Arsenic (As) contamination of the environment has emerged as a concerning issue recently for which phytoremediation has been suggested as a viable solution. Hydrilla verticillata (L.f.) Royle is a widely distributed rapidly growing aquatic weed possessing significant potential to accumulate As and is thus a potential candidate for the purpose of As phytoremediation. In the present study, an investigation of thiol metabolism was conducted in H. verticillata, which revealed differential effects upon exposure to arsenite [As(III)] and arsenate [As(V)]. The accumulation of arsenic was found to be higher upon exposure to As(III) than to As(V). Besides, As(III) was found to induce the activities of enzymes, such as cysteine synthase and γ-glutamylcysteine synthetase and the amounts of cysteine and glutathione (GSH) to higher levels than that observed with As(V). The activity of glutathione-S-transferase was, however, stimulated to a higher level upon exposure to As(V) than As(III). The activity of arsenate reductase was found to increase upon As(V) exposure at all concentrations and durations. In addition, a significant stimulation in the activity of phytochelatin synthase was noticed in vitro with an increase in As/GSH concentration and time of incubation. Arsenic detoxification in H. verticillata thus appeared to involve an induction of thiol synthesis and consumption in a coordinated manner, though differentially upon exposure to As(III) and As(V). The information gained through this study would help in better designing of the pilot experiment at the field level depending on the chemical composition of the contaminated water.

We evaluated the differences in the use of a quartz filter and a polytetrafluoroethylene (PTFE) filter as a first (F0)-stage filter in a four-stage filter-pack method. A four-stage filter-pack method can completely collect sulfur species (SO₂ and SO ₄ ²⁻ ), nitrate species (HNO₃ and NO ₃ ⁻ ), and ammonium species (NH₃ and NH ₄ ⁺ ) with little or no leakage irrespectively of the first-stage filter used. On the other hand, a seasonal variation was observed in the efficiency of collection between the quartz filter and the PTFE filter depending on the material to be collected. There was no seasonal variation in the efficiency of collection in sulfur species; in contrast, a clear seasonal variation was observed for the nitrate and ammonium species. As for NO ₃ ⁻ , the PTFE filter was more vulnerable than the quartz filter at air temperatures below 21°C, while the quartz filter was more vulnerable than the PTFE filter at air temperatures exceeding 21°C. A similar vulnerability for air temperature was observed for NH ₄ ⁺ , although the threshold air temperature was 23°C for NH ₄ ⁺ . Consequently, the evaporation loss of NO ₃ ⁻ would be mainly attributable to the volatilization of NH₄NO₃, although it is also partially due to the volatilization of NH₄Cl.

This study is aimed at assessing the ability of metal-resistant yeast, Candida tropicalis, to uptake cadmium from the liquid medium. The minimum inhibitory concentration of Cd²⁺ against C. tropicalis was 2,800 mg L⁻¹. The yeast also showed tolerance towards Zn²⁺ (3,100 mg L⁻¹), Ni²⁺ (3,000 mg L⁻¹), Hg²⁺ (2,400 mg L⁻¹), Cu²⁺ (2,300 mg L⁻¹), Cr⁶⁺ (2,000 mg L⁻¹), and Pb²⁺ (1,200 mg L⁻¹). The yeast isolate showed typical growth curves, but low specific rate of growth was observed in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 7. The metal processing ability of the isolate was determined in a medium containing 100 mg L⁻¹ of Cd²⁺. C. tropicalis could decline Cd²⁺ 57%, 69%, and 80% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd²⁺ 56% and 73% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and non-protein thiol levels by 146.15% and 59.67% at 100 mg L⁻¹ concentration, respectively. Metal tolerance and accumulation together with changes in the GSH status and non-protein thiols under Cd exposure were studied in C. tropicalis.

