Abolishing cadmium toxicity in Chlorella vulgaris by ascorbic acid, calcium, glucose and reduced glutathione

Addition of ascorbic acid, calcium (Ca2+), glucose and reduced glutathione (GSH) to the cadmium (Cd2+)-amended Kuhl medium significantly accelerated the growth and chlorophyll content of Chlorella vulgaris. This enhancement was found to be dose dependent. Their relative effectiveness against Cd2+ on growth and chlorophyll content has been arranged as GSH > Ca2+ > glucose > ascorbic acid. However, Ca2+ offered more protection against Cd2+ toxicity on protein contents, followed by ascorbic acid, GSH and glucose. The different concentrations of all amelioratives completely alleviated the toxicity of Cd2+ on total carbohydrates to exceed the control level. Photosynthetic oxygen evolution showed more response to Ca2+ and glucose in alleviating Cd2+ toxicity. On the other hand, at certain concentrations, GSH, Ca2+, ascorbic acid and glucose stimulated respiratory oxygen uptake over the control level. The uptake of Cd2+ dropped significantly in cultures supplemented with 20 microM ascorbic acid, glucose and GSH, while Ca2+ (30 microM) significantly lowered the Cd2+ uptake by 58% indicating that Ca2+ had a more antagonistic effect against Cd2+.     

Effects of copper, chromium and nickel on growth, photosynthesis and chlorophyll a synthesis of Chlorella pyrenoidosa 251

Individual and combined effects of three heavy metals; namely, copper, chromium and nickel, on growth, photosynthesis and chlorophyll a synthesis of the unicellular green alga, Chlorella pyrenoidosa 251, were determined. Within the concentration range of 0.1 to 1.0 mg litre(-1) of the three heavy metals tested on growth, photosynthesis and chlorophyll a synthesis of the alga, the order of toxicity of the three heavy metals was copper > chromium > nickel. The presence of one of the three heavy metals interacted synergistically with the other two heavy metals in various bimetallic combinations on growth, photosynthesis and chlorophyll a synthesis of the alga.     

Accumulation in and effects of lead and cadmium on waterfowl and passerines in northern Idaho

Waterfowl and passerines in northern Idaho in 1987 had high levels of lead in their blood and tissues that originated primarily from mining and smelting activities. Four Canada geese (Branta canadensis) and one common goldeneye (Bucephala clangula) found dead contained 8 to 38 microg/g (wet mass) of lead in their livers. These levels exceed the lower lethal limit of 5 microg/g in experimental birds. Two of the Canada geese (one each from the contaminated and reference areas) died with ingested lead shotgun pellets (shot) in their gizzards, whereas the other three birds from the contaminated area contained no ingested shot and evidently died from ingesting environmental lead in sediment or biota. Lead burdens in most American robins (Turdus migratorius) and mallards (Anas platyrhynchos) were high, whereas those in tree swallows (Tachycineta bicolor) were slightly elevated. Lead accumulated to potentially hazardous levels in blood and tissues of some nestling robins (maxima of 0.87 microg/g in blood and 5.6 microg/g in liver) and mallards (maxima of 10.2 microg/g in blood and 2.8 microg/g in liver). In mallards, lead levels and associated physiological characteristics of blood were significantly different in juveniles (HY) versus adults (AHY). Activity of delta-aminolevulinic acid dehydratase (ALAD) was about 87 to 95% lower than values for control birds in experimental studies. Activity of ALAD was significantly inversely correlated with blood lead levels. Cadmium was detected in kidneys of most birds, but even the maximum concentration of 7.5 microg/g in an AHY mallard was below known harmful levels.     

Arsenic accumulation and physiological attributes of spinach in the presence of amendments: an implication to reduce health risk

The current study examined the effect of calcium (Ca) and ethylenediaminetetraacetic acid (EDTA) on arsenic (As) uptake and toxicity to spinach (Spinacia oleracea) as well as assessed the potential human health risks. Spinach seedlings were exposed to three levels of As (25, 125, and 250 μM) alone or together with three levels of EDTA (25, 125, and 250 μM) and Ca (1, 5, and 10 mM). The effect of EDTA and Ca was assessed in terms of As contents in roots and shoots, hydrogen peroxide production, chlorophyll contents, and lipid peroxidation. The accumulation and toxicity of As to spinach plants increased with increasing As levels in nutrient solution. Exposure to As resulted in lipid peroxidation and reduced chlorophyll contents. The highest level of As alone (250 μM) showed highest human health risk (hazard quotient of 7.09 at As-250). Addition of EDTA enhanced As accumulation by spinach, while reduced As toxicity to spinach, as well as human health risk (hazard quotient of 4.01 at As-250). Similarly, Ca significantly reduced As toxicity to spinach and the human health risks (hazard quotient of 3.79 at As-250) by reducing its accumulation in spinach. Higher levels of Ca were more effective in reducing As uptake and toxicity as well as enhancing chlorophyll contents.     

