ADSORPTION–DESORPTION,PERSISTENCE, AND LEACHING BEHAVIOR OF DITHIOPYR IN AN ALLUVIAL SOIL OF INDIA

Investigations were undertaken to determine the adsorption–desorption, persistence and leaching of dithiopyr (S,S′-dimethyl 2-difluoromethyl-4-isobutyl-6-trifluoromethyl pyridine-3,5-dicarbothioate) in an alluvial soil under laboratory condition. The adsorption–desorption studies were carried out using batch equilibration technique. The mass balance studies showed that 83–97% of the pesticide was recovered during adsorption–desorption studies. The results revealed strong adsorption of dithiopyr in alluvial soil with K_d values ranging from 3.97–5.78 and Freundlich capacity factor (K_F) value of 2.41. The strong adsorption was evident from the hysteresis effect observed during desorption. The hysteresis coefficients ranged from 0.17–0.40.

The persistence studies were carried out at two concentrations (1.0 and 10.0 μg g^?1 level) under field capacity moisture and submerged condition by incubating the treated soil at 25±1°C. In general, dithiopyr persisted beyond 90 days with half-life varying from 11.5–12.9 days under different conditions. The rate of application and moisture regimes had no overall effect on the persistence. The leaching studies carried out in packed column under saturated flow condition revealed that dithiopyr was highly immobile in alluvial soil. Only small amounts (0.02–0.04%) were recovered from leachate whereas major portion (99.9%) remained in top layer of the soil column. The data suggest that strong adsorption of dithiopyr will cause a greater persistence problem in the soil. However, the chances of its movement to ground water will be negligible due to its immobility.     

Persistence of azadirachtin A and B in soil: Effects of temperature and microbial activity

Abstract

The persistence of two insecticidally active compounds from the neem tree, azadirachtin A and B, was determined at two different temperatures (15 and 25°C) in the laboratory after application of the commercial neem insecticide, Margosan‐O, to a sandy loam soil. The influence of microbial activity on degradation was also examined by comparing autoclaved and non‐autoclaved soils also at 15 and 25°C. Temperature influenced degradation rates. The DT ₅₀ (time required for 50% disappearance of the initial concentration) for azadirachtin A was 43.9 and 19.8 d for non‐autoclaved soil kept at 15 and 25°C, respectively. The DT ₅₀ for azadirachtin B was 59.2 and 20.8 d for non‐autoclaved soil kept at 15 and 25°C, respectively. Microbial activity was also responsible for faster degradation because DT ₅₀ ’s for autoclaved soil were much longer than for non‐autoclaved soils. DT ₅₀ ‘_s for azadirachtin A in autoclaved soil were 91.2 (15°C) and 31.5 d (25°C). DT50’s for azadirachtin B in autoclaved soil were 115.5 (15°C) and 42.3 d (25°C). Two degradation products of azadirachtin were detected, but were not identified. Higher levels of the two degradation products were detected in non‐autoclaved soil.     

Persistence of metsulfuron‐methyl in two soils

Abstract

The persistence of metsulfuron‐methyl in sandy loam and clay soil incubated at different temperatures and moistures contents was investigated under laboratory conditions using longbean (Vigna sesquipedalis L.) as bioassay species. A significant degradation of metsulfuron‐methyl was observed in non‐autoclaved soil rather than the autoclaved soil sample. At higher temperature, the degradation rate in non‐autoclaved soil improved with increasing soil moisture content. In non‐autoclaved sandy loam and clay soil, the half‐life was reduced from 9.0 to 5.7 and from 11.2 to 4.6 days, respectively when moisture level of sandy loam increased from 20 to 80% field capacity at 35°C. In the autoclaved soil, herbicide residue seems to have been broken down by non‐biological process. The rate of dissipation was slightly increased after the second application of the herbicide to non‐autoclaved soils but not in autoclaved soil, indicating the importance of microorganisms in the breakdown process.     

