HEAVY METAL ION MOBILISATION WITH USE OF ASPERGILLUS SPECIES

 

Diana Sári* and László Vermes

St. István University, Gödöllő Faculty of Horticulture, Dept. Soil Science and Water Management

Email: dsari@omega.kee.hu

 

Abstract

 

Laboratory experiment was carried out in order to determine the effect of organic acids synthesized by Aspergillus species on mobility of heavy metal ions in contaminated soils. The experiment was performed as a part of a complex work to establish the usefulness of that Aspergillus species for ex situ remediation of highly polluted soils.

Soil samples originated from A and B-horizons of a cambisol (Gyöngyösoroszi, Hungary) and from A horizon of a chernozem soil (Dombóvár, Hungary). The fermented solutions contained Aspergillus foetidus or Aspergillus niger species.

The solutions were added to the soils in a column experiment in 6 parts and the different fractions were examined separately.  In the leachate Zn, Pb, Cd, Cr, Ni and Cu ion concentration were determined by Varian SpectrAA10 atomic adsorption spectrometer.

For presenting substance balance the soils were analyzed before and after the column study.

The variability in the agent conditions resulted high level of deviation in the experimental results therefore a statistical establishment is prepared to estimate the specific effect of fermented solution.

We suppose that the sulfide ores would dissolute by fermented solution, which contain reducing components. In Gyöngyösoroszi soil the HNO3 soluble amount of Ni, Pb and Cd and in the Dombóvár soil the HNO3 soluble amount of Cr were increased after the treatment with fermented solution. The Ni ion indicates any hardly solute iron sulfide existence in the soil and the Pb and Cd refer to galena or zinc blende content of soils. The Aspergillus niger solution dissolve higher amount of Zn and Cu ions from the soils despite of the higher pH of this fermented solution. In acid soils this is true also for the Cd accompanying the Zn.

Specific affect of Aspergillus niger was found for Zn, Cd and Ni ions and less for Cu ions. Aspergillus foetidus is specific for Zn.

 

Introduction

 

Laboratory experiment was carried out in order to determine the effect of organic acids synthesized by Aspergillus species on mobility of heavy metal ions in contaminated soils. The experiment was performed as a part of a complex study to establish the usefulness of that Aspergillus species for ex situ remediation of highly polluted soils.

 

 

Materials and methods

 

Soil samples

Soil samples are originated from A and B-horizons of a cambisol (Gyöngyösoroszi, Hungary) and from A horizon of a calcareous chernozem soil (Dombóvár, Hungary). These soils are contaminated with heavy metal containing heavy metal ore remains.

 

Fermented solutions

The fermented solutions obtained from Aspergillus foetidus or Aspergillus niger culture. The Aspergillus species are producing different kind of organic acids.

 

Column experiment

Columns of 2-cm diameters and 20 cm length were filled with the soil samples. Both of the fermented solution was added to each soil sample by 6 parts. 50 cm3 of fermented solution was used in one step. The leachates were collected and analyzed separately.

 

Analyzes

After measuring the weight of the collected leachates these were evaporated with 2-cm3 5:2 HNO3/H2O2 mixture. The residue was dissolute in 50 cm3 2 M HNO3.

0.2 g of the original and treated soil samples were inserted in a platinum pot and digested with 5 cm3 5:2 HNO3/H2  mixture and evaporated. The residue was dissolute in 50 cm3 2 M HNO3.

Zn, Pb, Cd, Cr, Ni and Cu ions were determined in the solutions by Varian SpectrAA Atomic Adsorption Spectrophotometer in graphite tube. Additionally Fe, Mn, Mg and Ca ions were determined in flame.

 

Result and Discussion

 

Soil Samples

In Gyöngyösoroszi soil A horizon the HNO3 soluble amount of Ni and Pb ions and in the B horizon even the amount of Cd ions were increased after the treatment with fermented solution. In the Dombóvár soil the HNO3 soluble amount of Cr ions were increased.

The HNO3 cannot dissolve the mine ores. The experiment  performed by Mehra and Jackson showed that iron sulfide ores like pyrite and calcopyrite can be dissolute in a reductive solution containing citric acid. We can suppose that other sulfide ores like galena and zinc blende would be dissolute by the organic acids synthesized by Aspergillus species. That is according with the increasing soluble heavy metal concentration in soil samples after the treatment with fermented solution.

 

Table 1

The heavy metal amount dissolute by fermented solutions, % refers to the total HNO3 soluble ion content

soil                                          fermented                    Cd       Cr        Ni        Pb        Zn        Cu

                                                solution                                                    %

Dombóvár                               Asp. niger                   30        76        18        62        18        78

Dombóvár                               Asp.foetidus                66        69        27        90        17        66

Gyöngyösoroszi, A horizon      Asp. niger                   85        78        31        67        76        88

Gyöngyösoroszi, A horizon      Asp.foetidus                78        94        22        64        67        75

Gyöngyösoroszi, B horizon      Asp. niger                   78        68        8          70        39        47

Gyöngyösoroszi, B horizon      Asp.foetidus                71        82        10        76        20        27       

 

The increased amount of soluble Ni and Cr refer to any hardly soluble iron sulfide (pyrite) and the increased amount of Pb and Cd refer to galena or zinc blende.

