Dissipation and effects of tricyclazole on soil microbial communities and rice growth as affected by amendment with alperujo compost.

The presence of pesticides in surface and groundwater has grown considerably in the last decades as a consequence of the intensive farming activity. Several studies have shown the benefits of using organic amendments to prevent losses of pesticides from runoff or leaching. A particular soil from the Guadalquivir valley was placed in open air ponds and amended at 1 or 2% (w/w) with alperujo compost (AC), a byproduct from the olive oil industry. Tricyclazole dissipation, rice growth and microbial diversity were monitored along an entire rice growing season. An increase in the net photosynthetic rate of Oryza sativa plants grown in the ponds with AC was observed. These plants produced between 1100 and 1300kgha(-1) more rice than plants from the unamended ponds. No significant differences were observed in tricyclazole dissipation, monitored for a month in soil, surface and drainage water, between the amended and unamended ponds. The structure and diversity of bacteria and fungi communities were also studied by the use of the polymerase chain reaction denaturing gel electrophoresis (PCR-DGGE) from DNA extracted directly from soil samples. The banding pattern was similar for all treatments, although the density of bands varied throughout the time. Apparently, tricyclazole did not affect the structure and diversity of bacteria and fungi communities, and this was attributed to its low bioavailability. Rice cultivation under paddy field conditions may be more efficient under the effects of this compost, due to its positive effects on soil properties, rice yield, and soil microbial diversity.

Influence of green waste compost on azimsulfuron dissipation and soil functions under oxic and anoxic conditions.

Concerns have been raised over the sustainability of intensive rice cultivation, where the use of chemical fertilizers and pesticides has been associated with numerous environmental problems. The objective of this study was to test the effect of the herbicide azimsulfuron on important soil functions as affected by amendment with a byproduct of the olive oil industry. Soil was collected from a Mediterranean rice field. Part of it was amended with alperujo compost (AC). Amended and unamended soils were incubated for 43days in presence or not of azimsulfuron, under anoxic-flooded (AF) and oxic-unflooded (OU) conditions. We monitored the dissipation of the herbicide azimsulfuron, C mineralization, soil microbial biomass (SMB) and dissolved organic carbon (DOC) content and its nature. Under AF conditions, the application of compost produced an increase in the dissipation of the herbicide (up to 12.4%). It was related with the higher DOC content, 4 times higher than under OU conditions. Though increases in carbon turnover (under AF and OU conditions) and reduction of SMBC after herbicide application (only under AF conditions) were observed, the differences were not statistically significant. The application of this organic amendment is presented as an efficient management strategy to increase C turnover in agricultural soils and reduce some of the negative effects derived from the application of azimsulfuron under flooded conditions.

Effect of soil organic amendments on the behavior of bentazone and tricyclazole.

The effect of soil amendment with different organic residues from olive oil production on the sorption and leaching of two pesticides used in rice crops (bentazone and tricyclazole) was compared in order to understand their behavior and to improve soil properties by recycling an abundant agricultural residue in Andalucía (S. Spain). A residue from olive oil production (AJ), the organic compost derived from this organic waste (CA) and a biochar (BA) made from CA were used. A soil devoted to rice cultivation, IFAPA (I), was amended at 2% (w/w) of each amendment individually (I+AJ, I+CA and I+BA). In order to evaluate the effect of dissolved organic matter (DOM) from these amendments on bentazone and tricyclazole behavior, the DOM from the amendments was extracted, quantified and characterized by fluorescence spectroscopy and FT-IR. The affinity of DOM for soil surfaces was evaluated with (I) soil and two other soils of different physicochemical properties, ARCO (A) and GUAD (G). These studies revealed differences in DOM quantity, quality and affinity for the used soils among amendments which can explain the different sorption behavior observed for tricyclazole in the amended soils. Leaching assays under saturated/unsaturated conditions revealed a slight delay of bentazone in I+CA and I+BA soils when compared to I+AJ, that can be related to the higher DOM content and much lower specific surface area of AJ. In contrast, tricyclazole was not detected in any of the leachates during the leaching assay. Extraction of tricyclazole residues from soil columns showed that the fungicide did not move below 5cm in the higher sorptive systems (I+CA, I+BA). The sorption of DOM from amendments on soil during the transport process can decrease the mobility of the fungicide by changing the physicochemical properties of the soil surface whose behavior may be dominated by the adsorbed DOM.