Little is known about the transport of microorganisms through freeze-fractured clay soils. Normally consolidated clay (NCC) and compacted clay (CC) columns (representing a natural clay barrier and a compacted barrier, respectively) were exposed to six consecutive freeze-thaw cycles and permeated for 21 days with an Escherichia coli cell suspension (approximately 1 × 10⁷ colony forming units (CFU)/mL) containing a 2.1-mM bromide tracer. An unfractured sand column was also examined for comparison with the clay columns. While no E. coli was detected in the effluent of both untreated NCC and CC control clay columns, a relatively low density of E. coli (between 228 and 270 CFU/mL compared to 1 × 10⁷ CFU/mL in the influent) was first detected in the effluent of the freeze-fractured NCC and CC columns at 0.29 and 0.31 pore volumes (or at 5.4 and 4.1 h), respectively. It took 11 min for a full breakthrough of E. coli through the sand column, but only about 0.1% of the influent E. coli density was detected in the effluents of the freeze-fractured NCC and CC columns at day 21. These observations show that despite the high bacterial retention capacity of the freeze-fractured clay columns, the fractures were large enough for the E. coli to flow through. Based on batch sorption tests and the permeation data, it is estimated that 18%, 7%, and 84% of the freeze-fractured NCC, CC, and sand columns would be exposed to the influent, respectively, under a full E. coli breakthrough condition. Our data show that the high bacterial retention capacity of clay barriers can be compromised by freeze-thaw conditions.

Extensive use of synthetic pyrethroids has resulted in concerns regarding their potential effects on human health and ecosystems. In the present study, we evaluated the influence of coexisting Cu²⁺, Zn²⁺, soil water contents (15%, 25%, 40% by weight and waterlogged) and temperature levels (15°C, 25°C, 35°C, and 45°C) on the dissipation of cypermethrin, fenvalerate and deltamethrin in red soil. To further clarify the influence of Cu²⁺ and Zn²⁺ on biological and chemical dissipation processes, serial concentrations of the synthetic pyrethroids containing Cu²⁺ (21.3, 50, 100, and 400 mg kg⁻¹) and Zn²⁺ (35.8, 100, 250, and 500 mg kg⁻¹) were used to spike the soil and then incubated at 25°C in the dark at 25% moisture. The results revealed a very severe inhibitory effect on the dissipation rates with increasing Cu²⁺ and Zn²⁺ levels. Conversely, there were no significant decreases in dissipation rates in response to exposure to 50 mg kg⁻¹ Cu²⁺ or 100 mg kg⁻¹ Zn²⁺, and the dissipation rates decreased significantly (p < 0.05) when the Cu²⁺ and Zn²⁺ concentration increased to 100 and 250 mg kg⁻¹, respectively, which were the respective maximum field recommended rates. When compared with unsterilized batch treatments, the t ₁/₂ in sterilized (chemical dissipation) batch treatments increased by 1.0-4.8-fold. Additionally, there was a highly significant difference in the dissipation of pyrethroids in the 15% water content treatments and waterlogged treatments (p < 0.05). Finally, the difference in the dissipation rates at 15°C and 25°C was significant (p < 0.05).

Most alpine ecosystem climate change studies identify changes in biota, several report abiotic factors and conditions, few report temperature changes, and few to none discuss growing degree days (GDD) changes. This study provides results of data analysis on changes in number of GDD in the alpine desert of the San Luis Valley (SLV) whose community is dominated by an irrigated agricultural region. Analysis indicates significant increases (p < 0.05) in annual and growing season GDD₁₀, GDD₄.₄ (potato), and GDD₅.₅ (alfalfa) during 1994-2007 compared to 1958-1993. With one exception, all stations experienced significant increases in mean annual daily GDD between 0.12 and 0.50 day⁻² and growing season GDD day⁻² 0.21 and 0.81. Higher temperatures increase numbers of GDD, quickening growth of crops and maturity at the cost of reduced yield and quality. Increases in GDD indicate the Valley's agricultural region and economy may experience negative impacts as yields decrease and water use increases.

