Accumulation of selenium by different plant species grown under increasing sodium and calcium chloride salinity

High levels of naturally occurring selenium (Se) are often found in conjunction with different forms of salinity in central California. Plants considered for use in phytoremediation of high Se levels must therefore be salt tolerant. Selenium accumulation was evaluated for the following species under increasing salt (NaCl and CaCl) conditions:Brassica napus L. (canola),Hibiscus cannibinus L. (kenaf),Festuca arundinacea L. (tall fescue), andLotus tenuis L. (birdsfoot trefoil). The experimental design was a complete randomized block with four salt treatments of <1, 5, 10, and 20 dS m^-1, four plant species, three blocks, and six replicates per treatment. Ninety days after growing in the respective salt treated soil with a Se concentration of 2 mg Se kg^-1 soil, added as Na₂SeO₄, all plant species were completely harvested. Among the species tested, shoot and root dry matter yield of kenaf was most significantly (p<0.001) affected by the highest salt treatment and tall fescue and canola were the least affected species. Generally there was a decrease in tissue accumulation of Se with increasing salt levels, except that low levels of salinity stimulated Se accumulation in canola. Canola leaf and root tissue accumulated the highest concentrations of Se (315 and 80 mg Se kg^-1 DM) and tall fescue the least (35 and 7 mg Se kg^-1 DM). Total soil Se concentrations all harvest were significantly (p<0.05) lower for all species at all salt treatments. Removal of Se from soil was greatest by canola followed by birdsfoot trefoil, kenaf and tall fescue. Among the four species, canola was the best candidate for removing Se under the tested salinity conditions. Kenaf may be effective because of its large biomass production, while tall fescue and birdsfoot trefoil may be effective because they can be repeatedly clipped as perennial crops.     

Cadmium and zinc bioaccumulation by Phytolacca americana from hydroponic media and contaminated soils

Abstract

Hydroponic, greenhouse and field experiments were conducted to explore the potential of pokeweed (Phytolacca americana L.) to accumulate Zn and Cd from nutrient solutions and contaminated soils. The hydroponic results confirmed that this native species is a strong Zn and Cd bioaccumulator that does not experience severe phytotoxicity until quite high root and shoot concentrations, approaching 4000 and 1600?mg?kg^?1 of Zn, and 1500 and 500?mg?kg^?1 of Cd, respectively. These high Zn and Cd concentrations were accompanied by increased sulfur and lower manganese in both shoots and roots. However, in field and greenhouse trials with soils historically contaminated by a number of heavy metals including Zn and Cd, concentrations of Zn and Cd in shoots of P. americana reached concentrations less than 30% and 10%, respectively, of those achieved with hydroponics. The main constraint to phytoremediation of soils by P. americana was the low concentrations of Zn and Cd in soil solution. Pretreatment of the metal-contaminated soil by oxalic acid increased soluble Cd and Zn but failed to increase plant uptake of either metal, a possible result of higher solubility of competing metal ions (Cu, Mn) or low bioavailability of Cd and Zn-oxalate complexes.     

Selenium accumulation in durum wheat and spring canola as a function of amending soils with selenite, selenate and or sulphate

Aims

A comparison was performed between plant species to determine if extractable, rather than total soil Se, is more effective at predicting plant Se accumulation over a full growing season.

Methods

Durum wheat (Triticum turgidum L.) and spring canola (Brassica napus L.) were sown in potted soil amended with 0, 0.1, 1.0, or 5.0 mg kg^?1 Se as SeO₄ ^2? or SeO₃ ^2?. In addition, SeO₄ ^2?-amended soils were amended with 0 or 50 mg kg^?1 S as SO₄ ^2?. Soils were analyzed for extractable and total concentration of Se ([Se]). Twice during the growing season plants were harvested and tissue [Se] was determined.

Results

Plants exposed to SeO₃ ^2? accumulated the least Se. Fitted predictive models for whole plant accumulation based on extractable soil [Se] were similar to models based on total [Se] in soil (R²?=?0.73 or 0.74, respectively) and selenium speciation and soil [S] were important soil parameters to consider. As well, soil S amendments limited Se toxicity.

