Nickel-mediated lead dynamics and their interactive effect on lead partitioning and phytoremediation indices in spinach

A greenhouse research was conducted to monitor lead (Pb) translocation dynamics in spinach (Spinacia oleracea L.) mediated by nickel (Ni) application. Each of the four levels of Pb (0, 100, 150, and 300 mg/kg) and Ni (0, 100, 150, and 300 mg/kg) was applied in different combinations in the pot experiment. A fully matured spinach crop was harvested and divided into biomass samples from the roots and above ground. ICP-OES was used to determine the concentrations of Pb and Ni in the samples. The increase in Pb application rate in soil resulted in a decrease in dry matter yield of plant roots and above-ground biomass, according to the findings. Pb accumulation was also found in significant amounts in roots and above-ground biomass. Pb was accumulated in greater quantities in the spinach roots than in the above-ground biomass. Pb uptake in spinach roots and above-ground biomass decreased when high dose of Ni was applied. The Ni application in spinach crop had a negative impact on various parameters of Pb uptake, including translocation factor, bioconcentration factor, translocation efficiency, and crop removal of Pb. Pb toxicity was reduced when higher doses of Ni (100 to 300 mg/kg) were applied to Pb-contaminated soil. The findings of this study could help researchers better understand how Pb and Ni interact, as well as how to treat soil that has been contaminated by industrial wastewater containing nickel and lead.

Alteration of contamination threat due to dilution effect on metal concentration in maize-wheat biomass on sludge amended clayey soil

Industrial sludge often contains considerable amount of organic matter and plant nutrients to enhance crop production. However, its utilization in agriculture is viewed with concern as it also enhances the entry of toxic heavy metals into the agroecosystem. A field study was conducted to assess the potential of sludge generated from a soft beverage industry in cereal crops after critical analysis of benefits and contamination risks. The treatments were control, recommended doses of major fertilizers applied to both maize and following wheat crops, and organic amendments, viz., cattle dung manure and sludge at graded rates (2-50 t/ha) applied only to maize crop. Growth, yield, and heavy metal concentrations in plant parts were measured. Sludge application rates at ≥ 20 t/ha had significant direct as well as residual effects on crops in terms of enhancing their growth parameters and grain yields in comparison to the direct effects of fertilizer applications. It also enhanced Cu, Cd, Pb, and Zn concentrations in vegetative biomass of both crops even with the lowest rate of application, but had lower or little effect on their concentrations in grains. Sludge facilitated accumulation of metals in vegetative biomass of maize as indicated by increase in dynamic factor of bioaccumulation (BA_dyn) to > 1. Relative uptake of added metals by maize biomass increased with increasing sludge rate up to 10 t/ha, but decreased significantly at the highest application rate. Heavy metals concentration in biomass due to increasing rates of sludge application was the result of a trade-off between their "increasing entry in soil-plant system" and "dilution in biomass" due to enhanced crop growth. Strategy for safe application of this contaminated sludge in agroecosystem was discussed through analysis of heavy metals transfer characteristics in soil-plant system. The study indicates that conjoint application of lower rates of both sludge and N fertilizer can minimize risk of heavy metals contamination while ensuring higher crop yields.

Reducing chromium uptake through application of calcium and sodium in spinach

In peri-urban areas, the use of wastewater for crop production is a common practice due to water scarcity. Moreover, in the recent years, large quantity of wastewater generation and discharge as industrial effluent in water resources is another issue for reduction of water quality. The leather industries are significantly contributing chromium (Cr) in effluent, whereas, other industries may have salt and cationic load in their discharges are mixed up. Therefore, it is mandatory to study the interactive effect of different effluent constituents on crop plants. In this connection, a pot culture experiment was conducted at the ICAR-Indian Institute of Soil Science, Bhopal to compute the effect of application of calcium (Ca) and sodium (Na) ions on Cr uptake by spinach crop in Vertisol of central India. Three levels of Cr (0, 50, 100 mg kg^-1), calcium (0, 2, 4 mM), and sodium (0, 40, 80 mM) were applied in combinations. The spinach variety All Green was used as a test crop and harvested at full maturity. Results showed that application of Ca and Na reduced the Cr uptake in spinach crop. The reduction of Cr uptake was more in the root than shoot. Applied calcium acted as an essential plant nutrient and enhanced the crop biomass. Sole applications of Na adversely affected the crop biomass and Cr uptake in both root and shoot of spinach. In conclusion, application of Ca fertilizers reduced the Cr toxicity in spinach and could be used as a strategy for the safe utilization of tannery industrial effluents for crop production.

