Alegría Cabrera

Oxyfluorfen herbicide residues have been previously reported in surface and ground water in the Guadalquivir river basin in Spain. Soil factors and processes (sorption, dissipation, and leaching) influencing the potential offsite transport of oxyfluorfen to surface and ground water were characterized in laboratory experiments for two soils from Southern Spain. The influence of olive‐oil mill waste amendment on the soil processes was also determined. Oxyfluorfen sorption in unamended soils was not significantly affected by soil active components (organic matter and clay fraction). However, a significant increase in soil sorption of the herbicide was observed upon amendment. Laboratory half‐life values for oxyfluorfen in unamended sandy clay loam and silty clay soils at 40% moisture content and 25°C were 29 and 19 days, respectively, and it increased by a factor of four upon amendment. Oxyfluorfen's mobility along soil profile increased with the amendment in leaching studies at 25°C, suggesting that dissolved organic matter of amendment can play an important role enhancing soil vertical movement of the pesticide. The increase in soil adsorption and persistence observed with olive‐oil mill waste amendment can promote its losses by runoff following winter application, whereas vertical movement of oxyfluorfen can be enhanced following spring application when olive‐oil mill waste amendment is also applied.

Bentazone and S‐metolachlor are herbicides widely used for the control of broad leaf weeds in crops such as corn and soybean. The effect of the addition to soils with different texture and organic matter content of an organic waste (OW) from oil olive production (alperujo) on different processes affecting behaviour of both herbicides was evaluated. Sorption of S‐metolachlor increased upon amendment. A six‐fold increase could be observed for K_d values on the sandy soil amended at 10% rate and a five‐fold increase on the soil with higher content on clay (48%) and same rate of OW (10%). The results revealed that although an increase in soil total pore volume was found upon amendment (from 210 to 266 mm³ g⁻¹ in sandy (S) soil, from 215 to 251 in clayey (19% silt) (T) soil, and from 240 to 289 in clayey (50% silt) (E) soil), leaching of the herbicide S‐metolachlor was greatly reduced (from 61 to 3.5% in the S‐soil and from 37 to S‐metolachlor half‐life in T‐soil and a four‐fold increase for bentazone in E‐soil. Thus, the use of the by‐product from olive oil extraction can be a good strategy to reduce the off‐site movement of S‐metolachlor by increasing its soil sorption, and therefore the risk of water pollution can be diminished. However, the higher persistence of both herbicides in organic amended soils should be taken into account.

Aminocyclopyrachlor (6‐amino‐5‐chloro‐2‐cyclopropyl‐4‐pyrimidinecarboxylic acid), a new herbicide, was approved by US‐EPA (United States Environmental Protection Agency) in September 2010 for the control of broadleaf weeds, grasses, vines and woody species in non‐crops, turf, sod farms and residential areas. At typical soil pH levels, aminocyclopyrachlor is anionic. Anionic pesticides are generally weakly retained by most soil and sediment components and are subject to potential transport offsite. One strategy to minimize the risk of offsite transport associated with weakly sorbed, highly mobile pesticides is the application of these chemicals supported on a sorbent, such as modified clay minerals which contain exchangeable inorganic and organic cations. The aim was to determine the ability of unmodified and modified clay minerals to sorb aminocyclopyrachlor. Two montmorillonites (Ca‐Arizona montorillonite (SAz‐1) and Na‐Wyoming montmorillonite (SWy‐2)) were used as unmodified clay minerals and were also modified with an inorganic cation (Fe ³⁺ ), soil constituents (ferrihydrite, humic acid) and organic cations (hexadecyltrimethylammonium (HDTMA), hexadimethrine, spermine). Greater sorption of aminocyclopyrachlor was observed in the sorbent–solution systems with lower pH values, presumably because of protonation of the herbicide anion at low pH and subsequent sorption of molecular species and cationic species. FeSWy‐2 (SWy‐2 montmorillonite saturated with Fe ³⁺ ; system pH = 4.6) was the best sorbent for aminocyclopyrachlor (86% of applied). The best organo‐clay (SA‐HDTMA) (system pH = 6.1) sorbed 53% of the applied herbicide. Binary and ternary model sorbents (system pH > 6.7) did not sorb aminocyclopyrachlor. At the lowest pH value studied (2.8), the organo‐clay SW‐Sper was the best sorbent system for aminocyclopyrachlor. Our recommendation for the best adsorbent is the clay mineral modified with Fe ³⁺ , although at pH values <3, the use of the organo‐clay SW‐Sperm could be also convenient.

BACKGROUND: Sorption and dissipation of aged metolachlor were characterized in rehabilitated and eroded prairie soils using sequential batch slurry (conventional) and accelerated solvent extraction (ASE).RESULTS: In spite of an almost twofold difference in soil organic carbon (OC) content, S‐metolachlor sorption coefficients (K_d) and dissipation rates (DT₅₀) were the same in soils from different landscape positions within an eroded landform. Soil was moved within the landform to increase productivity. In areas receiving topsoil addition, S‐metolachlor K_d was higher and DT₅₀ was longer than in eroded areas. The efficiency of extraction was higher for ASE than for conventional extractions. No consistent aging effect on K_d was observed. Mineralization in 8 weeks accounted for < 10% of the applied metolachlor.CONCLUSION: The results of this laboratory study support a field dissipation study. Both showed that S‐metolachlor has the same retention and dissipation rate throughout an eroded landform, which was not expected owing to the large variability in soil properties, including OC concentrations. Altering soil properties by adding topsoil increased metolachlor sorption and persistence. The method of extraction (conventional versus ASE) affected calculated sorption coefficients and dissipation rates. In all cases, groundwater ubiquity scores (GUSs) categorized metolachlor as having intermediate mobility. Published 2012 by John Wiley & Sons, Ltd.