Conclusions

Soil quality guidelines (SQGs) based on extractable Se should be considered for risk assessment, particularly when Se speciation is unknown. Predictive models to estimate plant Se uptake should include soil S, a modifier of Se accumulation.     

Soil Nitrogen Fertilization Effects on Phytoextraction of Cadmium and Lead by Tobacco (Nicotiana tabacum L.)

A greenhouse experiment using 24 plastic pots filled with 6 kg of Pb- and Cd-contaminated soil was carried out. In all 24 pots, soils were heavy metal–contaminated with 10 mg Cd kg^?1 soil and 500 mg of Pb kg^?1 soil by using CdCl and PbNO₃. Two-month-old tobacco (Nicotiana tabacum L.) plants were used to extract these heavy metals. Results showed that tobacco is able to remove Cd and Pb from contaminated soils and concentrate them in its harvestable part, that is, it could be very useful in phytoextraction of these heavy metals. Increasing additions of ammonium nitrate to soil (50, 100, and 150 mg N kg^?1 soil) significantly (p ≤ .05) increased aboveground Cd and Pb accumulation during a 50-day experimental period, whereas increasing additions of urea to soil (50 and 100 mg N kg^?1 soil) did not show these effects at the same significance levels. Increasing additions of ammonium nitrate to soil shows as dry matter increases, both accumulated Cd and accumulated Pb also increase when tobacco plants are growing under Pb- and Cd-contaminated soil conditions. Higher Pb concentrations depress Cd/Pb ratios for concentrations and accumulations, suggesting that Pb negatively affects Cd concentration and/or accumulation.     

Soil boron and selenium removal by three plant species

High concentrations of boron (B) and selenium (Se) naturally found in the environment are detrimental to sustainable agriculture in the western USA. Greenhouse pot experiments were conducted to study B and Se uptake in three different plant species; Brassica juncea (L.) Czern (wild brown mustard), Festuca arundinacea Schreb. L. (tall fescue), and Brassica napus (canola) were grown in soil containing naturally occurring concentrations of 3.00 mg extractable B kg^–1 and 1.17 mg total Se kg^–1 soil. During the growing season, four intermediate harvests were performed on wild mustard and tall fescue. Final harvest I consisted of harvesting wild mustard, canola, and clipping tall fescue. Final harvest II consisted of harvesting wild mustard, which had been planted in soil in which wild mustard was previously grown, and harvesting previously clipped tall fescue. The greatest total amount of above ground biomass and below surface biomass was produced by tall fescue. Plants were separated into shoots and roots, weighted, and plant tissues were analyzed for total B and Se. The highest concentrations of tissue B were recovered in shoots of wild mustard and canola at final harvest I, while roots from tall fescue contained the highest concentrations of B irrespective of the harvest. Tissue Se concentrations were similar in all plants species. Soils were analyzed for residual B and Se. Extractable soil B concentrations at harvest times were lowered no less than 32% and total Se no less than 24% for all three species. The planting of wild mustard, canola, or tall fescue can reduce water-extractable B and total Se in the soil.     

LEAD TOLERANCE AND ACCUMULATION IN PTERIS VITTATA AND PITYROGRAMMA CALOMELANOS,AND THEIR POTENTIAL FOR PHYTOREMEDIATION OF LEAD-CONTAMINATED SOIL

A field survey was conducted to search for Pb accumulation in fern species at Bo Ngam Pb mine, Thailand. Eleven fern species including Pteris vittata accumulated Pb in the range of 23.3–295.6 mg kg^?1 in the aboveground parts. Hydroponic, pot, and field trial experiments were carried out to investigate Pb-accumulation ability in ferns; including P. vittata and the ornamental species, Pityrogramma calomelanos, Nephrolepis exaltata cv. Gracillimum, and N. exaltata cv. Smirha. In hydroponic experiment, Pi. calomelanos accumulated the highest concentration of Pb (root 14161.1 mg kg^?1, frond 402.7 mg kg^?1). The pot study showed that P. vittata, Pi. calomelanos, and N. exaltata cv. Gracillimum grew well when grown in soil Pb at 92900 mg kg^?1. N. exaltata cv. Gracillimum accumulated the highest Pb concentration in the frond (5074 mg kg^?1) and P. vittata accumulated the highest Pb concentration in the root (16257.5 mg kg^?1). All fern species exhibited TF values less than 1 in both hydroponic and pot experiments. When P. vittata and Pi. calomelanos were grown at mine soils for 6 months, P. vittata tolerated higher soil Pb (94584–101405 mg kg^?1) and accumulated more Pb in frond (4829.6 mg kg^?1) and showed TF > 1 after 2 months of growth. These results indicated that P. vittata can be potentially useful for phytoremediation of Pb-contaminated soil.     

