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Abstract
In this paper, the influence of metals (Cd, Pb, Cu, Co, Ni, Zn) on plants of
spring barley (Hordeum vulgare L.) was investigated in polluted sod podzolic
sandy loam on layered glacial sands and calcareous deep chernozem on loamy
loess soils. We propose to highlight the metals’ phytotoxicity with help of the
Phyto Maximum Allowable Concentration. The Phyto Maximum Allowable
Concentration is a permissible level of metals for plants in polluted soil and
represents the safe degree for plants in contaminated ecosystem. The Phyto
Maximum Allowable Concentration gives the possibility to estimate and to
forecast the danger of metals for plants as a biological object that plays a
very important role in the life of ecosystem. This approach may be applied for
another metals phytotoxicity assessment for other plants.
Keywords:Metals; Plants; Phyto Maximum Allowable Concentration;
Assessment, Pollution; Phytotoxicity
Introduction
Metals are significant environmental pollutants, and their toxicity is a
problem of increasing significance for ecological, evolutionary, nutritional
and environmental reasons Nagajyoti [1]; Bieby Voijant Tangahu [2]; Mamatha
[3]; Metals, such as cadmium, copper, lead, nickel, cobalt and mercury are
major environmental pollutants, particularly in areas with high anthropogenic
pressure. Metal accumulation in soils and plants is of concern in agricultural
production due to the adverse effects on food safety and marketability, crop
growth due to phytotoxicity, and environmental health of soil organisms. The
influence of plants and their metabolic activities affects the geological and
biological redistribution of heavy metals through pollution of the air, water
and soil Nagajyoti [1]; Gyuricza [4] Anthropogenic metals contamination of
ecosystems as a result of the application of industrial, transport, agrarian
and other technologies causes a damage of the functioning of plants as an
important component in ecosystem Bradl[5]; Alloway [6]; Kabata-Pendias [7]
Often plants are the main accumulator of metals in polluted ecosystem. In the
same time, plants play an important role in ecosystem as biomass producers and
as biodiversity creators Rombke [8]; Kabata-Pendias [7]; Sardar [9]. Usually
phytotoxicity is considered as a harmful influence of metal on plant growth and
development Kabata Pendias [7]; Nagajyoti [1]; Satpathy[10]; Gill [11] .
However, the setting of a safe level of toxicant for the plant is also very
important, because it can help to prevent and to control the negative effects
of metals in the ecosystem. Today a methodology that would determine the safe
concentration of metals directly for plants in the soil is absent. After all,
the existing standards for the content of metals in environmental objects are
sanitary-hygienic and focused just on human health Lewis [12]; Smirnov [13]; Warne
[14]. Determination of the metals safe level in the soil for plants can help to
objectively assess state of the ecosystem and prevent the metals dangerous
influence on plant Ryzhenko [15]. The Phyto Maximum Allowable Concentration
(PMAC) was suggested as safe level of metal in the soil for plants.
Materials and Methods
Spring barley (Hordeum vulgare L.) was selected as a model plant. Spring
barley (Hordeum vulgare L.) is one of the important cereals crop in Ukraine.
Mean standard deviations, variance, and minimum, maximum, standard errors were
calculated from at least three replicates. The experimental results were
interpreted using standard statistical methods. The soils of experimental pots
were: sod podzolic sandy loam on layered glacial sands (sod podzolic) and
calcareous deep chernozem on loamy loess (chernozem). Sod podzolic soil has the
following physic chemical characteristics: pHsalt 5,5; organic matter by Turin
0,87%, CEC 6,3mg eqv/100g. Chernozem soil has the following: pHsalt 6,2,
organic matter by Turin 2,89%, CEC 27,1mg eqv/100g. Background concentration of
metals in soil (1 M HCl, mg kg-1) was: Cd - 0,1; Pb - 0.3; Cu = 0.92; Zn - 2.4;
Ni - 1.1; Co-1,5 (sod podzolic); Cd = 0.11; Pb - 0.32; Cu - 2.6; Zn - 5.3; Ni -
2.3; Co - 2,5 (chernozem). Studied trace elements: Cd, Pb, Zn, Cu, Co, Ni were
applied separately in amount equal to the following concentration in the soils.