Simultaneous Determination of Imidacloprid,Thiacloprid, and Thiamethoxam in Soil and Water by High-performance Liquid Chromatography with Diode-array Detection

Abstract

A high-performance liquid chromatography method with diode-array detection (HPLC-DAD) is described for the determination of three neonicotinoid insecticides imidacloprid, thiacloprid, and thiamethoxam in soil and water. The soil samples were extracted with acetonitrile, while the water samples were extracted using C₁₈ cartridges. The mean recoveries plus standard deviations for spiked soil samples were 82 ± 4.2% for thiamethoxam, 99 ± 4.2% for imidacloprid and 94 ± 1.4% for thiacloprid. The recoveries for water samples ranged from 87 ± 3.4% for thiamethoxam to 97 ± 3.9% for imidacloprid and 97 ± 2.6% for thiacloprid. The limits of quantitation (LOQ) were 0.1, 0.1, 0.01 mg/kg in soil (5 g), and 2, 2, 0.5 µg/L in water (50 mL) for thiamethoxam, imidacloprid, and thiacloprid, respectively.     

Behavior of atrazine in soils of tropical zone

Abstract

Movement and degradation of ¹⁴C‐atrazine (2‐chloro 4‐(ethylamino)‐6‐(isopropylamino)‐s‐triazine, was studied in undisturbed soil columns (0.50m length × 0.10m diameter) of Gley Humic and Deep Red Latosol from a maize crop region of Sao Paulo state, Brazil. Atrazine residues were largely confined to the 0–20cm layers over a 12 month period Atrazine degraded to the dealkylated metabolites deisopropylatrazine and deethylatrazine, but the major metabolite was hydroxyatrazine, mainly in the Gley Humic soil. Activity detected in the leachate was equivalent to an atrazine concentration of 0.08 to 0.11μg/1.

The persistence of ¹⁴C‐atrazine in a maize‐bean crop rotation was evaluated in lysimeters, using Gley Humic and Deep Red Latosol soils. Uptake of the radiocarbon by maize plants after 14‐days growth was equivalent to a herbicide concentration of 3.9μg/g fresh tissue and was similar in both soils. High atrazine degradation to hydroxyatrazine was detected by tic of maize extracts. After maize harvest, when beans were sown the Gley Humic soil contained an atrazine concentration of 0.29 μg/g soil and the Deep Red Latosol, 0.13 μg/g soil in the 0–30 cm layer. Activity detected in bean plants corresponded to a herbicide concentration of 0.26 (Gley Humic soil) and 0.32μg/g fresh tissue (Deep Red Latossol) after 14 days growth and 0.43 (Gley Humic soil) and 0.50 μg/g fresh tissue (Deep Red Latossol) after 97 days growth. Traces of activity equivalent to 0.06 and 0.02μg/g fresh tissue were detected in bean seeds at harvest. Non‐extractable (bound) residues in the soils at 235 days accounted for 66.6 to 75% (Gley Humic soil and Deep Red Latossol) of the total residual activity.     

M‐(p‐Nitrobenzyl) pyridine as a spray reagent for the thin‐layer chromatographic detection of dimethyl tetrachloroterphthalate herbicide

Abstract

The developed thin‐layer chromatogram of DCPA (Dacthal) is sprayed with 4‐(p‐nitrobenzyl)pyridine chromogenic reagent followed by ammonium carbonate solution. The chromatogram is then heated in an oven at 130°C for 20 minutes. When cool, the chromatogram is sprayed with tetraethylenepentamine reagent. DCPA spots appear blue against a white background. The sensitivity of this test is about 1 μg. The procedure is useful to detect DCPA in water and in soil.     

