Trace metal uptake by tropical vegetables grown on soil amended with urban sewage sludge

Trace metal uptake was measured for tropical and temperate leafy vegetables grown on soil from an urban sewage disposal farm in the UK. Twenty-four leafy vegetables from East Africa and the UK were assessed and the five vegetable types that showed the greatest Cd concentrations were grown on eight soils differing in the severity of contamination, pH and other physico-chemical properties. The range of Cd concentrations in the edible shoots was greater for tropical vegetables than for temperate types. Metal uptake was modelled as a function of (i) total soil metal concentration, (ii) CaCl₂-soluble metal, (iii) soil solution concentration and (iv) the activity of metal ions in soil pore water. Tropical vegetables were not satisfactorily modelled as a single generic ‘green vegetable’, suggesting that more sophisticated approaches to risk assessment may be required to assess hazard from peri-urban agriculture in developing countries.     

Effects of lead and chelators on growth, photosynthetic activity and Pb uptake in Sesbania drummondii grown in soil

Effects of lead (Pb) and chelators, such as EDTA, HEDTA, DTPA, NTA and citric acid, were studied to evaluate the growth potential of Sesbania drummondii in soils contaminated with high concentrations of Pb. S. drummondii seedlings were grown in soil containing 7.5 g Pb(NO(3))(2) and 0-10 mmol chelators/kg soil for a period of 2 and 4 weeks and assessed for growth profile (length of root and shoot), chlorophyll a fluorescence kinetics (F(v)/F(m) and F(v)/F(o)) and Pb accumulations in root and shoot. Growth of plants in the presence of Pb+chelators was significantly higher (P<0.05) than the controls grown in the presence of Pb alone. F(v)/F(m) and F(v)/F(o) values of treated seedlings remained unaffected, indicating normal photosynthetic efficiency and strength of plants in the presence of chelators. On application of chelators, while root uptake of Pb increased four-five folds, shoot accumulations increased up to 40-folds as compared to controls (Pb only) depending on the type of chelator used. Shoot accumulations of Pb varied from 0.1 to 0.42% (dry weight) depending on the concentration of chelators used.     

Effects of amended compost on mobility and uptake of arsenic by rye grass in contaminated soil

Arsenic poses a major environmental and human health problem because of its carcinogenic nature and effect on the ecosystem. Therefore, a cost effective and socially acceptable technique is needed for its remediation. The effect of different combinations of compost amended with zeolite and/or iron oxide (up to 20% w/w) was tested on a contaminated soil with high arsenic levels (34470 mg kg(-1)). The bioavailability of arsenic was determined in terms of uptake by rye grass (Lolium perenne L.) under greenhouse experimental conditions. The results indicated that the arsenic concentrations in the rye grass was reduced to 2 mg kg(-1) dry weight by using 15% compost with 5% iron oxide and 15% compost with 5% zeolite. Less than 0.01% of the total arsenic content in the soil was being taken up by the plants. Both treatments were effective in establishing significantly higher plant growth on the contaminated soil compared to other treatments. The results from sequential extraction tests indicated that in all the compost-amended soils, there was a reduction in the soluble fraction (10-37%). Arsenic in soil was examined using Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy. The results indicated that arsenic was distributed mostly within the matrix of iron and oxygen in treated samples. Amongst various treatment mixtures tested, high percent of compost (15%) with zeolite (5%) and/or iron oxide (5%) is effective in reducing arsenic uptake by plants and establish re-vegetation on the contaminated soil.     

Probability of intellectual disability is associated with soil concentrations of arsenic and lead

Background

The association between metals in water and soil and adverse child neurologic outcomes has focused on the singular effect of lead (Pb), mercury (Hg), and arsenic (As). This study describes the complex association between soil concentrations of As combined with Pb and the probability of intellectual disability (ID) in children.

Methods

We used a retrospective cohort design with 3988 mother child pairs who were insured by Medicaid and lived during pregnancy and early childhood in South Carolina between 1/1/97 and 12/31/02. The children were followed until 6/1/08, using computerized service files, to identify the diagnosis of ID in medical records and verified by either school placement or disability service records. The soil was sampled using a uniform grid and analyzed for eight metals. The metal concentrations were interpolated using Bayesian Kriging to estimate concentration at individual residences.