That amount corresponds with adopted in Ukraine Maximum Allowed
Concentration (MAC) in soil (Medvedev [16]. The following metals salts:
Pb(NO3)2, ZnSO4. H2O, CuSO4.7H2O,
CdSO4, NiSO4·6H2O, CoSO4·7H2O were used for the trace
elements application. The investigation was conducted in green house
conditions. Plants grew in plastic Mitcherlikh’s pots. Soil preparation, pots
filling, and trials were carried out in accordance with standard methodic
Dospekhov [17]; Medvedev [16]. The metals were added to soil during soil
preparation before filling the pots. Then, spring barley germinated seeds were
planted into the pots and, in the stage of 3 leaves, the recommended population
was established. The studied elements were extracted by 1 M HCl from the soils.
The method of HM determination was thin layer chromatography (TLC). Method
widely was used in our previous investigation and officially recognized in
Ukraine Kavetsky [18].
Results and Discussion
In this study, the algorithm of calculation of PMAC was proposed similar to
the existing approach of calculation of Maximum Allowable Toxic Concentration
(MATC) (equation 1) Rand [19]. In the toxicology practice, the scheme to
substance toxicity assessment using the LOEC and NOEC is quite effective and
widely used Smirnov [12]; Warne [13] Environment Canada. Guidance document on statistical
methods for Environmental Toxicity Tests [20]; Globally Harmonized System of
Classification and Labeling of Chemicals (GHS), fourth revised version, [21].
These indicators are used also for calculate the Maximum Allowable Toxic
Concentration (MATC) on behalf of assessing the toxicity of substances in the
aquatic environment. MATC is calculated by the formula Rand [19]:
MATC=√((NOEC)*(LOEC)) , (1)
where NOEC is No Observed Effect Concentration.
LOEC is Lowest Observed Effect Concentration.
We propose to determine the Phyto Maximum Allowable Concentration by the
formula:
PMAC=√(C_contr*〖PhLD〗_5 ) (2)
where Ccontr – background concentration (on the control variant of
experiment–without additional metal input);
The PhLD5 is phytotoxic dose 5% (PhLD5) caused reduction of 5% of initial
weight (height, length of root etc.).
In our opinion, 5% reduction of initial weight (height, length of root etc.)
is the minimal effect, which is similar to the LOEC shows the preliminary
changes in the productivity of the plant population. Moreover, the level of
significance of deviations, which are considered sufficient for ecological and
biological research at the level of 5% (p <0.05) was chosen. The algorithm
of obtaining the PhLD5 was represented in previous papers Ryzhenko [22]. Table
2 shows the values of PhLD5 and PMAC for all investigated metals, as well as
the background concentration in soil (0-20 centimeters). PMAC was obtained with
the help of equation 2. The PMAC for Cd in sod podzolic soil was calculated in this
way:
The lowest value of the PMAC had Cd, the highest value of the PMAC had Zn in
two studied soils. The chornozem soil ad higher values of the PMAC than Sod
podzolic soil. It could be explained by higher content of organic matter,
granulometric composition of soil and other properties of chornozem soil.
According to the value of PMAC, the metals can be ranked in the following
descending order: Zn>Сo>Cu>Ni>Pb>Cd. The PMAC could be used as
an environmental standard that regulate the safe level of pollutants in the
soil for plant [23-25].
Conclusion
As a result of this investigation, it was proposed to use the Phyto Maximum
Allowable Concentration as a permissible level for plants in soil in the
polluted ecosystem. The algorithm of calculation of Phyto Maximum Allowable
Concentration based on the approach of the existing calculation of Maximum
Allowable Toxic Concentration (MATC). The Phyto Maximum Allowable
Concentrations were obtained for Hordeum vulgare L. for all researched metals
in two soils (mg kg-1;1 N HCl): Cd–1.21; Cu – 7.60; Co–9.77; Zn – 30.77; Ni –
7.40; Pb – 7.48 (sod podzolic sandy loam on layered glacial sands), and Cd –
1.46; Cu – 13.10; Co–13.61; Zn– 44.90; Ni – 12.69; Pb –9,20 calcareous deep
chernozem on loamy loess). The Phyto Maximum Allowable Concentration gives the
possibility to set the permissible level of metal in soil for plant as a
biological organism, but not from the point of view of hygienic regulation. The
using of concept of Phyto Maximum Allowable Concentration may be suitable for
receiving a permissible level of metals in different soils for other plants in
polluted ecosystems. Phyto Maximum Allowable Concentration gives the
possibility to estimate the danger of metals directly for plants as a
biological object that playing a very important role in the life of ecosystem.
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