Paula Pérez-Rodríguez

Simulating Washoff of Cu-Based Fungicide Sprays by Using a Rotating Shear Device

Foliar washoff causes a loss of copper-based pesticides sprayed on crops, leading to an increase in the number of applications and contamination of the soil with Cu. In field studies, the variables that determine the amount of Cu loss are difficult to control. An experimental setup based on a rotating shear device (RSD) was used to estimate the influence of physical factors in the loss of Cu due to washoff of three copper-based fungicides: copper oxychlorhide (CO), Bordeaux mixture (BM), and a mixture of copper oxychlorhide and propylene glycol (CO-PG). Full factorial designs were used to model the loss of Cu from fungicides sprayed on the polypropylene surface of the RSD. Variables in the experiments were rotation speed, wash water volume, and fungicide dose. Good reproducibility was obtained for Cu loss, with a coefficient of variation less than 8%. Mean Cu losses were 27.0, 33.0, and 13.5% of the copper applied in fungicide for the BM, CO, and CO-PG, respectively. Empirical equations were obtained to calculate Cu losses from the rotation speed, wash water volume, and dose, as well as their interactions. CO losses were consistent with a model of particle detachment in which such losses depended on a threshold boundary shear stress required to initiate particle motion. Also, percent CO losses were found to be significantly correlated with the linear momentum at the surface boundary. The momentum values obtained in the RSD tests were similar to those estimated for a rainfall event of 20 mm h(-1) lasting 10 min. The most important mechanism in the loss of CO was the erosion of Cu-bearing particles.

Lithological and land-use based assessment of heavy metal pollution in soils surrounding a cement plant in SW Europe.

We study the influence of phasing out a cement plant on the heavy metal (Hg, Pb and Cr) content in the surrounding soils, taking into account factors often neglected, such as contributions due to local lithology or land use. The range of total Hg was 10-144µg kg(-1), reaching up to 41 and 145mgkg(-1) for total contents of Pb and Cr, respectively. Forest soils showed higher concentration of Hg than prairie soils, indicating the importance of land use on the accumulation of volatile heavy metals in soils. In forest soils, total Hg showed a trend to decrease with soil depth, whereas in prairie soils the vertical pattern of heavy metal concentrations was quite homogeneous. In most cases, the distance to the cement plant was not a factor of influence in the soils content of the analyzed heavy metals. Total Pb and Cr contents in soils nearby the cement plant were quite similar to those found in the local lithology, resulting in enrichment factor values (EFs) below 2. This suggests that soil parent material is the main source of these heavy metals in the studied soils, while the contribution of the cement plant to Pb and Cr soil pollution was almost negligible. On the contrary, the soils surrounding the cement plant accumulate a significant amount of Hg, compared to the underlying lithology. This was especially noticeable in forest soils, where Hg EF achieved values up to 36. These results are of relevance, bearing in mind that Hg accumulation in soils may be an issue of environmental concern, particularly in prairie soils, where temporal flooding can favor Hg transformation to highly toxic methyl-Hg. In addition, the concurrence of acid soils and total-Cr concentrations in the range of those considered phytotoxic should be also stressed.

Modeling the influence of raindrop size on the wash-off losses of copper-based fungicides sprayed on potato (Solanum tuberosum L.) leaves

Modeling the pesticide wash-off by raindrops is important for predicting pesticide losses and the subsequent transport of pesticides to soil and in soil run-off. Three foliar-applied copper-based fungicide formulations, specifically the Bordeaux mixture (BM), copper oxychloride (CO), and a mixture of copper oxychloride and propylene glycol (CO-PG), were tested on potato (Solanum tuberosum L.) leaves using a laboratory raindrop simulator. The losses in the wash-off were quantified as both copper in-solution loss and copper as particles detached by the raindrops. The efficiency of the raindrop impact on the wash-off was modeled using a stochastic model based on the pesticide release by raindrops. In addition, the influence of the raindrop size, drop falling height, and fungicide dose was analyzed using a full factorial experimental design. The average losses per dose after 14 mm of dripped water for a crop with a leaf area index equal to 1 were 0.08 kg Cu ha−1 (BM), 0.3 kg Cu ha−1 (CO) and 0.47 kg Cu ha−1 (CO-PG). The stochastic model was able to simulate the time course of the wash-off losses and to estimate the losses of both Cu in solution and as particles by the raindrop impacts. For the Cu-oxychloride fungicides, the majority of the Cu was lost as particles that detached from the potato leaves. The percentage of Cu lost increased with the decreasing raindrop size in the three fungicides for the same amount of dripped water. This result suggested that the impact energy is not a limiting factor in the particle detachment rate of high doses. The dosage of the fungicide was the most influential factor in the losses of Cu for the three formulations studied. The results allowed us to quantify the factors that should be considered when estimating the losses by the wash-off of copper-based fungicides and the inputs of copper to the soil by raindrop wash-off.

