Quantitative Estimation of Synergistic Toxicity of Cu and Zn on Growth of Arabidopsis thaliana by Isobolographic Method.

Heavy metal is one of the most frequent soil contaminants and contaminated soils generally include numerous metals. Although exposure to multiple metals may increase the toxicity to humans and ecosystems, only additive effects are considered in the risk assessment. In this study, the synergistic effect of heavy metals (Cu and Zn) on a model plant, Arabidopsis thaliana, was quantified by the isobolographic method. The plant was cultured via the growth assay method on a plant agar containing individual heavy metals or combinations of Cu + Zn in a growth chamber. The concentration of Cu varied by eight levels from 0 to 200 µM and the concentration of Zn also varied by eight levels from 0 to 400 µM. In the combination of metals, each of the three levels of Cu (25-75 µM) and Zn (20-100 µM) were applied. After 8 days, plants were harvested for root/shoot weight and measured for leaf chlorophyll and carotenoid content. The primary and secondary root elongation of A. thaliana was estimated using image analysis to calculate total root length. The EC50 values of Cu and Zn on A. thaliana, based on the total root length, were 40.0 and 76.4 µM, respectively. When two heavy metals were administered in combination, the EC values decreased less than those of the individual metals. The average value of the combination index was 0.6, proving the synergistic toxic effect on the root growth of A. Thaliana. As a result, the isobolograhic method is a useful tool for estimating the quantitative toxic effect of chemicals on plants.

Phytoremediation of soil co-contaminated with heavy metals and TNT using four plant species.

We investigated the germination, growth rates and uptake of contaminants of four plant species, barnyard grass (Echinochloa crusgalli), sunflower (Helianthus annuus), Indian mallow (Abutilon avicennae) and Indian jointvetch (Aeschynomene indica), grown in soil contaminated with cadmium (Cd), lead (Pb) and 2,4,6-trinitrotoluene (TNT). These contaminants are typically found at shooting ranges. Experiments were carried out over 180 days using both single plant cultures and cultures containing an equal mix of the 4 plant species. Germination rates differed among the species in single culture (92% for H. annuus, 84% for E. crusgalli, 48% for A. avicennae and 38% Ae. indica). In the 4-plant mix culture, < 20% of seeds germinated for all 4 species. E. crusgalli and H. annuus grew slightly faster in the four-plant mix culture than in single culture, whereas A. avicennae and Ae. indica grew much slower in the 4-plant mix culture. In both single and 4-plant mix cultures, Cd concentrations in the roots of A. avicennae and E. crusgalliwere high, and Pb concentrations were high in A. avicennae and H. annuus. Cd and Pb concentrations in shoots were low to negligible in both treatment cultures for all species, except E. crusgalli in the 4-plant mix culture. The concentrations of TNT and its metabolites, 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT) were high in H. annuus, Ae. indica and A. avicennae. Total Cd removal from soil differed among species, with E. crusgalliremoving the most (50.1%) followed by H. annuus(41.3%), Ae. indica(41.1%) and A. avicennae(33.3%). The four-plant mix removed more Cd (25.8%) than a no-plant control (12.9%). Pb removal was negligible for all plant species. All plant species rapidly removed TNT and its metabolites, regardless of whether the culture was single or mixed. From in these results, we conclude that a phytoremediation for the removal of heavy metals and TNT from contaminated soils should use a single plant species rather than a mixture of several plants.

Human health risk assessment of explosives and heavy metals at a military gunnery range.

In this research, a risk assessment was undertaken in order to develop the remediation and management strategy of a contaminated gunnery site, where a nearby flood controlling reservoir is under construction. Six chemicals, including explosives and heavy metals, posing potential risk to environmental and human health, were targeted in this study. A site-specific conceptual site model was constructed, based on effective, reasonable exposure pathways, to avoid any overestimation of the risk. Also, conservative default values were adapted to prevent underestimation of the risk when site-specific values were not available. The risks posed by the six contaminants were calculated using the API's Decision Support System for Exposure and Risk Assessment, with several assumptions. In the crater-formed-area (Ac), the non-carcinogenic risks (i.e., HI values) of tri-nitro-toluene (TNT) and Cd were slightly larger than 1, but for RDX (Royal Demolition Explosives) was over 50. The total non-carcinogenic risk of the whole gunnery range was calculated to be 62.5, which was a significantly high value. The carcinogenicity of Cd was estimated to be about 10(-3), while that for Pb was about 5 x 10(-4), which greatly exceeded the generally acceptable carcinogenic risk level of 10(-4)-10(-6). It was concluded from the risk assessment that there is an immediate need for remediation of both carcinogens and non-carcinogens before construction of the reservoir. However, for a more accurate risk assessment, further specific estimations of the changes in environmental conditions due to the construction of the reservoir will be required; and more over, the effects of the pollutants to the ecosystem will also need to be evaluated.

Phytoremediation of soil contaminated with cadmium and/or 2,4,6-trinitrotoluene.

Phytotoxicity, microbial activity, plant uptake and microbial degradation were examined using Rumex crispus in TNT and/or cadmium contaminated columns (TNT: 100 mg/kg of soil and Cd: 10 mg/kg of soil). The growth of plants was significantly inhibited by TNT, but not by Cd. The microbial activity was highly increased by plant root growth, decreased by Cd, and slightly reduced by TNT. The plant uptake of Cd was relatively well in Cd-contaminated column, but lowered by TNT in TNT+Cd-contaminated column. The microbial degradation of TNT occurred much faster in planted columns than in unplanted columns with minor effect of Cd (less 2-ADNT was produced). Therefore, it may be effective to treat TNT first and then Cd using phytoremediation in the TNT plus Cd contaminated sites.

