Elsevier

Journal of Hazardous Materials

Volume 243, December 2012, Pages 223-231
Journal of Hazardous Materials

Modeling field-scale vertical movement of zinc and copper in a pig slurry-amended soil in Brazil

https://doi.org/10.1016/j.jhazmat.2012.10.022Get rights and content

Abstract

Organic amendments often represent a source of trace metals (TMs) in soils, which may partly leach into the groundwater. The objectives of this study were (1) to validate Hydrus-2D for modeling the transport of Zn and Cu in an Alfisol amended with pig slurry (PS) by comparing numerical simulations and experimental field data, and (2) to model the next 50 years of TM movements under scenarios of suspended or continued PS amendments. First, between 2000 and 2008, we collected detailed Zn and Cu data from a soil profile in Santa Maria, Brazil. Two hypotheses about Zn and Cu reactivity with the solid phase were tested, considering physical, hydraulic, and chemical characteristics of six soil layers. Using a two-site sorption model with a sorption kinetic rate adjusted based on laboratory EDTA extractions, Hydrus simulations of the vertical TM transport were found to satisfactorily describe the soil Zn and Cu concentration profiles. Second, the long-term fate of Zn and Cu in the soil was assessed using the validated parameterized model. Numerical simulations showed that Zn and Cu did not present risks for groundwater pollution. However, future Cu accumulation in the surface soil layer would exceed the Brazilian threshold for agricultural soils.

Highlights

► We performed a model validation of Zn and Cu settings in a pig-slurry amended soil. ► A two-site model with reduced kinetic constants present the best fit with field data. ► Future 50-years scenarios related to the pig slurry applications were simulated. ► Downward Zn and Cu solute fluxes will not present risk to groundwater pollution. ► Continuous pig slurry amendments will lead to a high Cu accumulation on soil surface.

Introduction

Soil amendment with organic waste is a common practice in agriculture worldwide. In different regions of Brazil, large-scale animal production generates large amounts of manure. These regions are often characterized by the predominance of family farming, in which each farmer has only a small land area to grow crops. The fertilizing value of organic waste, such as animal manure, is generally recognized, but its quality may vary widely. For example, pig slurry (PS) often has a relatively low nutrient content, making it uneconomical to transport over long distances. Hence, PS disposal criteria are primarily guided by a limited space, increasing risks of soil pollution by nitrate, phosphorus, and trace metals (TMs), notably zinc (Zn) and copper (Cu).

Regulatory agencies in many countries have established environmental guidelines for soil organic waste amendments [1], [2], [3], [4]. Basically, such guidelines restrict, or ban, applications of organic waste to soils where the total TM content exceeds the maximal allowed values. Brazilian laws currently allow for the maximum TM values, which are generally higher than those adopted in the European Union. The Companhia de Tecnologia de Saneamento Ambiental (CETESB) [3], and specifically the state of Sao Paulo, authorizes 2800 and 1500 kg ha−1 of Zn and Cu, respectively, as maximum loads that can be applied in a particular area. Moreover, the maximum soil TM content, when further applications of amendments to agricultural soils are prohibited, are 450 and 200 mg kg−1 for Zn and Cu, respectively [5]. For comparison, the European Union [1] allows the addition of 30 kg Zn ha−1 and 12 kg Cu ha−1 based on a 10-years average. The maximum allowed soil concentrations when further amendments are restricted are 150–300 mg kg−1 for Zn and 50–140 mg kg−1 for Cu, depending on soil pH. Brazil's federal legislation was expanded in the 1990s, based on the experiences of other countries. It was recognized that the total TM levels are not good environmental indicators for making decisions, and that the type of soil management needs to be taken into consideration. For example, the maximum TM levels established by the Brazilian legislation refer to any layer of the soil profile. In southern Brazil, about 50% of agricultural operations (almost 8.5 million hectares) are managed under no-tillage practices. Consequently, the organic waste applied on the soil surface is not incorporated deeper into the soil profile, thus enhancing a rapid increase of TM concentrations in the surface layer.

Soil water movement varies in time and space and determines to a large extent the spatial distribution of TMs in soils. Mathematical modeling of the fate of metals in soils in terms of their retention and transport is helpful to assess their environmental impacts [6]. Mathematical models, simulating water flow and transport and reactions of TMs in soils, provide additional information on risks of the transfer of TMs to the groundwater. Such transfer mainly depends on the amount of water moving through a particular type of soil and on the mobility of TMs in the soil solution. On the one hand, theoretical mathematical models require many parameters to describe complex processes of TMs reactivity with functional groups of the solid phase. On the other hand, empirical models often insufficiently consider physical and chemical soil characteristics or biological activity since such models merely rely on adsorption/desorption data. However, such adsorption/desorption processes are often influenced by various soil factors, which are difficult to measure or individually control.

The Hydrus software package [7] has been widely used to simulate the fate and transport of TMs in soils [8], [9], [10], [11], [12]. Hydrus includes mathematical modules that simulate variably-saturated water flow and solute transport in porous media. Recently, Mallmann et al. [13] demonstrated the effectiveness of the Hydrus two-site sorption sub-model [14] by simulating changes in Zn and Pb concentration profiles in metal contaminated soils over one century. Similar modeling by Rheinheimer et al. [15] predicted that Zn and Pb concentrations in the soil solution will not exceed the reference water quality values of the Council of the European Communities (CEC) [1] during the next 50 years. Additionally, Seuntjens [16] used Hydrus to simulate two remediation scenarios for a soil contaminated with cadmium (Cd). He concluded that Cd concentrations in the soil solution were reduced after adding an organic material and/or an acidity corrector to the soil. He also predicted a decreasing Cd loss from the soil. Moradi et al. [17] simulated Cd movement in a soil amended with a sewage sludge under an arid climate. While they noted that there is little risk of groundwater contamination by leached Cd, they observed an accumulation of TM in the soil surface layer, and an increased risk for TM absorption by plant roots and/or removal by surface runoff.

