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BY 4.0 license Open Access Published by De Gruyter Open Access October 28, 2022

Lead and cadmium removal with native yeast from coastal wetlands

Narda Fajardo Vidal EMAIL logo and Jorge Wong Dávila
From the journal Open Chemistry

Abstract

Water bodies affected by heavy metals have been characterized in some natural ecosystems such as coastal wetlands in Peru. For this reason, in the present study, the determination of heavy metals lead (Pb), cadmium (Cd), and others was carried out in the water bodies of the Regional Conservation Area (RCA) Wetlands of Ventanilla using the Induction Coupled Plasma method. Water samples were collected at the six most critical stations for Pb and Cd, for the isolation of lead-tolerant microorganisms in 2022 with the aim of evaluating native microorganisms with removal potential of Pb and Cd. Yeasts such as Candida guilliermondii, Candida famata, Cryptococcus laurentii, Cryptococcus humicola, and Rhodotorula mucilaginosa with tolerance to high concentrations of Pb were isolated. The yeast with the best Pb tolerance result was Candida guilliermondii isolated from groundwater (piezometer sampling J1); Pb sorption was conducted with active yeast (living biomass), whereas both Pb and Cd sorption were conducted with inactive yeast (dead biomass). The results were compared with those of a reference standard yeast strain Saccharomyces cerevisiae: the native yeast proved to have optimum behavior for the process.

1 Introduction

Wetlands are highly productive ecosystems that provide a number of services of significant value to mankind. Flood control, groundwater replenishment, sediment retention, water purification, recreation, as well as climate change mitigation and adaptation, are just a few of the many valuable ecosystem services that wetlands provide [1].

Ecosystem services are natural assets produced by the environment and utilized by humans such as clean air, water, food, and materials and contribute to social and cultural well-being [2].

In developing countries like those in Latin America, the conservation of ecosystems is a critical issue. In Peru, the Regional Conservation Area (RCA) Wetlands of Ventanilla (located in the Callao Region) is one of many regional habitat conservation systems protected by the Peruvian Government through the Natural Resources and Environmental Management Office.

One of the problems faced by the RCA Wetlands of Ventanilla is the accumulation of heavy metals, particularly lead (Pb), and cadmium (Cd), in its water bodies; these metals can bioaccumulate in fish and affect birds through the food chain. In addition to these metals, there would be other sources of contamination in these wetlands, such as poorly disposed mining tailings deposits in the buffer zone of the RCA Wetlands of Ventanilla.

On the other hand, it is known that among the separation processes for the potential removal of heavy metals from water, adsorption/biosorption could represent a technically and economically feasible mechanism for the respective decontamination [3,4]. Moreover, several studies have shown that the structural matrix of particular biomass sources, including biomass from microorganisms, can translate into efficient systems for sorption of heavy metals [5,6,7,8,9,10]. Particularly interesting is the application of sustainable compounds from biomass such as yeast (active or inactive), in whose organic and molecular structure there are polysaccharides with sorbent capacity, in addition to having a network of functional chemical groups that can ultimately result in an efficient-capacity global yeast for heavy metal sorption.

With the goal of proposing an alternative that represents a balance between biological [11] and chemical engineering processes for the remediation of the wetlands in question, a study was carried out to (a) determine the presence of potential native yeast microorganisms in the RCA Wetlands of Ventanilla and (b) evaluate the heavy metal sorbent capacity of said native yeast structures. When investigating the presence of heavy metals in the aquatic environment, it was decided to isolate yeasts tolerant to high concentrations of lead from the most critical sampling stations of the RCA Wetlands of Ventanilla ecosystem for bioadsorption tests in an experimental design where yeast Candida guilliermondii isolated from the RCA Wetlands of Ventanilla was compared with a commercial strain of Saccharomyces cerevisiae. The objective was to determine the biosorption efficiency of the native yeast of the RCA Wetlands of Ventanilla to continue in a future investigation with the removal of Pb from the ecosystem surface water under laboratory conditions.

2 Materials and methods

2.1 Location of area of study

This research work was carried out at the RCA Wetlands of Ventanilla. The protected natural area of the reserve is approximately 275 ha.

