Soils Of High Organic Matter Content Research Articles

Research progress of bio-slurry remediation technology for organic contaminated soil.

Bio-slurry remediation technology, as a controllable bioremediation method, has the significant advantage of high remediation efficiency and can effectively solve the problems of high energy consumption and secondary pollution of traditional organic pollution site remediation technology. To further promote the application of this technology in the remediation of organically polluted soil, this paper summarizes the importance and advantages of bio-slurry remediation technology compared with traditional soil remediation technologies (physical, chemical, and biological). It introduces the technical infrastructure and its technological processes. Then, various factors that may affect its remediation performance are discussed. By analyzing the applications of this technology to the remediation of typical organic pollutant-(polycyclic aromatic hydrocarbons(PAHs), polychlorinated biphenyls(PCBs), total petroleum hydrocarbons(TPH), and pesticide) contaminated sites, the following key features of this remediation technology are summarised: (1) the technology has a wide range of applications and can be used in a versatile way in the remediation projects of various types of organic-contaminated soil sites such as in clay, sand, and high organic matter content soil; (2) the technology is highly controllable. Adjusting environmental parameters and operational conditions, such as nutrients, organic carbon sources (bio-stimulation), inoculants (bio-augmentation), water-to-soil ratio, etc., can control the remediation process, thus improving the restoration performance. To sum up, this bio-slurry remediation technology is an efficient, controllable and green soil remediation technology that has broad application prospects.

Effect of soil salinity on internal browning of potato tuber tissue in two soil types

A study was carried out with potato (Solanum tuberosum; cv. Atlantic) during 2001 and 2002 to determine the effect of soil salinity on internal tuber browning. The effect of varying levels of soil salinity on proline content, polyphenol oxidase enzyme activity, and chlorogenic acid content in potato leaves and tubers was examined. NaCl treatments (2.1, 4.25, 6.38, 8.5 g NaCl L−1) were applied to the pots, the first 46 days after planting, and four additional treatments were applied, each about 7 days apart. Increasing NaCl concentrations resulted in an increase in browning of tuber tissue and proline content in the tubers. Chlorogenic acid content in the leaves increased up to 6.4 g NaCl L−1, but then decreased at 8.5 g NaCl L−1 and in tubers tended to be maximal at the highest saline concentration tested (8.5 g NaCl L−1). Increasing NaCl concentration resulted in a reduction in yield per plant and average tuber weight, and also increased tuber number. There were major differences in the impact of salinity over the 2-year period, which was probably due to the impact of the growing media; a low organic matter (about 1% OM) silty loam soil and a high organic content (about 90% OM) Muck soil were used in 2001 and 2002, respectively. Tuber browning increased linearly with salinity in 2002, but only markedly increased at 8.5 g NaCl L−1 in 2001. Sodium and chloride ion concentration was always greater (about two times) at equivalent application rates in the 2002 trial. The high organic matter content soil retained sodium and chloride ions more effectively than the silty loam soil and enhanced the impact of increased salinity concentration on physiological properties of potato plants and particularly on tuber tissue browning and proline accumulation.

Remediation of persistent organic pollutants (POPs) in two different soils

Persistent organic pollutants (POPs) are a set of chemicals that are toxic, persist in the environment for long periods of time, and biomagnify as they move up through the food chain. The most widely used method of POP destruction is incineration, which is expensive and could result in undesirable by-products. An alternative bioremediation technology, which is cheaper and environ-mentally friendly, was tested during this experiment. Two different soil types containing high and low organic matter (OM) were spiked with 100 mg/kg each of pyrene and Aroclor 1248 and planted with three different species of grasses. The objective of the study was to determine residue recovery levels (availability) and potential effectiveness of these plant species for the remediation of POPs. The results showed that recovery levels were highly dependent on the soil organic matter content—very low in all treatments with the high OM content soil compared to recoveries in the low OM soil. This indicates that availability, and, hence, biodegradability of the contaminants is dependent on the organic matter content of the soil. Moreover, the degree of availability was also significantly different for the two classes of chemicals. The polyaromatic hydrocarbon (PAH) recovery (availability) was extremely low in the high organic matter content soil compared to that of the polychlorinated biphenyls (PCBs). In both soil types, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls. Planting did not have any significant effect on the transformation of the PAHs in both soil types; however, planting with switchgrass was the best remedial option for both soil types contaminated with PCB.

