1Laboratory of Biochemistry and Environmental Toxicology, Higher Institute of Agronomy Chott-Meriem
2Regional Research Centre in Horticulture and Organic Agriculture, Chott-Mariem, Tunisia
3Laboratory of Biochemistry and Environmental Toxicology, Higher Institute of Agronomy Chott-Meriem, Tunisia
4Soil Analysis Laboratory, Supporting Station to the Nebhana, Monastir, Tunisia
5Laboratory of Biochemistry and Environmental Toxicology, Higher Institute of Agronomy Chott-Meriem
Submission: September 09, 2019; Published: October 15, 2019
*Corresponding author: Iteb Boughattas, Laboratory of Biochemistry and Environmental Toxicology, Higher Institute of Agronomy Chott-Meriem, Tunisia
How to cite this article: Iteb Boughattas, Sabrine Hattab, Marouane Mkhinini, Hssin Rochdi and Mohamed Banni. Dynamic of Organic Matter and AvailableNutrients in Heavy Metal Contaminated Soil Under the Effect of Eisenia Andrei Earthworms. Int J Environ Sci Nat Res. 2019; 22(1): 556077. DOI: 10.19080/IJESNR.2019.22.556077
Heavy metal contamination is an important environmental problem which couldaffect the durability and fertility of soils. For the enhancement of soil properties in mine soils, many technologies can be used. In this study, we have assessed the efficacity of vermeremdiation (The use of earthworms for remediation). In this context, this study investigate the effect of earthworms Eisneia andrei on physicochmical properties of soils. For this purpose, six polymetllaic contaminated soils from Jebel Ressass mine (ranged from the most contamianted one A to control one F) were incubated during 14, 28 & 60 days in presence and absence of earthworms Eisenia Andrei. Organic matter, available phosphorous, potassium and magnesium and active limestone were assessed in each incubation point. Our results schowed that earthworms increased organic matter content especially for soil A. Also, a rise was observed in the mineral content and active limestone within 14 days of addition. This cork showed the efficiency of earthworms on the amelioration of chemical properties of soils from mine site
Keywords: Heavy metal Mine soil Earthworms Chemical properties Soil
Heavy metals are considered as a natural constituent of the earth crust. Their sources in the environment can originate from natural and anthropogenic activities. Anthropogenic activities such as mining, smelting, industrial, and agricultural use increase the abundance of heavy metals in the environment [1-4]. They can be toxic to living organisms at very low levels of exposure. They did not only lead to soil contamination, but also affect food production, quality and safety [5-6].
Indeed, soil pollution by persistent metals concerns large areas at the global scale, particularly in industrial and mining environments . Indeed, numerous industrial or mining sites, often abandoned, are now in urban areas and are therefore likely to cause environmental and health risks to surrounding populations [8-10]. These sites are sources of fine particles enriched with pollutants leading to contamination of soils and plants [11-13].
In Tunisia, heavy metal pollution presents a critical problem affecting the ecosystem functioning and soil fertility. Jebel
Ressas mining activities started in 1892 and was used for the extraction of lead and zinc. The activity was intense for over forty years and was interrupted in 1959. Over decades, mining activities have accumulated large wastes which covered vast hectares of the agricultural farmlands and had deteriorated the quality and fertility of soils [14-15]. Up to now, few studies have been conducted on this site in order to rehabilitate its biological activity [16-17].
In this context and for the remediation of heavy metal soils, many strategies of decontamination were proposed. However, the biological methods play a crucial role in thoroughly cleaning up the contaminants in soils . For that, we use bioremediation for the stabilization/mineralization of heavy metals to reduce their bioavailability. The biological agents can be simple organisms (bacteria, plants, etc.). Compared to physicochemical methods conventionally used to decontaminate soils but which lead to a sharp decline in fertility and productivity, bioremediation is considered as a friendly environmental technology.
Besides, earthworms are ecosystem engineers, driving soil
structure and nutrient dynamics and their importance in soil
ecosystems has long been recognized. By feeding on litter and soil,
burrowing and releasing casts, earthworms change soil porosity,
bulk density, water infiltration, nutrient mineralization, gas
emissions, organic carbon stabilization and plant productivity
[19-22]. Moreover, in many studies, earthworms had been
proposed as actors for soil bioremediation, denominated Verme
remediation [23-24]. Their mechanisms for soil detoxification
are multiples. Earthworms could influence metal bioavailability
in soils through the mixing and comminution of soil particles and
by the humic materials and detritus contained in the earthworm
gut [25-26]. Moreover, earthworms could have direct effect on
heavy metals via uptaking it into their tissue, which was proved
by several studies [27-29] The other mechanism was the process
of mineralization and humification under the interaction
between earthworms and microorganisms, which could also
affect heavy metal transformation in soils [30-32].
For this purpose, we aimed in this present work to assess
if earthworms can change physicochemical properties of soil
originated from mine site. The final objective is to ameliorate
soil fertility in heavy metal contaminated soils.
The present work was conducted on Jebel Ressass mining.