Adsorption,desorption, soil mobility,aqueous persistence and octanol‐water partitioning coefficients of terbufos,terbufos sulfoxide and terbufos sulfone

Abstract

Terbufos, t. sulfoxide and t. sulfone (5 μg ml^‐1) were incubated in natural, sterilized natural and distilled water, with initial pH values of 8.8, 8.8 and 6.0, respectively, at 20°C. First‐order disappearance was observed for the three compounds. Rates in natural and sterilized water were similar indicating chemical degradation predominated. Terbufos disappeared rapidly (t½>=3 days) in all systems. T. sulfoxide and t. sulfone were more persistent in the natural (t½>=18–40 days) and distilled water (t½>=280–350 days). Adsorption data for the three compounds in four soil‐water systems showed the decreasing order of adsorption to be terbufos>>t. sulfoxide=t. sulfone. Desorption from soils fortified at 5 μg g^‐1 with water was examined for 4 successive 18‐hr cycles. T. sulfoxide and t. sulfone were totally desorbed; terbufos was too unstable to study. The mobility of the compound in soil eluted with water was in the order, t. sulfoxide=t. sulfone>> terbufos, in agreement with adsorption‐desorption results. The octanol‐water partitioning coefficients for terbufos, t. sulfoxide and t. sulfone, at 23°C, were 3:30 x 10 , 164, and 302, respectively.     

Screening pesticides for their ability to damage bacterial DNA

Abstract

Twenty‐six pesticides and pesticide degradation products were screened (125 μg ‐ 2000 μg) for their ability to induce unrepairable damage to bacterial DNA. Three repair test systems were utilized in this study, the Salmonella typhimurium (TA1538/TA1978), the E. coli K‐12 (Pol A₁ ⁺/Pol^‐ ₁) and the E. coli WP₂ (WP₂, WP₂ uvrA, WP67, CM611 and CM571). Aldicarb (1000 μg), benomyl (250 μg), 2‐aminobenzimidazole (2000 μg), captan (125 μg), fenazalor (500 μg), 5,6‐dichloro‐2‐trifluoromethylbenzimida‐zole (NC‐2983) (250 μg), isothymol (250 μg), maleic hydrazide(1000 μg), pentachloronitrobenzene (1000 μg) were DNA‐damaglng to one or more bacterial test systems. Isothymol and NC‐2983 affected all three test systems. Chlorinated hydrocarbon insec ticides, some being recognized as carcinogens, did not: produce a zone of inhibition in any of the tester strains possibly due to their poor solubility and diffusion in the agar overlay. It was concluded that these tests can be performed along with bacterial reversion tests to complement each other as short‐term screening tests for potential carcinogens and mutagens.     

Trace elements exposure influences proximate body composition and antioxidant enzyme activities of the species tilapia and catfish in Burullus Lake—Egypt: human risk assessment for the consumers

The trace elements concentration in the fish estimates the contamination degree in the aquatic environment. These toxic trace elements are transported into the human through the consumption of polluted fish. This study estimated the effect of Cd, Hg, Pb, As, and Al on tilapia species and catfish Clarias gariepinus (six for each species of fish) inhabiting Burullus Lake—Egypt 30° 33′–31° 08′ E and 30° 22′–31° 35′ N. The highest Pb concentrations recorded in the muscle of C. gariepinus 2.29 ± 0.29 μg/g while S. galilaeus was estimated the lowest Hg concentration of 0.54 ± 0.02 μg/g which indicated the presence of contaminants exceeded the limits permitted by FAO/WHO and EC. The maximum mean carbohydrate, lipid, and protein recorded in O. niloticus 18.66, 16.33, and 58.16 mg/g, respectively; moisture in O. aureus 67.33%; and ash 16.41% in O. niloticus. The lowest amount of carbohydrate was recorded in the T. zillii 14.1 mg/g, lipid, and ash in C. gariepinus 11.65 mg/g and 3.375%, respectively. Protein and moisture in the S. galilaeus were 53.75 mg/g and 60.75%, respectively. The results recorded a marked insignificant (P > 0.05) decrease in CAT, GR, and GPx activity in O. niloticus. GSH and SOD activity was an insignificant (P > 0.05) decrease in C. gariepinus. The results concluded that the trace elements concentrations exceed the maximum permissible limits recommended in fish samples set by Egypt, FAO, WHO, and EC. The estimated weekly intake of all elements through consumption of studied fish species inhabiting Burullus Lake by a child (15 kg) in Egypt is well above the PTWI recommended by FAO/WHO, whereas it is well below the PTWI for human consumption by young people (40 kg) and adult person (70 kg), at least in respect of residual levels of studied elements excluding Cd and Hg. Thus, for consumer protection, these fish species are unsafe and have hazardous effects for children, and about youth and adult consumption, caution must be taken to consider individuals eating significant amounts of fish.

