Journal of Environmental Quality

Silica sand contaminated with perchloroethylene (PCE) was effectively treated by Fenton's reagent. Silica sand contaminated with PCE at 1000 mg/kg was totally mineralized in 3 h by Fenton's reagent with initial concentration of about 2.1 M of H₂O₂ and 5 mM of FeSO₄. Results from gas chromatography‐mass spectroscopy (GC‐MS) revealed that dichloroacetic acid was the sole significant intermediate species generated, and was believed to be the limiting species leading to mineralization. Experimental measurements of chloride and total organic C suggested that total dechlorination was achieved before decarboxylation in the process of mineralization. A degradation pathway of PCE with Fenton's reagent is proposed based on experimental observations and reactions reported in literature. Formic acid is proposed to be the final intermediate species before it is mineralized to CO₂. Perchloroethylene and H₂O₂ followed pseudo first‐order decomposition kinetics and the rate constants were determined to be 1.65/h ± 0.475/h and 0.206/h ± 0.036/h, respectively.

Past disposal practices at munitions production facilities have generated numerous acres of 2,4,6‐trinitrotoluene (TNT)‐contaminated soil. We determined the potential of the Fenton reagent (Fe²⁺ and H₂O₂) to remediate TNT contamination in water, aqueous extracts of contaminated soil, and soil‐water slurries. The effects of H₂O₂ and Fe²⁺ concentrations, solution pH, temperature, and initial TNT concentration on transformation and mineralization rates were evaluated. Treating an aqueous TNT solution (70 mg TNT L⁻¹) with Fenton reagent (1% H₂O₂, 80 mg Fe²⁺ L⁻¹) in the dark resulted in 100% destruction of TNT within 24 h. This coincided with 40% mineralization. Subsequent exposure to light resulted in >90% mineralization. We observed generation of 2,4,6‐trinitrobenzoic acid and 1,3,5‐trinitrobenzene within 15 min following Fenton oxidation of TNT. This indicates that initial TNT destruction likely occurs by methyl group oxidation and decarboxylation. Subsequent transformations involve nitro moiety removal with ring hydroxylation and cleavage, as evidenced by the stoichiometric recovery of TNT‐nitrogen as NO⁻₃ and production of oxalic acid as the primary C‐containing end product. Upon exposure to light, Fe(II) was regenerated and the oxalate produced from ¹⁴C‐TNT oxidation disappeared; this coincided with a decrease in solution ¹⁴C activity. Similar observations were made when ¹⁴C‐oxalic acid was the starting substrate. Fenton oxidation was also effective in destroying TNT in aqueous extracts of contaminated soil and soil‐water slurries. Experimental data provide evidence that the Fenton reagent can effectively remediate TNT‐contaminated water and soil.

The treatment of soil contaminated with pentachlorophenol, trifluralin [2,6‐dinitro‐N, N‐dipropyl‐4‐(trifluoromethyl) benzenamine], hexadecane, and dieldrin (3,4,5,6,9,9‐hexachloro‐1a,2,2a,3,6,6a,7,7a‐octahydro‐2,7:3,6‐dimethanonaphth[2,3‐b]oxirene) using catalyzed hydrogen peroxide [H₂0₂ and iron(II)] was investigated in a soil of low development with organic C ranging from 2000 mg kg^–1 to 16 000 mg kg^–1. Soil treatment was conducted at pH 3 with 240 and 400 mg L^–1 iron additions and 120 000 mg L^–1 H₂O₂. Pentachlorophenol and trifluralin degradation rates decreased as a function of soil organic C content. However, soil organic C had no effect on the degradation rates of dieldrin and hexadecane. In addition, the four contaminants degraded at equal rates with soil containing organic C > 10 000 mg kg^–1. The ratio of first‐order rate constants for contaminant degradation to hydrogen peroxide consumption (k_contaminant/k_h2O₂) was used as an empirical measure of treatment efficiency. These ratios were sensitive to both the soil organic C content and to the concentration of iron added during treatment. The efficiency ratios were highest for treatment with no iron addition; these data suggest that iron minerals and H₂O₂ provide a system in which Fenton‐like oxidations are catalyzed. The ability of iron minerals and H₂O₂ to oxidize pentachlorophenol was evaluated in goethite‐, hematite‐, and magnetite‐silica sand at pH 3. Pentachlorophenol was degraded in the mineral‐silica sand systems, which was verified by the loss of organic C and the stoichiometric recovery of chloride.