Interaction of bioaccumulation of heavy metal chromium with water relation, mineral nutrition and photosynthesis in developed leaves of Lolium perenne L

Contamination by chromium (Cr) is widespread in agricultural soils and industrial sites. This heavy metal represents a risk to human health. In order to gain fundamental insights into the nature of the adaptation to Cr excess, the characterisation of physiological indices, including responses of photosynthetic gas exchange and chlorophyll a fluorescence along with changes in mineral nutrient contents and water status were studied in ray grass (Lolium perenne L.). Increased concentrations of Cr(VI) (0-500 microM Cr) in the Co?c and Lessaint nutrient solution were applied. The growth of Lolium perenne is decreased by chromium and the leaves have lost their pigments. Chromium accumulation was greater in roots than in leaves and reached 2450 and 210 microg g(-1) DW, respectively with 500 microM Cr(VI) in nutrient medium. The physiological parameters were severely reduced by this heavy metal. Cr induced toxicity arising from 100 microM Cr(VI) and resulted in a modification of mineral content in roots and leaves, especially for Ca, Mg and Fe. The chromium stress decreased CO2 assimilation rates mainly due to stomatal closure, which reduced water loss by transpiration without decreasing the cellular available CO2. The fluorescence parameters associated with photosystem II (PSII) activity and the photochemical activity are modified by chromium. Non-radiative energy dissipation mechanisms were triggered during stress since non-photochemical quenching was increased and efficiency of excitation capture by open centers was reduced.     

Impact of four pesticides on the growth and metabolic activities of two photosynthetic algae

The acute toxicity was determined for soil algae Chlorella kesslerei and Anabaena inaequalis, exposed to pesticides lindane, pentachlorophenol (PCP), isoproturon (IPU), and methyl parathion (MP). Toxicity markers included growth inhibition, chlorophyll biosynthesis, and total carbohydrate content, as a function of dose and time. Concentration response functions (EC50) were estimated by probit data transformation and weighted linear regression analyses. Lindane's toxicity to Chlorella increased sharply with time (EC50 = 7490, 10.3, 0.09 mg L(-1); 24, 48, 72 h), but remained nearly constant through 72 h with Anabaena (8.7-6.7 mg L(-1); 24-72 h). PCP at low concentrations stimulated algal growth and chlorophyll a production, an effect reversed at higher doses. Anabaena was less tolerant of PCP and MP than was Chlorella. The 96-h static EC50 values for Chlorella were: 0.003, 34, 0.05, and 291 mg L(-1) for lindane, PCP, isoproturon, and MP, respectively; for Anabaena, these were 4.2, 0.13, 0.21, and 19 mg L(-1). Carbohydrate production responses were similar to those of cell density (growth) and chlorophyll biosynthesis, with MP having the lowest adverse impact. The overall relative toxicity among the four tested pesticides was: for Chlorella, lindane > IPU > PCP > MP; and for Anabaena, PCP > IPU > lindane > MP. The results confirm that toxicants such as these pesticides may affect individual (though related) species to significantly different degrees.     

Chromium induced lipid peroxidation in the plants of Pistia stratiotes L.: role of antioxidants and antioxidant enzymes

In the plant, Pistia stratiotes L., the effect of different concentrations of chromium (0, 10, 40, 80 and 160 microM) applied for 48, 96 and 144 h was assessed by measuring changes in the chlorophyll, protein, malondialdehyde (MDA), cysteine, non-protein thiol, ascorbic acid contents and superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) activity of the plants. Both in roots and leaves, an increase in MDA content was observed with increase in metal concentration and exposure periods. In roots, the activity of antioxidant enzymes viz. SOD and APX increased at all the concentrations of Cr at 144 h than their controls. The GPX activity of the treated roots increased with increase in Cr concentration at 48 and 96 h of exposures, however, at 144 h its activity was found declined beyond 10 microM Cr. The level of antioxidants in the roots of the treated plant viz. cysteine and ascorbic acid was also found increased at all the concentrations of Cr at 144 h than their respective controls, however, an increase in the non-protein thiol content was recorded up to 40 microM Cr followed by decrease. The chlorophyll content decreased with increase in Cr concentrations and exposure periods. However, the protein content of both roots and leaves were found decreased with increase in Cr concentrations at all the exposure periods except an increase was recorded at 10 microM Cr at 48 h. In Cr treated plants, the no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for leaves chlorophyll and protein contents were 40 and 80 microM Cr, respectively after 48 h exposure while NOEC and LOEC for root protein content were 10 and 40 microM, respectively after 48 h. The analysis of correlation coefficient data revealed that the metal accumulation in the roots of the plant was found positively correlated with antioxidant parameters except SOD after 48 h of exposure, however, negatively correlated with most of all the parameters studied at 144 h in both part of the plant. It may be suggested from the present study that toxic concentrations of Cr cause oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, the higher levels of enzymatic and non-enzymatic antioxidants suggest the reason for tolerating higher levels of metals.     