Results

The probability of ID increased for increasing concentrations of As and Pb in the soil. The Odds Ratio for ID, for one unit change in As was 1.130 (95% confidence interval 1.048-1.218) for Pb was 1.002 (95% confidence interval 1.000-1.004). We identified effect modification for the infants based on their birth weight for gestational age status and only infants who were normal size for their gestational age had increased probability of ID based on the As and Pb soil concentrations (OR for As at normal weight for gestational age = 1.151 (95% CI: 1.061-1.249) and OR for Pb at normal for gestational age = 1.002 (95% CI: 1.002-1.004)). For normal weight for gestational age children when As = 22 mg kg⁻¹ and Pb = 200 mg kg⁻¹ the risk for ID was 11% and when As = 22 mg kg⁻¹and Pb = 400 mg kg⁻¹ the probability of ID was 65%.

Conclusion

The probability of ID is significantly associated with the interaction between Pb and As for normal weight for gestational age infants.     

Growth performance and biochemical responses of three rice (Oryza sativa L.) cultivars grown in fly-ash amended soil

The disposal of fly-ash (FA) from coal-fired power stations causes significant economic and environmental problems. Use of such contaminated sites for crop production and use of contaminated water for irrigation not only decreases crop productivity but also poses health hazards to humans due to accumulation of toxic metals in edible grains. In the present investigation, three rice cultivars viz., Saryu-52, Sabha-5204, and Pant-4 were grown in garden soil (GS, control) and various amendments (10%, 25%, 50%, 75% and 100%) of FA for a period of 90 days and effect on growth and productivity of plant was evaluated vis-a-vis metal accumulation in the plants. The toxicity of FA at higher concentration (50%) was reflected by the reduction in photosynthetic pigments, protein and growth parameters viz., plant height, root biomass, number of tillers, grain and straw weight. However, at lower concentrations (10-25%), FA enhanced growth of the plants as evident by the increase of studied growth parameters. The cysteine and non-protein thiol (NP-SH) content showed increase in their levels up to 100% FA as compared to control, however, maximum content was found at 25% FA in Saryu-52 and Pant-4 and at 50% FA in Sabha-5204. Accumulation of Fe, Si, Cu, Zn, Mn, Ni, Cd and As was investigated in roots, leaves and seeds of the plants. Fe accumulation was maximum in all the parts of plant followed by Si and both showed more translocation to leaves while Mn, Zn, Cu, Ni and Cd showed lower accumulation and most of the metal was confined to roots in all the three cultivars. As was accumulated only in leaves and was not found to be in detectable levels in roots and seeds. The metal accumulation order in three rice cultivars was Fe > Si > Mn > Zn > Ni > Cu > Cd > As in all the plant parts. The results showed that rice varieties Saryu-52 and Sabha-5204 were more tolerant and could show improved growth and yield in lower FA application doses as compared to Pant-4. Thus, Sabha-5204 and Saryu-52 are found suitable for cultivation in FA amended agricultural soils for better crop yields.     

Metal extraction by Arabidopsis halleri grown on an unpolluted soil amended with various metal-bearing solids: a pot experiment.

Most studies dealing with phytoremediation have considered metal extraction efficiency in relation to metal concentration of bulk soil samples or metal concentration of the soil solution. However, little is known about the effect of various metal-bearing solids on plant growth and metal extraction of hyperaccumulators. In this study, we investigated the ability of Arabidopsis halleri to grow and extract metals from different substrates consisting in an unpolluted soil amended with various metal-bearing solids collected in soils around a Zn smelter complex. The metal-bearing solids used as amendments were: fresh and decomposing organic residues in the soil, a soil clay fraction and two waste slags. Pure mono-metallic salt (ZnSO4) was also used. Two series of substrates were produced, one moderately polluted, and the other highly polluted. An additional substrate was formed by the unamended soil, and used as an unpolluted control. Zn, Cd, Cu, and Pb were measured in the substrates, and in the roots and shoots of A. halleri. The dry matter yield of A. halleri was shown not to depend on the nature of the metal-bearing solid used, except when Cu-toxicity was suspected. On highly-polluted substrates, Zn extraction by A. halleri depended on the nature of metal-bearing solids used, showing the following trend: pure mono-metallic salt > waste slags and soil clay fraction > fresh and decomposing organic matter. We explained these differences by the high solubility of Zn in the mono-metallic salt, whereas in the mineral metal-bearing solids and in both fresh and decomposing organic matter, Zn release required mineral weathering or organic matter mineralization, respectively. This work clearly showed that phytoremediation studies have to consider the nature of metal-bearing solids in contaminated soils to better predict the efficiency of plant extraction.     

