Effluent-irrigated Soils Research Articles

Impact of Plant Growth-Promoting Rhizobacteria on Spinach Growth Concerned with Industrial Effluents Contaminated with Chromium

Heavy metal pollution in soil poses a significant threat to the environment and human health as it accumulates throughout the food chain. Remediation of soil contamination involves biological, chemical, and physical methods. Plant growth-promoting rhizobacteria inoculation helps some plants stabilize heavy metals in polluted soil by forming chelates with the metals. An experiment was conducted to examine the impact of Plant growth-promoting rhizobacteria on spinach growth and heavy metal stability in polluted soil with industrial effluents. The study found that Plant growth-promoting rhizobacteria (S1 and S2) enhanced growth and yield parameters, with fresh weights reaching 18% and 14%, highest dry weights at 10% and 40%, and longest roots at 11%. The treatment with Plant growth-promoting rhizobacteria S1 recorded the highest SPAD values (27%). Chemical parameters revealed that Cr levels in roots peaked in treatments without PGPR. The results concluded that PGPR can effectively remediate heavy metal-contaminated soils and industrial effluent-irrigated soils used for food crop growth.

Reuse of Treated Wastewater for Crop Irrigation: Water Suitability, Fertilization Potential, and Impact on Selected Soil Physicochemical Properties

This study evaluates the suitability of treated wastewater (TWW: secondary effluent and membrane effluent) for crop irrigation and the resultant impact on crop growth and soil physicochemical characteristics. Carrot seeds (Daucus carota subsp. sativus) were grown on loam soil and irrigated with tap water (Tap), secondary effluent (SE), and membrane effluent (ME) until maturity. Bacteriological analyses showed four log counts of E. coli and thermotolerant coliforms for secondary effluent, making it unsafe for the irrigation of carrots. Tap water and membrane effluent fulfilled the microbial limit for water reuse and were suitable for irrigation. The sodium absorption ratio, Kelly index, and magnesium hazard assessments indicated that all three irrigation water streams were suitable for irrigation. The average mass of carrot fruits for Tap, SE, and ME was 2.14 g, 3.96 g, and 3.03 g, respectively. A similar trend was observed for the dry matter composition: Tap had 15.9%, SE had 18.3%, and ME had 16.6%. The soil pH increased from 7.08 to 7.26, 7.39, and 7.33 for tap water-, secondary effluent-, and membrane effluent-irrigated soils, respectively. Nitrate-nitrogen and potassium levels increased in the TWW-irrigated soil, while that of the tap water-irrigated soil decreased. Sodium levels in the TWW-irrigated soil increased significantly but did not induce soil sodicity. The application of the TWW enhanced the growth of the carrot plants and increased the soil nutrient levels. Hence, using TWW in agricultural irrigation could promote food production and also limit the overdependency on freshwater resources. However, TWW should be disinfected by using UV disinfection and ozonation to reduce the risk of microbial contamination. Such disinfection methods may not lead to the formation of toxic byproducts, and therefore secondary pollution to crops is not anticipated.

Occurrence of antibiotics in the different biological treatment processes, reclaimed wastewater treatment plants and effluent-irrigated soils

Reclaimed wastewater is increasingly being used for agricultural irrigation to address water scarcity, particularly in arid and semiarid areas. In this study, the occurrence and removal of 24 antibiotics were investigated in two wastewater treatment systems (WWTSs) and their irrigation areas located in the arid northwestern region of China. The different WWTSs included absorption–biodegradation (AB) + anaerobic–anoxic–oxic (AAO) and AAO + AAO + membrane bioreactor (MBR). Nineteen antibiotics were detected, with concentrations ranging from low to 60.8 μg/L. The dominant antibiotic classes were quinolones (QNs) and macrolides (MLs) in winter, and MLs and sulfonamides (SAs) in summer. The AAO + AAO + MBR system exhibited better removal efficiencies for most antibiotics, improving their adsorption and biodegradation. Except for ofloxacin (OFC) and norfloxacin (NFC), the concentrations of the detected antibiotics were higher in summer than in winter. However, the antibiotic removal efficiency increased by 2–141% in summer compared to winter due to the increase in microbial activity with temperature. Even though reclaimed treatment water plants contributed to the removal of antibiotics, residual antibiotics still affected the soil environment after green irrigation. In irrigated soil, QNs were predominantly detected, with a maximum concentration of 150.9 ng/kg for NFC. An ecological risk assessment showed that OFC, NFC, enrofloxacin, and lomefloxacin presented low or medium ecological risks in at least two irrigated sites. Thus, more attention should be given to the reuse of reclaimed wastewater, as it may pose toxicity risks to organisms in the soil environment.

