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Four cyanobacterial biofilms, raised from cyanobacterial mats and dominated by Phormidium and Oscillatoria spp., were successfully grown attached to polyester mesh discs, and were tested for their probable application in [Formula: see text] -P removal from domestic sewage and other nutrient enriched wastewaters. Biofilm # 2, dominated by Phormidium fragile, best removed [Formula: see text] -P; nevertheless, some of it also grew outside the substrate making harvesting difficult. Other biofilms also efficiently removed [Formula: see text] -P from the medium in the following order: Biofilm # 1 > Biofilm # 3 > Biofilm # 4. Their growths were restricted to discs and are therefore better candidates as they can be efficiently harvested after [Formula: see text] -P removal. [Formula: see text] -P removal was primarily due to its uptake during growth of the biofilm rather than because of precipitation as pH of the medium remained <8.5. [Formula: see text] -N concentration in the medium determined [Formula: see text] -P removal efficiency of the test biofilms and therefore optimum N:P ratio is necessary for optimizing [Formula: see text] -P removal. The test biofilms could also efficiently remove [Formula: see text] -N from the medium., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The response of a laboratory-raised phytoplankton assemblage to copper and zinc enrichment was studied. Higher intracellular accumulation of both the test metals caused disappearance of metal sensitive species, loss of diversity and species richness, reduced growth rate, Chl a and biovolume; however, the community could recover after 14 days of incubation. Cyanobacteria showed marked sensitivity to both the test metals besides some diatoms, such as, Cyclotella meneghiniana and Melosira granulata. Metal enrichment enhanced the relative abundance of species like Scenedesmus quadricauda, Oocystis borgei, Achnanthes exigua, Fragilaria capucina and Nitzschia amphibia, and these were apparently metal tolerant. Cu and Zn stress induces formation of lipid bodies (bigger in size as well as in number) and morphological abnormalities in diatoms. Among these two metals, Cu impact was higher than Zn despite the fact that the intracellular accumulation of Zn was higher than Cu. Deformed raphe and mixed deformities in diatoms were exclusively found under heavy metal stress which was well supported by regression analysis. Finally the present study gives new insight for using diatoms as an effective tool for biomonitoring and biofuel production.

The present study explores the tolerance and metal removal response of a well-developed 2-week-old Phormidium mat after long-term exposure to Cu(2+)-enriched medium. Cu(2+) enrichment inhibited increase in mat biomass in a concentration-dependent manner. Mat area and the number of entrapped air bubbles decreased as Cu(2+) concentration increased in the medium. Decrease in number of air bubbles obviously reflects the adverse effect of Cu(2+) on photosynthetic performance of the mat. Metal enrichment did not substantially alter the amount of pigments, such as chlorophyll a, chlorophyll b, carotenoids, and phycocyanin, in the mat. Enhancement of Cu(2+) concentration in the medium led to changes in species composition of the test mat; however, Phormidium bigranulatum always remained the dominant organism. Relative share of green algae and some cyanobacterial taxa, namely, Lyngbya sp. and Oscillatoria tenuis, in the mat were increased by Cu(2+) enrichment. The mat successfully removed 80 to 94 % Cu(2+) from the growth medium containing 10 to 100 μM Cu(2+). Extracellular polysaccharides, whose share increased in the mat community after metal addition, seem to have contributed substantially to metal binding by the mat biomass.