Optimization of biological phosphorus removal from contaminated sediments with phosphate-solubilizing microorganisms.

This study focused on the characteristics of phosphate-solubilizing microorganisms (PSMs) which can be applied for the removal of phosphorus from sediments to prevent eutrophication of lakes or ponds. A PSM isolated from rhizospheric soil and temporarily identified as Burkholderia glathei (MB 14) produced gluconate and acetate using glucose as a carbon source and its metabolic activity caused the pH of the liquid medium to decrease as low as 4.4. The molar ratio of solubilized PO4(3-)-P to total organic acids, gluconate and acetate, in the liquid medium was 1:2, which was lower than the theoretical molar ratio of 1:3 using Ca3(PO4)2 as a model phosphorus compound. In addition, biological PO4(3-)-P solubilization with MB 14 was more efficient than the direct addition of equivalent acid to the liquid medium. These results indirectly suggest that organic acids chelate Ca2+ during solubilization of PO4(3-)-P. The growth conditions for MB 14 that produced the maximum PO4(3-)-P solubilization were carbon sources of 8 g/l of glucose and 2 g/l of sucrose, and 0.1 g/l of arginine as a nitrogen source under an anoxic environment. The PSM species, MB 14, grown under these conditions was applied to treat contaminated dredged sediments in a bioslurry reactor. In 9 d, MB 14 solubilized 34.5% of total phosphorus in the contaminated dredged sediments.

EDTA-assisted phytoextraction of lead from lead-contaminated soils by Echinochloa crusgalli var. frumentacea.

The herbaceous plant Echinochloa crusgalli var. frumentacea is highly resistant to a wide range of heavy metal concentrations. In this study we tested the phytoextraction capacity of E. crusgalli var. frumentacea. Specifically, we compared the effect of EDTA on lead (Pb) accumulation in two groups of plants: those sown in lead contaminated soil and those transplanted to the contaminated soil as seedlings. The result of the time development of the Pb concentrations in the plants in the seedling and seed groups shows that for the seedling group, the effect of adding EDTA to the Pb-contaminated soil was even more pronounced in the shoots than the roots, which showed Pb concentrations 32-fold higher. Compared to the seedling group, the Pb concentrations in the roots of plants in the seed group were approximately 5 times higher in controls and 2 to 10 times higher in the presence of EDTA. Collectively, these results might be considered that EDTA elevates the bioavailability of Pb in soil and this native species is particularly suited to use in Pb phytoextraction.

Enhanced degradation of 2,4,6-trinitrotoluene (TNT) in a soil column planted with Indian mallow (Abutilon avicennae).

Phytoremediation of soil contaminated with 2,4,6-trinitrotoluene (TNT) was studied by growing Indian mallow (Abutilon avicennae) in a soil column reactor with 2 kg of TNT contaminated soil (120 mgTNT/kg) in the top and 18 kg of uncontaminated soil in the bottom. After 50 d, TNT remaining in the column with Indian mallow was 23.2% of the initial TNT, while 48.1% of the initial TNT remained in the column without Indian mallow. In the TNT contaminated column, the growth of Indian mallow decreased by 32.4% in roots and 34.3% in shoots on a dry weight basis, respectively, compared to the uncontaminated column. However, critical symptoms such as chlorosis and leaf loss were not observed. Of the 76.8% of the TNT that disappeared in the planted column, less than 0.2% of initial TNT was recovered in the shoot and root extracts of Indian mallow. TNT transformation products in plants include unidentified polar intermediates and aminodinitrotoluenes. The results showed that planting Indian mallow in TNT contaminated soil enhanced TNT reduction both by stimulating microbial activity that enhances microbial TNT transformation, and by direct uptake and phytotransformation of TNT.

Low heavy metal bioavailability in soil at contaminated Korean shooting sites.

The bioavailability of metals at eight military shooting ranges in the Kyungkido and Kangwondo districts in Korea was examined through measurements of the metal content of the tissues of plants growing at the sites. Analysis of the metals in soil samples showed that only a small fraction of the total metal in the soil was soluble (soluble Cd, 0.01-0.43 mg/kg; soluble Cu, 1.63-10.05 mg/kg; soluble Pb, 0.01-414.46 mg/kg; and soluble Zn, 0.01-0.32 mg/kg). Correlation analyses of the levels of Cd, Pb, Cu, and Zn in soil samples and in 14 plant species collected near the sites showed that plant concentrations of Cd and Pb (shoot and root) were significantly correlated to the levels of Cd and Pb in the soil, whereas the concentrations of Cu and Zn in shoot and root tissue showed no correlation with the concentrations of metal in soil. Moreover, no direct relationship was found between the soil microbial respiration activity and soil metal concentration. These results indicate that there are only small amounts of bioavailable metal in the soil at the military shooting ranges studied.

Heavy metal concentrations and enzyme activities in soil from a contaminated Korean shooting range.

Soil enzyme activities and heavy metal concentrations (Cd, Zn, Cu and Pb) were measured at a general shooting range in South Korea. Total heavy metal concentrations varied with pH, and were negatively correlated with moisture content and organic matter. Most enzyme activities (dehydrogenase, acid phosphatase and beta-glucosidase) and ATP values (measure of biomass) were lower in polluted soils, especially in bald spots contaminated by heavy metals and TNT (2,4,6-trinitrotoluene). These data indicate that concentrated shooting activity inhibits enzyme activity and microbial growth. Soil enzyme activities in richly vegetated spots around the general shooting range were higher (2- to 3-fold) than in bald spots, but lower in areas of heavy metal contamination. Our results demonstrate that the dominant plant species in richly vegetated spots accumulated heavy metals from soils, and suggest certain plants may be useful for decontaminating polluted soil.