An aerial view of the RCA Wetlands of Ventanilla; then including all available sampling stations M-1, M-2, M-3, M-4, M-5, M-6, M-7, M-8, M-9, M-10, M-11, M-12, M-13, M-14, M-15, M-16, and M-17 is shown in Figure 1. Based on results from former studies in the RCA Wetlands of Ventanilla, six stations were chosen as ideal in order to isolate microorganisms such as yeasts, actinomycetes and environmental fungi. We focused our research on yeasts that showed high tolerance to Pb (1, 5, 10 and 1,000 mg/L) in laboratory tests.

Figure 1 
                  Location of available sampling stations M-1, M-2, M-3, M-4, M-5, M-6, M-7, M-8, M-9, M-10, M-11, M-12, M-13, M-14, M-15, M-16, and M-17 at the Ventanilla Wetlands Regional Conservation Area (RCA Wetlands of Ventanilla), Callao, Peru, established in 2015. Sampling stations J1, J2, J3, J4, J5, and J6 were sampled in this work.
Figure 1

Location of available sampling stations M-1, M-2, M-3, M-4, M-5, M-6, M-7, M-8, M-9, M-10, M-11, M-12, M-13, M-14, M-15, M-16, and M-17 at the Ventanilla Wetlands Regional Conservation Area (RCA Wetlands of Ventanilla), Callao, Peru, established in 2015. Sampling stations J1, J2, J3, J4, J5, and J6 were sampled in this work.

2.2 Sampling

In August 2019, water samples were taken at each of the seventeen sampling stations established back in 2015, in order to determine which heavy metals were the most critical in the RCA Wetlands of Ventanilla ecosystem and to design a research project oriented to the isolation of microorganisms with bioremedication potential. The values of Pb and Cd reported by Fajardo [12] in the same 17 sampling stations were also considered. Of the 17 sampling stations established back in 2015, 15 were for surface water and 2 were for groundwater. Sampling stations M-1, M-2, M-3, M-4, M-5, M-6, M-7, M-8, M-9, M-10, M-11, M- 12, M-13, M-14, M-15 were surface water; of these, sampling stations M-8 and M-9 correspond to surface water channels. Two piezometers were also established, which consisted of stations M-16 and M-17 (for underground water). One simple sample was taken per station for total metals by induction coupled plasma mass spectrometry (ICP-MS) and 1 simple sample per station was put in a 250 mL sterile glass bottle for microorganism isolation procedure. Successful isolation was achieved in 2022, but (during the previous years samples were collected to adjust and improve the yeast isolation protocol). The sampling is representative of the RCA Wetlands of Ventanilla ecosystem because the 17 stations evaluated over the years are distributed in the permanent bodies of water and in two groundwater facilities that were built in 2015 and that were kept under permanent maintenance so as not to lose them. The criteria for establishing the stations considered the ecological importance as bird nesting areas, proximity to the population, and the water mirrors with access allowed only for research purposes (M-12). For those stations that were implemented within the environmental and safety safeguards required by Prociencia, a mobile and assemblable wooden bridge was built, which was only used during sampling.

For groundwater sampling, the work area around the piezometer was prepared, and a plastic cover was placed on the ground to prevent cross-contamination. As it was a monitoring piezometer, the cover was removed and the piezometer was purged. A suction system was used and a volume of water equal to at least three (03) times the volume of the piezometer was removed from the piezometer. During the purging procedure, the parameter stabilization criterion was applied, and only after they stabilized, sampling could begin. A bailer was used for each piezometer. The bailer was lowered gently until it came into contact with the surface of the water, avoiding at all times that the sediments were disturbed and that it came into contact with the walls of the piezometer, then the sample was collected. Once preserved, hermetically covered, and labeled, the samples were placed in coolers, in vertical position, with their respective cooling gels, at an approximate temperature of 4°C, and with their corresponding chain of custody.

The sampling of surface waters was carried out in non-turbulent zones, with a uniform current. Sampling at the surface and bottom of the surface water body was avoided. The bottles were submerged below the surface of the water to a depth of 20–30 cm, after which they were turned so that the mouth pointed toward the current (if it existed), or by creating said current by dragging the bottle on the inside of the water. For the sampling of total metals, the container was rinsed with the water to be sampled, at least twice before taking the sample.

The six stations selected for the 2022 sampling were chosen considering the historical data of Pb and Cd values reported in February, May, and August 2015 and August 2019 (Figures 2 and 3).

Figure 2 
                  Lead values reported in 2015 [12], the values obtained in 2019 and the results of the 6 sampling stations J1, J2, J3, J4, J5, and J6 of 2022.
Figure 2

Lead values reported in 2015 [12], the values obtained in 2019 and the results of the 6 sampling stations J1, J2, J3, J4, J5, and J6 of 2022.