Prompted by the fact that interaction of metals with cyanobacterial mats has been little studied, the present study evaluates the response of a cyanobacterial mat, dominated by Phormidium bigranulatum, to elevated concentrations of Cd²⁺ in the medium. The mat failed to grow at 7 μM of Cd²⁺ when the metal as also the mat inoculum were simultaneously added to the medium right in the beginning of the experiment due to marked sensitivity of P. bigranulatum, the main constituent of the mat, to high concentrations of Cd²⁺. However, the mat previously grown in Cd²⁺-free medium for a time period of 1-4 weeks grew successfully when exposed to media containing very high concentrations of Cd²⁺. Four-week-old mat could grow at 250 μM of Cd²⁺, which has been found toxic to many cyanobacteria and algae by previous researchers. Greater tolerance of older mats to Cd²⁺ may be due to greater proportion of exopolysaccharides, which are well known to sequester metal ions extracellularly, in them. Whereas the relative proportion of P. bigranulatum declined at high concentrations of the test metal that of green algae increased due most likely to their tolerance to Cd²⁺. Air bubbles were seen entrapped in the mat due obviously to photosynthetic activity. Elevated concentrations of Cd²⁺ reduced the number of air bubbles in the mat. Decline in number of air bubbles at high concentrations of metal ions was more prominent in the case of younger mat than in the older one. The present study also evaluated changes in species composition of mats of different age that were subsequently grown in Cd²⁺ enriched culture medium. Younger mats showed change in species composition at very low concentrations of Cd²⁺, but older mats showed little changes even at very high concentrations of the test metal. Hence older mats more strongly resisted to changes in its species composition than the younger ones upon exposure to high concentrations of Cd²⁺. The growing mat successfully removed Cd²⁺ from the medium, which was greater at lower concentrations of Cd²⁺ in the external environment., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The granules of Spirogyra neglecta biomass, diameter 0.2-0.5mm, were successfully prepared by boiling it in urea-formaldehyde mixture. Metal sorption performance of the column packed with Spirogyra granules was assessed under variable operating conditions, such as, different influent metal concentrations, bed heights and flow rates. These conditions greatly influenced the breakthrough time and volume, saturation time and volume, and the ability of the column to attain saturation after reaching the breakthrough. The experimental breakthrough curves obtained under varying experimental conditions were modeled using Bohart-Adams, Wolborska, Thomas, Yoon-Nelson and modified dose-response models. The first two models were valid only in representing the initial part of the breakthrough curves; however, the other three models were good in representing the entire breakthrough curve. The granule-packed column could be successfully used up to 6 and 9 cycles of sorption and desorption for the removal of Cu(II) and Pb(II), respectively. The column could efficiently remove different metals from real industrial effluents, and hence the test biomass (Spirogyra granules) is a good candidate for commercial application., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Live Phormidium bigranulatum-dominated mat successfully removed Pb(II), Cu(II) and Cd(II) from aqueous solution. Percent metal removal approached equilibrium within 4h, independent of mat thickness (0.2-1.6 mm), in batch system. But % metal removal increased with increase in mat thickness due to enhancement of biomass, which provided more metal binding sites. Metal accumulation decreased with increase in mat thickness due to lessened metal availability vis-à-vis biomass. Metal removal (%) increased with increasing mat area, but decreased with increasing metal concentration in the solution. In continuous flow system, metal accumulation increased with increasing volume of single or multi-metal solution passed over the mat. The mat removed all the tested metals from the multi-metal solution with almost the same efficiency. The maximum removal of the test metals occurred at the lowest tested flow rate. Raceway type ponds can be employed for large-scale use of Phormidium mat in bioremediation of metalliferous