     

Persistence of granular and EC formulations of chlorpyrifos in a mineral and an organic soil incubated in open and closed containers

Abstract

Samples of a mineral soil (Plainfield sand) and an organic soil (muck) were treated with granular and EC formulations of chlorpyrifos and incubated at 27±1°C and 65±5% RH in open and closed containers. Duplicate samples of each soil‐formulation‐container combination were analyzed for residual chlorpyrifos during a 23 wk period. The disappearance rates observed demonstrate that the relative importance of formulation and containment on overall persistence depends on soil type. For the mineral soil, disappearance was slower from closed containers and formulation had only a slight effect while, in the organic soil the granular formulation disappeared slower than the EC and there was little difference between open and closed containers. The relative importance of degradation and volatilization in the disappearance of chlorpyrifos from soil is discussed.     

Sorptive interactions and binding of δ‐endotoxin protein from bacillus thuringiensis subsp. kurstaki inforest soils

Abstract

The adsorption, desorption and binding of the insecticidal protein from Bacillus thuringiensis subsp. kurstaki (Btk toxin) onto autoclaved sandy and clay loam forest soils were studied at 23°C in a buffer medium (pH 10.2) using the precipitated protein mixture (active + inactive) obtained from a commercial Btk formulation. The active protein in the buffer solution was quantified by ELISA technique. Maximum adsorption of the toxin onto the sandy (301 μg/g) and clay (474 μg/g) loam soils was found to occur after 3 and 4 hours of agitation, respectively. Adsorption of the toxin was higher in the clay loam soil than in sandy loam. Adsorption parameters were calculated using the Freundlich and linear isotherm equations. The K_F and 1/n values for the soils were 1.12 and 1.48 (sandy), and 20.42 and 0.874 (clay), respectively, indicating stronger affinity of the toxin for the clay compared to the sandy loam soil. The linear model showed deviations at higher concentrations, nevertheless using the best fit, K_D and K_OC values were computed for the two soils. For sandy loam, the K_D and K_OC values were 9.38 and 391, respectively; the corresponding values for clay loam were 13.19 and 425, confirming the higher sorption affinity of the toxin for clay loam. The adsorption data did not fit the Langmuir equation because of heterogeneity of the soil surface. Desorption studies showed that more than half of the adsorbed toxic protein remained firmly attached to sandy (162.6 μg/g or 54.5%) and clay (314.0 μg/g or 67.4%) loam soils after six 0.5‐h washes (total 3.0 h wash time). Although the toxin appears to be a non‐leacher, its lateral mobility, soil persistence and biological consequences, including bioavailability of the bound residues, are poorly understood and require further investigation.     

Content and bioconcentration factors of mercury by Parasol Mushroom Macrolepiota procera