Influence of biochar amendments on the sorption-desorption of aminocyclopyrachlor, bentazone and pyraclostrobin pesticides to an agricultural soil.

The many advantageous properties of biochar have led to the recent interest in the use of this carbonaceous material as a soil amendment. However, there are limited studies dealing with the effect of biochar on the behavior of pesticides applied to crops. The objective of this work was to determine the effect of various biochars on the sorption-desorption of the herbicides aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropyl-4-pyrimidinacarboxylic acid) and bentazone (3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide) and the fungicide pyraclostrobin (methyl 2-[1-(4-chlorophenyl) pyrazol-3-yloxymethil]-N-methoxycarbanilate) to a silt loam soil. Aminocyclopyrachlor and bentazone were almost completely sorbed by the soils amended with the biochars produced from wood pellets. However, lower sorption of the herbicides was observed in the soils amended with the biochar made from macadamia nut shells as compared to the unamended soil, which was attributed to the competition between dissolved organic carbon (DOC) from the biochar and the herbicides for sorption sites. Our results showed that pyraclostrobin is highly sorbed to soil, and the addition of biochars to soil did not further increase its sorption. Thus, addition of biochars to increase the retention of low mobility pesticides in soil appears to not be necessary. On the other hand, biochars with high surface areas and low DOC contents can increase the sorption of highly mobile pesticides in soil.

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils.

Improving the existing knowledge on the enantioselectivity of processes affecting chiral pesticide enantiomers in the environment is necessary to maximize the efficacy and minimize the environmental impact caused by the use of pesticides with chiral properties. In this work, the enantioselectivity of the sorption, degradation, and leaching processes of the chiral fungicide metalaxyl in three slightly alkaline, agricultural soils from southern Spain was studied. Batch sorption experiments indicated that the sorption of racemic-metalaxyl on soils, their clay (<2 µm) fractions, and a number of model sorbents simulating naturally-occurring soil colloidal particles was non-enantioselective; the S-enantiomer was sorbed to the same extent as the R-enantiomer on all soil materials. Soil incubation experiments revealed that the R-enantiomer of metalaxyl was degraded faster than the S-enantiomer in all three soils, but the extent and enantioselectivity of metalaxyl degradation was soil-dependent, occurring more slowly and with less enantioselectivity in the fine-textured soil (soil 1) than in the coarse-textured soils (soils 2 and 3). For soils 2 and 3, S- and R-metalaxyl dissipation data were very well described by single first-order kinetics, whereas for soil 1 dissipation data were better fitted by two coupled first-order equations. It is suggested that sorption and entrapment of metalaxyl enantiomers in the abundant small-size pores of soil 1 (i.e., pore radius<100 nm) could have resulted in a fraction of the fungicide of reduced bioavailability, and consequently, protected from enantioselective degradation. Metalaxyl leaching through soil columns was also enantioselective; the concentration of S-metalaxyl in all leachates collected was greater than that of R-metalaxyl. Despite being non-enantioselective, sorption influenced the enantioselectivity of metalaxyl leaching, as it determined the residence time of the fungicide within the soil column, and consequently, the extent and enantioselectivity of its degradation during leaching.

Effect of olive-mill waste addition to soil on sorption, persistence, and mobility of herbicides used in Mediterranean olive groves.