Cadmium accumulation and its influence on lipid peroxidation and antioxidative system in an aquatic plant, Bacopa monnieri L

Bacopa monnieri L. plants exposed to 10, 50, 100 and 200 microM cadmium (Cd) for 48, 96 and 144 h were analysed with reference to the accumulation of metal and its influence on various enzymatic and non-enzymatic antioxidants, thiobarbituric acid reactive substances (TBARS), photosynthetic pigments and protein content. The accumulation of Cd was found to be increased in a concentration and duration dependent manner with more Cd being accumulated in the root. TBARS content of the treated roots and leaves increased with increase in Cd concentration and exposure periods, indicating the occurrence of oxidative stress. Induction in the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guiacol peroxidase (GPX) was recorded in metal treated roots and leaves of B. monnieri. In contrast, a significant reduction in catalase activity in Cd treated B. monnieri was observed. An increase was also noted in the levels of cysteine and non-protein thiol contents of the roots of B. monnieri followed by a decline. However, in leaves, cysteine and non-protein thiol contents were found to be enhanced at all the Cd concentrations and exposure periods. A significant reduction in the level of ascorbic acid was observed in a concentration and duration dependent manner. The total chlorophyll and protein content of B. monnieri decreased with increase in Cd concentration at all the exposure periods. Results suggest that toxic concentrations of Cd caused oxidative damage as evidenced by increased lipid peroxidation and decreased chlorophyll and protein contents. However, B. monnieri is able to combat metal induced oxidative injury involving a mechanism of activation of various enzymatic and non-enzymatic antioxidants.     

Screening of lead exposure among workers in Selangor and Federal Territory in Malaysia

The study of lead exposure among workers in Selangor and the Federal Territory was carried out based on the delta-aminolevulinic acid (ALA) level in urine. Occupations which are expected to have higher lead exposure were chosen in this research. The ALA level in the workers' urine was linked to a few variables which may contribute to the lead level in the body. The result of this study showed that the ALA level of the urine of university students (0.352 +/- 0.038 mg/100 ml) < clerical staff (0.560 +/- 0.043 mg/100 ml) < traffic police (0.612 +/- 0.064 mg/100 ml) < vehicle workshop workers (0.673 +/- 0.099 mg/100 ml) < petrol kiosk workers (0.717 +/- 0.069 mg/100 ml) < bus drivers/conductors (0.850 +/- 0.055 mg/100 ml) which was similar to workers in the printing industry (0.852 +/- 0.110 mg/100 ml). The ALA levels in the urine of the exposed workers were significantly different from the control group (university students). However, results obtained from clerical staff revealed that they were also in the exposed group category. Analysis of variance showed that the exposed groups are in a population which is different from the control population. Correlation tests suggest that there is no significant connection between the ALA level in the urine and the variables tested. Furthermore, Duncan's Multiple Range Test showed no significant differences between the smoking/non smoking group, alcoholic/non-alcoholic group, race and sex (p > 0.05).     