Figure 3 
                  Cadmium values reported in 2015 [12], the values obtained in 2019 and the results of the 6 sampling stations J1, J2, J3, J4, J5, and J6 of 2022.
Figure 3

Cadmium values reported in 2015 [12], the values obtained in 2019 and the results of the 6 sampling stations J1, J2, J3, J4, J5, and J6 of 2022.

Water samples were collected at seventeen sampling stations in order to carry out the chemical characterization of Pb. The 17 sampling stations were those established in 2015. Of the six sampling stations chosen, five were for surface water and one was for groundwater (J1); the groundwater samples were taken from piezometers. The six sampling stations selected were: M-1, M-4, M-5, M-10, M-15, and M-17 that were named for microbiological studies such as J1, J2, J3, J4, J5, and J6; the collected samples were seeded in 250 mL flasks with 100 mL YPG broth [13] for the isolation of microorganisms tolerant to heavy metals.

2.3 Harvest

The amount of each sample was 250 mL water, in new plastic containers, properly labeled. A HNO3 solution was added until pH <2 for the preservation of total metals; the samples were immediately frozen and were then sent to the General Analytical Services Environmental Laboratory SAG SAC (Lima, sagperu.com), accredited by the INDECOPI – National Institute for the Defense of Competition and Protection of Intellectual Property, where the samples were analyzed using ICP-MS, and in the six stations of sampling selected for the isolates of microorganisms (J1, J2, J3, J4, J5, and J6), samples were taken in 250-mL sterile glass bottles for the microbiological isolates in the laboratory and samples in plastic bottles for total metals, pH, temperature, conductivity, and dissolved oxygen were also measured in the field in order to better characterize the water from the sources of isolation of microorganisms.

2.4 Isolation of microorganisms

Isolation was performed in YPG broth of 5 g/L yeast extract, 10 g/L meat peptone, 20 g/L glucose, and 18 g/L agar (HiMedia Laboratories, Maharashtra/Sigma-Aldrich, St. Louis MO) with 0.02% chloramphenicol (Portugal brand of Peruvian origin, labportugal@laboratoriosportugal.com) at pH 5.5. The ingredients to formulate the yeast culture media were from Himedia, and the rest of the reagents used in the study were obtained from Sigma-Aldrich, St. Louis MO; the isolation system was in flasks of 250 mL capacity, with 100 mL of YPG broth at 150 rpm of agitation and at 24 degrees centigrade, two flasks per sampling station were prepared, six flasks named (J1, J2, J3, J4, J5, and J6) and the six flasks with YPG broth supplemented with 0.4 mg/L of lead from Sigma Aldrich brand lead nitrate salt, these systems were named (J1-JJJ, J2-JJJ, J3-JJ, J4-JJJ, J5-JJJ, and J6-JJJ). Of the 12 flasks of the protocol, 0.1 mL of process broth was seeded by dissemination with a drigalski spatula in Petri dishes with YPG agar. The plating procedure was performed at 24, 48, 72, 96, and 120 h of the process; the flasks with the samples were kept under constant agitation. Suspicious and interesting colonies were isolated in YPG broth at pH 5.5 to later generate pure cultures, and gram stains were also performed. Among the isolated microorganisms, we obtained some actinomycetes, environmental fungi, and nine native yeasts.

2.5 Identification of microorganisms

Nine wetland yeasts with typical morphology observed in the gram staining of the smears of the pure colonies were identified and biochemically identified by means of analysis kit API® ID 32C (Biomèrieux, Marcy-l'Étoile), which is a standardized system for the identification of yeasts composed of 32 assays of miniaturized assimilation. The identification output was coupled to a corresponding computer program, and the identified yeasts were Candida guilliermondii, Candida famata, Cryptococcus laurentii, Cryptococcus humicola and Rhodotorula mucilaginosa (Table 3); the yeasts were seeded in tubes with YPG broth at concentrations of 1, 5, 10 and 1,000 mg/L of lead and incubated at 24°C for 1 week. Readings were taken every day in order to determine if there was growth or inhibition (Table 4). The identified yeasts were transferred to cepario in cryovials with YPG broth supplemented with 10% vol glycerol and stored at −20°C.

