Abstract
The occurrence of heavy metals in industrial wastewater is unanimously considered a major concern since these pollutants cannot be chemically or biologically degraded and therefore have long residence times. Phytoremediation is one of the most widespread biotechnological applications worldwide, which consists in the use of plants to adsorb or accumulate a broad range of inorganic and organic contaminants from water, air, and soil. To improve the cost-effectiveness and sustainability of phytoremediation-based wastewater treatment systems, it is essential to use plants that are not only efficient in pollutants removal, but also abundant and easily accessible at the target site, requiring no-special culture conditions. In this study, we have evaluated the capacity of naturally-occurring aquatic macrophytes of the genus Salvinia (classified as Salvinia biloba) to phytoremediate water artificially contaminated with cadmium (Cd), copper (Cu), lead (Pb), or zinc (Zn) at equal molar concentrations (50 ± 2 and 100 ± 1 µM), during 48 h. Additionally, photosynthetic and antioxidant pigments (carotenoids, chlorophylls, anthocyanins, and flavonoids), and soluble carbohydrate content was also measured in floating leaves of Salvinia specimens to appraise heavy metals phytotoxicity. Elemental analyses to plant tissue indicate that S. biloba was able to bioconcentrate all four metals analyzed, albeit with different degrees of affinity. In addition, the mechanisms of uptake and detoxification were dissimilar for each ion, resulting in greater removal of Cu and Pb (≥96%, at both concentrations), in comparison to Cd (79 ± 4% and 56 ± 2% for 50 ± 2 and 100 ± 1 µM, respectively) and Zn (77 ± 5% and 70 ± 4% for 50 ± 2 and 100 ± 1 µM, respectively). Accordingly, the assessment of the selected physiological parameters in floating leaves suggests that different response mechanisms are triggered by each metal in S. biloba to counteract the corresponding toxicological stress.
Highlights
The rapid growth of industrialization has led to increasing environmental challenges on a global scale
Similar patterns have been described by other authors for the removal of several metal ions using a wide variety of aquatic macrophytes, including S. biloba [12,14,15,18]
The non-linear kinetics of Cd, Cu, Pb, and Zn elimination from the water column observed in Figure 1, suggests that S. biloba utilizes various mechanisms for the removal of these cations
Summary
The rapid growth of industrialization has led to increasing environmental challenges on a global scale. One such example is water contamination with heavy metals, which is widely considered a major threat to the environment and human health. Arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) are among the most frequent water contaminants [1]. The occurrence of these metal(loids) in industrial wastewater is unanimously regarded as a serious concern since these pollutants cannot be chemically or biologically degraded and have long residence times [2]. Several physicochemical technologies are usually employed to clean metal-polluted waters, many of these solutions are technically infeasible, expensive, environmentally hazardous, and/or far away from the desired performance [3,4]
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