The carpophores of Parasol Mushroom and underlying soil substrate collected from several unpolluted and spatially distant sites across Poland were examined to know content and bioconcentration potential of mercury by this species. The total mercury content of the caps of Parasol Mushroom for the particular sites ranged from 1.1 ± 1.0 to 8.4 ± 7.4 μ g/g dry matter (total range from 0.05 to 22 μ g/g dm), while in the stalks were from 0.53 ± 0.27 to 6.8 ± 7.1 μ g/g dm (total range from 0.078 to 20 μ g/g dm). A top soil layer (0–10 cm) showed baseline mercury concentration from 0.022 ± 0.011 to 0.36 ± 0.16 μ g/g dm (total range from 0.010 to 0.54 μg/g dm). Parasol Mushroom is an effective mercury accumulator in the carpophores and bioconcentration factor (BCF) values of this element in the caps and depending on the sampling site ranged from 16 ± 6 to 220 ± 110 (total range from 0.52 to 470), while for the stalks were from 7.6 ± 2.6 to 130 ± 96 (total range from 0.52 to 340). It seems reasonable to state that tolerance (maximum allowable concentration) of the total mercury in a single cap of Parasol Mushroom at unpolluted areas should not exceed 25 μ g/g dm. A value greater then 25 μ g/g dm will imply an elevated content due to site pollution problems. Nevertheless, knowledge on highly toxic methylmercury content and its fraction in the total mercury content of Parasol Mushroom is lacking.     

Polynomial response of 2,4-D mineralization to temperature in soils at varying soil moisture contents,slope positions and depths

The herbicide 2,4-D [2,4-(dichlorophenoxy) acetic acid] is a widely used broadleaf control agent in cereal production systems. Although 2,4-D soil-residual activity (half-lives) are typicaly less than 10 days, this herbicide also has as a short-term leaching potential due to its relatively weak retention by soil constituents. Herbicide residual effects and leaching are influenced by environmental variables such as soil moisture and temperature. The objective of this study was to determine impacts of these environmental variables on the magnitude and extent of 2,4-D mineralization in a cultivated undulating Manitoba prairie landscape. Microcosm incubation experiments were utilized to assess 2,4-D half-lives and total mineralization using a 4 × 4 × 3 × 2 factorial design (with soil temperature at 4 levels: 5, 10, 20 and 40°C; soil moisture at 4 levels: 60, 85, 110, 135 % of field capacity; slope position at 3 levels: upper-, mid- and lower-slopes; and soil depth at 2 levels: 0–5 cm and 5–15 cm). Half-lives (t_1/2) varied from 3 days to 51 days with the total 2,4-D mineralization (M _T ) ranging from 5.8 to 50.9 %. The four-way interaction (temperature × moisture × slope × depth) significantly (p< 0.001) influenced both t_1/2 and M _T. Second-order polynomial equations best described the relations of temperature with t_1/2 and M_T as was expected from a biological system. However, the interaction and variability of t_1/2 and M_T among different temperatures, soil moistures, slope positions, and soil depth combinations indicates that the complex nature of these interacting factors should be considered when applying 2,4-D in agricultural fields and in utilizing these parameters in pesticide fate models.     

Biodegradation of α and β Endosulfan in Soil as Influenced by Application of Different Organic Materials

Abstract

A laboratory pot experiment was conducted to study the effect of amending soil with four different sources of organic matter on the degradation rate of α and β endosulfan isomers. Poultry by-product meal, poultry manure, dairy manure, and municipal solid waste compost were cured, dried, ground (<1 mm) and thoroughly mixed with a calcareous soil at a rate of 2% and placed in plastic pots. Endosulfan was added at the rate of 20 mg kg^?1. The moisture level was kept near field capacity and the pots were kept at room temperature. Soil sub-samples, 100 g each, were collected from every pot at days 1, 8, 15, 22, 29, 43, and 57 for the measurement of endosulfan isomers. Endosulfan residues were extracted from the soil samples with acetone. The supernatant was filtered through anhydrous sodium sulphate, 5 mL aliquot was diluted to 25 mL with hexane, mixed well, and then two sub-samples from the filtrates were analyzed for α and β endosulfan isomers by gas chromatography. The results indicated that the half-life (T _½) of α-endosulfan in the poultry by-product meal treatment was 15 days compared to about 22 days in the other treatments. The T _½ of β-endosulfan was 22 days in the poultry by-product meal treatment and followed a bi-phasic pattern, 57 days in the municipal solid waste compost treatment and the extrapolated T _½ was about 115 days for the other three treatments.     