wastewaters., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The pH-dependent metal sorption by Oscillatoria- and Phormidium-dominated mats was effectively expressed by the Hill function. The estimated Hill functions can fruitfully predict the amount of metal sorbed at a particular initial pH. Pretreatment of biomass with 0.1 mmol L(-1) HCl was more effective than pretreatment with CaCl(2), HNO(3), NaOH, and SDS in enhancing metal sorption ability of the biomass. Desorption of metal ions in the presence of 100 mmol L(-1) HCl from metal-loaded mat biomass was completed within 1 h. After six cycles of metal sorption/desorption, sorption decreased by 6-15%. Only 6% and 11% of the biomass derived from the Oscillatoria sp.- and Phormidium sp.-dominated mats was lost during the cycling. The cyanobacterial mats seem to have better potential than several biomass types for use in metal sorption from wastewaters as they are ubiquitous, self-immobilized, and have good reusability., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The present study explores the suitability of chemical reaction-based and diffusion-based kinetic models for defining the biosorption of Cu(II), Cd(II) and Pb(II) by Phormidium sp.-dominated mat. The time-course data of metal sorption by the test mat significantly (r2=0.932-0.999) fitted to the chemical reaction-based models namely pseudo-first-order, -second-order, and the general rate law. However, these models fail to accurately describe the kinetics of metal biosorption due either to prefixed order or unjustifiable change in rate constant and reaction order with varying concentrations of metal and biomass in the solution. The diffusion-based models, namely, the intra-particle diffusion model and the external mass transfer model fitted well to the time-course metal sorption data, thus suggesting involvement of both external and intra-particle diffusion processes in sorption of test metals by mat biomass. However, the Boyd kinetic expression clearly showed that the external mass transfer is the dominant process., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Isotherm curves for the biosorption of Cu(II), Cd(II) and Pb(II) by the biomass of five different cyanobacterial mats (Mat # 1-5) showed concave shape and plateau. Suitability of ten different isotherm models was evaluated for the equilibrium modeling of these isotherm curves, however, only the Toth model was found appropriate. Mat # 2, dominated by Phormidium sp., was identified as an excellent metal biosorbent because: (i) the Toth estimated maximum biosorption capacity (mmol g(-1)) of Mat # 2 for Pb(II) (1.028), Cu(II) (0.696) and Cd(II) (0.549) was the highest among the tested mats and compares favourably with Langmuir estimated metal sorption capacity of many seaweeds, regarded as the best metal biosorbents, (ii) Na+, K+ and Ca2+ did not substantially inhibit the biosorption of the test metals, (iii) and total metal sorption ability of Mat # 2 increased or remained unaffected in binary and ternary metal systems., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The present study characterises sorption of two pesticides, namely, paraquat (PQ) and 2,4-dichlorophenoxyacetic acid (2,4-D) by an Oscillatoria sp.-dominated cyanobacterial mat. Sorption of PQ onto the test mat was not significantly affected by the pH of the solution within the pH range 2-7. However, 2,4-D sorption was strongly influenced by the solution pH and was maximum at pH 2. Whereas PQ sorption increased with increase in temperature, 2,4-D sorption showed an opposite trend. The sorption of PQ and 2,4-D achieved equilibrium within 1 h of incubation, independent of concentration of pesticide and mat biomass in the solution. The pseudo-second-order kinetic model better defined PQ sorption than the pseudo-first-order model, whereas 2,4-D sorption was well defined by both the models. Sorption isotherms of both the pesticides showed L-type curve. Freundlich model more precisely defined PQ sorption than Langmuir model, thereby suggesting heterogeneous distribution of PQ binding sites onto the biomass surface. However, the Langmuir model more correctly defined 2,4-D sorption, thus, indicating homogeneous distribution of 2,4-D binding sites onto the biomass surface. The test biomass is a good sorbent for the removal of PQ because it could, independent of pH of the solution, sorb substantial amount of PQ (q(max) = 0.13 mmol g(-1)).