Assessing bacterial diversity and antibiotic resistance dynamics in wastewater effluent-irrigated soil and vegetables in a microcosm setting

Water scarcity is one of the main challenges in sustainable agricultural development particularly in developing countries therefore, irrigation of food crops with wastewater effluent has become a common practice in order to meet the growing food demand. The aim of this study was to determine the impact of wastewater irrigation on bacterial community and antibiotic resistance dynamics in soil and vegetables in an agricultural setting. To determine bacterial diversity, occurrence and overall dynamics of antibiotic resistant genes (ARGs) in effluent irrigated soil and vegetables, 16S rRNA gene metagenomics, shotgun metagenomics and molecular PCR technique were utilized. A shift in bacterial community profile was observed as notable reduction in proteobacteria and increase in firmicutes phyla from the microcosm soil following wastewater effluent irrigation. Shotgun metagenomics revealed diverse ARGs belonging to at least nine different classes of antibiotics in the effluent wastewater. However, only blaTEM (beta-lactamase) and aadA (aminoglycoside) resistance gene sequences were identified in microcosm soil following irrigation and only blaTEM was detected on effluent irrigated vegetable surfaces (spinach and beetroots). From the study, only blaTEM gene was identified across all samples; effluent wastewater, effluent-treated soil, and vegetables. The data suggests a possible dissemination and persistence of the beta-lactamase blaTEM gene from effluent wastewater into agricultural soil and vegetables. This study enhances our understanding of antibiotic resistance spread and highlights the importance of monitoring antibiotic resistance in agro-systems, which is critical for informing policies aimed at sustainable use of wastewater effluent in water-stressed countries.

Occurrence of Antibiotics in the Different Biological Treatment Processes, Reclaimed Wastewater Treatment Plants and Effluent-Irrigated Soils

Occurrence of Antibiotics in the Different Biological Treatment Processes, Reclaimed Wastewater Treatment Plants and Effluent-Irrigated Soils

Metagenomics and Molecular Analysis of Bacterial Diversity and Antibiotic Resistance Dynamics in Wastewater Effluent-Irrigated Soil and Vegetables in an Agricultural Microcosm Setting

Metagenomics and Molecular Analysis of Bacterial Diversity and Antibiotic Resistance Dynamics in Wastewater Effluent-Irrigated Soil and Vegetables in an Agricultural Microcosm Setting

Characterization of sugar factory effluents from different factories of north coastal Andhra Pradesh, India and its effect on soil properties

