On-farm bioremediation of dimethazone and trifluralin residues in runoff water from an agricultural field

Bioremediation is the use of living organisms, primarily microorganisms, to degrade environmental contaminants into less toxic forms. Nine biobeds (ground cavity filled with a mixture of composted organic matter, topsoil, and a surface grass) were established at Kentucky State University research farm (Franklin County, KY) to study the impact of this practice on reducing surface runoff water contamination by residues of dimethazone and trifluralin herbicides arising from an agricultural field. Biobed (biofilter) systems were installed at the bottom of the slope of specially designed runoff plots to examine herbicides retention and degradation before entering streams and rivers. In addition to biobed systems, three soil management practices: municipal sewage sludge (SS), SS mixed with yard waste compost (SS + YW), and no-mulch rototilled bare soil (NM used for comparison purposes) were used to monitor the impact of soil amendments on herbicide residues in soil following natural rainfall events. Organic amendments increased soil organic matter content and herbicide residues retained in soil following rainfall events. Biobeds installed in NM soil reduced dimethazone and trifluralin by 84 and 82%, respectively in runoff water that would have been transported down the land slope of agricultural fields and contaminated natural water resources. Biobeds installed in SS and SS+YW treatments reduced dimethazone by 65 and 46% and trifluralin by 52 and 79%, respectively. These findings indicated that biobeds are effective for treating dimethazone and trifluralin residues in runoff water.     

Ascorbic acid, β-carotene, sugars, phenols, and heavy metals in sweet potatoes grown in soil fertilized with municipal sewage sludge

Municipal sewage sludge (MSS) used for land farming typically contains heavy metals that might impact crop quality and human health. A completely randomized experimental design with three treatments (six replicates each) was used to monitor the impact of mixing native soil with MSS or yard waste (YW) mixed with MSS (YW +MSS) on: i) sweet potato yield and quality; ii) concentration of seven heavy metals (Cd, Cr, Mo, Cu, Zn, Pb, and Ni) in sweet potato plant parts (edible roots, leaves, stem, and feeder roots); and iii) concentrations of ascorbic acid, total phenols, free sugars, and β-carotene in sweet potato edible roots at harvest. Soil samples were collected and analyzed for total and extractable metals using two extraction procedures, concentrated nitric acid (to extract total metals from soil) as well as CaCl? solution (to extract soluble metals in soil that are available to plants), respectively. Elemental analyses were performed using inductively coupled plasma mass spectrometry (ICP-MS). Overall, plant available metals were greater in soils amended with MSS compared to control plots. Concentration of Pb was greater in YW than MSS amendments. Total concentrations of Pb, Ni, and Cr were greater in plants grown in MSS+YW treatments compared to control plants. MSS+YW treatments increased sweet potato yield, ascorbic acid, soluble sugars, and phenols in edible roots by 53, 28, 27, and 48%, respectively compared to plants grown in native soil. B-carotene concentration (157.5 μg g?1 fresh weight) was greater in the roots of plants grown in MSS compared to roots of plants grown in MSS+YW treatments (99.9 μg g?1 fresh weight). Concentration of heavy metals in MSS-amended soil and in sweet potato roots were below their respective permissible limits.     

