Aqueous leachates

Experiment 1. Bioassays with allelochemical aqueous leachate. 

Principle Phytotoxic effects of the aqueous leachate of an allelopathic plant can be tested in vitro bioassays. Test or target plants are placed in contact with 0.5 % aqueous leachate from the allelopathic plant. Germination and radicle growth can be monitored during time-course experiments (i.e. after 24,48 and 72 h of treatment), but in this chapter we will include only the results obtained after 72 h of treatment. 

Material required Air-dried (27-30°C) aerial parts of S. deppei to prepare aqueous leachate, Seeds of tomato (Lycopersicon esculentum Mill. cv. Rio Grande), Osmometer, Growth Chamber Laminar flow hood. 

Procedure Allelopathic aqueous leachate is prepared by soaking dried leaves (lg/100 mL or 1% w/v) in distilled water for 3 h. This leachate is filtered through Whatman paper (No. 4) and then through a sterile Millipore membrane (0.45 mm). Then, it is poured in Petri dishes and mixed with agar (2%) for a final aqueous leachate concentration of 0.5%. The volume will depend on the size of the Petri dish, 3 mL of leachate plus 3 mL of agar are enough for a 6 cm Petri dish. Osmotic potential of the leachate is measured with a freezing-point osmometer (Osmette A, Precision System Inc.). 

Bioassays are performed under sterile conditions in a laminar flow hood. Tomato seeds are previously washed and disinfected with 1% sodium hypochlorite. Seeds are germinated in the Petri dishes containing the S. deppei aqueous leachate. For control, seeds are germinated in 1% agar. Twelve seeds are placed on each Petri dish and kept in the dark at 27°C in a growth chamber. For enzyme activities, 40-50 Petri dishes are used per treatment. Primary roots (radicles) are excised after 72 h, frozen in liquid nitrogen and kept at -70 °C until use. For root growth response, experiments... 

Observations Germination and radicle growth can be determined at 12, 24, 48 and 72 h and the inhibitory effect of the aqueous leachate can be calculated comparing root length of treated seedlings vs. data from control ones. In this case, we only used the 72 h treatment (Figure 1). 

Fig. 1 Effects of aqueous leachate of S. deppei on radicle growth of tomato after 72 h of treatment.

Observations Figure 2 shows confocal images of 48 h tomato roots exposed to S. deppei aqueous leachate and then stained with DCFDA. A higher fluorescence is observed in treated-root hairs. 

Phthalates are easily released into the environment because there is no covalent bond between them and plastics in which they are mixed. The major portion of phthalates that are found in the environment comes from the slow releases of phthalates from plastics and other phthalate containing articles due to weathering. At natural conditions, phthalates are hydrolyzed to some extent yielding their corresponding monoesters, which are also environmental pollutants [15]. They show poor mobility in soil but aqueous leachates from landfills may contain trace amounts of more soluble products of phthalate degradation [11, 16]. 

Root and leaf aqueous leachates of Ambrosia cumanensls did indeed produce a strong inhibition on the growth of weed species. Aqueous extracts of soil collected under A.cumanensls in July (during its flowering) were strongly allelopathic to weed growth. Decomposition of leaves and roots in pots caused inhibition of some weeds also. Microorganisms have a major role in this process, as shown by results from sterile and nonsterile soils (17). 

Figure 5. Effect of aqueous leachates of Eiohomia orassipes (leaves, roots and flowers) on the germination and growth of three species ( non significant).

Our own data for the chemical composition of Estonian combustion ashes (Table 7) based on 4-acid extracts and aqueous leachates of these (ratio of solid/water = 1/10) show that Hg... 

Bryan, P.J., Rittschof, D., and Qian, P.Y., Settlement inhibition of bryozoan larvae by bacterial films and aqueous leachates, Bull. Mar. Sci., 61, 849, 1997. 

The allelopathic effect of the three plants evaluated in this study depends on both the kind of chemical compounds in each aqueous leachate and the differential response of bean and tomato to each particular allelochemical stress.37... 

Cruz-Ortega, R., Ayala-Cordero, G., and Anaya, A. L. 2002. Allelochemical stress produced by the aqueous leachate of Callicarpa acuminata effects on roots of bean, maize, and tomato. Physiol. Plantarum 116, 20-27... 

Figure 4. HPLC separation of phenolic components of an aqueous leachate from the surface of corn leaves infected with Colletotrichum graminicola. a) untreated leachate b) base hydrolyzed leachate c) acid hydrolyzed leachate. Compounds 1 and 2 are isomers of p-coumaric acid. Compounds separated isocratically on a reversed phase C-18 column with a 70 % to 30 % mixture of absolute methanol and 1 % acetic acid. Reproduced with permission from Ref. 69. Copyright 1989 Academic Press, Inc.