Soils chosen in this work are characterized by a gradient of
heavy metal concentration [Table 1]. They ranged from the most
contaminated one (A) to the less contaminated one (F) constating
the site control. Soils from each site were sampled from a depth
of 30cm. Then, they were homogenized and transferred in the
laboratory. Soils were air-dried and sieved through a 2mm
screen and they were conserved until use.
Mature earthworms (with clitellum two months adult) of
the species E. Andrei were obtained from a local synchronized
culture in our laboratory and weighed individually (average
earthworm weight 500mg).
The experimental design was conducted as a completely
randomized factorial design with three factors. The first factor
is the level of contamination constituting by the six soils, the
second factor is the period of incubation: 14, 28&60 days and
the third factor had two levels (introduction or not of E. Andrei).
Three replicates per treatment were carried out, making a total
of 108pots. The experience was undertaken under controlled
conditions. One kilogram of dried and sieved (<2mm) soil was
placed in polyethylene pots. Twenty mature earthworms were
randomly placed in each pot. The half of pots being without
earthworms. Soil moisture was maintained at 60% of water
holding capacity using distilled water and temperature at 25°C.
This was maintained through the experience. Each pot was
covered with fine nylon to prevent soil loss and stop earthworm
escape. At the end of the exposure period, soils (three replicates
per treatment) were conserved at ambient temperature until
The same set of pulverized soil samples were analyzed
using an automated elemental analyzer to determine the total
C content. As the soil contains no inorganic carbon, the total
carbon estimated is OC itself. The soil samples were weighed
and encapsulated in tin foils and were introduced to the furnace
at 95 OC of the elemental analyser (Leco Corporation, USA,
Truspec CN) and flushed with oxygen for complete combustion.
The carbon containing compounds were oxidized to CO2 and
separated from all other oxides and lead to the infra-red gas
analyser for estimation. The instrument system was ABRAHAM
49 calibrated with soil standards supplied by Leco Corporation,
USA each time the estimations was carried out.
Plant available phosphorous (P) and potassium (K) were
determined by calciumacetate-lactate (CAL) extraction (ÖNORM
The R software was used for all the statistical analysis in this
paper. The normality of the distribution was carried out using
the Shapiro-Wilk test. For multiple comparisons, a parametric
one-way analysis of variance (ANOVA) was performed with
Tukey’s test. The student test was used to compare the soilenzymatic activities in the presence or absence of earthworms.
To compare the evolution of physicochemical properties of soils,
principal component analyses (PCAs) were performed using the
R software and the package ADE4TkGUI.
The organic matter content in Jebel Ressass soils has
changed significantly following the incorporation of Eisenia
andrei earthworms. Indeed, it increased only in the case of soil
A where means raised from 1.7% ±0.14 initially to 2.06% ±0.05
and 1.936% ±0.09, respectively after 28 & 60 days of incubation.
In the other soils, despite the increase noted after 14 days for
soils B and D and after 28 days for soils C and E, the content of
organic matter decreased after 60 days of incubation. In soil F,
SOM decreased by a range of 40%, which represents the largest
reduction comparing to all soils. Moreover, in comparison to
soils incubated without earthworms, the main difference was
observed in soils A and E after 30 days [Figure 1].
The incorporation of Eisenia Andrei worms into the six soils
of Jebel Ressass had provoqued changes in available phosphorus
content [Figure 2]. These changes had the same trend in all soils,
except for the control soil F. The results showed an increase in
the first two points of the kinetics (14 days for soils A, B, D and
E and 28days for soil C) followed by a crucial decrease after
60 days of incubation. In contrast, the available phosphorus
content in the control soil (F) decreased at the different points
of the kinetics. In addition, the effect of earthworms was mainly
observed in soils A, D and C where the P2O5 content was twice
more important in soils with earthworms compared to control
soils, successively after 14 days. incubation for the first two soils
and 28 days for the third soil.
The assimilable potassium content K2O changed in Jebel
Ressass soils [Figure 3] under the effect of earthworms Eisenia
Andrei. Indeed, the trend observed in soils B, C, D, E & F consists
of an increase firstly followed by a decrease after 60 days of
incubation. The largest increases were observed in soils D and F
with values of 402.04 ±7.54&446 ±4 ppm, respectively after 28
and 14 days for both soils. Soil A is the only one where the K2O
content didn’t increase after animals’ incorporation. In addition,
the earthworm effect was most observed in soils A, D, E and F
where the K2O content was significantly higher compared to
control soils (without earthworms). On the other hand, soil E
had the highest levels of K2O in all kinetic points.
Incorporation of E. Andrei earthworms into Jebel Ressass
soils affected available magnesium levels [Figure 4]. Results
showed that soils A and B had the same pattern of response
which is demonstrated by an increase after 14 days of incubation
followed by a decrease which leads to a lower content than the
initial one (0 day) for soil B. Magnesium content in soils C, D, E
had changed throughout the kinetics in a similar way. Indeed, a
decrease was noted after 14 days of incubation followed by an
increase reaching the maximum level observed for these soils
after 30 days. However, after 60 days of incubation, a decrease
was observed for the magnesium content of these soils. On the
other hand, in the control soil, a decrease in the Mg2+ content
was observed throughout the kinetics points. Despite this
decrease, the content remains higher than that of the others.