Combined application of arbuscular mycorrhizal fungi and steel slag improves plant growth and reduces Cd,Pb accumulation in Zea mays

Abstract

Little attention has been paid to the combined use of arbuscular mycorrhizal fungus (AMF) and steel slag (SS) for ameliorating heavy metal polluted soils. A greenhouse pot experiment was conducted to study the effects of SS and AMF?Funneliformis mosseae (Fm), Glomus versiforme (Gv) and Rhizophagus intraradices (Ri) on plant growth and Cd, Pb uptake by maize grown in soils added with 5?mg Cd kg^?1 and 300?mg Pb kg^?1 soil. The combined usage of AMF and SS (AMF?+?SS) promoted maize growth, and Gv?+?SS had the most obvious effect. Meanwhile, single SS addition and AMF?+?SS decreased Cd, Pb concentrations in maize, and the greater reductions were found in combined utilization, and the lowest Cd, Pb concentrations of maize appeared in Gv?+?SS. Single SS amendment and AMF?+?SS enhanced soil pH and decreased soil diethylenetriaminepentaacetic acid (DTPA)-extractable Cd, Pb concentrations. Furthermore, alone and combined usage of AMF and SS increased contents of soil total glomalin. Our research indicated a synergistic effect between AMF and SS on enhancing plant growth and reducing Cd, Pb accumulation in maize, and Gv?+?SS exerted the most pronounced effect. This work suggests that AMF inoculation in combination with SS addition may be a potential method for not only phytostabilization of Pb-Cd-contaminated soil but maize safety production.     

Protective effect exerted by soil phosphorus on soybean subjected to arsenic and fluoride

Objetive: Arsenic (As) and fluoride (F) are found in groundwater and soils around the world, causing different problems to crops. Because these elements compete against phosphorus (P) in soils and plants, their relationship is complex. The aim of this work was to study the oxidative stress of soybean plants subjected to different concentrations of As and F, and the effect of P.

Methods: The following 10 treatments were carried out in each of two soils with different P content: three As levels (low 10?mg?As?kg^-1, medium 50?mg?As?kg^?1 and high 100?mg As kg^?1), three F levels (low 160?mg?F?kg^?1, medium 250?mg?F?kg^?1 and high 500?mg?F?kg^?1) and three As?+?F levels (same concentrations), and the control treatment (soil with the background As and F concentrations) Lipid peroxidation, chlorophyll, gluthatione contents and antioxidant enzymes activities were determination.

Results: Increased lipid peroxidation and alterations in glutathione content, catalase, superoxide dismutase and peroxidase activities as well as in chlorophyll content revealed that As causes higher oxidative stress in plants grown in soils with low P content.

Conclusion: Stress parameters in F treatments were less affected. Plants grown in soils enriched with P revealed a decrease in the toxic effects caused by As and F.     

Phytoextraction of selenium from soils irrigated with selenium-laden effluent

This two-part study compared the efficacy of different plant species to extract Se from soils irrigated with Se-laden effluent. The species used were: Brassica napus L. (canola), Brassica juncea Czern L. and Coss (Indian mustard), and Hordeum vulgare L. (barley). In Study 1 we irrigated the plants with a saline effluent containing 0.150 mg Se L^–1, while in Study 2, the same species were planted in a saline soil selenized with 2 mg Se L^–1. Plants were simultaneously harvested 120 days after planting. In Study 1, there were only slight effects of treatment on dry matter (DM) yield. Plant Se concentrations averaged 21 g Se g^–1DM for the Brassica species, and 4.0 g Se g^–1 DM for barley. Total Se added to soils via effluent decreased by 40% for Brassica species and by 20% for barley. In Study 2, total DM decreased for all species grown in saline soils containing Se. Plant Se concentrations averaged 75 g g^–1 DM for Brassica species and 12 g Se g^–1 DM for barley. Total Se added to soils prior to planting decreased by 40% for Brassica species and up to 12% for barley. In both studies, plant accumulation of Se accounted for at least 50% of the Se removed in soils planted to Brassica and up to 20% in soils planted to barley. Results show that although the tested Brassica species led to a significant reduction in Se added to soil via use of Se-laden effluent, additional plantings are necessary to further decrease Se content in the soil.     

