Phytoremediation potential of charophytes: Bioaccumulation and toxicity studies of cadmium, lead and zinc

The ability for usage of common freshwater charophytes,Chara aculeolata and Nitella opaca in removal of cadmium (Cd),lead (Pb) and zinc (Zn) from wastewater was examined.C.aculeolata and N.opaca were exposed to various concentrations of Cd (0.25 and 0.5 mg/L),Pb (5 and 10 mg/L) and Zn (5 and 10 mg/L) solutions under hydroponic conditions for 6 days.C.aculeolata was more tolerant of Cd and Pb than N.opaca.The relative growth rate of N.opaca was drastically reduced at high concentrations of Cd and Pb although both were tolerant of Zn.Both macroalgae showed a reduction in chloroplast,chlorophyll and carotenoid content after Cd and Pb exposure,while Zn exposure had little effects.The bioaccumulation of both Cd and Pb was higher in N.opaca (1544.3 μg/g at 0.5 mg/L Cd,21657.0 μg/g at 10 mg/L Pb) whereas higher Zn accumulation was observed in C.aculeolata (6703.5 μg/g at 10 mg/L Zn).In addition,high bioconcentration factor values (> 1000) for Cd and Pb were observed in both species.C.aculeolata showed higher percentage of Cd and Pb removal (> 95%) than N.opaca and seemed to be a better choice for Cd and Pb removal from wastewater due to its tolerance to these metals.     

Isolation and characterization of lead-tolerant Ochrobactrum intermedium and its role in enhancing lead accumulation by Eucalyptus camaldulensis

In this study, the potential of rhizospheric bacteria in promoting the growth and Pb accumulation by the woody plant Eucalyptus camaldulensis under hydroponic conditions was investigated for the first time. Three Pb-tolerant bacteria were isolated from the rhizosphere of E. camaldulensis grown in Pb-contaminated soils in the Bo Ngam Pb mine, Thailand. Based on analysis of partial 16S rRNA gene sequence, the three isolates were identified as Microbacterium paraoxydans BN-2, Ochrobactrum intermedium BN-3, and Bacillus fusiformis BN-4. Among these strains, O. intermedium BN-3 showed the highest tolerance to not only Pb but also Cd and Zn. After growth in the presence of Pb, the membranes of O. intermedium BN-3 cells exhibited an increase in unsaturated fatty acid levels but a decrease in fluidity. In hydroponic studies, inoculation of O. intermedium BN-3 significantly increased the biomass and Pb accumulation by E. camaldulensis compared to the uninoculated control. The results suggested the role of the natural rhizospheric bacteria localized to the root surface of E. camaldulensis in promoting Pb accumulation and plant growth. Our results indicate that O. intermedium BN-3 and other indigenous rhizospheric bacteria have the potential to improve the efficiency of phytoremediation of Pb-contaminated sites.     

Toxicity and accumulation of lead and chromium in Hydrocotyle umbellata

The aquatic plant, Hydrocotyle umbellata, was studied for its toxicity and accumulation of lead (Pb) and chromium (Cr) in a synthetic solution. Plants were cultured in a modified Hoagland's nutrient solutions supplemented with 20, 40, 60, 80, and 100 mg Pb/l as lead nitrate [Pb(NO3)2] and 2, 4, 6, 8, and 10 mg Cr/l as potassium dichromate (K2Cr2O7). They were separately harvested after 3, 6, 9, and 12 days. Plants exposed to Pb and Cr showed significant decreases in the biomass productivity and total chlorophyll content when the exposure time and metal concentration were increased. The accumulation of Pb and Cr in the plants was significantly increased, but it was not linear with the exposure time and metal concentration. Both metals were accumulated higher in the roots than in the shoots. The bioconcentration factor of Pb was higher than that of Cr at the same exposure time, indicating a higher accumulation potential of Pb than Cr in H. umbellata. Toxicity symptoms of both metals showed a reduction in the production of new plantlets, withering of petioles, and change in color of roots from light green to dark brown. Pb caused leaf chlorosis, whereas Cr caused leaf necrosis. The toxicity symptoms increased when the exposure time and metal concentration were increased.     