Sugarcane is important sugar crop which is accounting for approximately 80 percent of world sugar production. Sugarcane is one of the important agro industrial crops of commercial importance grown in North Coastal Andhra Pradesh, India. During processing of cane, sugar mills will discharge huge amounts of wastewater as large quantities of water is utilized in sugar mills. However, water resources are limited and a wide gap exists between available water supply and the amount of water required for intensive cropping, appropriate use of industrial effluents may be helpful in meeting a part of the increased water demand. No systematic study has been carried out so far to assess the relative heavy metals availability in soils irrigated with effluent waters. Therefore, a study was undertaken to survey both surface and subsurface soils irrigated with effluent waters for availability of heavy metals and also to assess the contents of the pollutant elements in sugar industrial effluents at the point of source. Survey of effluents and irrigation waters for their quality (heavy metal, RSC, SAR, pH and EC) with special reference to sugarcane cultivation in different factory zones of North Coastal Zone was carried out during 2011-12 and 2012-13.Effluents samples were collected from all the five existing sugar factory areas of North Coastal Andhra Pradesh viz., M/s Thummapala Cooperative sugar factory, Anakapalle, M/s Etikoppaka Cooperative sugar factory, Darlapudi and M/s Govada Cooperative sugar factory, Chodavaram of Visakhaptanm district; M/s GMR Sugar factory, Sankili of Srikakulam district and M/s NCS sugars, Bobbili of Vizianagaram district. Results revealed that all sugar factory effluents are highly acidic with the pH values varying from 4.32 (M/s Govada Cooperative sugar factory, Chodavaram) to 5.50 (M/s Etikoppaka Cooperative sugar factory, Darlapudi). However after effluent treatment, the pH values in all the factory areas were reached to safer limits. Concentrations of magnesium, calcium, sodium and sodium absorption ratios are within the limits in all the factory effluents. Heavy metals viz., cadmium and lead also not recorded in factory effluents, whereas cobalt, nickel and chromium are found in traces. Hence, effluents from all the sugar factories can be used safely for irrigation with respect to concentration of heavy metals in the sugar factory effluents. Data on soil analysis results revealed that, effluent irrigated soils are neutral in reaction with non-saline in conductivity. Mean organic carbon content pertaining to all the five factory soils was medium in range. Hence, it is found safe to irrigate soils with treated sugar factory effluents as of soil physico-chemical and chemical properties are at permissible limits and for sugarcane cultivation.

Long-term irrigation with zinc smelter effluent affects important soil properties and heavy metal content in food crops and soil in Rajasthan, India

ABSTRACTUse of wastewater for irrigating agricultural crops is on the rise, particularly in the developing countries. The present study was undertaken to assess the long-term effect of irrigation with zinc smelter effluent on important soil properties including heavy metal status. Metal concentration in the edible parts of the crops grown on smelter effluent-irrigated soils was also measured. For this purpose, the agricultural lands which have been receiving the zinc smelter effluent irrigation for about five decades at Debari, Udaipur, India were selected. The adjacent tubewell water-irrigated fields were selected as reference. Long-term irrigation with smelter effluent resulted into significant buildup of ethylenediaminetetraacetic acid extractable Zn (57.7 fold), Cu (4.51 fold), Fe (3.35 fold), Mn (1.77 fold), Ni (1.20 fold), Pb (45.1 fold), and Cd (79.2 fold) in soils over tubewell water-irrigated fields. Total Zn, Cu, Mn, Ni, Pb, and Cd content in effluent-irrigated soils was also increased by 27.0, 1.60, 1.40, 1.30, 26.2, and 167 fold, respectively. Risk assessment indicated a very high to moderate potential ecological risk due to Cd, Pb, and Zn in soils close to the immediate vicinity of the smelter plant. Cadmium and Pb concentrations in edible parts of almost all the crops grown on effluent-irrigated soils were above the safe limit of CODEX commission. On an average, soil pH dropped by 0.31 units due to smelter effluent irrigation. Smelter effluent irrigation resulted into significant increase in soil organic carbon, electrical conductivity, and CaCO3 content. On an average, there was decrease in available N (21.0%) and P (20.8%) content in effluent-irrigated soils over the tubewell water-irrigated ones. An increase in available K (102%) and S (26.0 fold) was recorded in effluent-irrigated soils. Long-term irrigation with zinc smelter effluent resulted into reduced microbial activities in soil as evidenced from the level of microbial biomass carbon and dehydrogenase activity. In view of the buildup of heavy metals and subsequent imbalance in essential plant nutrients in smelter effluent-irrigated soils, appropriate remediation-cum-fertilization strategy needs to be adopted for better soil health and plant nutrition.