The most important change, observed under the effect of the
earthworms Eisenia Andrei, was noted in the soil D after 28 days
of incubation where the Mg2+ content was twice as great in the
soils containing earthworms by compared to controlled soils
The active limestone content has changed following the
incorporation of earthworms into Jebel Ressass soils [Figure
5]. These changes were mainly observed in soils B, C, D and E
where the content is 1.5 times higher in soils with earthworms
compared to control soils (without earthworms). On the other
hand, in soils A, B, C and D an increase in the concentration of
active limestone was observed and the maximum peak was
noted for soils A and C after 14 day of animal incorporation and
in soils B and D after 28 days. However, in these soils the active
limestone content decreased after 60 days in except of soil D. In
the least contaminated soils E and F, a decrease according to the
different incubation times was observed.
The evolution of physico-chemical properties of soil after 14,
28 and 60 days of Eisenia andrei addition is represented in Figure
6. PCA represented in Figure 6(a) illustrates change in physicochemical
parameters after 14 days of incubation. Axis 1 which
represent 37,02% of variability sepparate soil A and B from E
and F one. Axis 2 presenting 25,19 % of variability differenciates
soil A from C. Results schowed a change adter erathworms
addition, however, this effect was espceillay observed in soils A,
B, C and D.
After 28 days of incubation, the axes 1 and 2 of PCA [Figure
6(b)] present respectively 24.50 and 36, 30% of the total
variance. The first axis differentiates soils A and B from E and
F one. The second axis separates C from soils D, E and F. The
PCA showed a change in physico-chemical parameters under
the effect of earthworms in all soils, except in the case of soil D.
However, the most significant variation was noted in the most
polluted soils A, B and C.
After 60 days of incubation (figure 6(c)), the axes 1 & 2 of the
PCA represent respectively 26,18 and 34% of the total variance.
The first axis differentiates soils A and B from soils E and F. The
second axis separates soil E from C one. The PCA demonstrates
a change in physicochemical parameters, in the presence of
earthworms in all soils. However, the most important changes
was observed in soils A, B, C and D.
Beneficial roles of earthworms on soil fertility, nutrient
cycling and plant growth have been commonly observed.
However, few studies have focused on this effect in heavy
metal polluted soils. In this study, soils originated form mine
soils, Jebel Ressass, were incubated with earthworms EiseniaAndrei in view of assessing its effect on soil chemical fertility.
Our results demonstrated firstly an important increase on
organic matter in soil A which is the most contaminated one,
especially after 60 days of incubation. We can then hypothesize
then that earthworms in mine soils require an acclimation
period before starting to produce effects. Moreover, such results
create interesting perspectives on the use of earthworms in
the rehabilitation of mining cuttings. However, after 60 days of
incubation, organic matter decreased in the other soils under
the effect of earthworms. This result is consistent with the work
of which demonstrated the important role of the digestive tract
of earthworms in the decomposition of organic matter. Indeed,
earthworms feed on organic matter, break it down and release
the minerals to be available to plants. Consequently, organic
matter content decrease. However, this result is contradictory
with the work of which observed an increase in organic matter
content under the effect of earthworms in a Pb artificially
About the availability of nutrients P205, K20 & Mg0, our
results demonstrated that earthworms burrowing earthworms
increased the availability of nutrients in the first point of
incubation and secondary decreased it after 60 days of
incubation. Here, two assumptions can explain this result.
First, when worms are introduced, these latter degrade organic
matter and release nutrients, leading to an increase on their
bioavailability. After 60 days of incubation, the organic matter
content decreased causing the reduction of the bioavailability of
nutrients. Second, the intensity of organic matter degradation
and the release of nutrients are modified by change on the
structure of soil bacterial communities after earthworm’s
addition. This was demonstrated in a previous work. Therefore,
a change in the structure of soil bacterial communities will
induce variations in the mode of digestion of organic matter.
On the other hand, the positive effect of worms on soil
chemical fertility, specifically the increase in bioavailability
of nutrients has been widely demonstrated. However, very
few studies have investigated the effect of earthworms on
nutrient availability for soils contaminated with ETMs. In this
context showed, in the case of soils contaminated with Pb, that
Pontoscolex corethrurus increased the bioavailability of the
three major elements N, P and K. Earthworms can ameliorate
chemical fertility for soils by burrowing and casting, with the
formation of aggregates allowing easy penetration of water and
air. Also, earthworm activity modifies soil pH, a key chemical
factor affecting bioavailability of nutrient elements and heavy
metals in soils. Another explication for variation on nutrients
availability can be the change observed on soil enzymes activities
under the effect of earthworms. Indeed, soil enzymes constitute
the principal key in C, N and P cycling. In previous study, Eisenia
Andrei had increase enzymes activities in soils. These results can
generate an important change on chemical properties of soils.
Lessons learnt from this study implicate that earthworms
may be applied for soil management. Further, earthworms canbe used in bioremediation of soils contaminated by various
pollutant such as heavy metals.