ALAD genotypes and blood lead levels of neonates and children from e-waste exposure in Guiyu,China

Extensive e-waste recycling activity in Guiyu, China, has been conducted using primitive techniques for the last 20 years, resulting in serious heavy metal environmental contamination. A polymorphic variant of the δ-aminolevulinic acid dehydratase (ALAD) gene has been found to influence lead uptake and, thus, may influence an individual’s susceptibility to lead toxicity. We therefore explored whether the ALAD gene polymorphism affects blood lead levels of newborns and children in Guiyu. A total of 273 newborns and 504 children, and a combination of 2004/2005 and 2006 independent recruitments were used for this study. Umbilical cord blood from newborns (Guiyu/exposed group 189 vs. Chaonan/reference group 84) and venous blood from children (exposed group, 319 vs. Chendian/reference group 185) were collected. Blood lead levels (BLLs) were measured via graphite furnace atomic absorption spectrometry (GFAAS) for all samples, while ALAD genotyping was performed using PCR-RFLP for 273 neonate cord blood and 246 children’s blood. The median BBLs of neonates in exposed group vs. the reference group were 10.50 (2.36–40.78) vs. 7.79 (0.8–19.51) for 2004/2005 and 9.41 (9.28–47.60) vs. 5.49 (0.35–18.68) for 2006, while child mean BLLs were 15.31?±?5.79 vs. 9.94?±?4.05 for 2004/2005 and 13.17?±?5.98 vs. 10.04?±?4.85 for 2006. The genotype frequencies in newborns were 98.90 % for the ALAD-1/ALAD-1 homozygote and 1.10 % for the ALAD-1/ALAD-2 heterozygotes, while the values were 95.93 and 4.07 %, respectively, in children. The allele frequencies of the ALAD-1 and ALAD-2 were 99.45 and 0.55 % for newborns, but 97.97 and 2.03 % for children, respectively. No significant differences in blood lead levels were found between ALAD-1/ALAD-1 and ALAD-1/ALAD-2 either in newborns or in children. The frequency distribution of the ALAD-2 allele in newborns from the exposed group was lower than that of the reference group. There were no significant differences, between the two different ALAD genotypes in the lead load of newborns and children. The frequency distribution of ALAD gene does not influence the blood lead levels of newborns and children in this case, which means that the higher lead burden in the exposed children was possibly influenced by e-waste recycling, but not ALAD genotypes.     

5-Aminolevulinic acid ameliorates cadmium-induced morphological, biochemical, and ultrastructural changes in seedlings of oilseed rape

Due to its prolific growth, oilseed rape (Brassica napus L.) can be grown successfully for phytoremediation of cadmium (Cd)-contaminated soils. Nowadays, use of plant growth regulators against heavy metals stress is one of the major objectives of researchers. The present study evaluates the ameliorate effects of 5-aminolevulinic acid (ALA, 0, 0.4, 2, and 10 mg/l) on the growth of oilseed rape (B. napus L. cv. ZS 758) seedlings under Cd stress (0, 100, and 500 μM). Results have shown that Cd stress hampered the seedling growth by decreasing the radical and hypocotyls length, shoot and root biomass, chlorophyll content, and antioxidants enzymes. On the other hand, Cd stress increased the level of malondialdehyde (MDA) and production of H₂O₂ and accumulation of Cd in the shoots. The microscopic study of leaf mesophyll cells showed that toxicity of Cd totally destroyed the whole cell structure, and accumulation of Cd also appeared in micrographs. Application of ALA at lower dosage (2 mg/l) enhanced the seedling growth and biomass. The results showed that 2 mg/l ALA significantly improved chlorophyll content under Cd stress and decreased the level of Cd contents in shoots. Application of ALA reduced the MDA and H₂O₂ levels in the cotyledons. The antioxidants enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase, and superoxide dismutase) enhanced their activities significantly with the application of 2 mg/l ALA under Cd stress. This study also indicated that higher dosage of ALA (10 mg/l) imposed the negative effect on the growth of oilseed rape. Microscopic study showed that application of ALA alleviated the toxic effects of Cd in the mesophyll cell and improved the cell structure. Use of 2 mg/l ALA under 500 μM Cd was found to be more effective, and under this dosage, cell structure was clear, with obvious cell wall and cell membrane as well as a big nucleus, which was found with well-developed two or more nucleoli. Chloroplast was almost round in shape and contained thylakoids membranes and grana, but starch grains were not found in chloroplast comparatively to other treatments. On the basis of our results, we can conclude that ALA has a promotive effect which could improve plant survival under Cd stress.     