Solid phase speciation of Zn and Cd in zinc smelter effluent-irrigated soils

Solubility of metal in contaminated soils is a key factor which controls the phytoavailability and toxic effects of metals on soil environment. The chemical equilibria of metal ions between soil solution and solid phases govern the solubility of metals in soil. Hence, an attempt was made to identify the probable solid phases (minerals), which govern the solubility of Zn2+ and Cd2+ in zinc smelter effluent-irrigated soils. Estimation of free ion activities of Zn2+ (pZn2+) and Cd2+ (pCd2+) by Baker soil test indicated that metal ion activities were higher in smelter effluent-irrigated soils as compared to that in tubewell water-irrigated soils. Identification of solid phases further reveals that free ion activity of Zn2+ and Cd2+ in soil highly contaminated with Zn and Cd due to long-term irrigation with zinc smelter effluent is limited by the solubility of willemite (Zn2SiO4) in equilibrium with quartz and octavite (CdCO3), respectively. However, in case of tubewell water-irrigated soil, franklinite (ZnFe2O4) in equilibrium with soil-Fe and exchangeable Cd are likely to govern the activity of Zn2+ and Cd2+ in soil solution, respectively. Formation of highly soluble minerals namely, willemite and octavite indicates the potential ecological risk of Zn and Cd, respectively in smelter effluent irrigated soil.

English

The utilization of treated agro-industrial effluents has been recommended as sound option for agriculture irrigations practices and sustainable land management programme. This paper presents the impact of utilizing treated effluent form a distillery industry on physico-chemical properties of soils in an agriculture plot. The effluent was applied in 50 and 100% strength and a control plot received normal groundwater as irrigation water under wheat cropping system. No fertilizer was applied in effluent treated crop while field with groundwater received normal dose of chemical fertilizer. The distillery effluent treated plots showed considerable level of all major soil nutrients. The pH of effluent irrigated soils was in alkaline scale while EC of same soil suggests the high concentration of soil nutrients. The organic carbon (3.25 – 6.75 %) was high in effluent irrigated soils than control. The ranges of important soil nutrients: total P, total N, total K, total Ca, total Fe, total Mg and total Zn were relatively higher in effluent treated soils than control plots. Results suggested that distillery effluent can be a sustainable option for crop irrigation to solve twofold problems of agriculture system: soil nutrient deficiency and supply of water for crop irrigation

Risk Probability of Soil and Groundwater Pollution Due to Leaching Effect of Distillery Effluent Used for Agricultural Purpose

Distillery effluent is posing threat to the different components of the environment due to indiscriminate use of distillery effluent for irrigation of agricultural field, mainly affecting soil and water quality as the chemicals leaches to the groundwater table. The chemical substances transferred in soil profiles is a major environmental concern because even slow transport through the soil may eventually lead to deterioration of groundwater quality. The study reveals the physico-chemical characterisation of soil horizon of agricultural field which was regularly irrigated with distillery effluent for the observation of leaching effect of distillery effluent in soil horizons and ground water quality. The result showed that all the physico-chemical properties of soil horizons have high content of effluent irrigated soil compared to fresh water irrigated soils. It may be concluded that the higher value and indiscriminate use of distillery effluent on land affects the composition of the soil and groundwater quality due to leaching. The soil horizon showed higher value in surface soil while the values were less in lower soil horizons as compared to unaffected soil.

Multivariate data analysis for bioremediation of contaminated soil through Interactions between heavy metals, microbes and plants

Plant-assisted bioremediation (phytoremediation) is a promising technique for in-situ remediation of contaminated soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. This work presents a Pot experiment was conducted under green house conditions to test the effect of fungal inoculation on remediating heavy metal (HM) contaminated soil treated with sewage effluent for several years. Canola crop was used as accumulator plants. Results demonstrated that the dry matter yield of tested crops were significantly higher in soil irrigated for 50 years with sewage effluent than that in 20 years sewage effluent irrigated soil. Metal uptake and accumulation in different plant parts (shoot and root) was enhanced after inoculation with Aspergillus parasiticus (F1) and Fusarium oxysporum (F2). The reate of HM accumulation as higher in in soil treated irrigated sewage effluent for 50 years than that in 20 years sewage irrigated soil.