PHYTOEXTRACTION OF METAL POLLUTED SOILS AROUND A Pb-Zn MINE BY CROP PLANTS

In order to assess their practical capability for the absorption and accumulation of Pb, Zn, and Cu, five common crop plants, i.e. maize (Zea mays), sunflower (Helianthus annuus), canola (Brassica napus), barley (Hordeum vulgare) and White lupine (Lupinus albus) were tested in pot experiments using six soil samples taken from mine tailings, pasture and arable soils around an old Pb-Zn mine in Spain. Metal concentration ranges of the soils were 76.2–785 mg kg^?1, 127–1652 mg kg^?1, and 12.4–82.6 mg kg^?1 for Zn, Pb, and Cu, respectively. With the exception of the highest polluted sample, soil total metal concentration did not influence significantly biomass yields of each crop for the different growth substrates. The order found for the total metal accumulation rate (TMAR) in the crops was Zn>>Pb > Cu, with maize reaching the highest metal concentrations. Pb root concentrations were markedly higher than those of shoots for all the crops, while Zn and Cu were translocated to shoots more efficiently. Concentrations of metals extracted by EDTA and BCR sequential extraction were well correlated, in general, with both root metal content and TMAR. CaCl₂-extracted Zn was well correlated with root concentrations, TMAR and, in some cases, with shoot contents. Our study showed that the test crops were not feasible to remediate the heavily or moderately contaminated soils studied here in order to achieve the total metal soil concentrations required by the current European laws.     

Soil factors affecting selenium concentration in wheat grain and the fate and speciation of Se fertilisers applied to soil

UK crops have a low selenium (Se) status, therefore Se fertilisation of wheat (Triticum aestivum L.) at 10 field sites was investigated and the effect on the content and speciation of Se in soils determined. Soil characterisation was carried out at each field site to determine the soil factors that may influence wheat grain Se concentrations in unfertilised plots. Soil samples were taken after harvest from each treatment to determine the fate and speciation of selenate fertiliser applied to soil. Wheat grain Se concentrations could be predicted from soil Se concentration and soil extractable sulphur (S) using the following regression model: Grain Se?=?a?+?b(total soil Se)?+?c(extractable soil Se) - d(extractable soil S), with 86 % of the variance being accounted for, suggesting that these properties control Se concentrations in grain from unfertilised plots. Extractable soil Se concentrations were low (2.4 – 12.4 µg kg^?1) and predominantly consisted of selenite (up to 70 % of extractable Se) and soluble organic forms, whereas selenate was below the detection limit. Little of the added Se, in either liquid or granular form was left in the soil after crop harvest. Se fertilisation up to 20 g ha^?1 did not lead to a significant Se accumulation in the soil, suggesting losses of Se unutilised by the crop.     

Phytoremediation of fuel oil and lead co-contaminated soil by Chromolaena odorata in association with Micrococcus luteus

Phytoremediation is widely promoted as a cost-effective technology for treating heavy metal and total petroleum hydrocarbon (TPH) co-contaminated soil. This study investigated the concurrent removal of TPHs and Pb in co-contaminated soil (27,000 mg kg^?1 TPHs, 780 mg kg^?1 Pb) by growing Siam weed (Chromolaena odorata) in a pot experiment for 90 days. There were four treatments: co-contaminated soil; co-contaminated soil with C. odorata only; co-contaminated soil with C. odorata and Micrococcus luteus inoculum; and co-contaminated soil with M. luteus only. C. odorata survived and grew well in the co-contaminated soil. C. odorata with M. luteus showed the highest Pb accumulation (513.7 mg kg^?1) and uptake (7.7 mg plant^?1), and the highest reduction percentage of TPHs (52.2%). The higher TPH degradation in vegetated soils indicated the interaction between the rhizosphere microorganisms and plants. The results suggested that C. odorata together with M. luteus and other rhizosphere microorganisms is a promising candidate for the removal of Pb and TPHs in co-contaminated soils.     