Napropamide residues in runoff and infiltration water from pepper production

A field study was conducted on a Lowell silty loam soil of 2.7% organic matter at the Kentucky State University Research Farm, Franklin County, Kentucky. Eighteen universal soil loss equation (USLE) standard plots (22 x 3.7 m each) were established on a 10% slope. Three soil management practices were used: (i) class-A biosolids (sewage sludge), (ii) yard waste compost, each mixed with native soil at a rate of 50 ton acre(-1) on a dry-weight basis, and (iii) a no-mulch (NM) treatment (rototilled bare soil), used for comparison purposes. Devrinol 50-DF "napropamide" [N,N-diethyl-2-(1-naphthyloxy) propionamide] was applied as a preemergent herbicide, incorporated into the soil surface, and the plots were planted with 60-day-old sweet bell pepper seedlings. Napropamide residues one hour following spraying averaged 0.8, 0.4, and 0.3 microg g(-1) dry soil in sewage sludge, yard waste compost, and no-mulch treatments, respectively. Surface runoff water, runoff sediment, and napropamide residues in runoff were significantly reduced by the compost and biosolid treatments. Yard waste compost treatments increased water infiltration and napropamide residues in the vadose zone compared to sewage sludge and NM treatments. Total pepper yields from yard waste compost amended soils (9187 lbs acre(-1)) was significantly higher (P < 0.05) than yield from either the soil amended with class-A biosolids (6984 lbs acre(-1)) or the no-mulch soil (7162 lbs acre(-1)).     

Ascorbic acid, β-carotene,sugars, phenols,and heavy metals in sweet potatoes grown in soil fertilized with municipal sewage sludge

Municipal sewage sludge (MSS) used for land farming typically contains heavy metals that might impact crop quality and human health. A completely randomized experimental design with three treatments (six replicates each) was used to monitor the impact of mixing native soil with MSS or yard waste (YW) mixed with MSS (YW +MSS) on: i) sweet potato yield and quality; ii) concentration of seven heavy metals (Cd, Cr, Mo, Cu, Zn, Pb, and Ni) in sweet potato plant parts (edible roots, leaves, stem, and feeder roots); and iii) concentrations of ascorbic acid, total phenols, free sugars, and β-carotene in sweet potato edible roots at harvest. Soil samples were collected and analyzed for total and extractable metals using two extraction procedures, concentrated nitric acid (to extract total metals from soil) as well as CaCl₂ solution (to extract soluble metals in soil that are available to plants), respectively. Elemental analyses were performed using inductively coupled plasma mass spectrometry (ICP-MS). Overall, plant available metals were greater in soils amended with MSS compared to control plots. Concentration of Pb was greater in YW than MSS amendments. Total concentrations of Pb, Ni, and Cr were greater in plants grown in MSS+YW treatments compared to control plants. MSS+YW treatments increased sweet potato yield, ascorbic acid, soluble sugars, and phenols in edible roots by 53, 28, 27, and 48%, respectively compared to plants grown in native soil. B-carotene concentration (157.5 μg g^?1 fresh weight) was greater in the roots of plants grown in MSS compared to roots of plants grown in MSS+YW treatments (99.9 μg g^?1 fresh weight). Concentration of heavy metals in MSS-amended soil and in sweet potato roots were below their respective permissible limits.     

Heavy metal mobility in runoff water and absorption by eggplant fruits from sludge treated soil

Sewage sludge addition to agricultural lands requires judicious management to avoid environmental risks arising from heavy metal and nitrate contamination of surface water and accumulation in edible plants. A field study was conducted on a silty-loam soil of 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 x 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge and yard waste compost mix (SS-YW) at 15 t acre(-1), six plots were mixed with sewage sludge (SS) at 15 t acre(-1), and six unamended plots that never received sludge were used for comparison purposes. Plots were planted with eggplant, Solanum melongena L. as the test plant. The objectives of this investigation were to: 1) assess the effect of soil amendments on the transport of NO3, NH4, and heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) into surface water; 2) investigate the effect of soil amendments on heavy metal bioavailability in eggplant fruits at harvest; and 3) assess chemical and physical properties of soil following addition of soil amendments and their impact on the yield and quality of eggplant fruit. SS-YW treatments reduced runoff water by 63% while plots incorporated with sewage sludge alone reduced runoff water by 37% compared to control treatment. The SS-YW treatments transported more mineral nitrogen (NO3-N and NH4-N) in runoff water than SS treatments. Total marketable yield (lbs acre(-1)) and number of eggplant fruits were greatest in SS-YW treatments. This response may be due to improved soil porosity, water, and nutrient retention of the soil amended with SS-YW mixture. Concentrations of heavy metals in soil amended with sludge were below the U.S. Environmental Protection Agency (USEPA) limits. Chromium, Ni, Zn, and Cu were taken up by eggplant fruits but their concentrations were below the Codex Commission allowable levels.     