Multivariate data analysis for bioremediation of contaminated soil through Interactions between heavy metals, microbes and plants

Plant-assisted bioremediation (phytoremediation) is a promising technique for in-situ remediation of contaminated soils. Enhancement of phytoremediation processes requires a sound understanding of the complex interactions in the rhizosphere. This work presents a Pot experiment was conducted under green house conditions to test the effect of fungal inoculation on remediating heavy metal (HM) contaminated soil treated with sewage effluent for several years. Canola crop was used as accumulator plants. Results demonstrated that the dry matter yield of tested crops were significantly higher in soil irrigated for 50 years with sewage effluent than that in 20 years sewage effluent irrigated soil. Metal uptake and accumulation in different plant parts (shoot and root) was enhanced after inoculation with Aspergillus parasiticus (F1) and Fusarium oxysporum (F2). The reate of HM accumulation as higher in in soil treated irrigated sewage effluent for 50 years than that in 20 years sewage irrigated soil.

Accumulation of heavy metals in Spinacia oleracea irrigated with paper mill effluent and sewage

The present study on heavy metal contamination in soil and their accumulation in edible part (leaves) and roots of Spinacia oleracea (Spinach) on irrigation with paper mill effluent (PME)/sewage revealed that there was significant increase in the nickel (Ni, +227.17 %) content of the soil irrigated with PME, whereas in the soil irrigated with sewage chromium (Cr, +274.84 %), iron (Fe, +149.56 %), and cadmium (Cd, +133.39 %), contents were increased appreciably. The value of enrichment factor (EF) for Ni (3.27) indicated moderate enrichment in PME-irrigated soil. The EF of Fe, zinc (Zn), Cd, and Cr were <2 in PME effluent-irrigated soil which showed deficiency of minimal enrichment. In sewage irrigated soil, EF value for Cr, Fe, and Cd indicated moderate enrichment, while the values for Zn and Ni indicated deficiency of minimal enrichment. Among various metallic concentrations, the maximum concentration of Fe was observed in leaves (400.12 ± 11.47 mg/kg) and root (301.41 ± 13.14 mg/kg) of S. oleracea after irrigation with PME, whereas the maximum concentrations of Fe was found in leaves (400.49 ± 5.97 mg/kg) and root (363.94 ± 11.37 mg/kg) of S. oleracea after irrigation with sewage for 60 days. The bioaccumulation factor value was found maximum for Cd (2.23) in the plants irrigated with PME while that of Fe (0.90) in the plants irrigated with sewage. The undiluted use of PME/sewage for irrigation increased the concentration of Cr, Cd, Zn, Ni, and Fe metals which were accumulated in S. oleracea, posing a potential threat to human health from this practice of irrigation.

Ferti-irrigational impact of distillery effluent and Di-ammonium phosphate on the soil and growth characteristics of Egg plant (Solanum melongena L.)

A comparative study was conducted to assess the ferti-irrigational effect of Distillery effluent (DE) concentrations such as 10%, 25%, 50%, 75% and 100% along with control (Bore well water-BWW) and Di-ammonium phosphate (DAP) separately for the pot culture cultivation of Solanum melongena. The results revealed that DE concentrations had significant (P&lt;0.001) effect on EC, Cl¯, Mg2+, OC, HCO3–, exchangeable Na+, available K+, Ca2+, TKN, available P and SO42-, whereas non-significant (P&gt;0.05) effects were observed for water holding capacity(WHC) and bulk density (BD) of the soil. Irrigation with 100% concentration of DE, increased EC (+63.46%), Cl¯ (+292.37%), Mg2+ (+1162.72%), OC (+3763.63%), exchangeable Na+(+264.29%), available K+ (+48.39%), Ca2+ (+815.74%), TKN (+1449.18%), available P (+338.83%), SO42- (+80.07%), while decreased pH (-17.85%) total bacteria (-47.02 %), fungi (-52.17%) and actinomycetes (-82.89 %) in effluent irrigated soil. Application of diluted doses of DE significantly increased plant height, root length, chlorophyll content, leaf area, number of leaves, number of branches, number of flowers, fruit length, fruit diameter, fruit weight, number of fruit and crop yield of S. melongena, with the better results being obtained at a dilution of 50% of DE concentration in comparison to DAP and BWW.