Biochar, the solid residual remaining after the thermochemical transformation of biomass for carbon sequestration, has been proposed to be used as a soil amendment, because of its agronomic benefits. The effect of amending soil with six biochars made from different feedstocks on the sorption and leaching of fluometuron and 4-chloro-2-methylphenoxyacetic acid (MCPA) was compared to the effect of other sorbents: an activated carbon, a Ca-rich Arizona montmorillonite modified with hexadecyltrimethylammonium organic cation (SA-HDTMA), and an agricultural organic residue from olive oil production (OOW). Soil was amended at 2% (w/w), and studies were performed following a batch equilibration procedure. Sorption of both herbicides increased in all amended soils, but decreased in soil amended with a biochar produced from macadamia nut shells made with fast pyrolysis. Lower leaching of the herbicides was observed in the soils amended with the biochars with higher surface areas BC5 and BC6 and the organoclay (OCl). Despite the increase in herbicide sorption in soils amended with two hardwood biochars (BC1 and BC3) and OOW, leaching of fluometuron and MCPA was enhanced with the addition of these amendments as compared to the unamended soil. The increased leaching is due to some amendments' soluble organic compounds, which compete or associate with herbicide molecules, enhancing their soil mobility. Thus, the results indicate that not all biochar amendments will increase sorption and decrease leaching of fluometuron and MCPA. Furthermore, the amount and composition of the organic carbon (OC) content of the amendment, especially the soluble part (DOC), can play an important role in the sorption and leaching of these herbicides.

MCPA (4‐chloro‐2‐methylphenoxyacetic acid) is an acidic herbicide widely used on olive crops in Spain. Due to its anionic form at natural soil pH, there is high risk of leaching and groundwater contamination by the use of this herbicide. The aim of this work was to study the effects of organoclay‐based formulations of MCPA and olive oil waste amendment on MCPA leaching in a sandy loam soil. For this purpose, batch adsorption and column leaching studies were performed. The organoclays used to prepare the clay‐based formulations of MCPA were obtained by treating Wyoming montmorillonite (SWy‐2) and Arizona montmorillonite (SAz‐1) with an amount of hexadecyltrimethylammonium (HDTMA) cation equal to 100% of the CEC of the montmorillonites. The organic residue used in this study was a solid waste from olive oil production (olive oil waste, OOW). The soil was amended with the organic residue at the rate of 10% (w/w). Batch release and column leaching studies indicated that organoclay‐based formulations of MCPA reduced the release rate and the leaching of the herbicide as compared to the use of a conventional formulation containing the herbicide in an immediately available form. The increase in soil organic matter of the soil upon amendment with the organic residue also resulted in greater adsorption and reduced leaching of MCPA in the soil. Accordingly, both the use of organoclay‐based formulations and the amendment of soil with OOW are proposed as efficient strategies to reduce extensive leaching losses associated with the application of MCPA in high‐risk scenarios, such as Mediterranean olive groves.

The aim of this work was to study the effect of the application of a solid waste from olive oil production (alperujo) on the movement and persistence of the herbicide terbuthylazine (N²-tert-butyl-6-chloro-N⁴-ethyl-1,3,5-triazine-2,4-diamine). An experimental olive grove was divided in two plots: (i) Plot without organic amendment (blank) and (ii) Plot treated with alperujo during 3 years at a rate of 17920 kg of alperujo ha^{− 1}. Terbuthylazine was applied to both plots at a rate of 2 kg ha^{− 1} a.i. Triplicates from each plot were sampled at 3 depths (0–10, 10–20 and 20–30 cm), air-dried, remains of olive leaves, grass roots, and stones removed and sieved through a 5 mm mesh sieve. Terbuthylazine was extracted with methanol 1:2 weight:volume ratio, the extracts were evaporated to dryness, resuspended in 2 mL of methanol, filtered and anylized by high performance liquid chromatography (HPLC). Higher amounts of terbuthylazine were detected at each sampling depth in plots treated with alperujo. The increase in soil organic matter content upon amendment with alperujo slightly increased sorption, suggesting that other factors beside sorption affect terbuthylazine degradation rate in organic amended soils.

Amendments are frequently added to agricultural soils to increase organic matter content. In this study, we examined the influence of alperujo, an olive oil mill waste, on the availability of two triazine herbicides, terbuthylazine and atrazine, in two different sandy soils, one from Sevilla, Spain, and the other from Minnesota. The effect of aging on herbicide sorption and bioavailability was also studied. Soils were amended with alperujo at a rate of 3-5% (w:w) in laboratory studies. Apparent sorption coefficients for the triazine herbicides were calculated as the ratio of the concentrations of each herbicide sequentially extracted with water, followed by aqueous methanol, at each sampling time. These data showed greater sorption of terbuthylazine and atrazine in amended soils as compared to nonamended soils, and an increase in the amount of herbicide sorbed with increasing aging time in nonamended soils. The triazine-mineralizing bacterium Pseudomonas sp. strain ADP was used to characterize triazine bioavailability. Less mineralization of the herbicides by Pseudomonas sp. strain ADP was observed in soils amended with alperujo, as compared to the unamended soils, and, despite the increase in sorption with aging in unamended soils, herbicide mineralization also increased in this case. This has been attributed to Pseudomonas sp. strain ADP first using alperujo as a more readily available source of N as compared to the parent triazines. In summary, addition of alperujo to the soils studied was shown to increase triazine herbicides sorption and hence to reduce its availability and potential to leach.