Napropamide Residues in Runoff and Infiltration Water from Pepper Production

Abstract

A field study was conducted on a Lowell silty loam soil of 2.7% organic matter at the Kentucky State University Research Farm, Franklin County, Kentucky. Eighteen universal soil loss equation (USLE) standard plots (22 × 3.7 m each) were established on a 10% slope. Three soil management practices were used: (i) class-A biosolids (sewage sludge), (ii) yard waste compost, each mixed with native soil at a rate of 50 ton acre^?1 on a dry-weight basis, and (iii) a no-mulch (NM) treatment (rototilled bare soil), used for comparison purposes. Devrinol 50-DF “napropamide” [N,N-diethyl-2-(1-naphthyloxy) propionamide]was applied as a preemergent herbicide, incorporated into the soil surface, and the plots were planted with 60-day-old sweet bell pepper seedlings. Napropamide residues one hour following spraying averaged 0.8, 0.4, and 0.3 μ g g^{? 1} dry soil in sewage sludge, yard waste compost, and no-mulch treatments, respectively. Surface runoff water, runoff sediment, and napropamide residues in runoff were significantly reduced by the compost and biosolid treatments. Yard waste compost treatments increased water infiltration and napropamide residues in the vadose zone compared to sewage sludge and NM treatments. Total pepper yields from yard waste compost amended soils (9187 lbs acre^?1) was significantly higher (P < 0.05) than yield from either the soil amended with class-A biosolids (6984 lbs acre^?1) or the no-mulch soil (7162 lbs acre ^?1).     

Impact of soil amendments on metribuzin and DCPA half-lives and mobility into agricultural runoff water

The retention and behavior of two herbicides, metribuzin [4-amino-6-tert-butyl-4, 5-dihydro-3-methylthio-1, 2, 4-triazin-5-one] and DCPA [1, 4-Benzenedicarboxylic acid, 2, 3, 5, 6-tetrachloro-, dimethyl] ester, in runoff and seepage water from agricultural fields were investigated. The objectives of this investigation were to: (i) determine the dissipation and half-life (T _1/2) of metribuzin and DCPA herbicides in soil under three management practices: chicken manure (CM), sewage sludge (SS), and no-mulch native soil (NM); (ii) monitor herbicides residues in runoff and infiltration water following addition of soil amendments; and (iii) determine the impact of soil amendments on the transport of NO₃, NH₄, and PO₄ from soil into surface and subsurface water. Half-life (T _1/2) values of metribuzin were 24, 18, and 12 d in CM, SS, and NM treatments, respectively. Similarly, T _1/2 values of DCPA were greater in CM and SS incorporated soil (45.8 and 52.2 d, respectively) compared to NM native soil (26.2 d). Addition of CM and SS to native agricultural soil increased water infiltration, lowering runoff water volume and herbicide residues in runoff following natural rainfall events. We concluded that soil amendments could be used to intercept pesticide-contaminated runoff from agricultural fields. This practice might provide a potential solution to pesticide contamination of surface and seepage water from farmlands.     