2.6 Total metal analysis

Metal concentration was analyzed using ICP-MS. For the ICP-MS analyses of the samples from the flasks of the experimental design, the most efficient active yeast in Pb removal was Candida guilliermondii (isolated from the wetland piezometer) and was compared with Saccharomyces cerevisiae (pattern commercial strain); 10 mL aliquots were taken in each sampling at six different time intervals, put in 15 mL falcon tubes, centrifuged, and the supernatants were analyzed on Pb content to evaluate the percentage of lead removal in six time intervals. The flasks started with 1 mg Pb/L in YPG broth at pH 5 and 6, the process times were at 3, 7, 11, 24, 48 and 72 h, and the reaction took place in 250 mL flasks filled with 100 mL suspension each, at 150 rpm agitation speed and 30°C temperature. The set points were controlled by a shaker incubator, model TOU-120 (MRC Laboratory-Instruments, Holon, www.mrclab.com). The results of removal of the active yeasts are shown in Figure 4 for the native yeast Candida guilliermondii and Figure 5 for the commercial baker’s yeast Saccharomyces cerevisiae.

Figure 4 
                  Pb concentration during sorption by active biomass Candida guilliermondii.
Figure 4

Pb concentration during sorption by active biomass Candida guilliermondii.

Figure 5 
                  Pb concentration during sorption by active biomass Saccharomyces cerevisiae.
Figure 5

Pb concentration during sorption by active biomass Saccharomyces cerevisiae.

For the biosorption by inactivated yeast biomass, 1 g of inactivated yeast was applied at different thermal treatment procedures: at 45 and 121°C, drying after centrifugation of the biomass generated for 48 h in YPG broth and their respective washing with sterile distilled water followed by second centrifugation. The drying was carried out in a forced-air circulation oven, model UF110 (Memmert GmbH + Co. KG, Schwabach, www.memmert.com) at 45°C for 24 h for all treatments; of the biomass generated in YPG broth for 48 h growth for both yeasts, in the heat treatment at 121°C for 30 min in an autoclave, the biomass was centrifuged in 50 mL falcon tubes (Brand ISOLAB GmbHha of German origin, isolabgmbh.com), at 2,600 rpm for 10 min; the supernatant was discarded, and the sediment was suspended in sterile distilled water to proceed to second centrifugation as washing. The supernatant was again discarded, and the washed sediment was dried at 45°C in the oven for 24 h.

For the Pb and Cd biosorption system, 1 g of inactivated yeast was used in 250 mL flasks filled with 100 mL deionized water at pH 6 with an initial lead concentration of 3.2814 and 0.17135 mg/L of cadmium; 10 mL samples were taken in 15 mL falcon tubes at 1, 3, 24 and 48 h. The samples were centrifuged, and the supernatant was analyzed using ICP-MS. In other investigations in which Saccharomyces cerevisiae AUMC 3875 was evaluated for live and dead biomass, the maximum capacities for lead(ii) absorption were reached at pH 5.0, initial concentration of metal ions 300 mg/L and biomass dose 3 g/L. Maximum biosorption was reached after 3 h and 20 min for live and dead cells, respectively [14].

For biosorption as inactivated yeasts in water from the Ventanilla Wetlands Regional Conservation Area, 1 gram of inactivated yeast was worked at 121°C, drying after centrifugation of the biomass generated for 48 h in YPG broth and their respective washing with sterile distilled water and second centrifugation was carried out in a Memmert model UF110 oven at 45°C for 24 h for all treatments; of the biomass generated in YPG broth for 48 h of growth for both yeasts, in the heat treatment at 121°C for 30 min in an autoclave, the biomasses were centrifuged in 50 mL falcon tubes at 2,600 rpm for 10 min; the supernatants were eliminated, and the sediments were suspended in sterile distilled water to proceed to second centrifugation as washing. The supernatant was then eliminated, and the already washed sediments were dried at 45°C in an oven for 24 h. For the lead and cadmium biosorption system in water from the RCA Wetlands of Ventanilla, 1 gram of inactivated yeast was used in 250 mL flasks with 100 mL of water from the RCA Wetlands of Ventanilla, at 30°C at 150 rpm system in a TOU-50/120 series incubator shaker (from Israel) and with pH 6; the granulometry of the inactivated yeasts was D50 of 0.500 millimeters, for which the No. 35 U.S. Mesh sieve was used, the removal system was with a concentration of lead initial 0.0134 mg/L and for cadmium 0.00033 mg/L; 10 mL samples were taken in 15 mL falcon tubes at times of 1, 2, 3, 48 and 72 h. The samples were centrifuged, and the supernatant was analyzed using ICP-MS.