Comparison of arbuscular mycorrhizal and dark septate endophyte fungal associations in soils irrigated with pulp and paper mill effluent and well-water

We compared arbuscular mycorrhizal (AM) and dark septate endophyte (DSE) fungal associations in 2 crops and 31 weeds commonly occurring in pulp and paper mill effluent irrigated and well-water irrigated soils. Soil pH, organic C, N, P and K, were higher in pulp and paper mill effluent irrigated than in well-water irrigated soils. In contrast, the average AM fungal colonization, root length with AM fungal hyphae/hyphal coils, spore numbers and diversity were lower in pulp and paper mill effluent irrigated soils compared to well-water irrigated soils. However, no significant variation was found in DSE fungal colonization nor root length with AM fungal arbuscules/arbusculate coils and vesicles between pulp and paper mill effluent irrigated and well-water irrigated soils. A significant negative correlation existed between AM and DSE fungal colonization in both effluent and well-water irrigated soils. Twelve AM fungal spore morphotypes belonging to Acaulospora, Dentiscutata, Glomus, Racocetra and Scutellospora were isolated from the well-water irrigated soils, whereas spores of six morphotypes were isolated from effluent irrigated soils. AM fungal spore numbers were correlated significantly and positively to AM fungal colonization in effluent and well-water irrigated soils.

Treated domestic sewage irrigation effects on soil hydraulic properties in arid and semiarid zones: A review

In arid and semiarid regions, the use of treated domestic sewage (effluent) for irrigation is becoming a common practice, because of the shortage of freshwater resources. However, the use of effluent for irrigation could have an impact on the chemical and hydraulic properties of soils. This paper reviews the effects of irrigation with effluents that have undergone various treatments on hydraulic properties of semiarid and arid soils. Irrigation of semiarid clay and sandy soils with secondary effluent increased the salinity at depths down to ∼1.5 m, and the sodicity down to ∼1.5 and >4 m, respectively. The increase of the organic matter load in the effluents resulted in inconsistent effects on the organic matter content of the topsoil, but it could lead to its decrease in the subsoil because of a “priming effect” of the effluent. Percolation of effluent through the soil profile can reduce its saturated hydraulic conductivity ( K s ) to an extent that depends on the effluent quality, soil chemical properties, and the pore size distribution in the soil. Leaching a loamy and a clay soil with secondary effluent decreased the K s because of plugging of the pores with suspended solids, whereas the K s of a sandy soil was not affected because of its large average pore size. Irrigation of high sodicity, arid soils with effluent that had undergone reverse osmosis treatment decreased K s because of the low electrolyte concentration of the effluent, which enhanced soil swelling and clay dispersion. An increase of soil sodicity, caused by effluent irrigation, decreased the K s of a clay soil leached with water of low electrolyte concentration, as a result of enhanced clay swelling and dispersion. In a non-calcareous, sandy soil, the higher sodicity in the effluent-irrigated soil led, under rainfall conditions, to enhanced seal formation, reduced infiltration, and increased runoff, as a result of enhanced clay dispersion. In contrast, for calcareous soil under similar conditions, no effect of effluent irrigation on runoff and soil loss was observed. This was, probably, because of the release of Ca during the dissolution of CaCO 3; this Ca replaced exchangeable Na, thereby reducing the soil sodicity to its natural levels. Because of the interaction between effluent irrigation and soil properties, it is necessary to identify sensitive regions and soils prior to irrigation with effluents, to prevent possible deleterious effects on soil structure and hydraulic properties.