Laboratory and field experiments were conducted to evaluate the effect of olive-mill waste (OMW) addition to a Mediterranean olive grove soil on sorption, persistence, and mobility of two herbicides which are simultaneously applied for weed control in olive groves: terbuthylazine (TA) and fluometuron (FM). Laboratory batch sorption experiments showed that OMW addition to the soil at rates of 5 and 10% (w/w) greatly enhanced the sorption of both herbicides, thus suggesting that amendment with OMW could be useful to enhance the retention and reduce the mobility of FM and TA in the soil. Incubation experiments showed that OMW increased the persistence of FM and had little effect on the long persistence of TA in the soil studied. A demonstration field experiment was also conducted in field plots with a slope of about 5%, either unamended or amended with OMW at a rate of 10 kg m⁻², and then treated with a commercial formulation containing a mixture of TA and FM. Extraction of field soil samples, taken from different soil depths (0-5, 5-10, 10-20, and 20-30 cm) at different times after herbicide application, showed that both TA and FM moved deeper in unamended soil than in OMW-amended soil, and that OMW addition affected the persistence of FM in the toplayer, increasing its half-life from 24 to 58 days, while having little effect on the persistence of TA. Thus, data obtained under real field conditions were consistent with those obtained under controlled laboratory conditions. Preliminary herbicide runoff data indicated that the total herbicide runoff losses were also reduced upon OMW addition. Addition of OMW could be beneficial in reducing the mobility of TA and FM in olive grove soils, and also in increasing the persistence of FM in soils where this herbicide could be rapidly degraded.

Montmorillonite-chitosan bionanocomposites as adsorbents of the herbicide clopyralid in aqueous solution and soil/water suspensions.

Montmorillonite (SWy-2)-chitosan bionanocomposites (SW-CH) were prepared following different methodologies, characterized, and assayed as adsorbents of the herbicide clopyralid (3,6-dichloropyridine-2-carboxylic acid) in aqueous solution and soil/water suspensions, to assess the potential of the materials to prevent and remediate soil and water contamination by anionic pesticides. The SW-CH bionanocomposites were good adsorbents for the herbicide at pH levels where both the anionic form of the herbicide (pK(a)=2.3) and the cationic form of CH (pK(a)=6.3) predominated. The performance of the SW-CH bionanocomposites as adsorbents of clopyralid depended on the amount and arrangement of chitosan in the samples. Clopyralid adsorption was rapid and mostly linear up to herbicide concentrations as high as 0.5mM. High salt concentrations (0.1M NaCl) promoted desorption of the adsorbed pesticide from SW-CH, strongly suggesting that adsorption of clopyralid occurred primarily through an ion exchange mechanism on positively charged CH sites at the montmorillonite surface. Amendment of an acidic soil (pH=4.5) with SW-CH at rates of 5% and 10% led to a significant increase in clopyralid adsorption, whereas this effect was negligible when SW-CH was added to an alkaline soil (pH=8.0), reflecting the absence of positively charged sites in SW-CH at high pH values. Montmorillonite-CH bionanocomposites can be useful as adsorbents for the removal and/or immobilization of anionic pesticides in soil and water under mild acidic conditions.

Behaviour of simazine in soil amended with the final residue of the olive-oil extraction process.

Addition of organic wastes to agricultural soils is becoming a common practice as a disposal strategy and to improve the physical and chemical soil properties. However, in order to optimise the use of organic wastes as soil amendments, their effect on the behaviour of other compounds that are also used in agriculture, such as pesticides, needs to be assessed. In this work, we have investigated the effects of the addition of the final solid residue of the new technology of olive-oil extraction (extracted alperujo or solid olive-mill waste, SOMW2) on the sorption, degradation and leaching of the herbicide simazine in a sandy loam soil. The results are compared with those of a previous study, where the intermediary by-product of the olive-oil processing technology (unextracted alperujo or SOMW1) was applied to the same soil. The soil was amended in the laboratory with SOMW2 at two different rates (5% and 10% w/w). Simazine sorption isotherms showed a great increase in herbicide sorption after SOMW2 addition to soil. SOMW2 addition also increased sorption irreversibility. Incubation studies revealed reduced biodegradation of simazine in the soil amended with SOMW2 compared to the unamended soil. Breakthrough curves of simazine in handpacked soil columns showed that SOMW2 addition retarded the vertical movement of the herbicide through the soil and greatly reduced the amount of herbicide available for leaching. Interestingly, the results were quantitatively different from those obtained for the intermediary by-product SOMW1, illustrating the importance of the specific characteristics of the organic amendment in determining its effect on pesticide behaviour.

Hexazinone and simazine dissipation in forestry field nurseries.

