The Effect of Both Different Light Conditions and the pH Value on the Capacity of Salvinia minima Baker for Removing Cadmium, Lead and Chromium

Abstract

SummarySalvinia minima is a tropical aquatic floating plant, which has become a weed in the tropical and subtropical regions due to its high productivity and tolerance to a wide range of temperatures. The objective of this work was to evaluate the effect of two different light conditions (extreme light limiting conditions and non-limiting light conditions) and the pH (at different values, depending on the metal) on the capacity of Salvinia minima BAKER for accumulating and removing Cd (II), Pb (II) and Cr (VI) from aqueous solutions. The experimental units were exposed either to light and temperature "controlled" conditions (60 µmol/m 2 s and 25°C) or to the outdoor conditions of the City of Xalapa, Veracruz (subtropical region), during the period of April through June. It was found that under "controlled" conditions, the concentration of cadmium in the whole plant tissue was 10,930 mg/kg and the bioconcentration factor (BCF) was 2,718. In the case of "outdoor" conditions (1,044 µmol/m 2 s), the Cd concentration in the tissue reached 11,262 mg/kg and the BCF 2,694, for the same metal initial concentration (4 ± 0.18 mg/l). Lead bioaccumulation was also high for both light conditions. Under "controlled" conditions, the metal concentration in the plants supplied with 3.0 ± 0.27 mg/l was 9,780.0 mg/kg and the BCF was 3,304. With an average light intensity of 336 µmol/m 2 s, lead concentration reached 7,705 and the BCF was 2,822. Under "controlled" conditions, a bioaccumulation of Cr (VI) of 3,111 mg/kg at an initial concentration of 4.0 ± 0.03 mg/l and a corresponding BCF of 784 were attained. The pH had a significant influence on the capacity of Salvinia to remove Cd (II). At an initial concentration of 4 mg/l, this effect was highest at pH 7.0 (84.58 ± 1.43%) under "controlled" conditions. However, under outdoor conditions, the pH did not exert a significant influence on the removal capacity of Salvinia for Cd (II), being in the range of 81.00 to 82.59% for the range of pH from 5.0 to 8.0. Cadmium removal by Salvinia minima occurred very quickly during the first 5 hours of incubation, regardless of the initial Cd (II) concentration or the light conditions, indicating the possible occurrence of adsorption to the root's surface. Lead removal by S. minima was independent of the pH in the range of pH 3.0 to 5.0, but it was affected by the light intensity. A maximum removal of 97.44% was achieved at pH 4.0; under outdoor conditions at an initial concentration of 3 mg Pb (II)/l. The removal percentage of Cr (VI) at pH 3.0 to 5.0 was also very limited.

Copper Removal Efficiency in a Surface Water and Compartmentalization in the Floating Fern Salvinia minima

“…Therefore, plants may have possibly been in contact with a higher concentration of copper in its free ionic form during the first minutes to hours of the bioassay. Studies on the kinetics of heavy metals uptake by aquatic plants have revealed an initial phase of fast metal removal followed by a lineal slower phase [23] and, in accordance with this, [4] found that S. minima lead and cadmium uptake was 55 % and 60 %, respectively, during the first 4 to 6 hours of their bioassay. May S. minima's copper removal uptake been higher without metal precipitation?…”

“…In the control group, metal concentration was below the method detection limit. During the first few hours from the beginning of the bioassay, water in treatments T 4 and T 5 turned light blue. This indicated copper precipitation as a colloide.…”

“…Salvinia minima (Baker, 1886) is an aquatic free floating fern with a wide distribution in tropical and subtropical areas which has shown a large capacity to accumulate lead and cadmium [4]. In addition, S. minima has a fast growing rate, dense pseudoroots system and is tolerant to pollution, favorable properties in species to be used in phytoremediation.…”

The use of Salvinia auriculata as a bioindicator in aquatic ecosystems: biomass and structure dependent on the cadmium concentration

“…The ramets were cultivated in a greenhouse for 5 days, in pots with 25 L of Hogland's nutrient solution with pH between 6.5 and 7, with 1/5 of the original ionic strength (Hoagland and Arnon, 1950). The pH value was determined according to Olguín et al (2002). During the experimental period the average temperature was 21.9 °C.…”

Arsenic Tolerating Plants from Mine Sites and Hot Springs in the Semi‐Arid Region of Chihuahua, Mexico

“…Plants must have a great capacity to tolerate and transform to less toxic forms and/or accumulate the pollutant to be removed [6,7]. Wastewater treatment by means of phytoremediation involves either the use of aquatic floating plants in ponds [8,9] or the use of emergent aquatic plants in constructed wetlands [10]. Constructed wetlands have been sporadically applied for the treatment of acid drainages in mines, as well as in the minimisation and control of water pollution in general.…”