in wastewater. Duckweeds have also shown the ability to accumulate chromium substantially. Although duckweeds attain higher concentrations of chromium in their tissues than do other macrophytes, their bioconcentration factor (BCF) values were much lower than those reported in other aquatic species.A moderate accumulation of chromium has been found in emergent species. Plants ofScirpus validatus andCyperus esculentus accumulated 0.55 kg and 0.73 kg-1 Cr, respectively. InBacopa monnieri andScirpus lacustris accumulations of 1600 and 739 μg g-1 dw Cr, respectively, have been reported when exposed to 5 mg L-1 Cr for 168 hours in solution culture. The accumulation of Cr was greater in the root than the shoot. Higher accumulations of chromium in roots and least in shoots of emergent species have also been recorded.Phytotoxicity of chromium in aquatic environment has not been studied in detail. The mechanism of injury in terms of ultrastructural organization, biochemical changes, and metabolic regulations has not been elucidated. It has been pointed out that while considering the toxicity of heavy metals, a distinction should be made between elements essential to plants and metals that have no proven beneficial biochemical effects. For example, an increased level of chromium may actually stimulate growth without being essential for any metabolic process. In aquatic species—namely,Myriophyllum spicatum— the maximum increase in shoot length was found at 50 μgl-1 Cr. Higher concentrations up to 1000 μ gl-1 caused an almost linear reduction both in shoot weight and length. Duckweeds showed relatively greater tolerance to chromium. However, an inhibition of growth inSpirodela andLemna was found at 0.02 mM and 0.00002 mM Cr concentrations, respectively. Mortality ofL. aequinoctialis was found at 0.005 mM Cr and higher concentrations. The effective chromium concentrations (EC-50) for some aquatic species have been reported as follows:Lemna minor, 5.0 mg L-1, 14 days EC;L. Paucicostata, 1.0 mg L-1, 20 days EC;Myriophyllum spicatum, 1.9 mg L-1, 32 days EC; andSpirodela polyrrhiza, 50 mg L-1, 14 days EC.Chromium toxicity on biochemical parameters showed a reduction in photosynthetic rate at 50 μgl-1 Cr inMyriophyllum spicatum. Decrease in chlorophyll and protein contents were also recorded inNajas indica, Vallisneria spiralis, andAlternanthera sessilis with an increase in chromium concentration. InLimnanthemum cristatum, a slight reduction in chlorophyll and almost no change in control were found due to chromium toxicity. Submerged species (Ceratophyllum demersum, Vallisneria spiralis) and an emergent one (Alternanthera sessilis) showed decreases in chlorophyll as well as in protein contents when treated with chromium.Chromium-induced morphological and ultrastructural changes have been reported in several aquatic vascular plants: InLemna minor andCeratophyllum demersum, chromium-induced changes in chloroplast fine structure disorganized thylakoids with loss of grain and caused formation of many vesicles in the chloroplast. Chromium (VI) has caused stunting and browning of roots produced from the chromium-treated excised leaves ofLimnanthemum cristatum. At 226 μg/g Cr dry wt leaf tissue concentration, development of brown coloration in the hydathodes of juvenile leaves ofLimnanthemum cristatum is a characteristic chromiuminduced alteration.Aquatic vascular plants and algae may serve as effective bioindicators in respect to metals in aquatic environments. Chromium-induced morphological and ultrastructural changes inLimnanthemum cristatum have significant indicator values and could be used for assessing the level of chromium in ambient water.Wolffia globosa, a rootless duckweed, showed substantial chromium accumulation and high concentration factor (BCF) value at very low ambient chromium concentrations, suggesting its feasibility in detecting chromium pollution in water resources. Methylene blue-stained cells ofScenedesmus acutus become uniformly dark blue during chromium (VI) treatment. This may serve as an indicator of chromium pollution.

Do leaf surface characters play a role in plant resistance to auto-exhaust pollution?

Summary The significance of micro-morphologica1 leaf surface characters of plants in indication and mitigation of auto-exhaust pollution has been investigated. For the purpose of the study, the following plant species growing along roadsides in low and high traffic density areas have been selected: Asparagus racemosus , Azadirachta indica , Bougainvillea spectabilis , Cassia fistula , Ficus religiosa , Nerium indicum , Polyalthia longifolia and Thevetia neriifolia . These plants were continuously exposed to automobile emissions. As compared to control plants, the leaf surface structures changed significantly in the exposed plants. The epidermal cells collapsed, cell boundaries were irregularly fused, and a two-fold increase in stomatal frequency and trichome length could be observed. Epicuticular wax also lost its original shape, got disorganised and subsequently eroded, forming patches of a crust on the cuticle. While the surface structural changes were significant, the phenology of these plants remained unaffected by auto-exhaust pollution. The investigated species though manifesting above changes remained normal and healthy and, therefore, they may be recommended for growing along roadsides in areas polluted by automobile emissions.

Impact of fly ash soil amendment on seed germination, seedling growth and metal composition of Vicia faba L.

Abstract Fly ash disposal is a major problem in and around thermal power plants. In order to find out a solution to this problem, a study was conducted to test fly ash suitability for application to agricultural soils in a definite proportion for better plant growth. While lower application of fly ash enhanced seed germination as well as seedling growth, higher application either delayed or inhibited these processes drastically. Fly ash application to the agricultural soils increased Ni plant uptake but reduced that of Cr and Cu.

