Heavy metal (Cu, Zn, Cd and Pb) contamination of vegetables in urban India: a case study in Varanasi

The contributions of heavy metals in selected vegetables through atmospheric deposition were quantified in an urban area of India. Deposition rate of Zn was recorded maximum followed by Cu, Cd and Pb. The concentrations of Zn and Cu were highest in Brassica oleracea, Cd in Abelmoschus esculentus and B. oleracea, while Pb was highest in Beta vulgaris. Heavy metal pollution index showed that B. oleracea was maximally contaminated with heavy metals followed by A. esculentus and then B. vulgaris. The results of washing showed that atmospheric deposition has contributed to the increased levels of heavy metals in vegetables. Both Cu and Cd posed health risk to local population via test vegetables consumption, whereas Pb posed the same only through B. oleracea. The study concludes that atmospheric depositions can elevate the levels of heavy metals in vegetables during marketing having potential health hazards to consumers.     

A washing procedure to mobilize mixed contaminants from soil: I. Polychlorinated biphenyl compounds

We conducted a laboratory study to assess the feasibility of a washing process with nonionic and anionic surfactants in combination with ethylenediaminetetraacetate (EDTA) for the simultaneous mobilization of heavy metals and polychlorinated biphenyls (PCBs) from a field-contaminated soil. Unit processes consisting of complexometric extraction and surfactant-assisted mobilization were combined with reagent regeneration and detoxification steps to generate innocuous products. Ten minutes of ultrasonic mixing of the soil with a combination of 30 mL L(-1) surfactant suspension and a sparing quantity (2 mmol) of EDTA mobilized appreciable quantities of PCBs, virtually all of the available Cd, Cu, Mn, and Pb, and lesser amounts of the Zn, Ni, and Cr but only small quantities of Al and Fe. Relative to individual reagents, combinations of surfactant (Brij 98, Triton X-301, or Triton XQS-20) with EDTA did not influence PCB extraction efficiencies perceptibly. Of the three surfactants, the Brij 98 proved to be the most efficient for three successive extractions with a single charge, mobilizing 83% of the PCBs, whereas companion extractions that used fresh reagent each time mobilized 87% of the soil PCB content. The decreased PCB mobilization with the same quantity of anionic surfactant (71 or 68%) resulted from losses during the EDTA regeneration process with zero-valent Mg. In toto, these studies demonstrate that PCB compounds and selected heavy metals can be coextracted efficiently from soil with three successive washes with the same washing suspension containing EDTA and a nonionic surfactant.     

A washing procedure to mobilize mixed contaminants from soil: II. Heavy metals

We conducted a laboratory study to assess the efficiency of nonionic and anionic surfactants in combination with a sparing quantity of ethylenediaminetetraacetate (EDTA) to simultaneously extract heavy metals (HMs) and polychlorinated biphenyl (PCB) compounds from a field-contaminated soil. A soil wash that mobilized both HMs and PCBs was combined with back-extraction with hexane to remove PCBs from the aqueous wash. The aqueous washing suspension was then regenerated by precipitation of the HMs induced by corrosion and hydrolysis of zero-valent Mg to provide a cleaned soil and innocuous extract. Finally, the washing suspension was recycled twice to mobilize more contaminants from the soil particulate fraction. After ultrasonic equilibration, EDTA in admixture with a nonionic surfactant did not appreciably change the efficiency of mobilization of most heavy metals (Al, Cd, Cr, Fe Mn, Ni, and Zn), but did increase the recovery of Cu and Pb. The release of EDTA from HM complexes was efficient for most metals (99%) but was influenced by the chemical characteristics of the surfactant. The EDTA recovery (62-65%) after three cycles of soil washing, hexane back-extraction, and Mg(0) treatment was similar for all reagent combinations. In toto, these studies demonstrate that after treatment with ultrasound, selected heavy metals can be coextracted efficiently from soil with a single washing suspension containing EDTA and a nonionic surfactant.     

Competition between Native Populus deltoides and Invasive Tamarix ramosissima and the Implications for Reestablishing Flooding Disturbance

Abstract: Changes in historical disturbance regimes have been shown to facilitate non-native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii , but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima . We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix . We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above-ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three-dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus , we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post-flood hydrology can restore this ecosystem by promoting its dominant plant species.     

Monitoring of growth and yield and response to silvicultural treatments

The objectives for monitoring the growth and yield of forests can range from collecting data to validate current management on an ownership to collecting data at a regional level to develop models, measure treatment response, or observe long-term growth trends. Traditional inventory and research data each have drawbacks for observing growth and yield and treatment response. The actual design of a monitoring system should try to minimize these problems, but will depend on the specific objectives. Monitoring of operations may take an inventory-type approach, while gathering regional information to build models requires a design more like research. Each organization must be responsible for monitoring its own operations, however, cooperatives offer a viable and cost effective alternative to gathering regional growth and response data. Monitoring programs will lead to confidence and credibility in management practices and in the use of tested models.     

Review and evaluation of microcosms for assessing effects of stress in marine ecosystems

Representative estuarine-marine microcosms were reviewed and evaluated to provide recommendations and guidance for use in assessing effects of perturbations on coastal zone ecosystems. Properly designed marine microcosms can be effective assessment tools for evaluating the effects of stresses on coastal ecosystems. Critical design considerations include scaling of important physical factors, such as turnover rate and circulation, inclusion of appropriate trophic groups, minimization of side growth, and maintenance of realistic nutrient regimes. Selection of communities or major components to be included in design of microcosms should be based on the experimental hypothesis, ecologically and economically important organisms, ability to interpret test results, difficulties involved in scaling, and sensitivity of the community to the stress being investigated. In selection of response parameters, emphasis should be placed on key ecological components, particle size distribution, and those variables that reflect aggregate responses at the population or community level.     

FLEXIBLE PRICING IN WATER SUPPLY PLANNING–FOR FLEXIBLE ENGINEERS1

ABSTRACT. Preliminary results from a digital simulation model designed to test time-varying water pricing policies are presented. Stochastic inflows feeding a water supply reservoir are assumed for a hypothetical community with defined demand functions. Prices are allowed to vary as a function of reservoir level, generally rising as reservoir levels fall. Increasing, decreasing and constant rates are tested. It is concluded that varying the price to reflect the increased value of scarce supplies can greatly reduce the risk of water supply shortages. It is also concluded that varying incremental (conservational) pricing policies not only reduces the risk of shortages, but also lowers the average price to the community while rewarding the low consumption user with lower average rates.