Mobility of dimethoate residues from spring broccoli field

Dimethoate [O, O-dimethyl-S-(N-methylcarbamoyl-methyl) phosphorodithioate] is a broad-spectrum systemic insecticide currently used worldwide and on many vegetables in Kentucky. Dimethoate is a hydrophilic compound (log KOW = 0.7) and has the potential of offsite movement from the application site into runoff and infiltration water. The dissipation patterns of dimethoate residues were studied on spring broccoli leaves and heads under field conditions. Following foliar application of Dimethoate 4E on broccoli foliage at the rate of 0.47 L acre(-1), dimethoate residues were monitored in soil, runoff water collected down the land slope, and in infiltration water collected from the vadose zone. The study was conducted on a Lowell silty loam soil (pH 6.9) planted with broccoli under three soil management practices: (i) soil mixed with municipal sewage sludge, (ii) soil mixed with yard waste compost, and (iii) no-mulch rototilled bare soil. The main objective of this investigation was to study the effect of mixing native soil with municipal sewage sludge or yard waste compost, having considerable amounts of organic matter, on off-site movement of dimethoate residues into runoff and infiltration water following spring rainfall. The initial deposits of dimethoate were 6.2 and 21.4 micro g g(-1) on broccoli heads and leaves, respectively. These residues dissipated rapidly and fell below the maximum residue limit of 2 micro g g(-1) on the heads and leaves after 10 and 14 d, respectively, with half-lives of 5.7 d on broccoli heads and 3.9 d on the leaves. Dimethoate residues detected in top 15 cm of soil (due to droplet drift and wash off residues from broccoli foliage) one day (d) following spraying, were 30.5 ng g(-1) dry soil in the sewage sludge treatment, and 46.1 and 134.5 ng g(-1) dry soil in the yard waste and no mulch treatments, respectively. Water infiltration was greater from yard waste compost treatment than from no mulch treatment, however concentrations of dimethoate in the vadose zone of the three soil treatments did not differ.     

Effect of buffer strips and soil texture on runoff losses of flufenacet and isoxaflutole from maize fields

The influence of buffer strips and soil texture on runoff of flufenacet and isoxaflutole was studied for two years in Northern Italy. The efficacy of buffer strips was evaluated on six plots characterized by different soil textures; two plots had Riva soil (18.6% sand, 63.1% silt, 18.3% clay) while the remaining four plots had Tetto Frati (TF) soil (37.1% sand, 57% silt, 5.9% clay). Additionally, the width of the buffer strips, constituted of spontaneous vegetation grown after crop sowing, was also compared for their ability to abate runoff waters. Chemical residues in water following runoff events were investigated, as well as their dissipation in the soil. After the first runoff events, concentrations of herbicides in water samples collected from Riva plots were as much as four times lower in waters from TF plots. On average of two growing seasons, the field half-life of flufenacet in the upper soil layer (5 cm) ranged between 8.1 and 12.8 days in Riva soil, 8.5 and 9.3 days in TF soil. Isoxaflutole field half-life was less than 1 day. The buffer strip was very affective by the uniformity of the vegetative cover, particularly, at the beginning of the season. In TF plots, concentration differences were generally due to the presence or absence of the buffer strip, regardless of its width.     

Heavy metal mobility in runoff water and absorption by eggplant fruits from sludge treated soil

Sewage sludge addition to agricultural lands requires judicious management to avoid environmental risks arising from heavy metal and nitrate contamination of surface water and accumulation in edible plants. A field study was conducted on a silty-loam soil of 10% slope at Kentucky State University Research Farm. Eighteen plots of 22 × 3.7 m each were separated using metal borders and the soil in six plots was mixed with sewage sludge and yard waste compost mix (SS-YW) at 15 t acre^?1, six plots were mixed with sewage sludge (SS) at 15 t acre^?1, and six unamended plots that never received sludge were used for comparison purposes. Plots were planted with eggplant, Solanum melongena L. as the test plant. The objectives of this investigation were to: 1) assess the effect of soil amendments on the transport of NO₃, NH₄, and heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) into surface water; 2) investigate the effect of soil amendments on heavy metal bioavailability in eggplant fruits at harvest; and 3) assess chemical and physical properties of soil following addition of soil amendments and their impact on the yield and quality of eggplant fruit. SS-YW treatments reduced runoff water by 63% while plots incorporated with sewage sludge alone reduced runoff water by 37% compared to control treatment. The SS-YW treatments transported more mineral nitrogen (NO₃-N and NH₄-N) in runoff water than SS treatments. Total marketable yield (lbs acre^?1) and number of eggplant fruits were greatest in SS-YW treatments. This response may be due to improved soil porosity, water, and nutrient retention of the soil amended with SS-YW mixture. Concentrations of heavy metals in soil amended with sludge were below the U.S. Environmental Protection Agency (USEPA) limits. Chromium, Ni, Zn, and Cu were taken up by eggplant fruits but their concentrations were below the Codex Commission allowable levels.     