Histopathological alterations of Nile tilapia, Oreochromis niloticus in acute and subchronic alachlor exposure

Histopathological alterations in Nile tilapia, Oreochromis niloticus, aged 3 months and subjected to acute and subchronic alachlor exposure were studied by light microscopy LC50 values of alachlor for 24 hr 48 hr, 72 hr and 96 hr were 963.6, 563, 448, and 381.9 microg l(-1), respectively and the maximum acceptable toxicant concentration (MATC) was 350 microg l(-1). Fish were exposed to 381.9 (acute) and 35 microg l(-1) (sub-chronic) of alachlor for 24, 48, 72 and 96 hr and 90 days, respectively Gill lamellae and kidney tubules were the primary target organs for the acute toxic effect of alachlor while in the subchronic exposure, the toxic effect on the gills was less marked than that of the kidneys and liver Gill alterations included edema of the epithelial cell system, aneurisms with some ruptures, hypertrophy and hyperplasia of epithelial cells. The liver showed hydropic swelling of hepatocytes and vacuolation. Lipid vacuoles were observed in hepatocytes in the second and third month of subchronic exposure. The kidney showed hydropic swelling of tubular cells, lipid vacuole accumulation in many tubules, and nuclear pyknosis. The findings of this study could be used as a guideline forbiomonitoring programs on populations of Nile tilapia cultured near alachlor contaminated areas.     

Phytoremediation potential of Spirulina (Arthrospira) platensis: biosorption and toxicity studies of cadmium

This study examines the possibility of using Spirulina (Arthrospira) platensis TISTR 8217 to remove low concentrations of cadmium (less than 100 mg/l) from wastewater. The cyanobacteria were exposed to six different cadmium concentrations for 96 h, and the growth rate was determined using an optical density at 560 nm. The inhibiting concentration (IC50) was estimated using probit analysis. The IC50 at 24, 48, 72, and 96 h were 13.15, 16.68, 17.28, and 18.35 mg/l Cd, respectively. Cellular damage was studied under a light microscope and a transmission electron microscope. Swollen cells and fragmented filaments were observed. Cell injury increased with increasing concentrations of cadmium. Ultrastructural changes were observed in the algae exposed to cadmium concentrations both close to IC50 (14.68 mg/l) and at IC50 (18.35 mg/l). The alterations induced by cadmium were disintegration and disorganization of thylakoid membranes, presence of large intrathylakoidal space, increase of polyphosphate bodies, and cell lysis. In addition, the cadmium adsorption by algal cells was studied. Environmental factors were found to have an effect on biosorption. The uptake of cadmium was not affected by the temperature of the solution, but the sorption was pH dependent. The optimum pH for biosorption of algal cells was 7. The cadmium uptake process was rapid, with 78% of metal sorption completed within 5 min. The sorption data fit well to the Langmuir isotherm. The maximum adsorption capacity for S. platensis was 98.04 mg Cd per g biomass.     

Uptake and accumulation of cadmium, lead and zinc by Siam weed [Chromolaena odorata (L.) King & Robinson

The Siam weed, Chromolaena odorata (L.) King & Robinson, Family Asteraceae, was found to be a new Pb hyperaccumulator by means of field surveys on Pb soil and hydroponic studies. Plants from field collection accumulated 1377 and 4236mgkg(-1) Pb in their shoots and roots, respectively, and could tolerate soil Pb concentrations up to 100000 mgkg(-1) with a translocation factor of 7.62. Very low concentrations of Cd and Zn were found in plants collected from the field. Under nutrient solution culture condition, C. odorata from the contaminated site (CS) and from non-contaminated site (NCS) grew normally with all three metals (Pb, Cd, Zn) supplied. However, the relative growth rates of all treated plants decreased with increased metal concentrations. The percentage uptakes of Pb, Cd, and Zn by C. odorata increased with increasing metal concentrations. Pb concentration in shoots and roots reached its highest values (1772.3 and 60655.7mgkg(-1), respectively) at a Pb supply level of 10mgl(-1). While the maximum concentrations of Cd (0.5mgl(-1)) in shoots and roots of C. odorata were 102.3 and 1440.9mgkg(-1), and the highest concentrations of Zn (20mgl(-1)) were 1876.0 and 7011.8mgkg(-1), respectively. The bioaccumulation coefficients of Pb and Cd were greater than 1000. These results confirm that C. odorata is a hyperaccumulator which grows rapidly, has substantial biomass, wide distribution and has a potential for the phytoremediation of metal contaminated soils.     