Dust Collection Efficiency Analysis in a Two-Dimensional Circulating Granular Bed Filter

Abstract

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 ± 0.24, 21.50 ± 0.11, and 30.51 ± 0.57 g/sec at louver angles of 45°, 30°, and 20°, respectively. Optimal dust collection efficiency peaked with a louver angle of 30°. Average particle sizes of bed material by sieve diameters (μm) of 795 μm had higher dust collection efficiency than the average collector particle size of 1500 μm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

Organophosphorus insecticide residues in farm ditches of the Lower Fraser Valley of British Columbia

Abstract

Farm ditches flowing into three important rivers in the Lower Fraser Valley of British Columbia, Canada, were sampled periodically at seven locations from July to December in 1991, to determine the occurrence and levels of seven organophosphorus (OP) insecticides. Based oh sales records for the year, the uses of OP insecticides in this area were as follows: malathion > diazinon > parathion > dimethoate > azinphos‐methyl > fensulfothion, but no sales of chlorfenvinphos. Residues of parathion, diazinon, fensulfothion, dimethoate and chlorfenvinphos were detected at levels ranging from 1 ‐ 7,785 >μg/kg in cropped soils collected from areas adjacent to the sites for sampling ditch water and sediments. Malathion and azinphos‐methyl were not detected in any of the substrates studied, demonstrating their rapid degradation in the environment. Diazinon and dimethoate were consistently found in ditch water at seven locations, with an average concentration of 0.07 μg/L and 0.27 μg/L, respectively. Fensulfothion and parathion, with an average concentration of 0.08 μg/L and 0.17 μg/L, respectively, were sporadically found in ditch water at two locations. In ditch sediments, diazinon was detected at three locations and fensulfothion at two. The average concentrations of these two insecticides were 16 μg/kg and 9 jug/kg, respectively. The potential impact on aquatic organisms of these OP insecticides in ditches is discussed.     

生物强化处理石油污染土壤理化性质和微生物学特性的纵向分布特征

采用原位强化生物修复技术对某区块石油污染土壤进行为期16个月的生物修复,考察了处置后污染土壤理化性质、微生物学特性以及石油烃组成的纵向分布特征。实验结果表明,经过修复后各土层的石油烃去除率是表层土IN-3(50.42%)中层土IN-2(23.54%)底层土IN-1(10.51%);IN-1处于缺氧环境,存在硫酸盐还原和反硝化作用,使得土壤pH值从7.86±0.03降低至7.27±0.03,土壤总氮从2.53±0.13 g/kg降低至0.77±0.04 g/kg;厌氧菌的种群数量是IN-1(10.43±0.71×104CFU/g)IN-3(6.74±0.39×104CFU/g)IN-2(5.15±0.42×104CFU/g),放线菌数量与石油烃含量显著负相关(r=-0.989,p=0.0110.05);IN-3对饱和份和芳香份的降解率最高,分别达到了70.27%和54.52%,远高于IN-2和IN-1;模拟蒸馏结果表明,IN-3正构烷烃得到了很大程度的去除,缺氧的IN-1对正构烷烃去除得较少;厌氧菌数量与胶质和沥青质去除率之间成正相关关系,对于污染源较为分散的污染区域,采用原位生物强化修复时可以考虑引入厌氧修复。     

Adsorption/Desorption of Copper by a Sandy Soil Amended with Various Rates of Manure,Sewage Sludge,and Incinerated Sewage Sludge