The sorption of Cu(II) and Pb(II) by Pithophora markedly decreased as the concentration of the secondary metal ion, Cu(II) or Pb(II), increased in the binary metal solution. However, the test alga showed a greater affinity to sorb Cu(II) than Pb(II) from the binary metal solution. Mono-component Freundlich, Langmuir, Redlich-Peterson and Sips isotherms successfully predicted the sorption of Cu(II) and Pb(II) from both single and binary metal solutions. None of the tested binary sorption isotherms could realistically predict Cu(II) and Pb(II) sorption capacity and affinity of the test alga for the binary metal solutions of varying composition, which mono-component isotherms could very well accomplish. Hence, mono-component isotherm modeling at different concentrations of the secondary metal ion seems to be a better option than binary isotherms for metal sorption from binary metal solution.

Maximum sorption of Cu(II) and Pb(II) by dried filamentous green alga Pithophora oedogonia occurred at pH 4.5 and 5.0, respectively. Chemical pretreatment could not appreciably enhance the metal sorption ability of the biomass. HCl and EDTA desorbed 92-96% of the sorbed metal from the metal-loaded biomass. Sorption and desorption of both the test metals were very rapid attaining an equilibrium within 15 min. The time course data of both the processes fitted well to the pseudo-first and the pseudo-second-order Lagergren kinetic models with r2> or =0.979. The isotherm equilibrium of Cu(II) and Pb(II) followed the Redlich-Peterson and Sips model very well with r2> or =0.991. The sorption of Cu(II) and Pb(II) at varying biomass doses could be well defined by linear and hyperbolic decrease, respectively. The regenerated biomass of Pithophora has better reusability for Pb(II) than for Cu(II). A good mechanical strength of Pithophora biomass was apparent as only 10-15% loss of biomass occurred at the end of the fifth cycle.

Dried biomass of Spirogyra neglecta rapidly sorbed the test metals and the process became saturated in 10-20min. Maximum sorption of Pb(II) [116.1mgg(-1)] and Cu(II) [115.3mgg(-1)] occurred at 0.1gl(-1) biomass and 100mgl(-1) metal concentration in the solution. Sorption of Cu(II) and Pb(II) occurred optimally at pH 4.5 and 5.0, respectively. Lead(II) and Cu(II) sorption were lesser from binary metal solution than from single metal solution. Lead(II) more severely inhibited Cu(II) sorption than vice versa thus reflecting greater affinity of Pb(II) for the biomass. NaOH pretreatment slightly enhanced the metal removal ability of the biomass. During repeated sorption/desorption cycles, Pb(II) and Cu(II) sorption decreased by 11% and 27%, respectively, at the end of the fifth cycle due inter alia to 10-15% loss of biomass. Nevertheless, Spirogyra appears to be a good sorbent for removing metals Cu(II) and Pb(II) from wastewaters.

A 48 h exposure of Scenedesmus sp. to sublethal concentrations of Cu (2.5 and 10 microM) and Zn (5 and 25 microM) caused a concentration-dependent inhibition of growth, photosynthesis, respiration, NO(3)(-) uptake, and nitrate reductase (EC 1.6.6.1) activity, and a reduction in protein, carbohydrate, and photosynthetic-pigment levels with a concomitant increase in intracellular levels of the test metals. After exposure, algal cells were transferred to the basal medium without the excess level of test metals, to study the recovery of various processes. The growth of the test algae had not recovered up to 12 h after transfer to the basal medium, but some physiological parameters such as photosynthesis and respiration recovered within 6 h. The quicker recovery of photosynthesis and respiration might be used as acclimatory responses as they prepare a background for the recovery of other parameters, including growth, of the test alga by generating energy, forming photosynthate, and establishing the usual catabolism to attain normal conditions. Most of the processes recovered completely or almost completely after being stressed with 2.5 microM Cu or 5 microM Zn. However, the maintenance of a relatively high level of Cu and Zn in the cells previously exposed to 10 microM Cu and 25 microM Zn slowed down the recovery of different processes, which did not fully recover even at the end of the experiment after 96 h. The present study demonstrates that a chain of metabolic events, beginning with respiration and photosynthesis and continuing with assimilation and uptake of nutrients and subsequent restoration of other metabolic processes, is involved in the recovery of the algae from Cu and Zn stress. Each studied parameter seems to play an important role in balancing the cellular homeostasis during recovery from metal stress.