Hexazinone and simazine field dissipation was studied in two different soils from Spain (Toledo and Burgos), devoted to forest nurseries for Pinus nigra. Laboratory experiments (adsorption-desorption isotherms, leaching experiment and degradation study) were carried out to determine possible mechanisms of dissipation. Higher adsorption was observed for hexazinone in Toledo (KfT = 0.69) compare to in Burgos soil (KfB = 0.20) probably due to the higher organic matter (OM) content of Toledo soil. No differences in adsorption were obtained for simazine in both soils (KfT = 1.27; KfB = 1.34). In every case, adsorption was higher for simazine than for hexazinone, in both soils. The total recovery of hexazinone in the leachates from handpacked soil columns was higher in Burgos (100%) than in Toledo (80%), because of the larger adsorption of hexazinone in this last soil. No differences in simazine leaching between both soils were found, although the total amount of pesticide recovered in leachates (40% in the two soils) was lower for simazine than for hexazinone. Finally, lower degradation was found in Burgos (t1/2 = 91 d) vs Toledo (t1/2 = 47 d), directly related with the high OM content of Toledo. No half-life was calculated for simazine in Toledo because no changes in herbicide soil content were observed during the period of time studied. In the case of Burgos, the half-life for simazine was 50 days. The field residues study showed larger persistence of simazine than hexazinone mainly due to the higher adsorption and lower mobility of simazine in the two soils. The lower persistence of hexazinone in Toledo soil than in Burgos soil is related to the larger rainfall occurred in this soil besides the higher degradation of this herbicide observed in Toledo soil. The much lower temperature in Burgos than in Toledo soil during winter contribute to the higher persistence of the two herbicides in Burgos soil.

Organoclays for controlled release of the herbicide fenuron.

Organoclays were assayed as matrices in which to associate herbicides, with the aim of decreasing product losses that could give rise to water contamination from agricultural activities. Fenuron was selected as model of a very mobile and highly water-soluble herbicide. Two different organoclays of high (A-HDT) and low (H-C18) reversible fenuron sorption were selected. Herbicide-organoclay complexes were prepared from the two organoclays and with two different fenuron contents (20 and 40 g AI kg-1) and two different mixing times, so as to form a series of weak and strong complexes. The release of fenuron from those complexes into water and water/soil suspensions gave values of T50 (time to release 50% of the fenuron content) ranging from 0.3 min to 2400 h. The total fenuron released in these closed systems ranged from 48 to 80% of the fenuron in the complex. The organoclay type (high or low sorptivity) had the greatest influence on fenuron release, followed by the strong or weak complex, suggesting that herbicide-organoclay interactions are the main factors controlling release. Soil column leaching experiments showed fenuron-organoclay complexes to be effective in reducing the peak herbicide concentration in the leachate to a half (6 microns) or a quarter (3 microns) of that obtained from the free technical compound (12 microns). Herbicide lost through leaching was reduced from 78% for the free technical fenuron to 50-30%, depending on the organoclay used as carrier and the strength of the complex. Bioassay with ryegrass showed that the weak fenuron/H-C18 complex (40 g AI kg-1) gave the same herbicidal activity as technical fenuron. The potential suitability of low-sorptive organoclays for conferring slow-release properties on the fenuron complex has been demonstrated.

Sorption and photolysis studies in soil and sediment of the herbicide napropamide.

The influence of soil and sediment composition on sorption and photodegradation of the herbicide napropamide [N,N-diethyl-2-(1-naphthyloxy)propionamide] was investigated. Five soils and one sediment were selected for this study and the clay fractions were obtained by sedimentation. Sorption-desorption was studied by batch equilibration technique and photolysis in a photoreactor emitting within 300-450 nm wavelength with a maximum at 365 nm. Sorption increased with clay content and was not related to organic matter content. High irreversibility of sorption was related to the greater montmorillonite content. The presence of soil or sediment reduced photolysis rate due to screen effect and this process did not depend on solid composition but on particle size distribution.

Fenuron sorption on homoionic natural and modified smectites.

The adsorption isotherms of fenuron (1,1-dimethyl-3-phenylurea) on three smectites (SWy and SAz montmorillonites and SH hectorite) differing in their layer charge (SH

Natural soil colloids To retard simazine and 2,4-D leaching in soil.