Rainfall-induced removal of copper-based spray residues from vines.

The continuous use of copper against fungal diseases and off-target effects causes major environmental and agronomic problems. However, the rain-induced removal of Cu-based residues is known only for a limited number of crops. We present the results of rain-induced removal of fungicides from two monitored vineyard plots which were sprayed with two widely used Cu-based formulations: copper-oxychloride (CO) and Bordeaux mixture (BM), respectively. Cu removal per growing season was 0.60±0.12kgha(-1) (30% of the applied fungicide) for CO and 0.80±0.10kgha(-1) for BM (70% of the applied fungicide). Fractioning the Cu in soluble (CuS) and particulate fractions (CuP) showed that most of the Cu was removed as CuP, but CuS concentrations found in throughfall collectors exceeded the regulatory threshold for toxicity in surface waters. The first few millimeters of rain caused most of the Cu removal. Our findings agreed with the data reported in the scientific literature, in which a significant fraction of the Cu-based formulation is loosely attached to the plant surfaces. In addition, we found that rainfall energy had a minor influence on the removal.

Copper content and distribution in vineyard soils from Betanzos (A Coruña, Spain)

The sustained use of cupric compounds in grape production has contributed to a pronounced Cu accumulation in vineyard soils. We studied 32 surface (0-20 cm) vineyard soil samples from the Atlantic-influenced NW Iberian Peninsula, in order to assess the Cu levels in these soils. The total Cu (CuT) contents were high and variable (between 63-730 mg kg-1), similar to those previously found in the Ribeira Sacra and O Ribeiro denominations of origin, which were until now the areas with the highest CuT concentrations detected in vineyard soils of the NW Iberian Peninsula. Most Cu in the solid phase of the soil was bound to organic matter (18-373 mg kg-1), contrary to what happens in natural soils or with elements from natural sources, such as Zn, for which the residual fraction is quantitatively the most important. The exchangeable Cu fraction was the fraction that showed the highest geochemical mobility and its variance in the studied soils was mainly related to CuT and, secondly, to exchangeable Ca levels. The results of fractionation were clearly different from those of Zn, an element with a mainly natural origin, which was characterized by a dominant residual fraction. Finally, agricultural practices aimed at maintaining or increasing the amount of organic matter in vineyard soils should be encouraged, due to its role in decreasing the eventual toxic effects of high Cu levels both on plants and on soil microorganisms.

Predicting release and transport of pesticides from a granular formulation during unsaturated diffusion in porous media

The release and transport of active ingredients (AIs) from controlled-release formulations (CRFs) have potential to reduce groundwater pesticide pollution. These formulations have a major effect on the release rate and subsequent transport to groundwater. Therefore the influence of CRFs should be included in modeling non-point source pollution by pesticides. We propose a simplified approach that uses a phase transition equation coupled to the diffusion equation that describes the release rate of AIs from commercial CRFs in porous media; the parameters are as follows: a release coefficient, the solubility of the AI, and diffusion transport with decay. The model gives acceptable predictions of the pesticides release from commercial CRFs in diffusion cells filled with quartz sand. This approach can be used to study the dynamics of the CRF-porous media interaction. It also could be implemented in fate of agricultural chemical models to include the effect of CRFs.

Sepia ink as a surrogate for colloid transport tests in porous media

Abstract We examined the suitability of the ink of Sepia officinalis as a surrogate for transport studies of microorganisms and microparticles in porous media. Sepia ink is an organic pigment consisted on a suspension of eumelanin, and that has several advantages for its use as a promising material for introducing the frugal-innovation in the fields of public health and environmental research: very low cost, non-toxic, spherical shape, moderate polydispersivity, size near large viruses, non-anomalous electrokinetic behavior, low retention in the soil, and high stability. Electrokinetic determinations and transport experiments in quartz sand columns and soil columns were done with purified suspensions of sepia ink. Influence of ionic strength on the electrophoretic mobility of ink particles showed the typical behavior of polystyrene latex spheres. Breakthrough curve (BTC) and retention profile (RP) in quartz sand columns showed a depth dependent and blocking adsorption model with an increase in adsorption rates with the ionic strength. Partially saturated transport through undisturbed soil showed less retention than in quartz sand, and matrix exclusion was also observed. Quantification of ink in leachate fractions by light absorbance is direct, but quantification in the soil profile with moderate to high organic matter content was rather cumbersome. We concluded that sepia ink is a suitable cheap surrogate for exploring transport of pathogenic viruses, bacteria and particulate contaminants in groundwater, and could be used for developing frugal-innovation related with the assessment of soil and aquifer filtration function, and monitoring of water filtration systems in low-income regions.