Algae are exposed to elevated levels of heavy metals in water bodies generally for a long-term, and occasionally for a short-term duration. The present study deals with oxidative stress in Scenedesmus sp., commonly found in nutrient-rich freshwaters, during short- (6h) and long-term (7d) exposure to Cu(2+) and Zn(2+). The cells accumulated almost 2- and 4-times more Cu(2+) and Zn(2+) inside the cells during long-term than during short-term exposure to these metals. But the data on photosynthetic O(2) evolution and cell viability suggest that Scenedesmus sp. experienced lesser metal stress in long-term than in short-term experiment. Although malondialdehyde content was slightly higher in the long-term experiment, the amount produced by one unit intracellular metal was significantly lower than that in the short-term experiment. Superoxide dismutase activity of Scenedesmus sp. was >30% higher during long-term than during short-term exposure to Cu(2+) and Zn(2+). But, catalase and ascorbate peroxidase activities increased only at 2.5 microM Cu(2+) and 25 microM Zn(2+) when oxidative stress was mild, but were inhibited at 10 microM Cu(2+) under intense oxidative stress. Cu(2+) and Zn(2+) reduced glutathione reductase activity and total SH content of Scenedesmus sp. in both the experiments, with greater reduction occurring in the long-term experiment. The depletion of total thiol was positively related with the intracellular level of metals. Thiols might have helped Scenedesmus sp. in overcoming metal-induced oxidative stress, but depletion of thiol pool is known to make cells vulnerable to oxidative stress. The study suggests that antioxidant enzymes play a role only under mild oxidative stress. An increased accumulation of proline seems to be an important strategy for alleviating metal-induced oxidative stress in Scenedesmus sp. The study shows that Scenedesmus sp. could acclimatize during long-term exposure to toxic concentrations of the test metals.

Many algae have immense capability to sorb metals, and there is considerable potential for using them to treat wastewaters. Metal sorption involves binding on the cell surface and to intracellular ligands. The adsorbed metal is several times greater than intracellular metal. Carboxyl group is most important for metal binding. Concentration of metal and biomass in solution, pH, temperature, cations, anions and metabolic stage of the organism affect metal sorption. Algae can effectively remove metals from multi-metal solutions. Dead cells sorb more metal than live cells. Various pretreatments enhance metal sorption capacity of algae. CaCl2 pretreatment is the most suitable and economic method for activation of algal biomass. Algal periphyton has great potential for removing metals from wastewaters. An immobilized or granulated biomass-filled column can be used for several sorption/desorption cycles with unaltered or slightly decreased metal removal. Langmuir and Freundlich models, commonly used for fitting sorption data, cannot precisely describe metal sorption since they ignore the effect of pH, biomass concentration, etc. For commercial application of algal technology for metal removal from wastewaters, emphasis should be given to: (i) selection of strains with high metal sorption capacity, (ii) adequate understanding of sorption mechanisms, (iii) development of low-cost methods for cell immobilization, (iv) development of better models for predicting metal sorption, (v) genetic manipulation of algae for increased number of surface groups or over expression of metal binding proteins, and (vi) economic feasibility.

A 4-h exposure of Scenedesmus sp. to Cu or Zn enhanced intracellular levels of both test metals and proline. The level of intracellular proline increased markedly up to 10 microM Cu, but higher concentrations were inhibitory. However, intracellular proline consistently increased with increasing concentration of Zn in the medium. Cu and Zn induced oxidative stress in the test alga by increasing lipid peroxidation and membrane permeability, and by reducing SH content. Pretreatment of the test alga with 1 mM proline for 30 min completely alleviated Cu-induced lipid peroxidation, minimized K+ efflux and also reduced depletion of the SH pool. But proline pretreatment could only slightly reduce Zn-induced oxidative stress. Interestingly, proline pretreatment increased the level of Cu (25-54%) and Zn (19-49%) inside the cells. It did not affect the activities of superoxide dismutase, ascorbate peroxidase or catalase, but improved glutathione reductase activity under Cu and Zn stress. A comparison of the effects of proline pretreatment on lipid peroxidation by Cu, Zn, methyl viologen and ultraviolet-B radiation suggests that proline protects cells from metal-induced oxidative stress by scavenging reactive oxygen species rather than by chelating metal ions. Pretreatment of cells with a known antioxidant (ascorbate) and a hydroxyl radical scavenger (sodium benzoate) considerably reduced metal-induced lipid peroxidation and proline accumulation. However, sodium benzoate had a very mild effect on Zn-induced lipid peroxidation and proline accumulation. The present study demonstrates that proline possibly acts by detoxifying reactive oxygen species, mainly hydroxyl radicals, rather than by improving the antioxidant defense system under metal stress.