2.7 Adsorption isotherms

To obtain the adsorption isotherm, a procedure was carried out maintaining a fixed amount of bioadsorbent of 1 g in 100 mL and varying the initial concentrations of lead and cadmium in the range of 0.1–1 mg/L of Pb and 0.01–0.1 mg/L of Cd. In each flask, the mixture of the lead and cadmium solution with the biosorbent was kept under stirring for the equilibrium time determined in 4 h. All other parameters were kept constant (pH 6 and 150 rpm). With the results of the concentration of lead and cadmium adsorbed during biosorption, the values of the biosorption capacity at equilibrium (q e) were plotted against the final concentration of lead at equilibrium (C e); in this way, the isotherm was obtained biosorption at equilibrium. In all cases, at the end of the contact time of lead and cadmium with the bioadsorbent, the solid and liquid phases were separated by filtration, using filter paper. The liquid phases containing the residual concentration of Pb and Cd were analyzed using ICP-MS. The amount of lead ions retained by the biosorbent or biosorption capacity (q e, mg/g) and the removal percentage (R%) were calculated using equations (1) and (2), respectively, where C o and C e are the initial and equilibrium concentration of lead (mg/L) and cadmium (mg/L) ions in the solution, before and after biosorption, respectively; M is the mass of the biosorbent (g) lead and cadmium (mg/L), and V is the volume of the solution (L).

q e = ( C 0 C e ) × V M , ( 1 )

% R = ( C 0 C e ) C 0 × 100 . ( 2 )

The Freundlich isotherm model was the one that best fit the results obtained in the experiment for both yeasts.

log Q e = log K f + 1 n log C e .

2.8 Data processing

To evaluate the results of each of the sampling stations, tables were generated with the values obtained in each environmental monitoring, and the values of lead and cadmium in water are declared in Table 1.

Table 1

Concentration of Pb and Cd in bodies of water in the Ventanilla Wetlands Regional Conservation Area (RCA Wetlands of Ventanilla) during 2022

Samples Sampling station Pb (mg/L) January 2022 Pb-ECA 2017 Cd (mg/L) January 2022 Cd-ECA (mg/L) 2017
J1 Piezómetro 0.0257 0.0025 0.00103 0.00025
J2 Espejo Rojo 0.0066 0.0025 0.00021 0.00025
J3 Cañaveral 0.0040 0.0025 0.00019 0.00025
J4 Canal Cerco 0.0123 0.0025 0.00015 0.00025
J5 Filtro de agua 0.0110 0.0025 0.00076 0.00025
J6 Pisciplaya 0.0002 0.0025 0.00009 0.00025

Concentration expressed in mg/L.

The values of pH, temperature, dissolved oxygen, conductivity, and salinity of the six sampling stations are detailed in Table 2.

Table 2

Physicochemical parameters

Samples Sampling station pH Temperature (°C) Dissolved oxygen Conductivity (mS/cm) Salinity (%)
J1 Piezómetro 8.87 22 4.78 37.6 23.8
J2 Espejo Rojo 9.83 33.1 15.76 86.5 >42
J3 Cañaveral 9.52 33.3 12.73 21.9 12.82
J4 Canal Cerco 9.09 28.1 10.3 14.8 8.59
J5 Filtro de agua 8.72 27.6 7.31 15.4 8.8
J6 Pisciplaya 8.64 28.2 9.08 18.49 10.94

pH, temperature, dissolved oxygen, conductivity, and salinity in bodies of water in the Ventanilla Wetlands Regional Conservation Area during 2022. Concentration expressed in unit. pH, °C, mg/L, mS/cm year %, respectively.

The yeasts identified by Kit API® ID 32 C are shown in Table 3, where the sampling station from which they were isolated and the culture broth used are specified.