Tillage management to mitigate herbicide loss in runoff under simulated rainfall conditions

Conservation tillage mitigates soil loss in cropland because plant residues help protect the soil, but effects on pesticide movement in surface runoff are not as straightforward. Effects of soil disturbance on surface runoff loss of chlorimuron and alachlor were evaluated utilizing runoff trays. Soil in the trays was either disturbed (tilled) and kept bare or was not tilled, and existing decomposed plant residue was left on the surface. Rainfall (25mm, 20min) was simulated 1d after alachlor (2.8kg ha(-1)) or chlorimuron (54g ha(-1)) application, and runoff was collected. Runoff fractions were analyzed for herbicide and sediment. Total alachlor loss from bare plots was greater than that in no-tillage plots (4.5% vs. 2.3%, respectively). More than one-third of total alachlor lost from bare plots occurred in the first l of runoff, while no-tillage plots had less runoff volume with a more even distribution of alachlor concentration in the runoff during the rainfall simulation and subsequent runoff period. In contrast, more chlorimuron was lost from no-tillage plots than bare plots (12% vs. 1.5%) even though total runoff volume was lower in the no-tillage plots (10.6mm vs. 13.6mm). This was attributed to dense coverage with partially decomposed plant residue in no-tillage plots (1652kg ha(-1)) that intercepted chlorimuron. It was likely that chlorimuron, a polar compound, was more easily washed off surface plant residues and transported in runoff.     

Impact of soil management practices on yield,fruit quality,and antioxidant contents of pepper at four stages of fruit development

Peppers, a significant component of the human diet in many regions of the world, provide vitamins A (β-carotene) and C, and are also a source of many other antioxidants such as capsaicin, dihydrocapsaicin, and phenols. Enhancing the concentration of antioxidants in plants grown in soil amended with recycled waste has not been completely investigated. Changes in pepper antioxidant content in relation to soil amendments and fruit development were investigated. The main objectives of this investigation were to: (i) quantify concentrations of capsaicin, dihydrocapsaicin, β-carotene, ascorbic acid, phenols, and soluble sugars in the fruits of Capsicum annuum L. (cv. Xcatic) grown under four soil management practices: yard waste (YW), sewage sludge (SS), chicken manure (CM), and no-much (NM) bare soil and (ii) monitor antioxidant concentrations in fruits of plants grown under these practices and during fruit ripening from green into red mature fruits. Total marketable pepper yield was increased by 34% and 15% in SS and CM treatments, respectively, compared to NM bare soil; whereas, the number of culls (fruits that fail to meet the requirements of foregoing grades) was lower in YW compared to SS and CM treatments. Regardless of fruit color, pepper fruits from YW amended soil contained the greatest concentrations of capsaicin and dihydrocapsaicin. When different colored pepper fruits (green, yellow, orange, and red) were analyzed, orange and red contained the greatest β-carotene and sugar contents; whereas, green fruits contained the greatest concentrations of total phenols and ascorbic acid.     