Influence of plant growth promoting bacteria and its mutant on heavy metal toxicity in Brassica juncea grown in fly ash amended soil

In this study a metal tolerant plant growth promoting bacteria, NBRI K28 Enterobacter sp. was isolated from fly ash (FA) contaminated soils. The strain NBRI K28 and its siderophore overproducing mutant NBRI K28 SD1 were found capable of stimulating plant biomass and enhance phytoextraction of metals (Ni, Zn and Cr) from FA by metal accumulating plant i.e. Brassica juncea (Indian mustard). Concurrent production of siderophores, Indole acetic acid (IAA) and phosphate solubilization revealed its plant growth promotion potential. The strain also exhibited 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase activity. In most of the cases mutant of NBRI K28, exerted more pronounced effect on metal accumulation and growth performance of B. juncea plants than wild type.     

Saline irrigation and Zn amendment effect on Cd phytoavailability to Swiss chard (Beta vulgaris L.) grown on a long-term amended agricultural soil: a human risk assessment

Crops, particularly in the Northeast region of Mexico, have to cope with increasing soil salinization due to irrigation. Chloride (Cl^?) concentration has been strongly related to enhance cadmium (Cd) uptake by plants due to increased solubility in the soil solution. The effect of irrigation with slightly saline water from a local well was evaluated in this work on the accumulation and translocation of Cd in Swiss chard (Beta vulgaris L.) grown in soil historically amended with stabilized sewage sludge under a regime of phosphorus and zinc fertilization. A factorial pot experiment was conducted with two phosphate fertilizer levels (PF, 0 and 80 kg ha^?1 dry soil, respectively), two Zn levels (0 and 7 kg ha^?1 dry soil), and two sources of water for irrigation deionized water (DW) and slightly saline well water (WW) from an agricultural site. Additionally, a human risk assessment for Cd ingestion from plants was assessed. Results showed that Cl^? salinity in the WW effectively mobilized soil Cd and increased its phytoavailability. A higher level of Cd was found in roots (46.41 mg kg^?1) compared to shoots (10.75 mg kg^?1). Although the total content of Cd in the edible parts of the Swiss chard irrigated with WW exceeded permissible recommended consumption limit, bioavailable cadmium in the aboveground parts of the plant in relation to the total cadmium content was in the range from 8 to 32 %. Therefore, human health risks might be overestimated when the total concentration is taken into account.     

Behaviour of oxyfluorfen in soils amended with edaphic biostimulants/biofertilizers obtained from sewage sludge and chicken feathers. Effects on soil biological properties

We studied the behaviour of oxyfluorfen herbicide at a rate of 4 l ha^?1 on biological properties of a Calcaric Regosol amended with two edaphic biostimulants/biofertilizers (SS, derived from sewage sludge; and CF, derived from chicken feathers). Oxyfluorfen was surface broadcast on 11 March 2013. Two days after application of oxyfluorfen to soil, both biostimulants/biofertilizers (BS) were also applied to the soil. An unamended soil without oxyfluorfen was used as control. For 2, 4, 7, 9, 20, 30, 60, 90 and 120 days of the application of herbicide to the soil and for each treatment, the soil dehydrogenase, urease, β-glucosidase and phosphatase activities were measured. For 2, 7, 30 and 120 days of the application of herbicide to the soil and for each treatment, soil microbial community was determined. The application of both BS to soil without the herbicide increased the enzymatic activities and soil biodiversity, mainly at 7 days of beginning the experiment. However, this stimulation was higher in the soil amended with SS than for CF. The application of herbicide in organic-amended soils decreased the inhibition of soil enzymatic activities and soil biodiversity. Possibly, the low-molecular-weight protein content easily assimilated by soil microorganisms is responsible for less inhibition of these soil biological properties.     