Table 3

Identification of yeasts isolated from the RCA Wetlands of Ventanilla in 250 mL flasks with 100 mL of YPG broth and in YPG broth with lead

Sampling station Broth Strain Gram stain Identification by API® 32C
Cepa commercial YPG Saccharomyces cerevisiae Yeast Saccharomyces cerevisiae
J1 (M-17) YPG J1 Yeast Candida guilliermondii
J1 (M-17) YPG + Pb J1-JJJ Yeast Candida guilliermondii
J2 (M-10) YPG Not isolated
J2 (M-10) YPG + Pb Not isolated
J3 (M-4) YPG J3 Yeast Candida famata
J3 (M-4) YPG + Pb J3-JJJ Yeast Criptococcus laurentii
J4 (M-5) YPG J4 Yeast Rhodotorula mucilaginosa
J4 (M-5) YPG + Pb J4-JJJ Yeast Criptococcus laurentii
J5 (M-1) YPG J5 Yeast Candida famata
J5 (M-1) YPG + Pb J5-JJJ Yeast Rhodotorula mucilaginosa
J6 (M-15) YPG J6 Yeast Criptococcus humicola
J6 (M-15) YPG + Pb Not isolated

The identified yeasts and their tolerance to different Pb concentration values are shown in Table 4, where the sign +, ++, or +++ was placed according to the degree of turbidity observed in tubes with YPG broth with different concentrations.

Table 4

Yeasts isolated from RCA Wetlands of Ventanilla and degree of tolerance to different concentrations of Pb

Pb concentration in YPG broth (mg/L) 1 5 10 1,000
Code Strain Temperature (°C) pH 5 pH 6 pH 5 pH 6 pH 5 pH 6 pH 6
CC Saccharomyces cerevisiae 24 +++ +++ +++ +++ +++ +++ +++
J1 Candida guilliermondii 24 +++ +++ +++ +++ +++ +++ +++
J1-JJJ Candida guilliermondii 24 +++ +++ +++ +++ +++ +++ +++
J3 Candida famata 24 +++ +++ +++ +++ +++ +++ ++
J3-JJJ Criptococcus laurentii 24 ++ ++ + + + + +
J4 Rhodotorula mucilaginosa 24 +++ +++ +++ +++ +++ +++ ++
J4-JJJ Criptococcus laurentii 24 + + + + + + +
J5 Candida famata 24 +++ +++ +++ +++ +++ +++ ++
J5-JJJ Rhodotorula mucilaginosa 24 +++ +++ +++ +++ +++ +++ ++
J6 Criptococcus humicola 24 +++ +++ +++ +++ +++ +++ +++

3 Results and discussion

The analysis of the water samples showed values above the maximum permissible limit for the conservation of aquatic environments in some of the sampling stations (see Table 1). The lead and cadmium values of the RCA Wetlands of Ventanilla exceeded or were close to the national environmental quality standards for water in Peru, according to the standard established by the Ministry of the Environment; then, according to Peruvian regulations [15] for water intended for conservation of the aquatic environment (lakes – lagoons), the values found were above the standards, the limits are for lead (standard 0.0025 mg/L), cadmium (standard 0.00025 mg/L), and cadmium did not exceed the maximum permissible limits in most of the stations evaluated, just in two stations: J1 (Piezómetro) y J5 (Filtro de agua).

The most critical heavy metal in the RCA Wetlands of Ventanilla ecosystem was lead (0.0257 mg/L) at station J1, the problem of cadmium (0.00103 mg/L) at station J1, (0.00076 mg/L) in the stationJ5; piezometer (J1) also showed high values of lead and was the sampling station from which Candida guilliermondii (strain J1-JJJ) was isolated.

From the isolation of yeasts tolerant to high concentrations of lead and their identification, Candida guilliermondii was selected for presenting the best results of tolerance to high concentrations of Pb, growth at different pH, and its reports of biotechnological applications [16], due to the particular source of isolation at the RCA Wetlands of Ventanilla, namely from groundwater. The strain was compared with a commercial Saccharomyces cerevisiae yeast, which, according to the state-of-the-art, is one of the most effective strains in removing Pb. Both yeasts were evaluated in an experimental design matrix as active yeasts, the initial Pb concentration was 1 mg/L in the flask system with YPG broth. Similar Pb sorption trends were obtained for both yeasts in the same time intervals.

The Pb and Cd sorption trends were also studied for dead biomass inactivated at 45 and 121°C. The initial Pb and Cd concentration was 3.2814 and 0.17135 mg/L respectively, in flasks with deionized water at pH 6, loaded each flask with 1 g inactivated yeast.