Distribution of seven heavy metals among hot pepper plant parts

The main objective of this investigation was to monitor concentrations of seven metals (Cd, Pb, Ni, Mo, Cu, Zn, and Cr) in the fruits, leaves, stem, and roots of Capsicum annuum L. (cv. Xcatic) plants grown under four soil management practices: yard waste (YW), sewage sludge (SS), chicken manure (CM), and no-much (NM) bare soil. Elemental analyses were conducted using inductively coupled plasma mass spectrometer. Pb and Cd concentrations in soil amended with YW, SS, and CM were not significantly different (P < 0.05) compared to NM soil, whereas Mo and Cu concentrations were significantly greater in YW compared to SS, CM, and NM treatments. Concentrations of Cd in the fruits of plants grown in NM soil were greater compared to the fruits of plants grown in other treatments. Total Ni concentration (sum of Ni in all plant parts) in plants grown in NM bare soil was greater than in plants grown in SS-, YW-, and CM-amended soils. Values of the bioaccumulation factor indicated that pepper fruits of plants grown in YW, SS, and CM did not show any tendency to accumulate Pb, Cr, and Ni in their edible fruits.     

Pyrethrins and piperonyl butoxide adsorption to soil organic matter

The adsorption and mobility of pyrethrins (Pys), the major insecticidal components obtained from the pyrethrum daisy Tanacetum cinerariifolium, and piperonyl butoxide (PBO), a pyrethrum synergist, were determined in soil using batch-equilibrium and reverse-phase thin-layer chromatographic techniques. Two soil management practices were used, soil mixed with yard waste compost (COM) at 50 t acre(-1) on dry weight basis and no-mulch (NM) bare soil. Adsorption isotherm experiments were carried out using known concentrations of Pys (Py-I and Py-II) and PBO mixed with known amounts of COM or NM soil at constant temperature and pressure until equilibrium was attained. Pys and PBO in soil extracts were purified and concentrated using solid-phase extraction cartridges containing C18-octadecyl bonded silica. Pys and PBO residues were quantified using a high-performance liquid chromatograph equipped with a UV detector. Adsorption studies showed that compost amended soil adsorbed more Pys and PBO than native (NM) soil. Py-I adsorption was greater than Py-II and PBO. Adsorption of Pys and PBO to humic and fulvic acids was also studied by reverse-phase thin layer chromatography (RPTLC). Results indicated that humic acid, a significant component of organic matter, reduced Pys and PBO mobility. Pys and PBO mobility decreased as the concentration of humic acid in the mobile phase increased.     

Runoff and leaching of atrazine and alachlor on a sandy soil as affected by application in sprinkler irrigation

Rainfall simulation was used with small packed boxes of soil to compare runoff of herbicides applied by conventional spray and injection into sprinkler-irrigation (chemigation), under severe rainfall conditions. It was hypothesized that the larger water volumes used in chemigation would leach some of the chemicals out of the soil surface rainfall interaction zone, and thus reduce the amounts of herbicides available for runoff. A 47-mm rain falling in a 2-hour event 24 hours after application of alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide) and atrazine (6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2, 4-diamine) was simulated. The design of the boxes allowed a measurement of pesticide concentrations in splash water throughout the rainfall event. Initial atrazine concentrations exceeding its' solubility were observed. When the herbicides were applied in 64,000 L/ha of water (simulating chemigation in 6.4 mm irrigation water) to the surface of a Tifton loamy sand, subsequent herbicide losses in runoff water were decreased by 90% for atrazine and 91% for alachlor, as compared to losses from applications in typical carrier water volumes of 187 L/ha. However, this difference was not due to an herbicide leaching effect but to a 96% decrease in the amount of runoff from the chemigated plots. Only 0.3 mm of runoff occurred from the chemigated boxes while 7.4 mm runoff occurred from the conventionally-treated boxes, even though antecedent moisture was higher in the former. Two possible explanations for this unexpected result are (a) increased aggregate stability in the more moist condition, leading to less surface sealing during subsequent rainfall, or (b) a hydrophobic effect in the drier boxes. In the majority of these pans herbicide loss was much less in runoff than in leachate water. Thus, in this soil, application of these herbicides by chemigation would decrease their potential for pollution only in situations where runoff is a greater potential threat than leaching.     