COMPARISON OF PARTITION COEFFICIENTS FOR 54Mn AND SOIL-EXTRACTABLE Mn, INCLUDING RELATIONSHIP TO PLANT UPTAKE

The objective of this study was to compare the values, statistical characteristics and relationships of partition coefficients (Kd) computed from a short-term study of 54Mn sorption with those computed from DTPA extractions of soil Mn. Of particular interest were the frequency distributions, which must be very well known for use in stochastic modelling of environmental impacts. The study used 69 soils. Sorption of 54Mn, applied with stable 54Mn carrier, was measured after 24 h equilibration in suspension. The Kd for 54Mn was based on the single measurement of 54Mn in solution. Total soil Mn and DTPA + NaHCO3-extractable Mn were also measured and used to compute a Kd from two measurements. The frequency distributions of Kd values measured by either method were strongly skewed and conformed to lognormal, regardless of the statistical properties of the underlying measurements. The geometric mean Kd for 54Mn was 44 L kg−1 and was highest for high pH, high clay content and high organic matter content soils, as expected. The geometric mean Kd for DTPA-extractable Mn was 1070 L kg−1 and was not related in the same way to the soil properties. Clearly, the two Kd measurements were quite different. A significant correlation (r = 0.54, P < 0.001) between the Kd for 54Mn and plant Mn concentrations confirmed that this relationship is useful for modelling applications. The sorption of 54Mn was the best single measurement to predict the plant-availability of soil Mn, determined in a previous study. However, in concert with pH and clay content data, the DTPA + NaHCO3-extractable Mn gave the best correlation to plant uptake. Key words: Kd, frequency distribution, radionuclides, soil test, isotopic exchange

Degradation of ioxynil to CO 2 in soil

Degradation of ioxynil (4-hydroxy-3,5-diiodobenzonitrile) to CO 2 was detected in a clay loam, high organic matter content soil. The majority of radioactivity was recovered as 14CO 2 from both ring-labeled and cyano-labeled ioxynil; however, 14CO 2 was always released from cyano-labeled ioxynil at a much faster initial rate. No 14CO 2 was released in treated sterile soil, either aerobically or anaerobically. Production of 14CO 2 from cyanolabeled and ring-labeled ioxynil was greatly inhibited by HgCl 2 (10 −5 M), and p-chloromercuribenzoate (5 × 10 −5 M), but slightly inhibited by ferricyanide (10 −4 M). No 14CO 2 was evolved from ring-labeled ioxynil under anaerobic conditions. These observations indicated that the degradation of ioxynil to CO 2 in soil was a microbial action and was oxygen dependent. This is consistent with the known mechanism of oxygenases in degrading benzene rings. Anaerobically, a small amount of 14CO 2 was released from cyano-labeled ioxynil. Thin-layer chromatographic analyses of the culture supernatant revealed that 3,5-diiodo-4-hydroxybenzamide and 3,5-diiodo-4-hydroxybenzoic acid were intermediate metabolites.

Manganese studies in some soils with a high organic matter content

The total and ‘available’ forms of manganese in high organic matter content soils are reported. Most of the manganese is retained in an unavailable form either by organic matterper se or by some components of organic matter and, as a result, the ‘available’ forms are extremely low and fall below the critical limits. Retention studies indicate that, exchange processes in the soil are more responsible for the retention of added manganese than redox processes. Organic matter as such does not quantitatively represent the component or components that influence the manganese retentive capacity of the soil. There is an indication to suggest that, if most of the total manganese is in organic form then fixation of added manganese various inversely with total manganese content.