The OAh horizons in forest acid soils are reported to fix more radiocesium than the mineral horizons beneath and organic horizons above them. We determined the respective contributions of the Of, OAh, Ah, and Bw horizons in an acid brown soil to the total ¹³⁷Cs soil‐to‐plant transfer by using young spruce plants [Picea abies (L.) H. Karst.l grown on reconstituted micro‐pedons in which these respective horizons were contaminated by carrier‐free ¹³⁷Cs. The plants were grown in a greenhouse at 20°C during a period of 5 mo. The respective contributions to the ¹³⁷Cs soil‐to‐plant transfer were 92.71% in Of, 0.18% in OAh, 3.28% in Ah, and 3.83% in Bw. The very high contribution of Of was due to its high organic matter (OM) content, while the very low contribution of OAh was related to Cs⁺ fixation by vermiculitic clay minerals. The higher ¹³⁷Cs transfer from Ah and Bw vs. OAh was probably associated with Al interlayering of vermiculite. Our data suggest that plant roots and soil vermiculite acted as competitive sinks for ¹³⁷Cs in the acid brown soil.

Phosphorus (P) runoff from manure can lead to eutrophication of surface water and algae growth. This study evaluates the impacts of alternative P reduction practices on dairy farm net returns and on potential P runoff. The P control practices include dairy herd nutrient management, crop nutrient management, and runoff and erosion control. Four farms representative of dairies in the Virginia Shenandoah Valley are simulated including dairies with and without supplementary broiler enterprises and with average and below average land area. A mathematical programming model was developed to predict farm production and net returns and the GLEAMS model was used to predict potential P runoff. The farms are evaluated under four scenarios: Scenario 1, no constraint on P runoff with access to crop nutrient, runoff and erosion control strategies but no access to dairy herd nutrient control strategies; Scenario 2, no constraint on P runoff with access to all crop and dairy herd nutrient control strategies; Scenario 3, constraint on P runoff with access to crop nutrient, runoff and erosion control strategies but no access to dairy herd nutrient control strategies; and Scenario 4, constraint on P runoff with access to all crop and dairy herd nutrient control strategies. Under Scenario 2, the herd nutrient control strategies increase milk output per cow and net returns on both farms and reduce P content of manure and P runoff. Under Scenario 3, limiting P runoff reduces farm returns by 1 and 3% on the average and small farms, respectively. Under Scenario 4, the P runoff constraint is less costly, reducing returns by less than 1% on both farms. Animal nutrient control strategies should be an important part of pollution control policies and programs for livestock intensive watersheds.

Một thí nghiệm trong chậu được thực hiện để so sánh hai chiến lược xử lý ô nhiễm bằng thực vật: tích tụ tự nhiên sử dụng thực vật siêu tích tụ Zn và Cd là Thlaspi caerulescens J. Presl & C. Presl so với chiết xuất cải tiến hóa học sử dụng ngô (Zea mays L.) được xử lý bằng axit ethylenediaminetetraacetic acid (EDTA). Nghiên cứu sử dụng đất bị ô nhiễm công nghiệp và đất nông nghiệp bị ô nhiễm kim loại từ bùn thải. Ba vụ mùa của T. caerulescens trồng trong vòng 391 ngày đã loại bỏ hơn 8 mg kg⁻¹ Cd và 200 mg kg⁻¹ Zn từ đất bị ô nhiễm công nghiệp, tương đương 43% và 7% các kim loại trong đất. Ngược lại, nồng độ Cu cao trong đất nông nghiệp đã làm giảm nghiêm trọng sự phát triển của T. caerulescens, do đó hạn chế tiềm năng chiết xuất của nó. Quá trình xử lý bằng EDTA đã tăng đáng kể tính hòa tan của kim loại nặng trong cả hai loại đất, nhưng không dẫn đến tăng lớn hàm lượng kim loại trong chồi ngô. Chiết xuất Cd và Zn bằng ngô + EDTA nhỏ hơn nhiều so với T. caerulescens từ đất bị ô nhiễm công nghiệp, và nhỏ hơn (Cd) hoặc tương tự (Zn) so với đất nông nghiệp. Sau khi xử lý bằng EDTA, kim loại nặng hòa tan trong nước lỗ chân lông của đất chủ yếu tồn tại dưới dạng phức hợp EDTA-kim loại, duy trì trong vài tuần. Hàm lượng cao của kim loại nặng trong nước lỗ chân lông sau quá trình xử lý EDTA có thể gây nguy cơ môi trường dưới dạng ô nhiễm nước ngầm.