Instances of Soil and Crop Heavy Metal Contamination in China

Both general and specific investigations of soil and crop heavy metal contamination were carried out across China. The former was focused mainly on Cd, Hg, As, Pb, and Cr in soils and vegetables in suburbs of four large cities; the latter investigated Cd levels in both soils and rice or wheat in contaminated areas throughout 15 provinces of the country. The results indicated that levels of Cd, Hg, and Pb in soils and some in crops were greater than the Governmental Standards (Chinese government limits for soil and crop heavy metal contents). Soil Cd ranged from 0.46 to 1.04?mg kg^?1, on average, in the four cities and was as high as 145?mg kg^?1 in soil and 7?mg kg^?1 in rice in the wide area of the country. Among different species, tuberous vegetables seemed to accumulate a larger portion of heavy metals than leafy and fruit vegetables, except celery. For both rice and wheat, two staple food crops, the latter seemed to have much higher concentrations of Cd and Pb than the former grown in the same area. Furthermore, the endosperm of both wheat and rice crops had the highest portion of Cd and Cr. Rice endosperm and wheat chaff accumulated the highest Pb, although the concentrations of all three metals were variable in different parts of the grains. For example, 8.3, 6.9, 1.4, and 0.6?mg kg^?1 of Pb were found in chaff, cortex, embryo, and endosperm of wheat compared with 0.11, 0.65, 0.71, and 0.19?mg kg^?1 in the same parts of rice, respectively. Untreated sewage water irrigation was the major cause of increasing soil and crop metals. Short periods of the sewage water irrigation increased individual metals in soils by 2 to 80% and increased metals in crops by 14 to 209%. Atmospheric deposition, industrial or municipal wastes, sewage sludge improperly used as fertilizers, and metal-containing phosphate fertilizers played an important role as well in some specific areas.     

Developing a sustainable phytomanagement strategy for excessive selenium in western United States and India

Phytomanagement technology is recognized as an inexpensive and environmental friendly strategy for managing natural-occurring selenium (Se) in soils and in poor quality waters. Multi-year field and greenhouse studies were conducted with different plant species in California, USA and Punjab, India under high Se growing conditions. Some of the plant species included; canola (Brassica napus), mustard (B. juncea), broccoli (B. oleracea), spearmint (Mentha viridis), sugarcane (Saccharum officcinarum), guar (Cyamopsis tetragonoloba), wheat (Triticum aestivum), and poplar (Populus deltoides). California soils had a sodium-sulfate-dominated salinity between 6-10 dS m(-1), while Indian soils had a calcium carbonate salinity less than 1 dS m(-1). Results demonstrated that high sulfate conditions reduced plant Se accumulation more than 100 x in Californian grown plants compared to Se accumulation in Indian grown plants. Tissue concentrations generally did not exceed 10 and 200 mg kg DM(-1) in leaves of plants grown in California and India, respectively. At these plant concentrations, Se phytomanagement is more effective in Indian soils than in California soils. Successful management of Se by plants requires selecting crops or crop rotations that are tolerant of the soil condition and identifying and creating new viable Se-enriched products.     