Chromium toxicity mediated by application of chloride and sulfate ions in Vertisol of Central India

Chromium (Cr) is one of the toxic metals adversely affecting organisms including humans in the ecosystems, and it is present in considerable concentration in the tannery industrial effluent. Toxicity expression of Cr is suspected to be influenced considerably by other accompanying ions present in the effluent used for irrigation. In a screen house experiment, interactive effects of chloride and sulfate ions in a Vertisol on uptake of Cr by spinach crop were investigated and treatments imposed were three levels each of Cr (0, 50, 100 mg kg^-1), chloride (Cl^-) (0, 25, 50 mM kg^-1), and sulfur (S) (0, 4, 8 mM kg^-1) in possible combinations. Plant growth parameters and leaf Cr concentrations were recorded to find out the effect of anions on Cr dynamics in the plant. Increasing the concentration of Cl^- ions in soil reduced the Cr concentration in both root and shoot. Similarly, increasing the concentration of S from 4 to 8 mM kg^-1 also reduced the concentration and uptake of Cr. Application of sulfate ions augmented the plant growth and counters the negative effect of Cl^- ions and Cr. Thus, the study revealed that the addition of S fertilizers could minimize the Cr toxicity in high Cr contaminated soils.

Impact of Long-Term Application of Sewage on Soil and Crop Quality in Vertisols of Central India

Shortfall of rain and the decreased groundwater level force farmers to use poor quality water for crop production in developing countries. In this study, the quality of agricultural produce and soil health affected by sewage water (Patranala) irrigation was evaluated. Sewage sediment, soil and crop samples were analyzed for physico-chemical properties. Sewage water found to contain trace concentration of heavy metals. However, long-term application of this water for crop production could build up a significant amount of trace metals in both soil and sediments. The DTPA extractable heavy metals ranged Cu 2.7-7.59, Cd 0.04-0.06, Pb 1.29-2.05, Cr 0.01-0.04, Ni 0.24-1.03 and Zn 0.63-2.59 mg kg^-1 soil. The heavy metal risk assessment (hazard quotient, HQ) was calculated and found that HQ for these metals in the crops under study was in safe limits. From the study, it is concluded that growing vegetables using sewage water of Patranala is safe, but periodic monitoring to be carried out to avoid food chain contamination.

Geo-Accumulation Indices of Heavy Metals in Soil and Groundwater of Kanpur, India Under Long Term Irrigation of Tannery Effluent

Soil and groundwater from long-term (>50 years) tannery effluent irrigated areas of Kanpur were analyzed and significant buildup of heavy metals such as Cr, Ni, Cd, Pb, Zn, and As in the range of 252-972, 23-30, 2.3-14.1, 23.7-58.8, 138-338 and 6.8-11 mg kg^-1, respectively in soil was found. Few groundwater samples in the effluent irrigated areas also exhibited high Cr concentration above the permissible limit of United States Environmental Protection Agency. The tannery effluents contained 1.53-57.3 ppm Cr, 0-0.12 ppm Ni, 0-0.02 ppm Cd, 0-0.07 ppm Pb, 0-0.48 ppm Zn and 0-0.03 ppm As. The Geo-accumulation index (I_geo) revealed that soil samples were unpolluted to moderately polluted with Cu, Ni, Zn, Pb and As; moderately polluted in case of Cd; and heavily to extremely polluted by Cr.

Impact of pigeon pea biochar on cadmium mobility in soil and transfer rate to leafy vegetable spinach