Effects of arbuscular mycorrhizal fungi on Agrostis capillaris grown on amended mine tailing substrate at pot,lysimeter, and field plot scales

Applied research programs in the remediation of contaminated areas can be used also for gaining insights in the physiological and ecological mechanisms supporting the resistance of plant communities in stress conditions due to toxic elements. The research hypothesis of this study was that in the heavily contaminated but nutrient-poor substrate of mine tailing dams, the beneficial effect of inoculation with arbuscular mychorrizal fungi (AMF) is due to an improvement of phosphorus nutrition rather than to a reduction of toxic element transfer to plants. A concept model assuming a causal chain from root colonization to element uptake, oxidative stress variables, and overall plant development was used. The methodological novelty lies in coupling in a single research program experiments conducted at three scales: pot, lysimeter, and field plot, with different ages of plants at the sampling moment (six subsets of samples in all). The inoculation with AMF in expanded clay carrier had a beneficial effect on the development of plants in the amended tailing substrate heavily contaminated with toxic elements. The effect of inoculation was stronger when the quantity of expanded carrier was smaller (1 % vs. 7 % inoculum), probably because of changes in substrate features. The improvement of plant growth was due mainly to an improvement in phosphorus nutrition leading to an increase of protein concentration and decrease of oxidative stress enzyme activity (superoxide dismutase and peroxidase). In a single data subset, an effect of inoculation on the uptake of several toxic elements could be proved (decrease of As concentration in plant roots correlated with a decrease of oxidative stress independent from the effect of P concentration increase). The multi-scale approach allowed us to find differences between the patterns characterising the data subsets. These subset-specific patterns point out the existence of physiological differences between plants in different development states (as a result of sampling at different plant ages). From an applied perspective, conclusions are drawn with respect to the use of plants in the monitoring programs of contaminated areas and the use of inoculation with AMF in the remediation of tailing dams.     

Concurrent sorption of antimony and lead by iron phosphate and its possible application for multi-oxyanion contaminated soil

Environmental Science and Pollution Research - Concurrent stabilization of oxyanions such as antimony (Sb), arsenic (As), and heavy metals including lead (Pb) and manganese (Mn) in contaminated...     

The effects of magnesium and ammonium additions on phosphate recovery from greenhouse wastewater

Phosphorus recovery from greenhouse wastewater, using precipitation-crystallization, was conducted under three levels of calcium concentration, 304 mg/L (7.6 mmol/L), 384 mg/L (9.6 mmol/L), and 480 mg/L (12 mmol/L), and also with additions of ammonium and magnesium into the wastewater. Jar test results confirmed high phosphate removal, with more than 90% of the removal achieved with a pH as low as 7.7. Under the low calcium concentration, ammonium addition affected the chemical reactions at pH lower than 8.0, where struvite was produced; when the pH was raised to 8.8, other calcium compounds dominated the precipitation. Under the medium calcium concentration, ammonium and magnesium addition helped struvite precipitation in the low pH range. Hydroxyapatite (HAP) was the main product. Under the high calcium concentration, ammonium addition showed no effects on the precipitation.     