In former studies, the highest Pb and Cd uptake was obtained with Saccharomyces cerevisiae. The Pb biosorption capacity of all kinds of biomass was higher than that of Cd [17]. For inactivation, the biomass of both yeasts was generated separately in YPG broth at pH 6. At 48 h growth in YPG broth, centrifugation was carried out in 50 mL falcon tubes at 3,600 rpm for 5 min; the supernatants were removed and the sediments were suspended. in sterile distilled water to proceed to second centrifugation as washing. The supernatant was then removed, and the already washed sediments were dried at 45°C in an oven for 24 h. The inactivated yeasts were ground and sieved with US MESH number 35 of 0.5 mm, generating granulometry D50 (50% passing and 50% retained), the lead and cadmium removal trend graphs were similar for the first three times of 1, 3, and 24 h in both inactivated yeasts. In our research, we evaluated biosorption of lead and cadmium in an aqueous solution of the yeast Saccharomyces cerevisiae and Candida guilliermondii inactivated at 45 and 121°C; obtaining the best results in the first 24 h of contact where the lead values decreased to 0.3412 and 0.1159 mg/L and the cadmium values to 0.1159 mg/L at 24 h and 0.0106 mg/L at the time of contact with Candida guilliermondii at 45 and 121°C, respectively (Figure 6).

Figure 6 
               Pb and Cd concentrations during sorption by inactive biomass Candida guilliermondii at pH 6 and for two different thermal biomass deactivation treatments: 45 and 121°C.
Figure 6

Pb and Cd concentrations during sorption by inactive biomass Candida guilliermondii at pH 6 and for two different thermal biomass deactivation treatments: 45 and 121°C.

For Saccharomyces cerevisiae, the best results were also at 24 h of contact where lead values decreased to 0.0318 and 0.0817 mg/L and cadmium values to 0.01519 mg/L at 24 h and 0.01353 mg/L at 24 h. 3 h of contact at 45 and 121°C, respectively (Figure 7); in other investigations, good inactivation results were reported at 45°C for Saccharomyces cerevisiae [18].

Figure 7 
               Pb and Cd concentrations during sorption by inactive biomass Saccharomyces cerevisiae at pH 6 and for two different thermal biomass deactivation treatments: 45 and 121°C.
Figure 7

Pb and Cd concentrations during sorption by inactive biomass Saccharomyces cerevisiae at pH 6 and for two different thermal biomass deactivation treatments: 45 and 121°C.

Thermal treatment at different temperature values (to get the inactivated yeasts = dead biomass) had a significant effect on Pb removal using Candida guilliermondii and Saccharomyces cerevisiae similar to those reported on Cr removal by Saccharomyces cerevisiae [19].

Other studies [20] report Mediterranean forested wetlands as good sites for yeast isolation for dye bioremediation and highlight the importance of conserving these ecosystems. Among yeasts, the most studied are Candida, Pichia, Cryptococcus, and Saccharomyces [21,22]. This research reports Candida guilliermondii as a native yeast of the RCA Wetlands of Ventanilla with biosorbent properties for Pb and Cd.

It could be seen that the optimum pH for Pb adsorption by active Candida guilliermondii and active Saccharomyces cerevisiae was 5 and 6, respectively. In previous research, pH 5 was reported as optimum for Saccharomyces cerevisiae in removal processes [23].

In the results of lead and cadmium removal (Figures 8 and 9) from water from the RCA Wetlands of Ventanilla under laboratory conditions, using the yeasts Saccharomyces cerevisiae and Candida guilliermondii inactivated at 121°C in the 5 removal times of 1, 2, 3, 48, and 72 h, very close results are obtained for both yeasts, considering that Saccharomyces cerevisiae is a reference yeast in lead and cadmium removal according to the study of the art; the results obtained in Candida guilliermondii make it a good candidate as yeast native inactivated for remediation work in the Ventanilla Wetlands Regional Conservation Area.

Figure 8 
               Pb Concentration during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii from RCA Wetlands of Ventanilla water sample.
Figure 8

Pb Concentration during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii from RCA Wetlands of Ventanilla water sample.

Figure 9 
               Cd concentration during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii from RCA Wetlands of Ventanilla water sample.
Figure 9

Cd concentration during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii from RCA Wetlands of Ventanilla water sample.

Due to the removal results as active and inactivated yeast, Candida guilliermondii is presented as a native yeast with lead and cadmium removal potential for the Ventanilla Wetlands Regional Conservation Area.

The sorption patterns of cadmium and lead by biomasses inactivated with D50 of 0.5 mm granulometry of Saccharomyces cerevisiae and Candida guilliermondii respectively are shown in Figures 10 and 11.