Here, we use Hydrus-2D to model the past and future movements of Zn and Cu in a Brazilian Alfisol, contaminated by repetitive applications of PS, and compare the obtained results with a non-amended soil. First, we simulate changes in Zn and Cu concentration profiles in the soil using known metal inputs via PS amendments during 8 years. We consider two hypotheses for interactions between the soil solid phase and the soil solution, i.e., either a complete instantaneous equilibrium or a two-site sorption model with both equilibrium and kinetic sorption. The model's validity is assessed by comparing simulated and measured field TM distributions in 2008. Second, we predict the movement of Zn and Cu, using the adopted hypothesis, for the next 50 years under two scenarios of discontinued and continued PS applications.

Section snippets

Experimental site, soil, and other characteristics

The study was conducted on experimental fields of the campus of the Federal University of Santa Maria in the state of Rio Grande do Sul in Brazil (29°42′52″S and 53°42′10″W, 90 m altitude) and involved repetitive applications of PS. Soils, classified as a Typic Hapludalf [18], are well drained, and show a strong vertical clay gradient in the profile. The parent material is upper Triassic sandstone, locally referred to as the Santa Maria Formation [19]. The soil mineralogical composition includes

Simulation of Zn and Cu transport in the soil between 2000 and 2008

Simulations with hypothesis A (100% instantaneous equilibrium) produced a strong Zn and Cu retention in the soil surface layer (0–5 cm), although increasing TM contents were observed in the field down to a depth of about 25 cm (Table 3). In particular, about 97% of added Cu remained in the top 0–5 cm soil layer. Large differences between simulated and measured TM concentrations clearly indicate that the model based on hypothesis A cannot describe observed field metal concentration profiles.

Conclusion

We used Hydrus-2D with a two-site sorption model with a reduced kinetic rate constant and with measured soil hydraulic characteristics to reproduce vertical distributions of Zn and Cu measured in an experimental plot soil profile after 8 years of repeated pig slurry applications. We considered the satisfactory correspondence between simulated and field-observed TM distributions to represent a direct model validation. We then used the validated model to predict Zn and Cu movements during the

Acknowledgements

F.J.K. Mallmann acknowledges CAPES for postgraduate scholarship. The authors thank Reimar Carlesso and Mirta Petry (Sistema Irriga®) for providing daily evapotranspiration and local atmospheric data. They express their special gratitude to Maria Alice Santanna for her relevant contributions to the discussion.

References (54)

  • F.X. Han et al.

    New approach to studies of heavy metal redistribution in soil

    Adv. Environ. Res.

    (2003)
  • O. Abollino et al.

    Distribution and mobility of metals in contaminated sites. Chemometric investigation of pollutant profiles

    Environ. Pollut.

    (2002)
  • CEC

    Council of the European Communities, Council Directive 86/278/EEC of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture

    Official J.

    (1986)
  • USEPA, United States Environmental Protection Agency, 40 CFR–Part 503 - Standards for the use and disposal of sewage...
  • CETESB, Companhia de Tecnologia de Saneamento Ambiental, Relatório de Estabelecimento de Valores Orientadores para...
  • CONAMA, Conselho Nacional do Meio Ambiente, Resolução no. 375/2006, de...
  • CETESB, Companhia de Tecnologia de Saneamento Ambiental, Decisão de diretoria No. 195-2005-E, de...
  • J. Šimůnek et al.

    Development and applications of the HYDRUS and STANMOD software packages, and related codes

    Vadose Zone J.

    (2008)
  • L. Bahaminyakamwe et al.

    Copper mobility in soils as affected by sewage sludge and low molecular weight organic acids

    Soil Sci.

    (2006)
  • F. Degryse et al.

    Mobility of Cd and Zn in polluted and unpolluted spodosols

    Eur. J. Soil Sci.

    (2006)
  • M.N. Ngoc et al.

    Simulation of retention and transport of copper, lead and zinc in a paddy soil of the Red River Delta Vietnam

    Agric. Ecosyst. Environ.

    (2009)
  • J.-H. Huang et al.

    Fluxes and budgets of Cd, Zn, Cu, Cr and Ni in a remote forested catchment in Germany

    Biogeochemistry

    (2001)
  • F.J.K. Mallmann et al.

    Using a two site-reactive model for simulating one century changes of Zn and Pb concentration profiles in soils affected by metallurgical fallout

    Environ. Pollut.

    (2012)
  • M.T.H. Van Genuchten et al.

    Two-site/two-region models for pesticide transport and degradation: theoretical development and analytical solutions

    Soil Sci. Soc. Am. J.

    (1989)
  • D. Rheinheimer dos Santos, P. Cambier, F.J.K. Mallmann, J. Labanowski, I. Lamy, D. Tessier, F. van Oort, Prospective...
  • P. Seuntjens

    Field-scale cadmium transport in a heterogeneous layered soil

    Water Air Soil Pollut.

    (2002)
  • Soil Survey Staff

    Keys to Soil Taxonomy

    (2003)
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