Natural or synthetic sorbents for pesticides can be used to reduce contamination of soils and natural waters. The sorption of simazine and 2,4-D on montmorillonite minerals has been studied and their potential use to retard pesticide leaching in soil evaluated. Simazine and 2,4-D did not sorb on high-layer charge montmorillonite, whereas sorption on the lower layer charge montmorillonite SWy varied depending on the saturating cation. Simazine sorption increased in the order Ca(2+)SWy << K(+)SWy < Fe(3+)SWy. Simazine molecules sorb on hydrophobic microsites of the montmorillonite. Once protonated, further sorption through cation exchange takes place in the interlamellar space of the montmorillonite, as corroborated by X-ray diffraction and FT-IR studies. 2,4-D does not sorb on K(+)SWy or Ca(2+)SWy, but does sorb on Fe(3+)SWy, because the acidic character of this sorbent allows the molecular form of 2, 4-D to sorb by hydrogen bonding and/or by hydrophobic interactions. Leaching experiments in hand-packed soil columns indicate that simazine and 2,4-D application as a complex with FeSWy renders later breakthrough and lower maximum concentration peaks, and the total herbicide leached is lower than when applied as the pure analytical grade compound. These results suggest the possible use of natural soil colloids as sorbents for herbicides such as simazine and 2,4-D to retard pesticide leaching in soil, thus reducing their ground water contamination potential.

Sorption and desorption of triadimefon by soils and model soil colloids.

Sorption-desorption of the azole fungicide triadimefon [1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2, 4-triazol-1-yl)-2-butanone] on eight soils and a series of single, binary, and ternary model soil colloids was determined using the batch equilibration technique. Regression analysis between Freundlich sorption coefficients (K(f)) and soil properties suggested that both clay and organic C (OC) were important in triadimefon sorption by soils, with increasing importance of clay for soils with high clay and relatively low OC contents. Triadimefon sorption coefficients on soil were not significantly affected by the concentration of electrolyte or the presence of soluble soil material in solution, but they were highly dependent on the soil:solution ratio due to the nonlinearity of triadimefon sorption on soil. Freundlich sorption isotherms slopes were very similar for all soils (0.75 +/- 0.02). Desorption did not greatly depend on the concentration at which it was determined and showed higher hysteresis for more sorptive soils. Results of triadimefon sorption on model sorbents supported that both humic acid and montmorillonite-type clay constituents contribute to triadimefon retention by soil colloids.

Sepiolite, a potential excipient for drugs subject to oxidative degradation.

Sepiolite, a member of the fibrous mineral group of clays, is relatively free of surface ferric iron and does not accelerate significantly the oxidative degradation of hydrocortisone. The compatibility of sepiolite with drugs that can undergo oxidative degradation is in sharp contrast to the catalytic effect of attapulgite, another fibrous mineral, which contains a significant amount of surface ferric iron and which therefore accelerates oxidative degradation. Sepiolite adsorbs hydrocortisone by a weak adsorption mechanism, which was shown by IR spectroscopy to be chiefly due to hydrogen bonding. However, accelerated oxidative degradation of the adsorbed hydrocortisone does not occur. Maximum adsorption occurs at pH 7-8.5. Desorption occurs readily by washing with water. Sepiolite has similar rheological properties to attapulgite. The results of this study suggest that sepiolite may be useful as a pharmaceutical excipient for drugs that undergo oxidative degradation.

Oxidative degradation of hydrocortisone in presence of attapulgite.

Degradation of hydrocortisone in attapulgite suspensions was monitored by high-pressure liquid chromatography and UV spectrophotometry. The rate of oxidative degration of hydrocortisone was accelerated significantly in the presence of attapulgite. In addition, degradation appeared to be composed of two apparent first-order reactions rather than the single apparent first-order degradation reaction observed for hydrocortisone solutions. However, the same degradation products were obtained in both hydrocortisone solutions and attapulgite suspensions, indicating that interaction with attapulgite did not alter the degradation pathway. Kinetic and adsorption studies suggested that hydrocortisone is adsorbed weakly by attapulgite and undergoes oxidative degradation, which is catalyzed by adsorbed iron oxides or hydroxides as well as by structural ferric iron at the clay surface. Since clay minerals generally contain surface ferric iron, the potentiala for accelerating the oxidative degradation of drugs should be considered whenever clays and drugs are combined.