Reasonable air pollution control policies depend upon a comparison of the costs of air pollution losses with the costs of controls. Present estimates of national economic losses to agricultural and ornamental vegetation are based primarily on field observations and partially on growth and yield data obtained from closed‐top field chambers and greenhouses. This research describes the design and evaluation of an open‐top field chamber that was developed to provide an environment more closely resembling ambient conditions than the environment found in closed‐top chambers.

Temperature and relative humidity within open‐top chambers were similar to ambient conditions. Direct sunlight reached the plants for a portion of each day and rain entered, although not always uniformly over the chamber base. Chambers receiving charcoal‐filtered air protected sensitive ‘Bel W₃’ tobacco plants (Nicotiana tabacum L.) from ambient ozone concentrations. Plants growing in chambers receiving unfiltered air or in ambient air plots were severely injured.

Manipulation of the diets of pigs may alter the composition of the manure and thereby the environmental and agricultural qualities of the manure. Laboratory studies were performed to quantify the effect of manipulation of pig diets on the chemical composition of the derived manure (slurry), the potential emission of methane (CH₄) and ammonia (NH₃) during anaerobic storage of the manure, and the potential nitrous oxide (N₂O) and carbon dioxide (CO₂) emission after application of the manure to soil. The diets differed in contents of crude protein and salt (CaSO₄), and the type and contents of nonstarch polysaccharides (NSP). Emissions of NH₃ and CH₄ during storage were smaller at a low than at a high dietary protein content. The emission of NH₃ was significantly related to the contents of ammonium (NH₄), total N, and pH. The emission of CH₄ was significantly related to contents of dry matter, total C, and volatile fatty acids in the manure. The effect of manure composition on N₂O emission markedly differed between the two tested soils, which points at interactions with soil properties such as the organic matter content. These types of interactions require soil‐specific recommendations for mitigation of N₂O emission from soil‐applied pig manure by manipulation of the diet. From the tested diets, decreasing the protein content has the largest potential to simultaneously decrease NH₃ and CH₄ emissions during manure storage and N₂O emission from soil. An integral assessment of the environmental and agricultural impact of handling and application of pig manure as a result of diet manipulation provides opportunities for farmers to maximize the value of manures as fertilizer and soil conditioner and to minimize N and C emissions to the environment.

Sorption of hydrophobic compounds in soils often shows nonlinearity, competition, and hysteresis. Since such behaviors have been associated with organic polymers in glassy state, it has been postulated that some forms of soil humic substances are glassy. The glassy state is favored by properties that decrease the flexibility of macromolecules, such as cross‐linking, presence of unsaturated bonds, and high molecular weight. Polyvalent metal ions, which are abundant in soils, may cross‐link humic substances by coordinating to multiple functional groups on different strands. Accordingly, we prepared an Al³⁺–cross‐linked humic acid (Al‐HA) from the H⁺ form (H‐HA) of a soil humic acid by a flocculation technique that leaves Al ions bound to organic groups. Sorption of naphthalene and 1,2,4‐trichlorobenzene (TCB) on H‐HA was nonlinear, competitive, and slightly hysteretic, in agreement with previous studies showing glass transition temperatures of humic acids that lie above room temperature. Nonlinearity, competition, and hysteresis were all enhanced in Al‐HA, validating the hypothesis that metal ion cross‐linking enhances nonideal sorption. Application of a glassy polymer sorption model reveals that cross‐linking increases the affinity of solutes for the hole domain relative to the dissolution domain. The results (i) indicate that isolated, purified soil humic acid behaves like a glassy solid, (ii) indicate that metal‐ion cross‐linking creates a more rigid‐chain structure and supports a link between nonideal sorption and the glassy character of soil organic matter, and (iii) underscore the importance of metal ions on humic structure in relation to sorption of hydrophobic organic compounds.