Haematological parameters as predictors of blood lead and indicators of lead poisoning in the black duck (Anas rubripes)

The validity of various haematological parameters as indicators of blood lead concentration and lead poisoning in the black duck (Anas rubripes) is discussed. Elevated (> 40 microg dl(-1)) blood lead (PbB) levels were recorded in 41% of the 229 wild birds examined. No correlation was found between PbB concentration and haematocrit. Zinc protoporphyrin (ZPP) was positively correlated with PbB. Haemoglobin, delta-aminolevulinic acid dehydratase (ALA-d) activity and non-activated/activated ALA-d ratios were negatively correlated with PbB. The minimum PbB levels at which these parameters were affected varied greatly. ZPP and haemoglobin were relatively insensitive to PbB concentrations; whilst ALA-d activity and ALA-d ratio were influenced by PbB concentrations of < 5 microg dl(-1). Log(10) ALA-d ratio was more strongly correlated with PbB (r = -0.953) than log(10) ALA-d activity (r = -0.914) and the predictive validity (% false -ve and +ve predictions) of the ratio method was higher. The high individual variability in ALA-d activities at low PbB levels was greatly reduced by the use of the ALA-d ratio method. The ALA-d ratio method proved the most efficient for screening black duck for lead poisoning in the field.     

Method for determining toxicologically relevant cadmium residues in the earthworm Eisenia fetida

In the present study, we investigated the contribution of methylsulfonyl metabolite derived from 1,2,4-trichlorobenzene (1,2,4-TCB) on the delta-aminolevulinic acid (ALA) synthetase induction by the parent compound in rats. The time courses of increasing of hepatic microsomal total cytochrome P450 content after a single i.p. administration of 1,2,4-TCB (1.36 mmol/kg), and 2,3,5- and 2,4,5-trichlorophenyl methyl sulfones (2,3,5- and 2,4,5-TCPSO2Mes) (50 micromol/kg each) were in parallel with those of increasing of the total heme content in liver microsomes. 1,2,4-TCB significantly increased the heme oxygenase activity, but 2,3,5- and 2,4,5-TCPSO2Mes did not. On the other hand, 1,2,4-TCB and 2,3,5-TCPSO2Me markedly enhanced the ALA synthetase activity. No change was observed in this enzyme activity after the administration of 2,4,5-TCPSO2Me. After the administration of 1,2,4-TCB to the rats treated with DL-buthionine-(S,R)-sulfoximine (BSO) and to the non-BSO-treated rats, the concentrations of both 2,3,5- and 2,4,5-TCPSO2Mes were significantly lower in liver of the BSO-treated rats than in liver of the non-BSO-treated rats. Additionally, the 1,2,4-TCB did not elevate the ALA synthetase activity in the BSO-treated rats. On the other hand, the administration of 2,3,5-TCPSO2Me to BSO-treated rats resulted in induction of ALA synthetase. The results strongly suggest that the methyl sulfone derived from 1,2,4-TCB, i.e., 2,3,5-TCPSO2Me, contributes highly to the induction of the ALA synthetase activity by the parent compound.     

The copper tolerance strategies and the role of antioxidative enzymes in three plant species grown on copper mine

This study was undertaken to identify the strategies and the status of antioxidant enzyme activities involved in three plant species tolerance against Cu-toxicity in copper mine. The following methods were used for evaluations in three wild type species; Datura stramonium, Malva sylvestris and Chenopodium ambrosioides. The level of chlorophyll and the activities of superoxide dismutase (SOD), glutathione peroxidase (GPX) and catalase (CAT) by spectrometry, malondialdehyde (MDA) and dityrosine by HPLC and the levels of Cu in tissues and soils by atomic absorption spectrometry (AAS).

Analysis showed that total and available copper were at toxic levels for plants growing on contaminated soil (zone 1). However, there were not any visual and conspicuous symptoms of Cu toxicity in plant species. Among three species, excess copper was transferred only into the D. stramonium and C. ambrosioides tissues. The C. ambrosioides accumulated Cu in roots and then in leaves, in which the leaves chloroplasts stored Cu around two times of vacuoles. In D. stramonium most of Cu was accumulated in leaves in which the storage rate in vacuoles and chloroplasts were 42% and 8%, respectively. In zone 1, the chlorophyll levels increased significantly in leaves of C. ambrosioides with respect to the same plant growing on uncontaminated soil (zone 2). There was insignificant decrease in chlorophyll content of D. stramonium leaves, collected from zone 1 with respect to zone 2. The D. stramonium and C. ambrosioides in zone 1, both revealed significant increase in their tissues antioxidant enzyme activities in comparison with the same samples of zone 2. There was significant elevation in oxidative damage biomarkers; MDA and dityrosine, when the aerial parts of D. stramonium in zone 1 were compared with the same parts of zone 2.

We concluded that there were different tolerance strategies in studied plant species that protected them against copper toxicity. In M. sylvestris, exclusion of Cu from the roots or its stabilization in the soil restricted Cu toxicity effects. On the other hand D. stramonium and C. ambrosioides, elevated their antioxidative enzyme activities in response to cu-toxicity. In addition, the species D. stramonium accumulated excess of Cu in leaves vacuoles.     