Influence of pore water velocity on the release of carbofuran and fenamiphos from commercial granulates embedded in a porous matrix.

Pore water flow velocity can influence the processes involved in the contaminant transport between relative stagnant zones of porous media and their adjacent mobile zones. A particular case of special interest is the occurrence of high flow rates around the controlled release granules containing pesticides buried in soil. The release of the pesticides carbofuran and fenamiphos from commercial controlled release formulations (CRFs) was studied, comparing release tests in a finite volume of water with water flow release tests in saturated packed sand at different seepage velocities. For water release kinetics, the time taken for 50% of the pesticide to be released (T(50)) was 0.64 hours for carbofuran and 1.97 hours for fenamiphos. In general, the release rate was lower in the porous matrix than in the free water tests. The faster release rate for carbofuran was attributed to its higher water diffusivity. The seepage velocity has a strong influence on the pesticide release rate. The dominant release mechanism varies with the progress of release. The evolution of the mechanism is discussed on the basis of the successive steps that involve the moving boundary of the dissolution front of the pesticide inside the granule, the concentration gradient inside the granule and the flow boundary layer resistance to solute diffusion around the granule. The pore water velocity influences the overall release dynamics. Therefore, seepage velocity should be considered in pesticide release to evaluate the risk of pesticide leaching, especially in scenarios with fast infiltration.

Effect of particle size on copper oxychloride transport through saturated sand columns.

Understanding the mechanisms behind the transport of particulate contaminants in porous media is crucial with a view to evaluating their potential impact on the environment. Much of the copper used in agriculture is sprayed as colloidal copper oxychloride, and despite its potential environmentally adverse consequences, colloidal transport of particulate formulations of copper remains poorly understood. In this work, transport of copper colloids from a commercial copper oxychloride based fungicide formulation was studied by measuring its breakthrough in saturated quartz sand columns. The influence of ionic strength and flow rate on the test results suggests that retention of copper oxychloride based colloids is governed by weak forces. The particle deposition dynamics of the studied copper formulation was consistent with a two-site kinetic attachment model. The proposed colloid retention mechanisms are highly sensitive to the fungicide particle size. A comparison of our test results with reported data for other copper oxychloride wettable powder fungicide formulations revealed that transport of copper oxychloride is strongly influenced by its particle size. This is consistent with the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO), but only if binding occurs at the secondary minimum in the potential, where attachment is less favorable with small particles. The influence of particle size is also consistent with the results of previous studies where deposition was ascribed to retention at a secondary minimum. The mobility of colloidal formulations of these copper-based fungicides in saturated porous media increases with increasing particle size.

Nitrogen mineralization dynamics in acid vineyard soils amended with bentonite winery waste

ABSTRACT An excess of available nitrogen (N) in vineyard soil is considered detrimental for vine growth, making a thorough assessment of N mineralization dynamics in vineyard soils before the addition of winery waste necessary. This study assesses the changes in N mineralization in acid vineyard soils amended with bentonite winery waste (BW). Non-amended soil (control), BW and soil-waste mixtures (SBWM) with a low (+L) or high (+H) dose of BW were incubated for six weeks. After 7, 14, 21 and 42 days of incubation, the control soils, BW and SBWM were analysed for net ammonified N, net nitrified N and net mineralized N. Parameters related to the kinetics of N mineralization were also determined. The addition of BW increased the potentially mineralizable N (N0) in the amended soils (58–144% for the highest BW dose), although the mineralization rate was governed by the soil characteristics. Mineralizable N was only a small fraction (<4%) of the total organic nitrogen added to the soil through the BW addition, mainly due to the dominance of the nitrification process in the BW amended soils. These experimental results suggest that the addition of BW may be a suitable amendment for nitrogen fertilization in acid vineyard soil.