Mobility of dimethoate residues from spring broccoli field

Dimethoate [O, O-dimethyl-S-(N-methylcarbamoyl-methyl) phosphorodithioate] is a broad-spectrum systemic insecticide currently used worldwide and on many vegetables in Kentucky. Dimethoate is a hydrophilic compound (log K_OW = 0.7) and has the potential of offsite movement from the application site into runoff and infiltration water. The dissipation patterns of dimethoate residues were studied on spring broccoli leaves and heads under field conditions. Following foliar application of Dimethoate 4E on broccoli foliage at the rate of 0.47 L acre^?1, dimethoate residues were monitored in soil, runoff water collected down the land slope, and in infiltration water collected from the vadose zone. The study was conducted on a Lowell silty loam soil (pH 6.9) planted with broccoli under three soil management practices: (i) soil mixed with municipal sewage sludge, (ii) soil mixed with yard waste compost, and (iii) no-mulch rototilled bare soil. The main objective of this investigation was to study the effect of mixing native soil with municipal sewage sludge or yard waste compost, having considerable amounts of organic matter, on off-site movement of dimethoate residues into runoff and infiltration water following spring rainfall. The initial deposits of dimethoate were 6.2 and 21.4 μ g g^?1 on broccoli heads and leaves, respectively. These residues dissipated rapidly and fell below the maximum residue limit of 2 μ g g^?1 on the heads and leaves after 10 and 14 d, respectively, with half-lives of 5.7 d on broccoli heads and 3.9 d on the leaves. Dimethoate residues detected in top 15 cm of soil (due to droplet drift and wash off residues from broccoli foliage) one day (d) following spraying, were 30.5 ng g^?1 dry soil in the sewage sludge treatment, and 46.1 and 134.5 ng g^?1 dry soil in the yard waste and no mulch treatments, respectively. Water infiltration was greater from yard waste compost treatment than from no mulch treatment, however concentrations of dimethoate in the vadose zone of the three soil treatments did not differ.     

Dissipation and runoff transport of metazachlor herbicide in rapeseed cultivated and uncultivated plots in field conditions

The environmental fate of metazachlor herbicide was investigated under field conditions in rapeseed cultivated and uncultivated plots, over a period of 225 days. The cultivation was carried out in silty clay soil plots with two surface slopes, 1 and 5 %. The herbicide was detectable in soil up to 170 days after application (DAA), while the dissipation rate was best described by first-order kinetics and its half-life ranged between 10.92 and 12.68 days. The herbicide was detected in the soil layer of 10–20 cm from 5 to 48 DAA, and its vertical movement can be described by the continuous stirred tank reactor (CSTR) in series model. Relatively low amounts of metazachlor (less than 0.31 % of the initial applied active ingredient) were transferred by runoff water. More than 80 % of the total losses were transferred at the first runoff event (12 DAA), with herbicide concentrations in runoff water ranging between 70.14 and 79.67 μg L⁻¹. Minor amounts of the herbicide (less than 0.07 % of the initial applied active ingredient) were transferred by the sediment, with a maximum concentration of 0.57 μg g⁻¹ (12 DAA), in plots with 5 % inclination. Finally, in rapeseed plants, metazachlor was detected only in the first sampling (28 DAA) at concentrations slightly higher than the limit of quantification; when in seeds, no residues of the herbicide were detected.