The Stringfellow Superfund site in California poses analytical problems similar to those encountered with most waste sites across the United States and that may be best addressed via LC/MS based methods. Most of the organic compounds in aqueous leachates from this site cannot be characterized by GC/MS based methods. Analysis of Stringfellow bedrock groundwater shows that only 0.78% of the total dissolved organic materials are identifiable via purge and trap analysis (IQ). These are compounds such as acetone, trichloroethylene etc, whose physical properties are ideally suited for GC/MS separation and confirmation. Another 33% of the dissolved organic matter is characterized as "unknown", i.e., not extractable from the aqueous samples under any pH conditions and thus not analyzed via GC. Another 66% is 4-chlorobenzene sulfonic acid (PCBSA), an extremely polar and water soluble compound that is also not suitable for GC analysis. This compound, a waste product from DDT manufacture, is known to occur at this site because of the history of disposal of "sulfuric acid waste from industrial DDT synthesis. 

Figure 7. Anion exchange chromatogram with UV detection (230 and 254 nm) of a lyophilized extract of an aqueous leachate from the Stringfellow hazardous waste site.

Acid digestion is recommended for the analysis of waste oils from of vehicles. A few jxL of the resulting aqueous leachates can then be pipetted onto Ag powder and the slurries dried and pressed into polyethylene slugs to produce pins that can eventually be submitted to GD-MS analysis for the assay of their Pb contents [658], Determinations can be performed by isotope dilution and concentrations as low as 3 pg/g Pb determined with a precision of better than 5%. GD-MS has also been used for the analysis of crude oils [659] and Cr, Cu, Fe. Mg, Na, Ni, Pb, Si, Sn and Ti can be determined in NIST SRMs, SPEX organometallic standard oils and refined oil composites. The method performs very well for limited amounts of sample, but the polyatomic interferences are a drawback. 

Figure 9. UV spectra of PAH-contaminated-soll aqueous leachates (dilution 10).

The use of UV spectrophotometry has been studied in order to evaluate the potentiality of this technique for the proposal of an index of maturity. Figure 16 shows the aqueous leachates of composts with a great difference between fresh and treated compost. 

Leaching of pollutants to ground or surface waters is a major pathway of environmental contamination. Leaching of TCDD from soil containing 8-26,300 ng/g yielded aqueous leachates of... 

An excellent review or LLE applications in the food industry is given by Hamm,17 Since solvent toxicity is a major consideration, supercritical solvents, such as CO, which are nomoxic and LLE from an aqueous leachate are two popalar means of deriling with this problem. Figure 7.8-11 is a cooceptual supercritical extraction flowsheet. Because Tc is much lower than either 7 or rB, the solvent (e.g., C02) simply is flashed from the solute by throttling (an isenthalpic process). Then the vapors are compressed (an isentropic process) and cooled (an isobaric step) to complete the solveni recycle. Usually, costs are determined by the compressor requirearerUs. Several potential applications of supercritical or near-critical solvents are discussed in more datail else where,... 

Standard Practice for the Separation of Americium from Plutonium by Ion Exchange Standard Test Method for Pu-238 Isotopic Abundance by Alpha Spectrometry Standard Test Method for Analysis of Aqueous Leachates from Nuclear Waste Materials Using Inductively Coupled Plasma-Atomic Emission Spectrometry... 

Rondinella, V. V., Betti, M., Bocci, F., Hiernaut, T., and Cobos, J. 2000. IC-ICP-MS applied to the separation and determination of traces of plutonium and uranium in aqueous leachates and acid rinse solutions of UO2 doped with Pu-238. Microchem J 67(1-3), 301-304. 

Even if atmospheric extraction is employed, applications in the food industry tend to favor the use of volatile, low-molecular weight solvents that are distilled easily from the solutes. Typically, the extract is produced, concentrated, and then backwashed with water to recover the solute. Figure. 7.8-12 illustrates a typical configuration. In this case, water is used to leach the solute from the solid food to form an aqueous te hate feed to the extraction unit. Then the aqueous leachate is contacted with a suitable solvent (which may be toxic) that extracts the solute. The extract is concentrated by solvent evaporation (perhaps 90% of the solvent is volatilized), and the concentrated solvent may be contacted again with water to remove the solute from the corrcentrate. The lean solvent is combined with the condensed solvent from the evaporator and recycled to LLE contactor 1. In this fashion, the food is never in direct contact with the toxic solvent and the solute is recovered in an aqueous stream. In order for such a LLE process to be efficient, the solvent should possess (1) a high volatility, (2) a low heat of vaporization, (3) a low aqueous solubility, and (4) a high solute solubility. 

XRF is carried out on pressed briquettes or fused beads. Lithium and boron caimot be determined by XRF. Fusion with sodium carbonate is carried out before the aqueous leachate is subjected to AAS,... 

---