A study of the effects of elevated levels of Cu2+ and Zn2+ on NO3- uptake and nitrate reductase (NR) activity in Scenedesmus sp. was carried out. The two metals inhibited NR and NO3- uptake in a concentration-dependent manner, with the latter process being inhibited more strongly than the former. After withdrawal of metal stress, NR activity and NO3- uptake recovered in a metal ion concentration-dependent manner. Dark pretreatment of the alga enhanced the toxic effects of the metal ions on NR activity and NO3- uptake. The recovery from metal stress was slower in the dark-pretreated cells in comparison to the light-pretreated cells. No recovery of NR and NO3- uptake occurred in the presence of the photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), suggesting that photosynthesis was required for the recovery from metal stress. Cycloheximide blocked the recovery of NR activity in metal-treated alga, suggesting that new enzyme synthesis was required for the recovery from metal stress.

Elevated concentrations of Cu and Zn inhibited Anabaena doliolum more severely in semicontinuous culture than in batch culture with growth and protein, chlorophyll a, and carotenoid contents generally more than two-fold more sensitive in the former culture system. The greater sensitivity of A. doliolum to test metals in semicontinuous culture was associated with their greater accumulation. The level of inhibition of various parameters of the test organism remained almost constant in semicontinuous culture, but considerable alleviation of the inhibitory effect occurred in batch culture with time concomitant with a regular decline in metal content of cells. However, metal content of cells in semicontinuous culture remained more or less constant with time, thereby causing no change in the level of inhibition. Unlike semicontinuous culture, batch culture showed considerable depletion of phosphate from the medium and a rise in pH (from 7 to 7.8). In conclusion, batch culture is not appropriate for long-term assessment of metal toxicity as it might substantially underestimate toxic effects of heavy metals.

Adsorption and uptake of Cu2+ by Chlorella vulgaris were distinguished by extracting the surface-bound Cu2+ with EDTA. The uptake of Cu2+ followed Michaelis Menten kinetics. The maximum rate of Cu2+ uptake (0.362fmolcell(-1) h(-1)) was obtained at pH 6.0. The rate of Cu2+ uptake was greater for cultures in the exponential phase of growth, and increased with a rise in temperature from 6 to 25 degrees C, thus pointing towards an active mechanism. The maximum number of Cu2+ binding sites was 3.245 fmol cell(-1) at pH 4.5. Adsorption of Cu2+ was strongly pH-dependent thereby indicating that the number and nature of metal binding sites on the cell surface change with changing chemistry of the solution. Unlike uptake, the adsorption remained unaffected by small changes in temperature. Older cultures displayed a higher Cu2+ adsorption capacity than the exponentially growing ones thus suggesting generation of new and/or additional Cu2+ binding sites on older cells of C. vulgaris. By pH titration, the cation-exchange capacity of Chlorella, measured in terms of H+/ Na+ exchange, was about 17 fmol cell(-1) at pH 10.5. Negligible cation exchange capacity at and below pH 5.0 indicated that ion exchange was not the sole mechanism of Cu2+ adsorption by Chlorella. The uptake and adsorption of Cu2+ were inhibited by 100 microM of various cations including other heavy metal ions. The general concept that cations competitively inhibit accumulation of metals in living organisms does not hold for C. vulgaris. Non-competitive, uncompetitive and mixed inhibition of Cu2+ uptake and adsorption by various cations were more common than competitive inhibition.

Kinetics and capacity of Ni2+ and Cu2+ sorption by Chlorella vulgaris were studied using single and binary metal solutions at various concentrations of these metal ions. The second-order rate law best described the kinetics of metal sorption from both single and binary metal systems. C. vulgaris preferentially sorbed Cu2+ over Ni2+ in the binary system. In comparison to the single metal system, the amounts of Ni2+ and Cu2+ sorbed at equilibrium (qe) were respectively 73% and 25%, and the initial rate of sorption (h) was ca. 50% in the case of the binary metal system. The test metals inhibited sorption of each other, thereby indicating competition between Ni2+ and Cu2+ for sorption onto non-specific binding sites. The present study showed that C. vulgaris has specific as well as non-specific sites for the binding of Ni2+ and Cu2+. Participation of these sites for sorption depended on the ratio of Ni2+ and CU2+ in solution. The maximum metal sorption capacity of C. vulgaris was 6.75 mmol g(-1) from the binary metal solution at the tested biomass concentration (100 mg dry weight l(-1)). Total metal sorption was enhanced with increasing total concentration of both the metals up to 1.6 mM, beyond which a decrease occurred. Two-dimensional contour plots were successfully used for the first time for the evaluation of metal sorption potential.

