Phytoremediation Assessment of Mentha crispa L. in Zinc-Contaminated Oxisols: Tolerance and Accumulation Dynamics

Abstract

This study assessed the phytoremediation potential of Mentha crispa L. grown in Oxisol contaminated with varying zinc concentrations. Mentha crispa was cultivated in soil with Zn levels from 0 to 1920 mg kg^-1. Growth parameters, Zn concentrations in plant parts, bioaccumulation, and translocation factors were measured. The results revealed that Mentha crispa exhibited a high tolerance to elevated Zn levels, accumulating up to 1875 mg kg^-1 in its leaves and 2047 mg kg^-1 in its roots. The bioaccumulation factor ranged from 1.2 to 4.5, and the translocation factor ranged from 1.2 to 2.7, indicating effective Zn uptake and distribution within the plant. The metal extraction rates varied across treatments, with the estimated time for Zn removal ranging from 12 to 34 years. These findings underscore the suitability of Mentha crispa as a candidate for phytoremediation of Zn-contaminated tropical soils, particularly Oxisols, which are characterized by high metal adsorption capacity. Additionally, its ability to produce essential oils enhances its viability for integrated environmental and economic applications.

Keywords: bioaccumulation factor; growth analysis; metal extraction rate; tolerance; translocation factor.

Figure 1

Distribution of aqueous Zn species as a function of pH, considering the Zn-acetate salt, using Visual MINTEQ modeling.

Figure 2

Langmuir and Freundlich’s isotherms applied to Zn adsorption in Oxisol.

Figure 3

(A) Mentha crispa after 7, 15, 45, and 90 days of cultivation in Zn-contaminated soil with different concentrations (T₁ to T₇) and the control (T₀), with one seedling per pot. (B) Image of the cleaned and dried roots after 105 days of growth, with treatments ranging from T₁ to T₇ and T₀ as the control.

Figure 4

Growth of Mentha crispa cultivated for 105 days in Zn-contaminated soil, showing the average number of shoots (A), leaves (B), and height (C) for the applied treatments (T₁ to T₇) with T₀ as the control. (D) Mean and standard deviation values for Zn concentration (mg kg^–1, dry weight) in the roots, stems, and leaves under the same treatments. Equal letters indicate that the values are not significantly different between the treatments (Tukey’s Test, p < 0.05).

Figure 5

Correlation of the parameters: height, shoots, and leaves as a function of the 105-day cultivation period through Canonical Discriminant Analysis (Wilk’s Lambda = 0.19; F = 0.3491; p < 0.0001).

Figure 6

Scores of axes 1 and 2 of the Canonical Discriminant Analysis (CDA) for the growth variables responses of Mentha crispa (plant height, number of shoots and leaves) in the different Zn concentrations in the Oxisol (T₁ to T₇ treatments, and T₀ as control). Values in parentheses correspond to the standardized coefficients of plant growth variables for the respective axes of the CDA (Wilk’s Lambda = 0.68; F = 6.03; p < 0.0001).

Figure 7

Scores of axes 1 and 2 of the canonical discriminant analysis for the Zn accumulation responses in the parts of the Mentha crispa (roots, stems, and leaves) in the different Zn concentrations in the Oxisol (T₁ to T₇ and T₀ as control). Values in parentheses correspond to the standardized coefficients of body variables for the respective axes of the CDA. (Wilk’s lambda = 0.000730; F = 22.06; ρ < 0.001).