     

A remediation strategy based on active phytoremediation followed by natural attenuation in a soil contaminated by pyrite waste

Phytoremediation of metal-polluted soils can be promoted by the proper use of soil amendments and agricultural practices. A 4-year phytoremediation programme was applied to a site affected by the toxic spill of pyrite residue at Aznalcóllar (Spain) in 1998, contaminated with heavy metals (Zn, Cu, Pb, Cd) and arsenic. This consisted of active phytoremediation, using organic amendments (cow manure and compost) and lime and growing two successive crops of Brassica juncea (L.) Czern., followed by natural attenuation without further intervention. Changes in soil pH, extractable metal and As concentrations, organic carbon content and microbial biomass was evaluated. The initial oxidation of metal sulphides from pyrite residues released soluble metals and reduced soil pH to extremely acidic values (mean 4.1, range 2.0-7.0). The addition of lime (up to 64 t ha(-1)) increased soil pH to adequate values for plant growth, resulting in a significant decrease in DTPA-extractable metal concentrations in all plots. The natural attenuation phase showed also a decrease in extractable metals. Organic treatments increased the soil total organic carbon, which led to higher values of microbial biomass (11.6, 15.2 and 14.9 g kg(-1) TOC and 123, 170 and 275 microg g(-1) biomass-C in control, compost and manure plots, respectively). Active phytoremediation followed by natural attenuation, was effective for remediation of this pyrite-polluted soil.     

Winter runoff losses of phosphorus from paddy soils in the Taihu Lake Region of South China

A winter wheat field plot experiment was conducted on two types of paddy soils, from November, 2000 to June, 2001 to assess P losses to its surrounding watercourses by runoff in the Taihu Lake Region. Commercial NPK compound fertilizer and single superphosphate fertilizer were applied to furnish 0, 20, 80, and 160 kg P ha(-1). The experiments consisted of six replicates of each treatment in Changshu site and four replicates in Anzhen site, with a plot size of 5x6 m2 in a randomized block design. Results revealed that the average concentration of dissolved P (DP), particulate P (PP), and total P (TP) in runoff water during the winter season was 0.13, 0.90 and 1.04 mg P l(-1) respectively, from P20 plots in Anzhen site. While it was 0.67, 1.08 and 1.75 mg P l(-1) respectively, from P20 plots in Changshu site. The seasonal TP load (mass loss) from P20 plot ranged from a low of 290.88 g P ha(-1)season(-1) to a high of 483.54 g P ha(-1)season(-1), with a mean of 382.29 g P ha(-1)season(-1) in Anzhen, but from 444.92 to 752.21 g P ha(-1)season(-1), with a mean of 539.13 g P ha(-1)season(-1) in Changshu. Both in Anzhen and Changshu PP represented a major portion of the TP lost in runoff, the average PP/TP was about more than 80% in P0 and P20 plot, but it was decreased with the increase of P rate. The average seasonal P loads (DP, PP, and TP) in Changshu were greater than in Anzhen although runoff volume in Anzhen (45 mm season(-1)) was more than in Changshu (36 mm season(-1)). This was probably associated with the differences of soil physical and chemical properties between the two sites. Phosphate fertilizer rate significantly affected P concentrations and P loads by runoff. Both the mean concentrations and the average seasonal P loads from the P80 plots were lower than from the P160 plots, but obviously higher than from the P20 and P0 plots. There was no significant difference found between the P20 plots and the P0 plots both in Anzhen and Changshu sites. It indicated that P loads by runoff would be greatly increased in 5-10 years due to the accumulation of soil P if 20 kg P ha(-1) applied each wheat season in this area.     

Dissipation and mobility of permethrin in the field with repeated applications under tropical conditions

Studies on persistence, mobility and the effect of repeated application of permethrin on its half-life were carried out under field conditions. The half-life of permethrin in the top 20 cm of the soil increased from 11.5 to 23.6 days as the application rates increased from 35 to 140 g ha(-1). Induced by heavier rainfall, more residues moved downward in trial 2 than in trial 1. Repeated applications enhanced degradation rates and mobility of permethrin in the soil. The residue level in the 0-5-cm layer was reduced at day 28 after 17 consecutive applications to a level lower than after 5 applications. The half-life of permethrin was reduced from 15.9 days to 11.2 days after 5 and 17 applications, respectively. The residue reached the 15-20 cm layer much earlier (approximately 3 days after treatment) in soil that received 17 applications as compared to those with two applications.