The arsenic contamination of Bangladesh groundwater involves heavy arsenic inputs to irrigated rice fields. Beside adsorption on soil colloids, iron-arsenic co-precipitation phenomena can affect arsenic retention in soils. In paddy fields of Satkhira District, Bangladesh, the study of the arsenic and iron forms in the irrigation waters and in soils at different times and distances from the irrigation well evidenced that a higher Fe/As ratio in the well water was related to a faster oxidation of Fe(II) and As(III) in water and to a close Fe-As association in soils, together with a greater accumulation of arsenic and poorly ordered iron oxides. The concentration of arsenic and of labile iron forms decreased with the distance from the well and with the depth, as well as the reversibility of arsenic binding. The fate of the arsenic added to the soils by irrigation hence resulted strongly influenced by iron-arsenic co-precipitation, depending on the Fe/As ratio in water. Irrigation systems favouring the sedimentation of the Fe-As flocks could help in protecting the rice from the adverse effects of dissolved arsenic.

More than 50 tanneries are operated in Kula, Turkey which is located on highly permeable geological units. The untreated effluents from the tanneries discharged onto the ground surface may cause pollution in surface waters, in groundwater, and in soil. Since the water resources of the region are used for drinking, agricultural, and industrial purposes, the quality assessment of groundwaters and surface waters is completed in the content of this study. Additionally, the surface soil samples are analyzed for their heavy metal content to describe the size of the pollution. The results obtained from the analysis of the water samples show that the concentrations are mostly within drinking water limits. But, concentrations are expected to increase in the next years as no effective effluent collection and treatment is present in the tanneries. Although the concentrations of K, SO₄, Mg, Na, and Cl exceed the permissible limits for drinking water in some cases, they may not directly be caused by tannery activities. Nevertheless, they should be assessed as an indicator of the beginning of groundwater pollution. Also, soil samples collected near the tannery district are extremely polluted. This paper discusses the assessment of the geochemical dispersals of Cr and other pollutants derived from the tannery activities within soil and water in Kula.

The research and interest towards the use of constructed floating wetlands for (waste)water treatment is emerging as more treatment opportunities are marked out, and the technique is applied more often. To evaluate the effect of a floating macrophyte mat and the influence of temperature and season on physico-chemical changes and removal, two constructed floating wetlands (CFWs), including a floating macrophyte mat, and a control, without emergent vegetation, were built. Raw domestic wastewater from a wastewater treatment plant was added on day 0. Removal of total nitrogen, NH₄-N, NO₃-N, P, chemical oxygen demand (COD), total organic carbon and heavy metals (Cu, Fe, Mn, Ni, Pb and Zn) was studied during 17 batch-fed testing periods with a retention time of 11 days (February-March 2007 and August 2007-September 2008). In general, the CFWs performed better than the control. Average removal efficiencies for NH₄-N, total nitrogen, P and COD were respectively 35%, 42%, 22% and 53% for the CFWs, and 3%, 15%, 6% and 33% for the control. The pH was significantly lower in the CFWs (7.08 ± 0.21) than in the control (7.48 ± 0.26) after 11 days. The removal efficiencies of NH₄-N, total nitrogen and COD were significantly higher in the CFWs as the presence of the floating macrophyte mat influenced positively their removal. Total nitrogen, NH₄-N and P removal was significantly influenced by temperature with the highest removal between 5°C and 15°C. At lower and higher temperatures, removal relapsed. In general, temperature seemed to be the steering factor rather than season. The presence of the floating macrophyte mat restrained the increase of the water temperature when air temperature was >15°C. Although the mat hampered oxygen diffusion from the air towards the water column, the redox potential measured in the rootmat was higher than the value obtained in the control at the same depth, indicating that the release of oxygen from the roots could stimulate oxygen consuming reactions within the root mat, and root oxygen release was higher than oxygen diffusion from the air.