Effects of nitrogen dioxide on leaf chlorophyll and nitrogen content of soybean

One-month-old soybean (Glycine max [L.] Merrill), cultivar 'Williams', plants were exposed to nitrogen dioxide (0.1, 0.2, 0.3 and 0.5 ppm) and carbon filtered air (control), 7 h per day, for 5 days, under a controlled environment. Leaf chlorophyll content (Ch a, Ch b, and total Ch content) and foliar nitrogen content (%N) were determined before and after the exposure. The influence of NO(2) treatments up to 0.3 ppm on leaf chlorophyll content was negligible although a stimulatory effect was evident in Ch a and total Ch content with 0.2 ppm NO(2). Marked decline in Ch content was observed with 0.5 ppm treatment; the reductions in Ch a and total Ch were 45% and 47%, respectively. Foliar-N contents of plants treated with 0.2 and 0.3 ppm NO(2) were higher than the control; plants exposed to 0.5 ppm NO(2) showed a 41% reduction in foliar-N compared to pre-exposure values.     

Excess chromium alters uptake and translocation of certain nutrients in citrullus

Citrullus plants were grown in refined sand with varying levels of chromium to determine their tolerance limit to excess chromium. The plants were maintained in control nutrient solution for 24 days and on the 25th day chromium as dichromate was added at 0.05, 0.1, 0.2, 0.3 and 0.4 mM. A control set of plants was grown in the same nutrient solution without chromium. At chromium levels >0.2 mM plants showed growth depression, with chlorosis and loss of turgor of middle leaves. Affected leaves had narrow lamina; tendrils were thin, short and did not have coiling property. Later chlorosis became severe and changed to necrosis in patches. Petiole along with lamina became wilted, rugged and hung down due to complete loss of water. At lower chromium concentration, (0.05, 0.1 and 0.2 mM) only depression in growth was observed. With increase in chromium concentration of nutrient solution accumulation of chromium in different parts of Citrullus was increased. Increase in concentrations of phosphorus, manganese and decrease in iron, copper, zinc and sulphur were observed in leaves. Toxicity of chromium was greater at 0.2-0.4 mM, compared to lower concentrations. Threshold of toxicity and toxicity of Cr in old leaves were, respectively, 0.9 and 3.9 microg g(-1) dry matter of citrullus.     

Effects of nitrogen dioxide on biochemical and physiological characteristics of soybean

One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).     

Effect of humic acid on water chemistry, bioavailability and toxicity of aluminium in the freshwater snail, Lymnaea stagnalis, at neutral pH

The influence of humic acid on the water chemistry of environmentally relevant concentrations of Al at neutral pH was studied, together with its effect on the bioavailability and toxicity of Al in Lymnaea stagnalis. Humic acid significantly reduced the loss of Al from the water and increased the fraction of filterable Al, although this was a relatively small fraction of total Al. Filterable Al concentration in the presence or absence of humic acid was independent of initial Al concentration. Humic acid only partly reduced toxicity, as observed by a reduction in behavioural suppression, and had no effect on the level of Al accumulated in tissues. These results suggest that humic acid maintains Al in a colloidal form that is bioavailable to L. stagnalis. However, these colloidal Al-humic acid species were less toxic since behavioural toxicity was reduced. Humic acid may play an important role in limiting the toxicity of Al to freshwater organisms.     

Accumulation of chromium (VI) from aqueous solutions using water lilies (Nymphaea spontanea)

This study describes an investigation using tropical water lilies (Nymphaea spontanea) to remove hexavalent chromium from aqueous solutions and electroplating waste. The results show that water lilies are capable of accumulating substantial amount of Cr(VI), up to 2.119 mg g(-1) from a 10 mg l(-1) solution. The roots of the plant accumulated the highest amount of Cr(VI) followed by leaves and petioles, indicating that roots play an important role in the bioremediation process. The maturity of the plant exerts a great effect on the removal and accumulation of Cr(VI). Plants of 9 weeks old accumulated the most Cr(VI) followed by those of 6 and 3 weeks old. The results also show that removal of Cr(VI) by water lilies is more efficient when the metal is present singly than in the presence of Cu(II) or in waste solution. This may be largely associated with more pronounced phytotoxicity effect on the biochemical changes in the plants and saturation of binding sites. Significant toxicity effect on the plant was evident as shown in the reduction of chlorophyll, protein and sugar contents in plants exposed to Cr(VI) in this investigation.