Cd AND Zn TOLERANCE AND ACCUMULATION BY SEDUM JINIANUM IN EAST CHINA

Field survey, hydroponic culture, and pot experiments were carried out to examine and characterize cadmium (Cd) and zinc (Zn) uptake and accumulation by Sedum jinianum, a plant species native to China. Shoot Cd and Zn concentrations in S. jinianum growing on a lead/Zn mine area reached 103–478 and 4165–8349 mg kg^?1 (DM), respectively. The shoot Cd concentration increased with the increasing Cd supply, peaking at 5083 mg kg^?1 (DM) when grown in nutrient at a concentration of 100 μmol L^?1 for 32 d, and decreased as the solution concentration increased from 200 to 400 μmol L^?1. The shoot-to-root ratio of plant Cd concentrations was > 1 when grown in solution Cd concentrations ≤ 200 μmol L^?1. Foliar, stem, and root Zn concentrations increased linearly with the increasing Zn level from 1 to 9600 μmol L^?1. The Zn concentrations in various plant parts decreased in the order roots > stem > leaves, with maximum concentrations of 19.3, 33.8, and 46.1 g kg^?1 (DM), respectively, when plants were grown at 9600 μmol Zn L^?1 for 32 d. Shoot Cd concentrations reached 16.4 and 79.8 mg kg^?1 (DM) when plants were grown in the pots of soil with Cd levels of 2.4 mg kg^?1 and 9.2 mg kg^?1, respectively. At soil Zn levels of 619 and 4082 mg kg^?1, shoot Zn concentrations reached 1560 and 15,558 mg kg^?1 (DM), respectively. The results indicate that S. jinianum is a Cd hyperaccumulator with a high capacity to accumulate Zn in the shoots.     

Effect of soil cadmium application and pH on growth and cadmium accumulation in roots, leaves and fruit of strawberry plants (Fragaria × ananassa Duch.)

Three strawberry (Fragaria × ananassa Duch.) cultivars Rainier, Totem and Selva were grown under greenhouse conditions in a Parkhill sandy loam soil with a background DTPA-extractable Cd concentration of 0.18 mg kg^-1 and a pH of 5.1. Experimental treatments included combinations of 4 Cd applications (0, 15, 30 and 60 mg Cd kg^-1 soil) applied as CdSO₄ and 2 soil pH values 5.1 and 6.8. Both the application of Cd and pH of the soil significantly affected plant growth, yield and Cd accumulation in plant tissue anf fruit. Although roots accumulated the highest concentrations of Cd of all plant parts investigated, increased soil Cd application reduced leaf weight more than root weight. In general, yield of strawberries was decreased by an increase in amount of soil-applied Cd, however the yield response varied among cultivars. At 60 mg Cd kg^-1 soil, yield of Rainier cultivar was reduced to 17.6% of control plants. Over 90% of total Cd taken up by plants grown in Cd-treated soil accumulated in roots, regardless of the Cd level in the soil. Root Cd concentrations ranged from 2.6 mg kg^-1 (control plants) to 505.7 mg kg^-1 (Totem plants grown in soil at highest Cd and a soil pH 5.1) and were directly related to soil Cd concentrations. Cd translocation from roots to leaves and fruit was very limited, resulting in a maximum Cd concentration in root leaf tissue of 10.2 mg kg^-1. Accumulation of Cd in fruit was found to correlate well with leaf Cd, although even at the highest amount of applied Cd, fruit Cd concentration did not exceed 700 g kg^-1 of fresh weight.Contribution no. 951     

Accumulation and subcellular distribution of cations in relation to the growth of potassium-deficient barley

Abstract Growth of barley (Hordeum vulgare L., cv. Georgie) was insensitive to soil K content above about 150 mg kg^?1, but at lower levels it declined. The reduction in yield was greater in soils containing approximately 10 mg Na kg^?1 than in soils with about 90 mg kg^?1 of Na. Growth was unaffected by changes in shoot K concentration above 75 mol m^?3, but declined at lower concentrations, and the decrease was less in plants grown in soils with high Na. Growth responses were not simply related to tissue K concentrations because plants grown in soils with extra Na had higher yields but lower K concentrations. When soil Na was low, plants accumulated Ca as tissue K declined, but when Na was provided this ion was accumulated. Plant Mg concentrations were generally low but increased as K decreased. The Ca and Mg were osmotically active. There were highly significant inverse linear relationships between yield and either the Ca or Mg concentrations in the shoots. X-ray microanalysis was used to examine the compartmentation of cations in leaves from barley plants (cv. Clipper) grown in nutrient solutions with high and low K concentrations. In plants grown with 2.5 mol m^?3 K, this was the major cation in both the cytoplasm and vacuole of mesophyll cells. However, in plants grown with 0.02 mol m^?3 K it declined to undetectable levels in the vacuole, although it was still detectable in the cytoplasm. In all plants, Ca was mainly located in epidermal cells. The implication of the results for explaining responses to K. in terms of compartmentation of solutes is discussed.     