Introduction of heavy metals in the environment by various anthropogenic activities has become a potential treat to life. Among the heavy metals, cadmium (Cd) shows relatively high soil mobility and has high phyto-mammalian toxicity. Integration of soil remediation and ecosystem services, such as carbon sequestration in soils through organic amendments, may provide an attractive land management option for contaminated sites. The application of biochar in agriculture has recently received much attention globally due to its associated multiple benefits, particularly, long-term carbon storage in soil. However, the application of biochar from softwood crop residue for heavy metal immobilization, as an alternative to direct field application, has not received much attention. Hence, a pot experiment was conducted to study the effect of pigeon pea biochar on cadmium mobility in a soil-plant system in cadmium-spiked sandy loam soil. The biochar was prepared from pigeon pea stalk through a slow pyrolysis method at 300 °C. The experiment was designed with three levels of Cd (0, 5, and 10 mg Cd kg(-1) soil) and three levels of biochar (0, 2.5, and 5 g kg(-1) soil) using spinach as a test crop. The results indicate that with increasing levels of applied cadmium at 5 and 10 mg kg(-1) soil, the dry matter yield (DMY) of spinach leaf decreased by 9.84 and 18.29 %, respectively. However, application of biochar (at 2.5 and 5 g kg(-1) soil) significantly increased the dry matter yield of spinach leaf by 5.07 and 15.02 %, respectively, and root by 14.0 and 24.0 %, respectively, over the control. Organic carbon content in the post-harvest soil increased to 34.9 and 60.5 % due to the application of biochar 2.5 and 5 g kg(-1) soil, respectively. Further, there was a reduction in the diethylene triamine pentaacetic acid (DTPA)-extractable cadmium in the soil and in transfer coefficient values (soil to plant), as well as its concentrations in spinach leaf and root, indicating that cadmium mobility was decreased due to biochar application. This study shows that pigeon pea biochar has the potential to increase spinach yield and reduce cadmium mobility in contaminated sandy soil.

Effect of methods of preparation on distribution of heavy metals in different size fractions of municipal solid waste composts

The present study compares the distribution and nature of heavy metals in composts from 12 cities of India, prepared from different types of processed urban solid wastes, namely mixed wastes (MWC), partially segregated wastes (PSWC), and segregated bio-wastes (BWC). Compost samples were physically fractionated by wet sieving, followed by extraction of heavy metals by dilute HCl and NaOH. Bigger particles (>0.5 mm) constituted the major fraction in all three types of composts and had a relatively lower concentration of organic matter and heavy metals, the effect being more pronounced in MWC and PSWC in which a significant portion of the heavy metals was distributed in finer size fractions. Cd, Ni, Pb, and Zn were extracted to a greater extent by acid than by alkali, the difference being greater in MWC, which contained a higher amount of mineral matter. In contrast, Cu and Cr were extracted to a greater extent by dilute alkali, particularly from BWC containing a higher amount of organic matter. Water-soluble heavy metals were generally related to the water-soluble C or total C content as well as to pH, rather than to their total contents. This study concludes that wet sieving with dilute acid can effectively reduce heavy metal load in MWC and PSWC.

Accumulation of few heavy metals in sewage sludges, soils and plants of Coimbatore, Tamil Nadu (India)

A study was carried out in Coimbatore district of Tamil Nadu (India) to assess the distribution pattern of heavy metals in the soils and plants irrigated with sewage effluent/sludge. About 69 soil samples (surface and subsurface), 65 plant samples as well as 34-sewage sludge samples were collected from various tehsils of Coimbatore. Six tehsils in Coimbatore have been identified and categorized into two groups--Class I City (densely populated tehsils) and Class II city (thinly populated tehsils). The available micronutrients like Fe, Mn, Zn and Cu; heavy metals: Cr, Cd, Ni, and Pb were within the safe limits. However, the total Cr and Cd concentrations were relatively higher in the sludge samples collected from Coimbatore and Tiruppur tehsils compared to other tehsils, while for Ni, the sequence was in the order Coimbatore > Tiruppur > Palladam > Pollachi > Avinashi > Mettupalayam and for Pb, Coimbatore > Mettupalayam > Palladam > Tiruppur > Avinashi > Pollachi. Soil analysis results indicated that heavy metal concentration recorded higher level in soils of Class I city (densely populated tehsils) compared to Class II city (thinly populated tehsils). The plant samples analyzed had also registered higher concentration of total Cd, Ni and Pb, which were classified under toxic, excessive and below excessive level, respectively. Correlation analysis revealed that iron (Fe), zinc (Zn), copper (Cu), cadmium (Cd) and lead (Pb) were significantly negatively correlated with pH of soil. EC had a significant positive correlation with available iron (Fe), zinc (Zn), cadmium (Cd) and lead (Pb). A significant positive correlation of Fe, Mn, Zn, Cu, Cd and Pb was also registered with OC. Among the plant samples collected, it was evident that heavy metal concentrations were recorded higher in grass spp followed by Amaranthus spp. It was inferred from the study that soils samples had higher levels of heavy metals even though the values recorded were below the critical value/toxic limit. However, long-term and indiscriminate application of untreated (raw) sewage sludge and/or letting of sewage effluent directly to agricultural field without prior treatment may result in accumulation of toxic metals in surface and subsurface soils and subsequent biotransfer (bioaccumlation) into the food chain, it may further lead to toxicity not only to plants and animals but also to consumers of the harvested crops.