Effects of lead and cadmium nitrate on biomass and substrate utilization pattern of soil microbial communities

A study was conducted to evaluate the effects of different concentrations of lead (Pb) and cadmium (Cd) applied as their nitrates on soil microbial biomass carbon (C(mic)) and nitrogen (N(mic)), and substrate utilization pattern of soil microbial communities. The C(mic) and N(mic) contents were determined at 0, 14, 28, 42 and 56 days after heavy metal application (DAA). The results showed a significant decline in the C(mic) for all Pb and Cd amended soils from the start to 28 DAA. From 28 to 56 DAA, C(mic) contents changed non-significantly for all other treatments except for 600 mgkg(-1) Pb and 100 mgkg(-1) Cd in which it declined significantly from 42 to 56 DAA. The N(mic) contents also decreased significantly from start to 28 DAA for all other Pb and Cd treatments except for 200 mgkg(-1) Pb which did not show significant difference from the control. Control and 200 mgkg(-1) Pb had significantly lower soil microbial biomass C:N ratio as compared with other Pb treatments from 14 to 42 DAA, however at 56 DAA, only 1000 mgkg(-1) Pb showed significantly higher C:N ratio compared with other treatments. No significant difference in C:N ratio for all Cd treated soils was seen from start to 28 DAA, however from 42 to 56 DAA, 100 mgkg(-1) Pb showed significantly higher C:N ratio compared with other treatments. On 56 DAA, substrate utilization pattern of soil microbial communities was determined by inoculating Biolog ECO plates. The results indicated that Pb and Cd addition inhibited the functional activity of soil microbial communities as indicated by the intensity of average well color development (AWCD) during 168 h of incubation. Multivariate analysis of sole carbon source utilization pattern demonstrated that higher levels of heavy metal application had significantly affected soil microbial community structure.     

Influence of temperature and soil type on the toxicity of three pesticides to Eisenia andrei

Expansion of agriculture in the tropics has increased the use of pesticides that may affect the soil ecosystems. Few studies so far determined the effects of pesticides in the tropics and tropical risk assessment therefore often relies on data from temperate conditions. Hence we compared the toxicity of chlorpyrifos, carbofuran and carbendazim to the earthworm Eisenia andrei at two different temperatures reflecting temperate and tropical conditions. The toxicity of the three pesticides in both conditions decreased in the order carbendazim > carbofuran > chlorpyrifos. For chlorpyrifos and carbofuran, but not for carbendazim, survival was more sensitive at the higher temperature, probably due to increased earthworm activity. Sub-lethal effects (reproduction and growth) however, varied inconsistently with temperature and soil types. We conclude that toxicity of pesticides in tropics may not be predicted from data generated under temperate conditions, even within the same species.     

Leaching of benzimidazole antiparasitics in soil columns and in soil columns amended with sheep excreta

Environmental Science and Pollution Research - Benzimidazoles are anthelmintics frequently used in sheep farming due to the high susceptibility of these animals to parasitic diseases. Sheep excreta...     

Effect of in situ soil amendments on arsenic uptake in successive harvests of ryegrass (Lolium perenne cv Elka) grown in amended As-polluted soils

Several iron-bearing additives, selected for their potential ability to adsorb anions, were evaluated for their effectiveness in attenuation of arsenic (As) in three soils with different sources of contamination. Amendments used were lime, goethite (alpha-FeOOH) (crystallised iron oxide) and three iron-bearing additives, iron grit, Fe(II) and Fe(III) sulphates plus lime, applied at 1% w/w. Sequential extraction schemes conducted on amended soils determined As, Cu, Zn and Ni fractionation. Plant growth trials using perennial ryegrass (Lolium perenne var. Elka) assessed shoot As uptake. This was grown in the contaminated soils for 4 months, during which time grass shoots were successively harvested every 3 weeks. Goethite increased biomass yields, but clear differences were observed in As transfer rates with the various iron oxides. In conclusion, whilst Fe-oxides may be effective in situ amendments, reducing As bioavailability, their effects on plant growth require careful consideration. Soil-plant transfer of As was not completely halted by any amendment.     

Effects of sterile storage,cation saturation and substrate additions on the degradability and extractability of nonylphenol and phenanthrene in soil

The main objective of this study was to determine the effects of long-term abiotic processes during aging of organic pollutants in soil on their microbial degradability and formation of non-extractable residues. The specific aims of our study were to investigate how the fate of p353-nonylphenol (NP) and phenanthrene (Phe) in soils might be affected by: (i) saturation of soil by cations with different valency (Na⁺, Ca²⁺ or Al³⁺), (ii) addition of organic substrate (wood flour) during incubation period and (iii) different soil moisture levels.