Figure 10 
               Cadmium sorption model by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii.
Figure 10

Cadmium sorption model by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii.

Figure 11 
               Lead sorption model during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii.
Figure 11

Lead sorption model during sorption by inactive biomass Saccharomyces cerevisiae and Candida guilliermondii.

The Freundlich isotherm model was the one that best fit the results obtained in the experiment for Saccharomyces cerevisiae and Candida guilliermondii as yeasts inactivated at 121 degrees and dried at 100°C in the 0.5 mm grain size.

No yeast was isolated from station J2, the pH was 9.83, and the salinity was extreme in the water sample, being the impacted in lead (0.0066 mg/L) of all the sampling stations.

4 Conclusions and recommendations

This study has determined the presence of heavy metals such as lead and cadmium in surface water bodies and the one underground water stations J1 of the RCA Wetlands of Ventanilla in the years 2022; the most critical heavy metal in the ecosystem was lead with a maximum value of 0.0257 mg/L at station J1.

The sampling stations most affected by lead were those established in the Piezómetro J1, en Espejo Rojo J2, in the buffer zone “Cañaveral” J3, Canal Cerco J4 and Filtro de Agua J5; the most optimal yeast in lead removal was Candida guilliermondii isolated from piezometer J1 (groundwater).

Tolerance tests to different concentrations of lead made it possible to evaluate the nine isolated native yeasts in growth time, determining that some are slow-growing, such as Cryptococcus laurentii (strain J3-JJJ); however, Candida guilliermondii (J1-JJJ) presented tolerances to high concentrations of lead, optimal growth at pH 5 and 6, a characteristic that allows the strain to be maintained in different culture media and evaluated in different experimental optimization designs.

The yeast Rhodotorula mucilaginosa (J5-JJJ) showed high tolerance to different concentrations of lead, but its growth was not optimal at pH 6 with a lead concentration of 1 mg/L and it is a yeast that is frequently found in natural ecosystems.

The yeast Candida guilliermondii was the one that presented the best results of tolerance to different concentrations of lead, and its removal results are very similar to those of Saccharloomyces cerevisiae (reference yeast) evaluated as active yeasts in an experimental design of Pb removal with three repetitions.

Applications in removal of lead and cadmium by the yeast Candida guilliermondii (J1-JJJ) are reported and its potential in bioremediation of coastal wetlands is evidenced.

Candida guilliermondii and Saccharomyces cerevisiae yeasts as inactivated yeasts with lead and cadmium removal capacity presented similar results in the first 3 h of evaluation.

The native yeast Candida guilliermondii presented good results as inactivated yeast at 121°C in the removal of lead and cadmium in the waters from the RCA Wetlands of Ventanilla under laboratory conditions, so it would be a yeast with bioremediation potential for this ecosystem.

The isolation of yeasts from groundwater in coastal wetland ecosystems affected by heavy metals is recommended, in order to explore possible applications in bioremediation with native yeasts in affected ecosystems.

Nomenclature

RCA

Regional Conservation Area

EQS

environmental quality standard

Acknowledgments

The results presented are part of the doctoral research project sponsored by the National Fund for Scientific, Technological Development and Technological Innovation (FONDECYT), currently PROCIENCIA, one of ten doctoral programs financed by PROCIENCIA in Peru – Contract 04-2018-FONDECYT/BM. The authors acknowledge and are thankful to the DSR for the technical and financial support.

  1. Funding information: This research has been financed by the Concytec-World Bank Project “Improvement and Expansion of the Services of the National System of Science, Technology and Technological Innovation” 8682-PE, through its executing unit ProCiencia [Contract 04-2018-FONDECYT/BM], with the aim of contributing to research in priority lines that includes fragile ecosystems such as Coastal Wetlands.

  2. Author contributions: Narda Fajardo Vidal – conceptualization, formal analysis, funding acquisition, research, resources, visualization, writing-original draft; Jorge Wong Dávila – methodology, project administration, supervision, validation, writing-review and editing.

  3. Conflict of interest: The authors declare no conflict of interest.

  4. Ethical approval: The conducted research is not related to either human or animal use.

  5. Data availability statement: All data generated or analysed during this study are included in this pubblished article.

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Received: 2022-07-09
Revised: 2022-08-30
Accepted: 2022-09-04
Published Online: 2022-10-28

© 2022 Narda Fajardo Vidal and Jorge Wong Dávila, published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 International License.

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