Seasonal dynamics of methane emission from wetlands

Abstract In view of its impact on the earth’s climate, methane despite its low atmospheric concentration, has assumed importance in recent years. Natural wetlands are one of the major sources for methane emission to the atmosphere. This study was carried out to find out the seasonal fluctuation in CH 4 fluxes from water bodies and the difference in the methane efflux from vegetated and unvegetated surfaces of natural and man-made water bodies as well as to investigate the edaphic factors controlling the methane production and emission. The results revealed that there were seasonal fluctuations in methane emission from both the natural and man-made water bodies. Evidently, CH 4 emission from the vegetated surface was many times higher than that from the unvegetated surface of the same water body, indicating the importance of vegetation in methane transport from sediments to atmosphere. Study of several edaphic factors like pH, redox potential, temperature and organic carbon of 10 water bodies, including 5 man-made ponds showed that all these factors largely determined CH 4 production in the sediment as reflected by its emission from water bodies.

Mitigation Strategy to Contain Methane Emission from Rice-Fields

Methane is primarily a biogenic gas, which is implicated in global climate change. Among all the sources of methane emission, paddy fields form the most dominant source. An experiment was conducted with a common paddy crop (Oryza sativa var. Vishnuparag) by amending the soils with different organic manures and biofertilizers with a view to find out an inexpensive strategy to mitigate methane emission from the rice-fields. The results revealed that there was a seasonal change in the CH4 flux, registering a peak at heading stage in all treatments. The application of rice straw before flooding and the biofertilizer after flooding enhances CH4 efflux from the rice-fields significantly, while composts of cowdung and leaves did not stimulate CH4 production and, rather, decreased CH4 fluxes. As soil pH and temperature were optimum for methanogenesis, it was likely that the organic C and the redox potential mainly modulated methane production and its emission through rice plants.

Response of Calendula officinalis L. to long-term fumigation with SO2

Abstract Seedlings of Calendula officinalis L. (30-days old) were raised in 1 m 2 plots and fumigated with 1 and 2 μg litre −1 SO 2 on alternate days. Analysis of plant samples collected at pre-flowering, flowering and post-flowering stages showed that photosynthetic pigments were degraded and leaf extract pH and protein content declined in SO 2 treated plants. In addition, scanning electron microscopic studies revealed that SO 2 stimulated the widening of stomatal pores in fumigated plants.

Effect of diesel exhaust pollution on cuticular and epidermal features of Lantana camara L. and Syzygium cuminii L. (Skeels.)

Abstract Cuticular and epidermal features of leaves of two common plant species namely, Lantana camara L. and Syzygium cuminii L. (Skeels.), growing in polluted and healthy (control) environments were studied under light and scanning electron microscopes. Polluted leaf samples were collected from the plants growing near a diesel generating set used in running a tube well. The study shows that in polluted populations of Lantana camara, the trichome frequency had increased four fold. In Syzygium cuminii, the stomatal openings were filled with dust and a tendency towards callus formation was also observed. The epidermal cells were comparatively thick walled and walls were broken at certain places. The changes observed in the cuticular and epidermal features of polluted populations of the investigated species indicate their significance as bioindicators of atmospheric pollution.

Existence of micropores on the tiller surface of Schoenoplectus subalatus: the probable port for methane emission

To find the ports for methane exit in Schoenoplectus subalatus, a known emitter of this gas, the tiller surface in different segments was examined under a scanning electron microscope, and the methane concentration was simultaneously analysed. The methane concentration dropped to one-third immediately in the third segment above the water surface where there was an aggregation of slit-like micropores. Above this segment, the frequency of micropores declined to half. This suggests that the micropores are exit ports for methane gas. The micropores were located on the papillae, were irregular in shape, and appeared to have resulted from the rupture of the cuticle, possibly under high gas pressure.

Foliar metal content and changes in epidermal traits of Lagerstroemia parviflora (L.) Roxb.

A comparative study of the physico-chemical properties of soil, leafmetal content and foliar surface traits in Lagerstroemia parviflora(L.) Roxb. plants, growing in an iron-rich mineralized and anon-mineralized area was carried out. Metal accumulation wasmaximum in summer; in the peak growing season, it declined duringthe rainy season but picked up again in winter. In leaves sampled froma mineralized region, epidermal cells were much smaller in size buthigher in number per unit area. Changes in the number and size of glandular papillae were also observed. Characteristic non-glandular,elongate trichomes with acute tip were also recorded in mineralizedpopulations. Scanning electron microscopic examination of the foliarsurface configuration revealed distortions in epicuticular wax structuresand wider cuticular striations with typically parallel arrangement inthese populations.The present study shows that high Fe-accumulation in leaves of L.parviflora during the exponential growth phase as well as changes inthe epicuticular structures may be indicators of metal stress in the populations of the mineralized area.

Photosynthesis, stomatal response and metal accumulation in Cineraria maritima L. and Centauria moschata L. grown in metal-rich soil

Two plant species, Cineraria maritima L. and Centauria moschata L. were tested for their tolerance/sensitivity in metal-rich soils derived from iron ore in Lalitpur (Girar), India, which contained high levels of Fe with appreciable amounts of Mn and Cu. The two plant species growing in the mineralized soil showed higher accumulations of Fe, Mn and Cu than those grown in non-mineralized soil. The growth of both plant species in the mineralized soil was hampered compared with those in non-mineralized soil. The rates of photosynthesis and chlorophyll content were reduced in C. maritima but not in C. moschata. The stomatal conductance and resistance were affected in C. moschata but not in C. maritima. Overall results indicate that C. maritima is more sensitive to mineralized soil than C. moschata. Secondly, C. maritima is also a good accumulator of all three metals and may be regarded as a metal efficient plant. This plant may be grown for the removal of Fe, Mn and Cu from the contaminated soils.