Effects of pH, temperature, EDTA and photosynthetically available radiation on the uptake and toxicity of Cd was investigated in Spirodela polyrhiza (L.) Schleid. and Azolla pinnata R. Br. In general, Cd toxicity was accentuated in conditions which favoured enhanced intracellular Cd uptake. Extracellular binding and intracellular uptake of Cd were lowered at pH values > 7 due to reduced availability of the aquo ion; consequently, toxicity was markedly reduced. At pH value < 7, extracellular binding remained unaffected, although intracellular uptake and toxicity of Cd were enhanced. This perhaps resulted from changes in membrane permeability as extracellular Cd binding was not affected by the decline in pH from 7 to 4. Moreover, speciation of Cd is known to remain unchanged throughout this pH range as most of the Cd (> 99%) remains available as the aquo ion. The presence of EDTA in the medium decreased extracellular binding, intracellular uptake and toxicity of Cd in test plants. This was due to formation of Cd-EDTA complex which was obviously not available to test plants. Elevation of temperature increased intracellular Cd uptake and this resulted in enhanced toxic effects. Similarly, increase in photosynthetically available radiation caused a slight increase in Cd uptake and toxicity in test plants. Obviously, rise in temperature or PAR increased metabolic activities of test plants thereby leading to increased Cd transport and toxicity.

A. pinnata showed a remarkable ability of taking up Cd from the external medium. Of the total Cd taken up by the test plant, surface adsorption was about 90%. Cd adsorption did not occur at a constant rate, however, an equilibrium was reached in 2 h. The uptake of Cd occurred at a constant rate. Test cations, including heavy metals (Ca, Mg, K, Na, Ni, Fe, Cu and Zn), inhibited adsorption as well as uptake of Cd. Cd adsorption was competitively inhibited by Cu, Fe and Zn, whereas Ca, Mg, K, Na and Ni caused non-competitive inhibition. Similarly, Cd uptake was competitively (Ca, Mg, Fe) or non-competitively (Na, K, Ni, Zn) inhibited by cations. Inhibition of Cd uptake by Cu was not wholly competitive.

The aqueous extract of Assam crude inhibited the uptake of NO3-, NH4+, and PO4(3-) in Anabaena doliolum and the response was essentially concentration dependent. Inhibition was most severe for the uptake of NH4+ followed in decreasing order by PO4(3-) and NO3-. Uptake of nutrients was competitively inhibited as in all the cases oil extract did not change Vmax; however, apparent Km was increased. The nature of oil components competing with nutrient ions is not certain at present. Oil-induced inhibition of nutrient uptake in cyanobacteria might be reversed in eutrophic waters rich in nutrients.

Inhibition of photosynthesis was more severe than that of respiration in Anabaena doliolum exposed to Assam crude oil, furnace oil, petrol, diesel, and kerosene. Variabilities in toxicity of these oils, which seem to be related to their aromatic and asphaltic contents, were observed. Diesel and furnace oil, due to greater concentrations of aromatics, were more toxic than other oils. The toxic effects of asphaltic fractions were similar to those of aromatics. The study showed that the effects of a particular fraction vary from oil to oil. Therefore, toxicity of an oil cannot be correctly predicted by mere estimation of its various fractions. Lower concentrations of Assam crude stimulated photosynthesis and respiration of blue-green algae (cyanobacteria); however, green algae did not show such a response. Stimulation was exerted only by paraffinic fractions of the test oils.