Uptake and accumulation of lead by plants from the Bo Ngam lead mine area in Thailand

A field survey of terrestrial plants growing on Bo Ngam lead mine area, Thailand, was conducted to identify species accumulating exceptionally high concentrations of lead. Plant and soil samples were collected from five areas. Lead concentrations in surface soil ranged from 325 to 142,400 mg/kg. The highest lead concentration in soil was found at the ore dressing plant area and lowest at a natural pond area. In different areas, the concentrations of lead in plants were different when comparing various study sites. A total of 48 plant species belonging to 14 families were collected from five sampling sites. Twenty-six plant species had lead concentrations more than 1000 mg/kg in their shoots. Three species (Microstegium ciliatum, Polygala umbonata, Spermacoce mauritiana) showed extremely high lead concentrations in their shoots (12,200-28,370 mg/kg) and roots (14,580-128,830 mg/kg).     

Toxicity and bioaccumulation of cadmium and lead in Salvinia cucullata

The toxicity and accumulation of heavy metals, cadmium (Cd) and lead (Pb) in aquatic fern, Salvinia cucullata were studied. Plants were cultured in Hoagland's medium which was supplemented with 0.5,1,2, and 4 mg/l of Cd and 5, 10, and 40 mg/l of Pb and were separately harvested after 2,4,6, and 8 days. The toxicity symptoms of Cd and Pb to S. cucullata showed chlorosis on leaves. There were significant derceases in the relative growth, biomass productivity and total chlorophyll content when the exposure time and concentration were increased. The accumulation study showed the significant increases of both metals when the exposure time and concentration were increased. The roots of S. cucullata had higher Cd and Pb contents than leaves suggesting that the metals were bound to the root cells and were partially transported to the leaves.     

Alterations of organ histopathology and metallolhionein mRNA expression in silver barb, Puntius gonionotus during subchronic cadmium exposure

Common silver barb,Puntius gonionotus,exposed to the nominal concentration of 0.06 mg/L Cd for 60 d,were assessed for histopathological alterations(gills,liver and kidney),metal accumulation,and metallothionein(MT)mRNA expression.Fish exhibited pathological symptoms such as hypertrophy and hyperplasia of primary and secondary gill lamellae,vacuolization in hepatocytes,and prominent tubular and glomerular damage in the kidney.In addition,kidney accumulated the highest content of cadmium,more than gills and liver.Expression of MT mRNA was increased in both liver and kidney of treated fish.Hepatic MT levels remained high after fish were removed to Cd-free water.In contrast,MT expression in kidney was peaked after 28 d of treatment and drastically dropped when fish were removed to Cd-free water.The high concentrations of Cd in hepatic tissues indicated an accumulation site or permanent damage on this tissue.     

Growth and lead accumulation by the grasses Vetiveria zizanioides and Thysanolaena maxima in lead-contaminated soil amended with pig manure and fertilizer: a glasshouse study

Bo Ngam lead mine soils contain high concentrations of lead (up 1% total Pb) and low amounts of organic matter and major nutrients (N, P, K). A glasshouse study was conducted to compare growth performance, metal tolerance and metal uptake by two grasses, Thysanolaena maxima (Roxb.) O. Kuntze and four ecotypes of Vetiveria zizanioides (L.) Nash, syn. Chrysopogon zizanioides (L.) Roberty (three from Thailand: Surat Thani, Songkhla and Kamphaeng Phet, and one from Sri Lanka) and to study the effects of pig manure (20% and 40% w/w) and inorganic fertilizer (75 and 150 mg kg(-1)) amendments to this lead mine soil. The results showed that both T. maxima and V. zizanioides (Surat Thani and Songkhla) could tolerate high Pb concentrations in soil (10750 mg kg(-1)) and had very good growth performance. Application of pig manure increased electrical conductivity (EC) and reduced DTPA-extractable Pb concentration in the soils. Pig manure application improved the growth of vetiver, especially at 20%, application dosage. Vetiver had the highest biomass. T. maxima could not tolerate high EC values. The uptake by roots and transport of Pb to shoots of both species was reduced when soils were amended with pig manure. Application of inorganic fertilizer did not improve growth of vetiver but did improve that of T. maxima. Fertilizer application did not have any great influence on the Pb uptake in vetiver while T. maxima took up more Pb as a result of the fertilizer enhancing its biomass yield. Both species transported low Pb concentrations to shoots (8.3-179 mg kg(-1)) and accumulated higher concentrations in roots (107-911 mg kg(-1)). In summary, both species may be species well suited for phytostabilization in tropical lead mine areas.