Organic Amendments to Enhance Atrazine and Metamitron Degradation in Two Contaminated Soils with Contrasting Textures

Among all types of xenobiotics, pesticides such as herbicides play a significant role in soil and water pollution due to their wide usage all over the world. This study addresses the ability of organic amendments to enhance atrazine and metamitron degradation in two herbicide-contaminated soils with contrasting textures under laboratory conditions. Soil samples were collected from surface soils with textures of sandy loam and silty clay, from northeastern Iran. Initial concentration of herbicides was 50 mg · kg^{? 1} soil. Contaminated soil samples were treated with manure, compost and vermicompost at rates of 0, 0.5, and 2% (w/w). Residual concentrations of atrazine and metamitron were determined by HPLC at the end of incubation periods of 20, 40, and 60 days. Residual concentrations of atrazine were 46.5, 38.9, and 36.2 mg · kg^{? 1} after 20, 40, and 60 days incubation, respectively. Residual metamitron concentrations were clearly lower than atrazine. After 20, 40, and 60 days, concentrations of metamitron were 2.9, 1.0, and 0.6 mg · kg^{? 1}, respectively. Organic amendments at the rates of 0.5 and 2% showed similar effects on the enhancement of herbicide degradation in soils. However, no statistically significant effect was observed among types of organic amendments (α = 0.05). Degradation was affected by soil textures. Residual concentrations of herbicides were higher in sandy loam than in silty clay soil.     

Combined application of citric acid and 5-aminolevulinic acid improved biomass,photosynthesis and gas exchange attributes of sunflower (Helianthus annuus L.) grown on chromium contaminated soil

Abstract

Phytoremediation is an important technique to remove heavy metals from contaminated soils due to its efficiency and cost-effectiveness. The present study was conducted to assess the synergistic role of 5-aminolevulinic acid (ALA) and citric acid (CA) in improving the phyto-extraction of chromium (Cr) by sunflower. Sunflower plants were grown in soil, spiked with different concentrations of Cr (0, 5, 10, 20?mg kg^?1). Various concentrations of 5-ALA (0, 10, 20?mg L^?1) and CA (0, 2.5, 5?mM) were applied exogenously at juvenile stage. A significant decrease was observed in biomass and agronomic traits of sunflower under Cr stress alone. Further, Cr toxicity significantly decreased the plant growth, soluble proteins and photosynthetic pigments. However, exogenously applied ALA and CA significantly improved the plants’ physiological as well as agronomic attributes by lowering the production of reactive oxygen species and reducing electrolyte leakage. Moreover, Cr uptake was increased with increasing concentration of Cr in spiked soil, which was further enhanced by combined application of ALA and CA.     

Oil bioremediation in a high and a low phosphorus soil

Phosphorus (P) content may influence bioremediation of soils contaminated with crude oil. A soil testing high in plant available P (Weswood, 194 mg P kg^?1 soil) and one testing low in plant available P (Lufkin, 2 mg P kg^?1 soil) were selected for laboratory experiments on oil biodegradation. Plant available P content was determined using acidified ammonium acetate at pH 4.2 as the soil extractant. Soils were amended with 3, 6, and 9% crude oil by weight and incubated for 120 d at 25°C. Treatments consisted of a factorial arrangement, with soil, N, P, and oil concentration as factors. Addition of P without N generally did not enhance biodegradation. Addition of N without P approximately tripled the quantity of oil degraded. Addition of P and N together did not increase biodegradation of oil more than addition of N alone when oil concentration was 3%. At 6 and 9% oil concentrations, CO₂ evolution increased for both soils by adding P and N together in comparison to adding N alone, and total petroleum hydrocarbon (TPH) bio‐degradation increased by 30% for the Weswood soil by 60 d and at least 25% for the Lufkin soil by 30 d. The quantity of plant‐available P or total P in soil was not very useful in predicting need for supplemental P. Addition of P to soil to enhance oil degradation was only beneficial for oil concentrations above 3% and the positive effect for higher concentrations was transitory.