Organic amendments are sometimes applied to agricultural soils to improve the physical, chemical, and microbiological properties of the soils. The organic fractions in these soil amendments also influence metal reaction, particularly the adsorption and desorption of metals, which, in turn, determine the bioavailability of the metals and hence their phytotoxicities. In this study, a Quincy fine sandy (mixed, mesic, Xeric Torripsamments) soil was treated with 0 to 160 g kg^?1 rates of either manure, sewage sludge (SS), or incinerated sewage sludge (ISS) and equilibrated in a greenhouse at near field capacity moisture content for 100 days. Following the incubation period, the soil was dried and adsorption of copper (Cu) was evaluated in a batch equilibration study at either 0, 100, 200, or 400 mg L^?1 Cu concentrations in a 0.01M CaCl₂ solution. The desorption of adsorbed Cu was evaluated by three successive elutions in 0.01M CaCl₂. Copper adsorption increased with an increase in manure rates. At the highest rate of manure addition (160 g kg^?1 soil), Cu adsorption was two-fold greater than that by the unamended soil at all rates of Cu additions. With increasing rates of Cu additions, the adsorption of Cu decreased from 99.4 to 77.6% of Cu applied to the 160 g kg^?1 manure amended soil. The desorption of Cu decreased with an increase in rate of manure amendment. Effects of sewage sludge amendments on Cu adsorption were somewhat similar to those as described for manure additions. Likewise, the desorption of Cu was the least at the high rate of SS addition (160 g kg^?1), although at the lower rates there was not a clear indication of the rate effects. In contrast to the above two amendments, the ISS amendment had the least effect on Cu adsorption. At the highest rate of ISS amendment, the Cu adsorption was roughly 50% of that at the similar rate of either manure or SS amendments, across all Cu rates.     

Effect of some herbicides on activities of microorganisms and enzymes in soil

Abstract

Laboratory tests were conducted with eight herbicides, atrazine, butylate, ethalfluralin, imazethapyr, linuron, metolachlor, metribuzin and trifluralin, applied to a loamy sand at rate of 10 μg/g to determine if these materials caused any serious effects on microbial and enzymatic activities related to soil fertility. Some herbicides showed an effect on bacteria and fungi for the first week of incubation, but, subsequently, the populations returned to levels similar to those obtained in the controls. After several herbicide treatments there appeared to cause a slight depression of nitrification. Sulfur oxidation was better than that obtained with untreated soil in all treatments. Oxygen consumption was increased significantly after 96 hr incubation with atrazine. The soil dehydrogenase and amylase activities were inhibited by ethalfluralin treatment respectively for 1 wk and 1 day, and p‐nitrophenol liberation was inhibited for 2 hrs by all herbicide treatments. Results indicated that the herbicidal treatments at the level tested were not drastic enough to be considered deleterious to soil microbial and enzymatic activities which are important to soil fertility.     

A Box-Behnken design for determining the optimum experimental condition of the fungicide (Vapam) sorption onto soil modified with perlite

In the present study, response surface methodology (RSM) based on the Box-Behnken design (BBD) was employed to investigate the effects of the different operating conditions on the removal of the fungicide (Vapam) onto soil modified with perlite using sorption process. The process parameters such as pH of the fungicide solution (2, 5 and 8), temperature (15, 25 and 35°C), shaking time (2, 13 and 24 h) and the percentage of perlite in the modified soil (0, 2 and 4 %) were investigated using a four-factor-three-level Box-Behnken design at an initial fungicide concentration of C₀ = 1.6 mg/L as a fixed input parameter. A second-order quadratic model suggested the optimum conditions to be as follows: fungicide solution pH of 3.57, temperature of 15°C, shaking time of 3.5 h and 4% of perlite in the modified soil which resulted in the improvement of Vapam sorption. Under optimum conditions, the fungicide (Vapam) removal was predicted 12.88 μg/g by BBD. The confirmatory experiments were conducted and the results revealed that the fungicide removal was 13.14 μg/g which indicated that the predicted and the observed values of response (Vapam removal) were in close agreement. Therefore, the soil modified with perlite holds good potential for Vapam sorption. This is the first report on fungicide Vapam sorption onto soil modified with perlite using statistical experimental design employing response surface methodology.