Long-term impacts of pasture irrigation with treated sewage effluent on nutrient status of a sandy soil in Zimbabwe

Declining freshwater resources and the need to safely dispose wastewater have led to a rapid increase in wastewater reuse in developing countries. However, empirical evidence on the effects of effluent-irrigation on soil fertility is limited. The study investigated the nutrient status of a sandy soil after 26 years of effluent irrigation. Soil samples from effluent-irrigated and non-irrigated sites were analysed for pH, electrical conductivity (EC), soil organic carbon (SOC), total and plant available forms of N and P, exchangeable bases and trace metals. Analysis of effluent quality showed that, besides Cr and Cd, all measured parameters were within acceptable limits for wastewater irrigation. Our results revealed that effluent-irrigation significantly (P < 0.05) enriched the soil with essential nutrients for plant growth, which are commonly deficient in most soils of Zimbabwe. Effluent-irrigated soils had significantly (P < 0.05) higher pH, EC, SOC, total and available N and P and, exchangeable Ca and Mg at 0–30 cm-depth. However, apart from Cr accumulation, effluent irrigation significantly (P < 0.05) depleted Zn, Cu and Cd probably due to plant uptake and enhanced mobility under acidic soil pH. Cr accumulation and depletion and mobility of Zn, Cu and Cd in effluent-irrigated soils could threaten the sustainability of the practice. We recommend a review of the current management practices based on crop water requirements, effluent quality and environmental considerations.

Phytoremediation efficiency of Portulaca tuberosa rox and Portulaca oleracea L. naturally growing in an industrial effluent irrigated area in Vadodra, Gujrat, India

Phytoremediation is a novel, solar-driven and cost-effective technology for the remediation of heavy metal contaminated environments through exploitation of plants ability to accumulate heavy metals in their harvestable shoot parts. In the present investigation, we collected plants of two species of Portulaca i.e. P. tuberosa and P. oleracea from field sites in Vadodra, Gujrat, India. At one site, field was being irrigated with industrial effluent while at other with tube well water. Analysis of heavy metals was performed in industrial effluent, tube well water, soils irrigated with them, and in different parts viz., roots, stem, leaves and flowers of the plant samples. Industrial effluent and soil irrigated with it had very high level of heavy metals (Fe, Zn, Cd, Cr and As) as compared to the tube well water and soil irrigated with that. Plants of both the species growing in effluent irrigated soils showed high accumulation of metals in all plant parts with the maximum being in roots and the least in flowers. Interestingly, both species of Portulaca hyperaccumulated more than one heavy metal viz., Cd, Cr and As. The total shoot concentrations (microg g(-1) dw) of Cd, Cr and As in P. tuberosa were 1,571, 7,957 and 3,118, respectively while in P. oleracea, these were 1,128, 7,552 and 2,476, respectively. Portulaca plants have good biomass and high regeneration potential; hence appear to be suitable for the remediation of effluent (metal) contaminated areas.

Absorption of gypsum solution by a potassic soil: a data set

Reliable experimental data required to test hydrodynamic dispersion/chemical reaction models are scarce. This paper provides such a dataset based on absorption of gypsum solution by horizontal columns of relatively dry soil with an initially high exchangeable potassium ratio. Initial and boundary conditions are well defined. Water and cation concentration profiles measured after 200 and 400 min lay on single curves when graphed in terms of distance divided by the square root of time. Cation exchange occurred close to the intake surface and calcium derived from the gypsum was confined to a narrow band well behind the notional piston front that separates the absorbed solution from that originally present. Anion exchange was negligible and the solution concentration up to the piston front approximated the anion concentration of the invading solution. The interval between the region of cation exchange and the piston front maintained the original cation adsorption ratios but at a total cation solution concentration approximating that of saturated gypsum (~25 mmolc/L). Some implications of this phenomenon are discussed. Comparison of cation exchange isotherms observed when the virgin soil absorbs effluent-like solutions and when effluent-irrigated soil absorbs saturated gypsum suggest that, operationally, these isotherms may be considered to be unaffected by hysteresis in the exchange reactions.