The experiment showed that the fermented solutions could be used to mobilize the hardly soluble ores.

Considering the total amount of soluble ions we can suppose that Gyöngyösoroszi soils are containing high amount of Zn and Pb originated from galena and zinc blende and Dombóvár soil contain high amount of Cu and Cr refer to non-ferrous metal ores.

 

Table 2

Average amount of dissolved heavy metal in the fermented solutions

soil                                          fermented                    Cd       Cr        Ni        Pb        Zn        Cu

                                                solution                                                   ppm

Dombóvár                               Asp. niger                   0.01     6.2       0.9       0.68     6.6       11

Dombóvár                               Asp.foetidus                0.01     6.8       1.9       1.7       2.3       7.9

Gyöngyösoroszi, A horizon      Asp. niger                   0.45     2.1       2.6       4.8       53        1.8

Gyöngyösoroszi, A horizon      Asp.foetidus                0.20     2.2       2.8       5.2       49        1.7

Gyöngyösoroszi, B horizon      Asp. niger                   0.37     2.0       2.1       3.3       52        0.9

Gyöngyösoroszi, B horizon      Asp.foetidus                0.23     1.9       2.4       2.6       46        0.6

 

The Cr ion was easier mobilized in the calcareous Dombóvár soils than in the other soils. It shows the oxidized form of Cr (CrVI). The Zn ore dissolution accompanied by Cd.

 

Fermented solutions

The effect of fermented solution based on two features: the organic acid content and the pH. The total organic acid content was the same in the two type of fermented solution, but the acid composition and the pH were different. The colinearity of these affects recommended the use of multivariate statistical evaluation. Multivariate ANOVA and cluster analysis was applied.

The Aspergillus niger solution in each case dissolute more Zn, Mn and Cu than the Aspergillus foetidus solution independently the higher pH of the Aspergillus niger solution. The difference in solubility of these metal ions by Aspergillus foetidus and Aspergillus niger was lower in the calcareous soil. In Gyöngyösoroszi soil that is true for the Cd ion too, probably because the Cd accompany the Zn originated from zinc blende.

Strong complex formation was detected for Zn, Cd and Ni ions and less for Cu ion in Aspergillus niger solution and for Zn in Aspergillus foetidus solution.

 

Aspergillus niger species dendogram

* * * * * * H I E R A R C H I C A L  C L U S T E R   A N A L Y S I S * * * * * *

 Dendrogram using Average Linkage (Between Groups)

 

                         Rescaled Distance Cluster Combine

 

    C A S E      0         5        10        15        20        25

  Label     Num  +---------+---------+---------+---------+---------+

 

  CD          1   -+---+

  ZN          6   -+   +---+

  SOIL        7   -----+   +-------------+

  NI          4   ---+-----+             +-------------------------+

  CU          3   ---+                   I                         I

  PB          5   -------------+---------+                         I

  PH          9   -------------+                                   I

  CR          2   -------------------------------------------------+

 

Aspergillus foetidus species dendogram

* * * * * * H I E R A R C H I C A L  C L U S T E R   A N A L Y S I S * * * * * *

 

 

 Dendrogram using Average Linkage (Between Groups)

 

                         Rescaled Distance Cluster Combine

 

    C A S E      0         5        10        15        20        25

  Label     Num  +---------+---------+---------+---------+---------+

 

  CR          2   -+---------------+

  NI          4   -+               +-----------------+

  PH          9   -----------------+                 +-------------+

  PB          5   -----------------------------------+             I

  CD          1   -+-----------------+                             I

  ZN          6   -+                 +-----+                       I

  SOIL        7   -------------------+     +-----------------------+

  CU          3   -------------------+-----+

 

 

 

High Ca, Mg, Fe and Mn leaching was experienced at each soils and leachate. Based on the statistical evaluation we can suppose that if the Ca ions coming from basic (carbonate) components the Ni and Zn mobilization was inhibited.

 

Table3

One way ANOVA analysis by Ca and the pH

Ion       F by Ca           sig. by Ca        F by pH           sig. by pH

Cd       0.209               0.605               0.270               0.605

Cr        0.672               0.851               0.482               0.490

Cu       1.058               0.486               2.106               0.472

Ni        13.920             0.000               0.522               0.151

Pb        0.897               0.635               0.508               0.479

Zn        3.752               0.006               0.750               0.390

 

Fractions

Decreasing of the concentration of the soluble Zn and Cd was experimented in the consequently fractions of Aspergillus foetidus solution.

Also decreased the Pb and Cd concentration in Aspergillus niger.

The Pb ion concentration significantly increased in Aspergillus foetidus solution.

Other trend was not found.

 

Conclusion

 

The Aspergillus species are useful for ex situ remediation of high polluted soils, but it should be taken into consideration the leaching of Ca, Fe, Mn and other nutrients and the final pH of the remedied soil.